Contributions of Russian Scientists to Catalysis

Contributions of Russian Scientists to Catalysis J . G . TOLPIN. G . S. JOHN. AND E . FIELD Standard Oil Company (Zndiana). Chicago. Illinois

Page 217 1 . Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217 2 . Generalsurvey . . . . . . . . . . . . . . . . . . . . . . . . . 219 I1 . Schools of Thought on Catalysis . . . . . . . . . . . . . . . . . . . 224 111. Investigation of Adsorption Phenomena . . . . . . . . . . . . . . . . 238 1. Determination of the Distribution Function of the Heats of Adsorption and Interaction Function . . . . . . . . . . . . . . . . . . . . . 238 2. Determination of the Distribution Function of the Activation Energies of Adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . 242 3 . Adsorption upon Structural Defects . . . . . . . . . . . . . . . . . 249 IV . Kinetics of Heterogeneous Catalytic Reactions . . . . . . . . . . . . . 254 V . Modification of Catalysts . . . . . . . . . . . . . . . . . . . . . . 256 1 . Promoters and Poisons . . . . . . . . . . . . . . . . . . . . . . 256 264 2 . Selective Poisoning . . . . . . . . . . . . . . . . . . . . . . . . VI Catalytic Conversions . . . . . . . . . . . . . . . . . . . . . . . . 266 1 . Dehydrogenation-Hydrogenation . . . . . . . . . . . . . . . . . . 266 272 2 . Dehydrocyclization . . . . . . . . . . . . . . . . . . . . . . . . 3 . Theory of Methylene Radicals . . . . . . . . . . . . . . . . . . . 275 4. Hydrogenation of Carbon Monoxide . . . . . . . . . . . . . . . . 276 5 . Hydration-Dehydration . . . . . . . . . . . . . . . . . . . . . . 279 6. Acetylene Chemistry . . . . . . . . . . . . . . . . . . . . . . . 281 7. Polymerization . . . . . . . . . . . . . . . . . . . . . . . . . . 282 8. Isomerization . . . . . . . . . . . . . . . . . . . . . . . . . . 283 9. Alkylation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286 10. Cracking . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 11 . Oxidation. . . . . . . . . . . . . . . . . . . . . . . . . . . . 290 12. Other Reactions . . . . . . . . . . . . . . . . . . . . . . . . . 292 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293

I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . .

.

I . INTRODUCTION 1. Scope Critical reviews of Russian contributions to various fields of science are necessary today because of the limited availability and utilization of the Russian technical literature. Under conditions of normal contacts between scientists of various countries it would be undesirable to segregate the contributions from any single country, as this tends t o give a distorted perspective of scientific progress . 217

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This paper attempts to survey the more significant Russian contributions t o the study of catalysis th at have come to the attention of the writers, with special emphasis being placed upon recent researches. Older studies and those researches carried out by scientists who no longer reside in Russia, for instance by Professor V. N. Ipatieff, are either omitted or used only as background information. Considerable attention is being paid by Russian chemists and physicists t o catalytic phenomena. The various publications on the subject coming from many Soviet research institutes bear witness to this. These publications have appeared in a number of Russian journals as well as in book form. Several symposia have resulted from special meetings devoted t o catalysis. One such meeting in 1947 was reported t o have been attended by 800 participants. Another meeting commemorating earlier contributions by L. V. Pisarzhevskil was held in Kiev in 1948 and resulted in a Pisarzhevskii memorial volume (303). Nearly all phases of the physics and chemistry of catalysis are under active study in Russia. Some phases have considerable tradition of research behind them; others are only in the formative stage, stimulated by reports in the non-Russian scientific literature. The series of publications entitled “Problems of Kinetics and Catalysis” edited by S. Z. Roginskii is a noteworthy source of information on the fields of catalysis under discussion. The latest two volumes of this series, namely VI and VII, were published in 1949 (333). Of these, Volume V I was not available to the writers. Surveys appearing in Uspekhi Khimii (Progress of Chemistry) and in other Russian journals have also been useful in presenting the point of view of the Russian contributors to the field. If they discuss Russian researches specifically, they overemphasize them. In this category belong the reviews published on various state occasions, even when they are written by competent scientists. The survey of Russian researches on isomerization during 1917-47 by S. N. Danilov is a typical example (55). Books on catalytic chemistry, whether textbooks (64) or surveys of special fields (291,305), are not uniformly useful sources of information on original Russian contributions to catalysis. The status of Russian studies on catalysis immediately before World War I1 is shown by the Transactions of the Meeting on Catalysis of May 13-16, 1940 (387) and by the volume describing the progress of Soviet chemistry during 1917-42 (362). A bibliography of publications of the Karpov Institute during 1934-43 lists many researches on catalysis among its 825 items (12). Reports on Russian researches on catalytic conversions of possible industrial value are now withheld from free circulation outside of Russia and it remains to speculate on the value and the exact nature of some researches referred t o in the publications which are available t o us.

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2 . General Survey

Catalytic conversions were experimentally studied in Russia toward the end of the nineteenth century, and especially in the twentieth century, and regularities were empirically established in a number of cases. The work of A. M. Butlerov (1878) on polymerization of olefins with sulfuric acid and boron trifluoride, hydration of acetylene to acetaldehyde over mercury salts by M. G. Kucherov (1881) and a number of catalytic reactions described by V. N. Ipatieff beginning with the turn of the century (139b) are widely known examples. S. V. Lebedev studied hydrogenation of olefins and polymerization of diolefins during the period 1908-13. Soon after World War I he developed a process for the conversion of ethanol t o butadiene which is commercially used in Russia. This process has been cited as the first example of commercial application of a double catalyst. Lebedev also developed a method for the polymerization of butadiene to synthetic rubber over sodium as a catalyst. Other Russian chemists (I. A. Kondakov; I. Ostromyslenskii) were previously or simultaneously active in rubber synthesis. Lebedev’s students are now continuing research on catalytic formation of dienes. The industrial utilization of certain catalytic processes in the U.S.S.R. is indicated by the following figures. TABLE I Production in the U.S.S.R. Thousands of tons

Synthetic Fuela Synthetic Rubber6 Sulfuric Acidb Plasticsb Hydrogenation of vegetable oils and animal fatse

1938

1950

85 1500-1600

900” 250 2500’ 30’ 250

-

1lfJd

Source: Shvernik, et al. (416s). Source: Vinokurov (416b). 0 Source: Dolgov (66). d Figure for 1940. This figure IS given in the official five-year plan (1946-1950). It includes coal hydrogenation, but also shale processing; a more recent estimate (416c) indicates that Soviet synthetic 011 production, both by the Fischer-Tropsch process and by coal hydrogenation, has reached 2-3 million tons per year. f Figure for 1949. 5

b

The Institute of High Pressures founded by V. N. Ipatieff, the Institute of Organic Chemistry headed by N. D. ZelinskiI, Moscow State University, the “ Khimgas ” Institute, the Institute of Applied Chemistry, the Institute of Coal Chemistry, and the Institute of Mineral Fuels have carried out many studies on catalytic conversions in the 1930’s and

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1940’s. I n recent times the Karpov Institute of Physical Chemistry and the Institute of Chemical Physics have been among the major contributors of research on catalytic phenomena and the theory of catalysis. In the field of hydrocarbon conversions, N . D. Zelinskii and his numerous co-workers have published much important information since 1911. Zelinskii’s method for the selective dehydrogenation of cyclohexanes over platinum and palladium was first applied to analytical work (155,351,438,439), but in recent years attempts have been made t o use it industrially for the manufacture of aromatics from the cyclohexanes contained in petroleum. I n addition, nickel on alumina was used for this purpose by V. I. Komarewsky in 1924 (444) and subsequently by N. I. Shuikin (454,455,456). Hydrogen disproportionation of cyclohexenes over platinum or palladium discovered by N. D. Zelinskii (331,387) is a related field of research. Studies of hydrogen disproportionation are being continued, and their application is being extended to compounds such as alkenyl cyclohexanes. The dehydrocyclization of paraffins was reported by this institute (Kazanskii and Plate) simultaneously with B. L. Moldavskii and co-workers and with Karzhev (1937). The catalysts employed by this school have also been tested for the desulfurization of petroleum and shale oil fractions by hydrogenation under atmospheric pressure. Substantial sulfur removal was achieved by the use of platinum and nickel on alumina (392). At the end of the nineteenth century, A. F. Fttvorskii and his students were studying catalytic conversions of acetylene, including those occurring in the presence of alcoholic potash. His students have continued this series with work on vinylation, hydrolysis of some of the vinyl alkyl ethers (M. F. Shostakovskii), and conversions of vinylethynylcarhinols (1. N. Nazarov). Studies of hydrogenation, including destructive hydrogenation (Nemtsov, Prokopets, Dyakova), reported in the 1 9 3 0 ’ ~may ~ have been utilized by now for industrial processes. A. V. Frost has been conducting research on the kinetics of cat,alytic reactions and on catalytic cracking. Frost and M. D. Tilicheev are co-editors of a series of publications on physical constants of hydrocarbons which may be used as a source of information on the synthesis of individual hydrocarbons. Other Russian groups have contributed (N. D. Zelinskii, A. D. Petrov) to this field. Some of this work involves catalytic reactions; however, in this review mere mention of it may sufice. Duriiig the last two decades vigorous development of several schools of thought on the nature of catalysis has been taking place in Russia. The major contributors to these schools have been A. A. Balandin, S. Z. Roginskil, and N. I. Kobozev.

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Soviet physicists and chemists have been reporting research on the peculiarities of adsorption on solid surfaces and the apparent deviations from the derived laws expressing adsorption phenomena, e.g., deviations from the Langmuir laws. S. Z. Roginskii has treated the nonuniformity of the surface and adsorption under conditions of limited extent of coverage of the surface in a number of articles. Of historical importance are the researches of A. F. Ioffe and Ya. I. Frenkel’ on the physics of solid bodies which began in the early 20’s of the present century and were concerned with the electrical and mechanical properties of crystals and the mechanism of origination of voids and distortions in a crystal lattice under the influence of thermal motion (137b). It is likely that Ioffe’s researches served as the starting point for present-day researches of some Russian investigators such as F . F. Vol’kenshtein, dealing with properties of solids of significance in catalysis. Ioffe’s observation that the ultramicroscopical cracks affected the surface conductivity of salts and the mechanical strength of a crystal was used by P. D. Dankov (58) to explain the formation of catalytic surfaces. Active platinum, nickel, and iron catalysts (27) were prepared by sublimation and were examined as to the effect of lattice parameter, atomic radii and dispersion (crystallite size) upon their catalytic activity. Dankov (58) stressed the importance of atomic radii in a review published in 1934, basing some of his conclusions upon the earlier studies of L. V. Pisarzhevskii. Dankov also pointed out that the layers between metal crystals, which probably consist of amorphous material, are visualized by some metallographers as being important for the mechanical strength of the metal, since they are the most rigid element of a polycrystalline body (38,388). This may be considered in connection with Kobozev’s theory of catalysis described elsewhere in this paper, which regards atoms of the amorphous phase of the catalyst, constituting an “ensemble,” as the carrier of catalytic activity; the crystalline phase serves as the catalyst support. Dankov recently returned to electron diffraction studies of crystals and their orientation in thin films and surface layers of solid bodies (343). The influence of the crystallite size of catalysts upon such reactions as hydrogenation or dehydrogenation over platinum or nickel has been investigated by Eubinshtein and others (376). Roginskii’s school has applied mathematical statistics to systems formed by primary monocrystals of a catalyst; the cracks and pores of varying dimensions created by these crystals predetermine the nature of the resulting porosity. The application of the statistical method t o the theory of adsorption and catalysis was recently described by V. I. Levin (200) and an equation for adsorption on nonuniform surfaces derived by Ya. Zel’dovich and S. Z.

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Roginskii was given by the former in a treatment of his statistical theory of the Freundlich isotherm of adsorption (433). Further research resulted in a theory of processes occurring on nonuniform surfaces and a statistical treatment of such surfaces by Zel’dovich (432). M. I. Temkin independently developed a theory of adsorption on nonuniform surfaces. Temkin’s work a t the Karpov Institute of Physical Chemistry was directed toward an interpretation of the adsorption isotherms of hydrogen on platinum obtained by A. N. Frumkin and co-workers. The observed deviations from the Langmuir isotherm were explained by energetic nonuniformity of the surface (386) which gave rise to a logarithmic isotherm (125). The further development of the theory of nonuniform surfaces in the U.S.S.R. was helped by the mathematical methods of Zel’dovich and Roginskii (200,201,331). A. V. Frost analyzed some work on the subject (mostly Russian) in a recent review (10) and concluded that a n equation derived by him on the assumption that the reactants are adsorbed on a uniform surface and that no significant interactions take place between the adsorbed molecules, satisfactorily described many reactions on nonuniform surfaces including cracking of individual hydrocarbons and petroleum fractions, hydrogen disproportionation, and dehydration of alcohols. From the experimental results i t was concluded that the catalytic centers on the surface were not identical with the adsorption centers. The catalysts used consisted of different samples of silicaalumina and pure alumina. The formal connection of the views of present day chemists with those of L. V. Pisarzhevskii (301,341) is now stressed by some Russian writers on catalysis (458). The electronic mechanism of catalysis postulated by Pisarzhevskii without much experimental evidence in an early (1925-28) attempt a t correlating the physical attributes of a solid with its catalytic activity stated th at the ability of a metallic catalyst to promote hydrogenation depended on the ability of a hydrogen molecule to penetrate the crystal lattice of the metal and consequently depended upon the interionic distances in this metal. The existence of highly mobile, free (conduction) electrons in metals, as well as in oxides, was thus of great significance in catalytic phenomena, according t o Pisarzhevskii (302). Adsorption was regarded by Pisarzhevskii as a n interaction between the adsorbate molecule and the entire structure of the catalytic particle. The adsorption process could occur on the surface or in the interior of the crystal. For the process to occur in the interior of the crystal the magnitude of the lattice parameter and the atomic radii must satisfy certain restrictive conditions which have been discussed in detail by Dankov (58).

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Many of the ideas advanced by Pisarzhevskii were also expressed in Nyrop’s work (262) published between 1931 and 1937. The views of Nyrop were unfavorably received by many catalytic chemists a t that time, as is indicated by the criticism of Emmett and Teller (101). LennardJones (199) and Schmidt (361) realized that a catalytic solid could be regarded as an electron source or sink during the course of a catalytic reaction necessitating an electron transfer in ion or radical formation. I n the presence of hydrogen-containing materials, the catalytic solid could also act as a proton reservoir. I n the hands of Roginskii and Vol’kenshtein, these views have provided an electronic theory of catalysis wherein electrons of the crystalline lattice participate in physical and chemical reactions occurring on the surface. The effect of foreign inclusions and temperature upon the nature and formation of lattice “defects” has been studied by Vol’kenshtein. The effect of the catalyst support on resistance to poisoning and sintering was investigated in the 1930’s by I. E . Adadurov and co-workers (1-9). They emphasized the favorable effects of a large difference between the ionic radii of the cations of the support and that of the catalyst. Increasing the charge of the cation raised its stability to poisoning. Adadurov’s conclusions did not greatly influence the thinking of Russian students of catalysis. No special significance was ascribed by Adadurov t o the change in the lattice constants of the catalyst (platinum, chromic oxide), resulting from the adsorption of a poison. Several other students of catalysis in the U.S.S.R. have been investigating various aspects of the influence of the support on the catalyst. These include A. A. Balandin and co-workers (30), A. S. Shekhter (363), N. Z. Kotelkov (177), and others. Of the methods employed by the workers of the Institute of Organic Chemistry who supported Ralandin’s theory, x-ray analysis of catalysts is noteworthy. A. M. Rubinshtein studied (346-349) catalysts employed in hydrogenation, dehydrogenation, and dehydration and correlated the effects of dispersion (particle size) and lattice parameters with their catalytic properties. He gave data (346) indicating that for nickel supported on alumina or for platinum on charcoal, definite sizes of the primary crystallites favor a given reaction: for hydrogenation it is approximately 40 A.; for dehydrogenation 70-80 A. These studies have been extended t o other catalysts including oxides. Rubinshtein’s x-ray data (353) supported Balandin’s theory by indicating that the octahedral faces [lll]of platinum supported on charcoal are the only active faces and no other faces are of significance in the catalytic performance of platinum. The relative activity of catalysts of low metal content (0.034.0% Pt, Pd, Co, and Ni supported chiefly on charcoal) has been compared in

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dehydrogenation of cyclohexane and hydrogenation of benzene (261,353,354,373,374). For palladium it was demonstrated that upon the absorption of the proper amount of hydrogen the parameters of its lattice were deformed to a favorable extent and this was more significant in raising the activity of the catalyst than increasing the palladium content to 10 %.

11. SCHOOLS OF THOUGHT ON CATALYSIS The last two decades have been marked by a n ever increasing interest in the theory of solids as is indicated by the development of the electronic band approximation which has been so successful in the understanding and interpretation of the optical, electrical, and magnetic properties of solids. This and similar advances made by the physicists have provided new tools for the interpretation and elucidation of the catalytic efficacy of a solid. These tools had been sorely needed and long awaited, for it was RoginskiI and Schultz (337) and Russell (357) who had emphasized the importance of the electronic factor even before the introduction of the geometric factor by Balandin (13) and the ensemble principle by Kobozev. The three principal Russian schools of thought concerning the mechanisms of heterogeneous catalysis have been identified with different theories on the subject, namely Balandin’s multiplet theory, Kobozev’s ensemble theory and Roginskii’s theories of supersaturation and micropromotion. Of the three theories, the pultiplet theory of Balandin has received the most attention in the non-Russian literature. The multiplet theory postulates that bond rupture is accomplished by the adsorbed atoms being attracted to different catalyst atoms whereas bond formation arises from the adsorbed atoms being attracted to the same catalyst atom. On the surface of the catalyst the course of the reaction is influenced by the interactive forces between the reactant molecules and the catalyst atoms, these forces being determined largely by the geometry of the catalytically active structure and the spatial configuration of the reactant molecule(s). The catalytically active structure is regarded by Balandin as a small group or “multiplet” of atoms contained in the crystalline lattice of the catalyst. I n contrast, Kobozev regards the activity as being centered in a n amorphous precrystalline phase which forms a number of “migration” cells containing mobile surface atoms whose lateral displacements are limited by microfissures. These microfissures constitute the geometrical boundaries of the “migration” cells. The smallest group of catalytically active atoms in these cells forms an ensemble. The theories of Balandin and Kobozev are largely geometric in nature and consequently possess many similarities with regard to the active

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configurations required for specific catalytic reactions. The two theories do differ, however, in that Balandin assumes that the catalytically active structure is a part of a stable crystalline phase and immobile, whereas Kobosev assumes that the active structure is composed of mobile atoms contained in an amorphous precrystalline phase. Quantitative information concerning this precrystalline phase is difficult to obtain; consequently the influence of spatial geometry upon the course of a catalytic reaction is more readily interpretable in terms of Balandin’s theory than Kobozev’s. The latter theory does have the advantage that the action of poisons and promoters can be formulated in terms of their influence upon the activity of the ensemble. The theories developed by Roginskii consider the thermodynamic and electronic properties of the catalyst rather than the purely geometric attributes of its structure. His school has put forward two concrete views which are supported by recent studies of certain Russian physicists. These are the effect of minute quantities of impurities on the catalytic activity of a surface and the principle of “supersaturation in a solid surface.” Systems with an excess of free energy are termed supersaturated systems by Roginskii. The excess free energy per gram-mole is a measure of supersaturation. The theory of supersaturation was formulated by Roginskii following the observations made by Dobychin on nickel oxide used in hydrogenation, dehydrogenation, and oxidation reactions. It was noted that the activity of the catalyst was greatly enhanced when its structure possessed free energy in excess of that possessed by the bulk material. By preparing catalysts by simultaneous condensation of vapors of a metal with that of the promoting admixture on cold surfaces in a high vacuum, Roginskii and co-workers demonstrated th a t pure films of a number of metals are totally inactive in reactions such as low-temperature hydrogenation of ethylene, and they become active when gases such as oxygen, hydrogen, nitrogen are occluded on their surfaces in optimal amounts (328,331,343). Above that amount the promoter may poison the catalyst, which explains, according to Roginskii, some contradictory data on the effect of the same substance on a given catalyst. Whether the occluded admixture creates a new active surface or stabilizes distortions of the lattice of the solid already existing there, is a problem under study. An active catalyst should be prepared, on the basis of these views, under conditions as far from equilibrium between the reactants in question as possible. It was stated by Roginskii that his theory of supersaturation was qualitaavely verified on a number of catalysts and was employed in practice with success, for instance, in the preparation of nickel catalysts for fat hydrogenation, ircn catalysts for ammonia synthesis, and molybdenum dioxide for destructive hydrogena-

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tion. We do not have complete details on all these researches. The study of micropromotion has been extended to other systems, and the influence of promoters has been interpreted in terms of the changes produced in the specific rate constant and activation energy of the reaction. As a result of these studies the basic concepts have been broadened and the general phenomenon has been termed “modification of catalysts” by Roginskii. It should be recognized that the geometric theories of Balandin and Kobozev and the theories of RoginskiI represent different approaches to the same phenomena and must, therefore, contain large areas of agreement and internal consistency. The work of Balandin has been recently reviewed by Trapnell (405). A significant supplement to this theory was published in 1945 and 1946 by Balandin and Eidus (20,22). It pertains to chemisorption of unsaturated molecules. For the dehydrogenation of cyclohexanes the multiplet theory requires that the six-membered ring be fitted upon a sextet of atoms and a catalytically active metal should possess face-centered cubic or hexagonal lattices with atomic radii between 1.244 and 1.385 A. These investigators have considered the principle of conservation of valence angles first applied by Twigg and Rides1 (413) to the chemisorption of ethylene on nickel and by Herington t o acetylene (135). However, unlike the British investigators, they applied it to the transitional state of ethylene adsorbed on the catalyst. It was concluded that acetylene molecules are chemisorbed with greater ease on a crystal plane abundant in Ni-Ni bonds of 3.50 A. in length whereas ethylene molecules prefer those with 2.47 A. Experimental hydrogenation of olefins on nickel reported by Twigg and Rideal(413) and Beeck and co-workers (37) were quoted in support of this principle. This principle of conservation of the valence angles extends the list of metals on which hydrogenation of olefins can occur t o include those having atomic radii approximately within the limits mentioned, but crystallizing in a body-centered cubic lattice (W, Mo, Cr, and Fe). The literature clearly indicates that Balandin has received support from Russian as well as non-Russian investigators. Among the Russian works lending confirmation to Balandin’s hypothesis the studies of Dankov and Rubinshtein are particularly notable (346,347,348,349,350). Since modern views of catalysis regard active centers as local distortions of the primary crystalline lattice it is important to characterize these elementary crystallites by the following attributes: ( a ) Radii of atoms or ions which compose the lattice. ( b ) Type of lattice and forms of crystal. (c) Parameters of the crystalline lattice.

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(d) Dispersion, i.e. dimeriaions of the crystallites. ( e ) Extent of distortion of the lattice. These factors have been studied by many workers; however, no mutually acceptable concepts with regard to the significance of each of these factors have been developed. This has been due in part to the contradictory data appearing in the literature. The factor (a) above has been considered by Balandin (14),Schmidt (360), PisarzhevskiI(302), Adadurov (1-9), Huttig (136), Beeck (36), and others. Adadurov’s studies of the factor (a) are unique in that the catalyst support rather than the catalyst was the center of attention. The first studies were devoted to the platinum catalysts used in the oxidation of SO2. The metallic platinum was supported on the surface of the sulfates of the di-, tri-, and tetravalent elements, and investigations were made upon the activity, the sensitivity to poisoning with AsZ03, and regenerability of the platinum catalyst after poisoning. Among the divalent metals studied (Be, Mg, Ca, Sr, Ba) the sulfates of beryllium and of magnesium demonstrated the greatest activity, minimal resistance t o poisoning and maximal regenerability after poisoning. The trivalent elements (Al, Cr, Fe) and tetravalent metals (Si, Ti, Sn, Zr, Th) were less susceptible to poisoning; the most favorable results being obtained with Sn(S04)2and Zr(S0,)2. Similar studies were carried out with a nickel hydrogenation catalyst supported upon the sulfates of divalent metals and the oxides of the tetravalent elements. Adadurov correlated these results with the ionic radius of the cation in the catalyst support and concluded that the greater the difference between the radii of cations of the support and of the catalyst, the lower the susceptibility of the platinum to poisoning with As203 and the lesser the sintering tendency of the nickel catalyst. An increase in the charge of the cation of the support was found to increase the activity of both of these catalysts. The factor ( b ) above was investigated by Bredig and Allolio (43) in the hydrogenation of ethylene over nickel. Of the two modifications of nickel, cubic and hexagonal, only the first was active as was also found by LeClerc (191,192) and his co-workers and recently reaffirmed by the work of Freldlin and Ziminova (113,114) who also established that in hydrogenation reactions, hydrogen is an essential promoter of the nickel catalysts. A linear interdependence was established between the catalytic activity and the amount of hydrogen dissolved in the nickel. These data may be considered as contradictory to the results recently reported by Sherburne and Farnsworth (365) concerning the activation of nickel metal by extensive outgassing at temperatures considerably above the usual baking temperature. Similar studies were made upon both Raney and Sabatier cobalt by

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Dupont and Piganiol (70) who observed that the Sabatier cobalt had a cubic structure and was quite active whereas the Raney cobalt had the structure of the hexagonal modification and was considerably less active in the hydrogenation of allocymene. I n contrast, Rubinshteh arid Pribytkova (356) have recently observed that in typical hydrogenation and dehydrogenation reactions the activity of the hexagonal modification of cobalt prepared by reducing its oxide a t low temperatures ( T 5 360°C.) was much higher than the face-centered cubic modification obtained during high temperature reduction (5" 5 6OO0C.). The crystallites of cobalt were supported on either charcoal or metallic cobalt during the test reactions which consisted of the hydrogenation of benzene, cyclohexene, acetone, ethylene, or carbon monoxide, and of the dehydrogenation of cyclohexane and ethanol. It was thought by the authors that the high reduction temperature reduced the extent of lattice distortion in the cubic modification and consequently reduced its activity. The loss in activity due to possible crystal growth during hightemperature reduction was not considered. In the very early studies on catalysis little attention was paid to the influence of factors ( c ) , ( d ) , and ( e ) . It is notable, however, that Fricke and co-workers (118,119) did connect the pyrophoric nature of copper and of nickel preparations with their lattice distortions and dispersion. Taylor, Kistiakowsky, and Perry (385) studied the effect of dispersion of platinum in the oxidation of carbon monoxide and sulfur dioxide and obtained the greatest activity with primary crystallites of the order of 30 A. Recently, Rubinshtein, Minachev, and Shuikin (353) investigated the minimal concentration of supported metal catalysts effective in hydrogenation and dehydrogenation reactions. In the case of platinum, concentrations from 0.1 to 1.0% on carbon were studied. The estimated size of the platinum crystals was 40-50 A. in agreement with the findings of Dankov and Kochetkov (59). The x-ray data indicated that the activity of the catalyst was due predominantly to the [ill] octahedral faces of platinum which is in agreement with Balandin's multiplet theory. I n comparison, elementary crystallites of palladium, 40 A. in size, produced by vacuum evaporation were found to be active in the hydrogenation of ethylene. A drop in activity was associated with recrystallization and growth of the crystallites in the fatigued layers. The extreme importance of the dispersion and extent of distortion of the lattice has been established, principally through the extensive experimental studies of Rubinshtein which were recently presented in summary (350). The systems studied were (a) nickel supported on alumina, used in the hydrogenation of benzene and carbon monoxide, dehydrogenation

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of cyclohexane and formic acid, and dehydration and dehydrogenation of alcohols; and (b) magnesia used for the dehydration and dehydrogenation of normal butyl alcohol. Activity-dispersion curves for selected dehydrogenation reactions over nickel on alumina are depicted in Fig. 1. The structure of the molecule undergoing dehydrogenation affects only the course of the curve but does not alter the occurrence of the maximum in activity a t a dispersion of 70-80 A. The studies of magnesia were carried out in great detail with special attention having been paid to (i>

FIG.1.

50

70 80 90 100 110 120 DISPERSION in A. Activity-dispersion isotherms for dehydrogenation. 40

60

1. CsH1?a t 320°C. 2. HCOOH a t 200°C. 3. i-CsH1,OH at 240°C. 4. i-CsH,OH a t 260°C.

the effect of dispersion at constant lattice parameter and (ii) the effect of deformation at constant dispersion. This study differentiated the specific influence of these factors upon the catalytic attributes of the material. The following series of preparations of magnesia were studied by Rubinshteh:

( a ) Preparations having the same degree of dispersion, 28 k 5 A. ( b ) Preparations having: (1) The lattice parameter a = 4.17 & 0.01 A. (2) The lattice parameter a = 4.20 i 0.01 A. (3) The lattice parameter a = 4.23 & 0.01 A.

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The selectivity and activity of these preparations in the dehydrogenation and dehydration of n-butyl alcohol were determined. The reactions were conducted a t atmospheric pressure with temperatures between 400" and 46OoC., and an hourly space velocity of 1.3 which precluded thermodynamic equilibrium. The activities were expressed in milliliters (STP) of gaseous product formed by each of the reactions per milliliter of alcohol

+-* \

I

I

25

I

I

I

I

30 35 40 DISPERSION in A.

I

I

45

50

FIG.2. Activity-dispersion isotherms a t constant lattice parameter a. 1. Dehydrogenation: a = 4.20 i-0.02 A. 2. Dehydrogenation: a = 4.17 k 0.01 A. 3. Dehydration: a = 4.20 k 0.02 A. 4. Dehydration: a = 4.17 f 0.01 A.

per gram of catalyst. The selectivity coefficient for dehydrogenation was defined as the ratio k , / ( k , lcz), where kl is the reaction velocity for dehydrogenation and k 2 is the reaction velocity for dehydrogenation. The effect of dispersion upon the activity a t constant lattice parameter is shown in Fig. 2 a t 440' and 460", whereas the effect of lattice parameter upon the activity a t ronstant dispersion is depicted in Fig. 3. The lattice parameter also influenced the selectivity of the catalyst. At all temperatures the selectivity coefficient for dehydrogenation decreased with increasing lattice parameter, which indicates that the

+

23 1

CONTRIBUTIONS O F RUSSIAN SCIENTISTS

dehydrogenation was favored by a compressed lattice and low operating temperature whereas dehydration was favored by an expanded lattice and high temperature. The influence of dispersion a t coiistant lattice parameter upon the selectivity is indicated by the isothermal curves of Fig. 4. The compressed lattice is given by curves ( l ) , the normal lattice by curves (2),

O U - ' 4.16 4.11 4.18

I

4.19

I

I

4.20 4.21

I

1

I

4.22 4.23 424

I

4.25

LATTICE PARAMETER in A.

FIG, 3. Activity-lattice parameter isotherms a t a constant dispersion of:% 1. 2. 3. 4.

k 5 A.

Dehydrogenation at 460°C. Dehydrogenation a t 440°C. Dehydration a t 460°C. Dehydration a t 440°C.

and the expanded lattice by curves (3). The expanded lattice favored dehydration only at the higher temperature where the coefficient of selectivity was only slightly influenced by dispersion. The compressed lattice (curves (1)) showed most markedly the influence ,of dispersion. A sharp minimum occurred in these curves a t ca. 40 A. which indicates that a dispersion of this order favored dehydration. The minimum in the selectivity-dispersion curve occurred a t lower dispersion (25-30 A.) for the undeformed lattice and was not as clearly expressed as that for the compressed lattice.

232

J. G. TOLPIN, G. S. JOHN, AND E. FIELD

0 95 0.90

-

0.75

-

T = 440' C

W

0

>

20

I

I

I

I

I

I

1

T = 460. C

25

30

35

45

40

50

55

60

65

DISPERSION in A..

FIG.4. Effect of dispersion upon selectivity at constant lattice parameter a. 1. a = 4.17 = 4.21 3. a = 4.23

2. a

w0

- 0.01 A. - 0.01 A. - 0.01 A.

400' C

0.95-

E 0.90-

4.16

4.17

4.18

4.19

4.20

4.21

4.22

4.23

4.24

4.25

LATTICE PARAMETER in A.

FIG.5 . Effect of lattice parameter upon selectivity of the catalyst at constant dispersion.

CONTRIBUTIONS O F RUSSIAN SCIENTISTS

233

Figure 5 contains isothermal selectivity-lattice parameter curves. A simple linear dependence was established between the selectivity and the parameters of the crystalline lattice a t all temperatures investigated; however, the slope of these isothermal lines did increase with increasing temperature. The curves of Fig. 4 demonstrate excellently the interrelationship th a t was found t o exist between the dispersion and extent of distortion of the lattice and further emphasize the importance of these factors in the formation and selection of catalysts. A similar study was carried out by Kukina (183) upon chromic oxide used in the simultaneous dehydrogenation and dehydration of isopropyl alcohol. Thermographic as well as x-ray analyses were carried out upon individual preparations of the catalyst. The method of preparation had a pronounced effect upon the specificity and selectivity of the chromic oxide as well as on the thermograms. However, a parallelism was not observed between specificity and the average change of the lattice parameters. This was previously shown by Balandin and by RubinshteIn t o be in accord with the multiplet theory; the latter regard the enhanced dehydration only as a result of increasing lattice parameter (183). The importance of dispersion and distortion in catalysis was recognized by Dankov as the result of his very early investigations. I n this connection his studies prompted Kobozev to interpret the phenomenon of optimal dispersion in terms of his theory of fluctuation and active ensembles. The conditions for attaining the optimal dispersion were given a theoretical interpretation by Roginskii in terms of his theory of supersaturation. Balandin examined (30) the influence of two types of asbestos on the formation of a platinum (8%) catalyst and concluded that the nature of the asbestos determined both the number and the nature of active centers on the catalyst and that chrysotile asbestos was preferable t o amphibole asbestos for dehydrogenation. Electron-microscopical studies of asbestos and other materials used for catalyst supports are being made by Shekhter (363a). Atoms of platinum, palladium, silver, and gold were found to creep on several supports with rise of the temperature. The final distribution of the catalyst, the extent of dispersion and the shape of the particles depended upon the nature of the support (36313). Different faces of a palladium and perhaps platinum crystal may exhibit different stabilities to this lateral displacement of atoms. Furthermore, the extent of changes in the different (‘zones” on a palladium surface is influenced by the reaction itself (363c). For zinc oxide, electron-microscopical, x-ray, and adsorption data were correlated with the effectiveness of the samples in decomposition of methanol a t 328”. The results were interpreted as showing no definite correspondence between the catalytic

234

J. G . TOLPIN, G . 6 . JOHN, AND E. FIELD

activity and the x-ray structure of the catalysts, but pronounced differences in the electron-microscopical data corresponded to differences in the performance (363c). Recently Roginskil reviewed this field including Shekhter’s contributions (334) and concluded that electron microscopy is of no decisive advantage over other methods in the study of dimensions of individual particles, but is superior to other methods for a statistical study of distribution of larger aggregates of particles and pores. The value of oxidized nichrome as a support for platinum catalysts has also been explored by a group of workers (26,126,177). Criticisms of Balandin’s purely geometric multiplet theory have arisen in the Russian and in the non-Russian literature; one of the most recent arose as the result of work carried out at the Karpov Institute of Physical Chemistry with platinum, nickel, copper, and chromia. Work reported by Kagan (145a) was interpreted to show that the results on dehydrogenation of cyclohexane over platinum contradicts the multiplet theory. According to Kagan cyclohexene was first formed and underwent subsequent hydrogen disproportionation. This process is not compatible with the mechanism envisioned on the basis of Balandin’s sextet model. Similarly copper, which is unsuitable for either the hydrogenation of benzene or dehydrogenation of cyclohexane, hydrogenates cyclohexene or promotes hydrogen disproportionation in it. This behavior of copper is thought by Kagan to be contrary to Balandin’s concepts. Dehydrocyclization of paraffins was also used by Kagan as a means by which his disagreement with the multiplet theory was demonstrated (145b). On the basis of limited experimental data on the conversions of heptaneheptene mixtures over chromia-alumina at 484”, Kagan and co-workers rejected the applicability of the multiplet theory to the explanation of the mechanism of dehydrocyclization. Instead of this theory and of the views of Herington and of Pitkethly and co-workers, Kagan postulates random orientation of adsorbed paraffinic radicals, leading t o cyclization or dehydrogenation alone, depending upon the position of the second carbon atom adsorbed. Hydrogenation of some of the olefins charged may also occur. Kobozev’s inductive theory of active ensembles (l68,169,171,172a,b) postulates that the carrier of catalytic activity is a phase present in high dilution on the support. This phase, which is in the amorphous precrystalline state, consists of a number of cells separated by geometrical barriers (microfissures) which are impenetrable to molecules for movement from one group of cells to another. Thus there is no exchange of catalyst atoms, reactant molecules or catalyst poisons between these cells. The smallest group of catalytically active atoms in the cells form an ensemble which constitutes the carrier of the catalytic activity and to

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235

a first approximation is independent of the nature of the support. The number of atoms in each ensemble and the area within which the catalyst atoms can migrate can be determined from experimental kinetic data and physical properties of the active component of the catalyst by means of formulae developed by Kobozev. Other formulae developed by him make it possible t o calculate the activity of an ensemble as a function of temperature, the number of ensembles and of “migration cells” present on the surface of the catalyst and the poisoning coefficient of a poison adsorbed onto the catalytic surface. The cells act as “potential valleys” within which active atoms congregate into ensembles, a t the point of the highest adsorption potential. The distribution of these atoms is governed by the laws of probability. Resonance between closely adjacent atoms of an ensemble activates the latter. The “migration cell” concept was connected by Kobozev (172b) with some modern views of Russian and non-Russian students of the crystalline state, indicating that crystals are built u p of microcrystalline units of the order of magnitude of cm., which is close t o the size of the “migration cell” (137a). The catalytically active structures were grouped by Kobozev into the following basic classes: (a) Structures conforming to the ensemble principle, namely, the combination of 2, 3, or more atoms attached t o a carrier. These-structures resemble the multiplets postulated by Balandin. Palladium, platinum, and iron which may be employed in ammonia synthesis, and molybdenum used in the hydrogenation of olefinic linkages constitute members of this category. The catalysts of this class are essentially unaffected by the nature of the support. (b) Structures complying with the aggravation principle, i.e., active elements attached to a catalytically inactive group or t o a supporting substrate. The aggravation principle appears to be a new term devised t o represent the well-known effects of supports on the activity of a catalyst. Since the formulation of his concepts in 1939 Kobozev has carried out many investigations in the attempt t o verify their general validity. I n the decomposition of HzOzand the oxidation of NaZS03, the specific effect (173) of small amounts of iron (0.0005 t o 40%) added to copper on carbon and the converse in which small amounts of copper were added t o iron on carbon were studied. The activity of these catalysts was very effectively promoted by these additives, the extent of promotion being proportional t o the concentration of the additives. The catalytic synthesis of ammonia by iron supported on carbon or asbestos was also studied. The results of this study and similar studies of catalytic

236

J. G . TOLPIN, G. S. JOHN, AN D E. FIELD

oxidation-reduction reactions and hydrogenation processes were interpreted by Kobozev as supporting his ensemble principle (1 70). The nature of the active centers of supported platinum catalysts for hydrogenation of olefins and aromatics was investigated by Koboxev arid Reshetovskaya (172a). They concluded that the double bonds of benzene hydrogenate consecutively and that the active ensemble is identical with that involved in the hydrogenation of olefins. These conclusions are in disagreement with those of t,he Balandin school. Experiments were also performed comparing catalysts made from H2PtC1, with those from K2[C13Pt-CH2-CH=CH-CH2-PtC13].H20. Presumably the latter can yield only even numbers of Pt atoms in an ensemble and the observed differences in behavior were ascribed to this fact. Applying Kobozev’s method of calculation of the number of platinum atoms in an active ensemble they found that activation of one type of molecules (e.g., hydrogen molecules in the reduction of nitro compounds) is involved in reactions occurring on ensembles of one or five platinum atoms; when two types of molecules are activated, as in hydrogenation of olefinic (maleic acid) or aromatic (phenol) compounds, the ensemble consists of two or six atoms of platinum. According t o their data, secondary catalytic structures are occasionally formed by deposition of a single platinum atom or a doublet upon a catalyst face consisting of four platinum atoms, rather than on the catalyst support; this results in a n imperfect new structure of high catalytic activity. Limited support of Kobozev’s theory has appeared in the Russian literature with little or no mention in the non-Russian literature. Among his Russian advocates is Frost, a thermodynamicist who has been studying the kinetics of the reactions involved in catalytic cracking. Frost and his co-workers found evidence of the existence of a n ensemble of two aluminum atoms in hydrogen disproportionation over catalysts prepared by impregnating pure silica gel with acidified aqueous aluminum sulfate (132a) and in dehydrogenation of cyclohexane over palladium and nickel supported on charcoal and on magnesia (132b). The data for palladium agreed with those of Kobozev (172b). The theory of Kobozev is open to criticism of the character recently stated by Kummer and Emmett (184), who observed that there was a very rapid exchange between the isotopes of nitrogen in the presence of singly and doubly promoted iron synthetic ammonia catalyst. Kobozev (167) had concluded earlier that iron synthetic ammonia catalysts consisted of an ensemble of iron atoms to which were attached the promoter molecules. Each ensemble was capable of adsorbing only one nitrogen molecule; further, in accordance with his theory, these ensembles, separated from one another by geometrical barriers, would make the

CONTRIBUTIONS OF RUSSIAN SCIENTISTS

237

exchange of nitrogen between them impossible. The data of Kummer and Emmett cannot be reconciled with the ensemble principle as it stands. Several theories with regard to mode of preparation, promotion, poisoning, and modification of catalysts have been advanced by Roginskii (324-329,336,339). Very early Roginskii postulated the significance of the role of supersaturation in reaction kinetics; recently this concept has been extended to include catalyst preparation. During the preparation of a catalyst a number of chemical, mechanical, and physical effects are operative. The relative significance of each of these factors has been discussed by Roginskii in terms of the phenomenon of supersaturation (excess free energy). Supersaturation may be achieved in a number of different ways, several of which are: (1) catalytic preparations by crystallization : (a)From solution-have the solutions containing the reactants forming the catalyst as concentrated as possible. ( b ) From vapor-have the surface upon which condensation occurs as cold as possible and the condensation rate high. (2) Catalysts prepared by a gaseous reaction through: ( a ) Decomposition-maintain low concentration of products a n d high concentration of reactants. For example, the preparation of nickel catalyst by decomposition of N i(C 0 )4 : Ni(CO)a--+ Ni

+ 4CO.

An attempt should be made to maintain a low concentration of co. ( b ) Reduction-maintain minimum concentration of reaction products and maximum Concentration of reactants. For example, in the reduction of metal oxides with hydrogen or carbon monoxide, the product gas is water or carbon dioxide; the concentration of these substances in the exit stream should be held to a minimum. Likewise it is equally import a nt that oxygen and product gases be absent from the entrant gas. The importance of removing traces of impurities from the reducing gas has recently been demonstrated by Taylor (384) and McGeer (229). In the investigation of the isotopic exchange reaction of NZ3Oand NZz8 over an iron-alumina ammonia synthesis catalyst,l McGeer observed th a t the rate of isotopic exchange was strikingly dependent upon the purity of the hydrogen employed in reducing the catalyst prior to its use. The

238

J. G . TOLPIN, G. S. JOHN, AND E . FIELD

presence of minute traces of oxygen and water vapor in the hydrogen made it impossible t o free the catalytic surface completely of the effective oxygen poison. Roginskil suggests that during the formation of a catalyst by reactions in the solid state the addition of a substance which forms a solid solution with the reaction products resulting from the formation of the catalyst, but not with the reactants, is beneficial to the production of supersaturation, i.e., excess free energy. This excess free energy possessed by a solid catalyst is essential to the formation of active structures which are principally responsible for the catalytic activity. The effect of free energy of formation on the catalytic activity has been investigated for a number of systems by Roginskii and his co-workers. 111. INVESTIGATION OF ADSORPTION PHENOMENA

A fundamental advance in the theory of adsorption phenomena was made in 1916 when Langmuir suggested that adsorption was to be regarded as a chemical process occurring on an energetically uniform surface and that the adsorbed phase was a unimolecular layer of noninteractive molecules. However, it soon became impossible to describe some important phenomena of catalysis without denying the concept of a uniform surface. Modern developments of the theory of adsorption have been directed toward studies of the interactions between adsorbed molecules and of the energetic heterogeneity of the surface. Following the pioneering work of Constable (1926), Roginskil and Zel’dovich introduced (328,331,362) statistical concepts for the quantitative description of the nonuniformity of catalysts. I n these studies the energetic nonuniformity of the surface has generally been characterized by distribution functions for the energies of activation and heats of adsorption. Methods for the determination of these distribution functions from equilibrium and kinetic data have been one of the principal goals. 1. Determination of the Distribution Function of the Heats of Adsorption

and Interaction Function The theory of equilibrium adsorption and kinetics of adsorption upon the surface of adsorbents have been thoroughly treated in the Russian literature since experimental results were obtained which did not agree with Langmuir’s initial assumptions: (1) that the surface of the adsorbent is energetically uniform; (2) that the adsorbed particles do not interact with one another; (3) that the surface is covered by only a monolayer of the adsorbate, If the third assumption is retained then three alternative possibilities are offered: (a) assumption (1) is rejected and assumption (2)

CONTRIBUTIONS OF RUSSIAN SCIENTISTS

239

is retained; ( b ) assumption (1) is retained and assumption (2) is rejected; (c) assumptions (1) and (2) are both rejected. From a catalytic point of view the situation (a) which pertains to rejection of the uniformity condition is of greatest interest. This particular situation was investigated by Zel’dovich (432), Temkin (386), and recently by Levin (202). In 1935 Zel’dovich (432) carried out a special theoretical treatment concerning the origin of the parabolic isotherm typified by the type I1 isotherm. It was demonstrated that this type of isotherm could result from the nonuniformity of a surface characterized by an exponential distribution function p ( Q ) with respect to the heat of adsorption defined by p(Q) = Ccn* where Q is the heat of adsorption and C and a are constants. A similar study was carried out by Cremer and Flugge (51) and later by Halsey and Taylor (134). Temkin (386) assumed an equilibrium distribution on the surface with respect to the heat of adsorption given by p(Q) =

const. = C

and theoretically founded the logarithmic isotherm of adsorption @(PI = b In (ap)

which was empirically obtained by Frumkin and Shlygin (125). If the distribution function p ( & ) for the heat of adsorption Q is known, it is not difficult in principle to calculate the adsorptive properties of the surface through the adsorption isotherm @ ( p ) . Far more difficult is the inverse problem of deducing the distribution function p ( Q ) from the adsorption isotherm @ ( p ) . The latter problem, important both to adsorption and to catalysis, has been investigated principally by RoginskiI, Zel’dovich, Elovich, and Temkin. The study has extended over a number of years and has resulted in the development by Roginskii of a general theory of processes occurring on nonuniform surfaces. The progress of this work was held up for some time due largely to mathematical difficulties involved in the solution of the integral equations which arise in the determination of p ( & ) from a general experimental isotherm. Roginskii suggested a simplified method of analysis for processes occurring on a nonuniform surface which made it possible to surmount these mathematical difficulties without excessive distortion of the physical model. The method has general applicability to statistical processes; however, its application to adsorption equilibrium only will be discussed here.

240

J . G . TOLPIN, G . S . JOHN, AND E. FIELD

The adsorption isotherm @ ( p ) on a nonuniform surface was expressed b y Roginskii as a function of the pressure p in the form

where p ( Q ) is the distribution function of the hcat of adsorption &, Q1 and Q2 are the lower and upper limits of the heats of adsorption on the surface,

FIG.6. Graph of the function B ( Q ) .

and bo is a quantity which is independent of Q. The distribution function p(Qj is defined such that

Let us define a function

e(Q) as follows:

It is seen from Fig. 6 that e(Q) has an inflection point, the abscissa of which is QrI = RT In (bolp) and the ordinate is BI1 = 45. A typical distribution function p ( Q ) is plotted in Fig. 7 together with 6(Q) . p ( Q ) . The shaded area limited by this latter curve with abscissa Q I and Qz amounts to the integral given in Equation (1). Substituting this shaded area by the equal area ABQ2QDRis equivalent t o substituting the integral in Equation (1) by the equal integral

CONTRIBUTIONS OF RUSSIAN SCIENTISTS

24 1

If p ( Q ) does not change too rapidly and if the interval between Q1 and is sufficiently large, one can assume approximately th a t the point Q,, coincides with the abscissa of the turning point of O(Q), that is, Q2

QGR 02 Q Graphical interpretation of Roginskil's method.

QI FIG.7.

When Equation (2) is evaluated for the distribution functions p(Q) =

or

p(Q) =

one obtains $(p)

or

=

const. (Qz - RT In bo

const. Ce-aQ

+ RT In p ) = C1 + Cz In P

respectively which is in agreement with the results obtained by other more rigorous methods.

242

J. G . TOLPIN, G . 8. JOHN, AND E. FIELD

If Equation (2) is differentiated with respect t o the lower limit we obtain

which makes the determination of p ( Q ) possible. A number of investigations have been made along the line of improving the Langmuir theory by assuming a uniform surface and introducing the possibility of interaction between the particles. Russian and nonRussian investigators participated in this effort, including Frumkin, Langmuir, Wang, Roberts, Kobozev, and Temkin. Recently Vo1’kenshteh (417) reinvestigated the problem with the object of finding a convenient method for the determination of the form of function +(r) from the experimental isotherms ‘P(p), where +(r) is the function representing the interaction energy of two adsorbed molecules in terms of their distance of separation r. The experimental isotherm does not provide sufficient information t o indicate which one of the two basic assumptions of the Langmuir theory should be rejected. Consequently Vol’kenshtein (417) has undertaken the task of deducing the interrelationship between the functions 4(r) and p ( Q ) which give rise t o the same isotherm ‘P(p). The heat of adsorption Q per molecule has been related t o the energy of a molecule upon the surface, this energy being expressed in terms of the interaction energy of the adsorbed molecule with the lattice of the adsorbent and of the interaction energy with other adsorbed molecules. This relationship in turn was used in the adsorption isotherm to deduce the adsorbate interaction energy function. Vol’kenshteln has evaluated the distribution function p ( Q ) of heats of adsorption and the adsorbate interaction energy function +(r) = Av(r) for a number of typical isotherms and his results are summarized in Table 11. I n this table H , n, bo, and c are constants. Qo is the heat of adsorption of the free surface, Qm., is the maximum heat of adsorption, and T is the effective diameter of the adsorbate molecule on the surface. 2. Determination of the Distribution Function of the Activation Energies

of Adsorption

In addition to the theoretical studies of equilibrium adsorption, noginski1 has conducted extensive investigations of the kinetics of adsorption on nonuniform surfaces and has shown that the character of the kinetics of adsorption is dependent upon the presence or absence of surface migration. Migration of the adsorbate molecules brings about a redistribution which conforms with the values of the adsorption coeffi-

TABLE I1 Distribution function

p(&)

11. Uniform distribution, a particular case of the above, where n = 0 p = H

IV. Exponential distribution p

=

He-4

Law of interaction Au(r)

A L ~= 011

=

QO

+ r7 where

Isotherm 8 ( p )

Q2

a1

-7

- Qmax

~1

=

HkT =

kT

e

= c1 In p

-YO' a2

c2 = K k T In boeQmax/kT =

Au =

7

a1

- c2, where

+ ro2kT In boe-Qo/kT a2

- c2, where

where

c1 =

244

J. G . TOLPIN, G . S. JOHN, .4ND E. FIELD

cients on the individual portions of the surface. The nature of the functional dependence between the energy of activation E and the heat of adsorption Q on each section of the surface determines the kinetics of adsorption. Thus Roginskii has considered the kinetics of (1) adsorption without redistribution of the adsorbate molecules, and ( 2 ) adsorption with redistribution of the adsorbate molecules, in the absence of a functional connection between the activation energy E and heat of adsorption Q. In the absence of redistribution of molecules on the surface the velocity of the adsorption process is determined solely by the distribution function of activation energies. The velocity of adsorption on sections of the surface characterized by the activation energy E is expressed in terms of the change in the fractional surface coverage e(E,t) with the time t by do( h',t ) = lcop(l - O)e-E/RT. --dt

(3)

Integration of Equation (3) under conditions of constant pressure gives 1 - @(E,t)= exp [ - k ~ p t e - " / ~ ~ ]

(4)

which represents the fraction of the free surface of a section characterized by the activation energy E a t time t. Let us now multiply this expression (4) by p(E)dE, where p(E) is the distribution function of activation energies, arid integrate overall values'of E between h'1 and Ez. The result of this operation gives the fraction of the total free surface 9 a t the time t , that is

where +(t) is the fractional coverage of the entire surface. In adsorption with redist,ribution in which there is no functional relationship between E and Q , it is assumed that the velocity of redistribution is larger than the velocity of adsorption. Consequently the various sections of the surface will be occupied in the order of decreasing heats of adsorption and a t all times all sections will be involved in the adsorption irrespective of the magnitude of their activation energy. However, due to the exponential dependence of the velocity of adsorption upon the activation energy the character of the adsorption will be determined principally by the processes occurring upon sections with minimal values of E. These sections form on the graph p ( E ) , as shown in Fig. 8, a relatively narrow vertical band the position of which determines the

245

CONTRIBUTIONS O F RUSSIAN SCIENTISTS

velocity of the process. RoginskiI has termed this band the controlling band since this band controls the nature of the adsorption. With increasing coverage of the surface the controlling band will not alter in position but will decrease in height, i.e., the number of sections with small values of the activation energy will decrease continually, and a s a

FIG.8. The kinetics of adsorption when E is independent of &. (The area under curve t l is the fraction of the free surface a t the time t l ; that under curve t 2 the fraction a t the time tS. The letters C.B. denote the controlling band.)

consequence the velocity of the total process will decrease. of adsorption will be expressed by d+ - = kop(l dt

+)p(E,,,)e-Emin’RT

= k,,’(1 -

The velocity

@)e--EmidRr.

which is equivalent to the kinetics observed on a uniform surface. Roginskii also treats the cases in which the functional relationship between E and Q is prescribed. If E’ and Q vary in the same respect from section t o section the kinetics of adsorption are defined by

@ = dt

kOPP(Emin)e-Emin’~~

=

ko’e-Ernin/RT.

On the other hand, if E and Q vary conversely to one another then the controlling band shifts with coverage toward higher values of E and the kinetics will coincide practically with the kinetics of adsorption on a nonuniform surface without redistribution discussed previously.

246

J . G . TOLPIN, G . S. JOHN, AND E. FIELD

Roginskif (331) has treated the problem of determination of the distribution function p ( E ) of activation energies by this approximate statistical method. The details are very similar t o those discussed above for the determination of p ( & ) from the experimental adsorption isotherm. The energetic nonuniformity of catalytically active nickel oxide was investigated by Keier (161). The kinetics of activated adsorption was studied under constant pressure a t several temperatures and the data were described by the expression

At'/" (6) where A and l / n are constants, and t is the time required to adsorb the q =

quantity, q, of adsorbate. Employing the approximate theory of non-unif orm surfaces developed by Roginskii the distribution function p ( E ) of activation energies E was determined to be p ( E ) = lieuE where H = A ~ ( T @ and~ a~ = 1/nRT. quantity T O is defined by the relation

In the expression for H , the

~ , A,, nT,are the characteristic constants The quantities ATI, n ~ and of Equation (6) evaluated at temperatures T Iand T zrespectively. Of equal importance in the characterization of a catalytic surface is the determination of the dependence of the change of activation energy of adsorption upon the extent of surface coverage. This change in energy of activation with coverage has been related by Roginskii to the change of log t of adsorption in the following manner t

E = 2.3RT log -*

70

Substituting into this equation values of log t corresponding t o given extents of adsorption, the energy of activation as a function of coverage can be found. Levin (202) presented a more exact solution of the problem with regard to the determination of the distribution function p(E) of activation energies which does not possess the limitations imposed by Roginskii's met,hod. The method employed the Laplace transform to solve the integral Equation (5). The following transformation was carried out: y=lnl

x=-

E'

RT

CONTRIBUTIONS OF RUSSIAN SCIENTISTS

which yielded J/(eU)= assuming E l

=

J0

0 and E , =

O0

00.

247

exp [ - ? ~ ~ p e v - ~ ] p ( s J d z Both sides were then multiplied by e-”d y

and integrated from - 00 t o

+

00,

thus

Interchanging the order of integration on the left and integrating the resulting expression with respect t o y the following was obtained

where r (-8) is a gamma function. When the inversion of the Laplace transform was used, the expression

was obtained. Levin then gave means of evaluating the integral over y when experimental data concerning are available. Thus an extremely useful method for the determination of p ( E ) from experimental data was rigorously developed. I n the case of the adsorption of acetylene upon nickel oxide it is observed that the activation energy increases pronouncedly with surface coverage. From this study Keler states that the adsorption characteristics on nickel oxide are explicable on the basis of a nonuniform surface without the imposition of interactive forces between adsorbed molecules. However, final judgment has been reserved by Keler until a study employing the differential isotopic method developed by Roginskii (338) has been carried out. This technique, formulated by RoginskiI in 1946, consists essentially in utilizing tracer molecules t o distinguish between energetically uniform and nonuniform surfaces. On a uniform surface, in the presence of interactive forces, all adsorbed molecules are under identical conditions. However, on an energetically nonuniform surface this is not the case. Thus the method cQnsists of covering a portion of the surface with one isotope and a subsequent portion with another. The composition of successive samples of gas desorbed from these labeled sites reveals the desired energetic information.

+

248

J . G. T O L P I N , G. S. J O H N , A N D E. F I E L D

Keier and Roginskii have experimentally investigated the heterogeneity of the surface of metallic nickel and ZnO (163) catalysts on sugar charcoal (162). In the activated adsorption of hydrogen on sugar charcoal it was shown that the connection between the activation energies of adsorption and of desorption is quite complicated. In the region of small surface coverage an increase in the activation energy of adsorption is accompanied by an increase in the activation energy of desorption whereas a t large surface coverages the converse is true. I n the application of this method it should be pointed out th a t mobility of the adsorbed phase on a nonuniform surface will yield results th a t are equivalent to those of a uniform surface. However, making use of information obtained from the kinetics of adsorption and from studies employing the differential isotopic method, these difficulties can frequently be resolved. I n their study of metallic and ZnO catalysts, Roginskii and Keier obtained results conclusively demonstrating the surface heterogeneity TABLE I11 Conditions of adsorption Step I Adsorption of Df p = 1.48 mm. of ITg Q D ~= 0.095 CC. (STP) t = 9 min. 1 = room temp. Step I1 Adsorption of Hz p = 3.08 mm. of Hg yuz = 0.04 CC. (STP) t 9 min. I" = room temp. , I

DZ%

H2%

3 4 5

5 0 0 40 95

95 100 100 65 5

6 7

100 100

0 0

5

100 100 100 55 0

0 0 0 45 100

Room temp. Room tcmp. 63-78 84-100 197-253

6

5

95

380

Portion KO.

T'C.

Step I11 Desorption 1 2

Room temp. 20-65 170-220 300-320 420-470 520 530

=i

Step I Adsorption of Hz p = 1.51 mm. of Hg YE, = 0.06 CC. (STP) t = 8 min. I" = room temp. Strp I1 Adsorption of D, p = 2.02 mm. of Hg ( I H ~= 0.01 CC. (STP) t = 8 min. T = room temp.

Step I11 Desorption

1 2 3

4

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249

of these catalysts. The ZnO was studied in the same manner as the sugar charcoal discussed above. In the investigation of the metallic nickel the adsorption was carried out at room temperature upon a sample which had been previously outgassed a t 580°C. The desorption of the gas was produced by gradually increasing the temperature from room temperature t o 500°C. The desorbed gas was pumped from the reaction chamber and analyzed. Two portions of gaseous hydrogen differing in isotopic composition (light hydrogen and 99% deuterium being used in these studies) were initially adsorbed. Table I11 gives the results of some experiments in which the adsorption was carried out in various orders to insure the absence of an isotope effect. As is seen, the composition of the gas first desorbed agrees with that of the gas last adsorbed. This initial desorption is followed by a region of gaseous mixtures, of the two isotopes and the last portion desorbed is of the same or nearly the same composition as the first gas adsorbed. 3. Adsorption upon Structural Defects

Vol’kenshtein (422) has also treated adsorption phenomena on solids in terms of defects in the periodic lattice of the adsorbent. These disturbances embrace all macroscopic and microscopic distortions of the strictly periodic structure of the lattice. This classification was categorically made on the basis of the range of their perturbing influences. The macroscopic distortions extend over regions many times larger than the unit cell and are characterized by cracks, dislocations and even faces and edges of a crystal. On the other hand, the microscopic distortions are confined to domains that are of the same order of magnitude as the unit cell of the crystalline solid and arise from Schottky and Frenkel defects, abnormal valency in an ion a t its normal position in a heteropolar lattice and foreign atoms in substitutional or interstitial sites in the lattice. The microscgpic distortions or micro-defects possess a mobility which is characterized%y an energy of activation. This energy of activation is dependent upon the nature of the defect, lattice structure, and direction of migration of the defect. Micro-defects also possess the ability of interacting with one another, giving rise to new defects which possess different properties. These interactions may be regarded as reactions between the defects having characteristic heats of reaction and activation energies. The totality of defects in a unit volume of the crystal is termed the ‘(disorder” of the crystal. This disorder is assumed to be small and composed of defects having either a biographical or a thermal origin. The biographical disorder, denoted by X , is irreversible and preserved

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J. G. TOLPIN, G. S. JOHN, AND E. FIELD

down t o 0°K. The thermal disorder is reversible and superimposed upon the biographical. Thus the total disorder a t any temperature T is the sum of the biographical disorder existing at 0°K. and thermal disorder characteristic of the temperature T ; consequently a t T = T,,, the total disorder Y is a maximum of which X is biographical and ( Y - X ) is thermal. This latter number is a characteristic constant for a given surface. Clearly two extreme cases can exist: (1) that in which +,he disorder is purely biographical and (2) that in which it is purely thermal. For the intermediate cases the relative importance of the two types of defects is dependent upon temperature and previous history of the material. Vol’kenshtein regards these micro-defects as sites for adsorption and is thus free from the basic assumptions of conventional adsorption theories, (1) constancy of number of adsorption centers with temperature and coverage, and (2) immobility of adsorption sites. The presence of defects does not imply that the surface is energetically heterogeneous. Nonuniformity of the surface arises from adsorption sites having different heats of adsorption. Vol’kenshtein assumed that only one definite type of defect characterized by the heat of adsorption q is involved in adsorption and that only one adsorbate molecule can be attached t o each site. The adsorption process is regarded by Vol’kenshtein as a reaction between the adsorption site A with the gaseous adsorbate molecule G . This reaction which produces a new defect B may be written symbolically

A+G+B,

AH=q.

(8)

If the concentration of the defects A , G, and B at any given temperature T is denoted respectively by N L , No, and Ns,then their equilibrium concentrations are related in the following manner

Assuming that the total number of adsorption sites a t any temperature is given by N = N, N B (10) then

+

which is equivalent to the conventional Langmuir expression if N remains constant for all temperatures, which implies that the defects have a biographical origin.

CONTRIBUTIONS O F RUSSIAN SCIENTISTS

25 1

I n addition t o the adsorption reaction it is admitted that the defects

A can undergo reactions involving other defects on the surface. These

reactions among the defects may be either monomolecular, bimolecular, or more complex. Examples of the first two cases have been discussed in detail by Vol’kenshtein. I n the monomolecular case it is assumed th a t in addition t o the defects A and B a third type of defect C exists which undergoes the following reaction AH = -u.

CGA,

(12)

At equilibrium Equation (11) is supplemented by

where N c denotes the concentration of the defects C. Evidently the maximum thermal disorder Y is given by

Y

=

NA

+ NB + Nc

(14)

and the biographical disorders X a t T = 0°K. is given by X = 0. Making use of the latter expression and Equation (10) it is possible t o write Equat,ion (13) in the form

N - Ns --

-

Y - N

0.

Using Equations (11) and (15) it is possible t o solve for the unknowns NB, the number of adsorbed molecules and N , the total number of adsorption centers. I n the bimolecular case it is assumed th at in addition to the defects A and B there are defects of the type C and D characterized by the reaction C&A+D, AHZ-U. (16) As in the previous case, at equilibrium Equation (11) is supplemented by

N AND -p NC

=

POg-u/kT

(17)

where ND is the concentration of the defects D. I n the most general case the biographical disorder X * a t T = 0 will be equal t o

X = Nn

+ Ng -

whereas the maximum disorder Y a t

Y = NA

T

=

N D

T,,, is given by

+ N s + Nc.

* The coefficient of N D is the negative of

(18)

that given by Vol’kenshtein.

(19)

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J. G . TOLPIN, G . 5. JOHN, AND E. FIELD

The quantities X and Y are invariant with temperature. Therefore, making use of Equations (lo), (18), and (19) it is possible to rewrite Equation (17) in the form

which may be solved for N giving

N

= +{

Ne - P

+ X - d ( N B - /3 - X)’ + 4 B Z }

(21) where 2 = ( Y - X) is the thermal disorder. This expression* gives the dependence of the total number N of adsorption sites upon the number N e of occupied sites. If the expression (21) is substituted into Equation (11) and the resulting expression solved for N R there is obtained

where

If it is assumed that the disorder is predominantly biographical in origin, i.e., 2 = 0, the conventional Langmuir isotherm is obtained. If, on the other hand, the disorder is assumed t o have a thermal origin, i.e., X = 0, then the characteristic Freundlich isotherm 9 = kp”” is obtained. The differential heat of adsorption is readily calculated from the change in the total energy E of the crystal produced by increasing the extent of adsorption. On the surface of the crystal there are N defects of which N n are free and NB are occupied. Of the total number of defects X are biographical defects and N - X are thermal defects. The production of each defect consumed the energy u. Adsorption on each of these No sites liberates the energyq; therefore the total energy E is given by E = ( N - x)U - NBQ. The differential heat of adsorption Q will be expressed by Q = - -

dE dN = -u-+q. dNB dNe

* This expression in Vol’kenshtcin’s article has a positive sign before the radical; this root, however, gives a physically unreal result when 2 = 0. The root with the negative sign before the radical, on the other hand, gives the correct number of adsorption sites under the above condition.

CONTRIBUTIONS OF RUSSIAN SCIENTISTS

253

Differentiating Equation (21) with respect to N, and substituting the resulting expression* into Equation (23) gives

When Z = 0 (purely biographical disorder), Equation (24) becomes Q = q = const.

Thermal disorder introduces the dependence of Q upon N B ; the greater the value of Z the stronger the effect. The kinetics of adsorption upon defects have also been studied by Vol'kenshteIn. Defects which are manifested through a bimolecular reaction will give the conventional Langmuir kinetics, if the disorder is purely biographical. On the other hand if the disorder is purely thermal, deviations from the Langmuir kinetics are obtained in the region of sufficiently low temperature where p << NB2/Y. I n this region it is found that the number of occupied sites changes with the time t according to

where a is a temperature dependent constant. I n the region of high temperatures where ,8 >> N B the kinetic expression coincides with the Langmuir expression. Defects which arise as the result of a monomolecular reaction will yield the characteristic Langmuir kinetics if /3 >> 1; however if /3 << 1 kinetics will be observed which are typical of activated adsorption, that is,

I n the theory of activated adsorption the occurrence of a potential barrier between the surface and the gaseous molecules gives rise t o a kinetic expression similar to Equation (25) with k defined by Equation (26). The energy term u in this case, however, is associated with the height of the potential barrier a t the surface of the crystal instead of being associated with the heat of reaction between the defects according t o Equation 12 or 16.

* The sign before the expression involving the radical is just the opposite of tha t given by Vol'kenshteIn.

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J. G . TOLPIN, 0. S. JOHN, AND E. FIELD

IV. KINETICSOF HETEROGENEOUS CATALYTIC REACTIONS The kinetics of catalytic reactions on nonuniform surfaces have been discussed by KoginskiI (330,331) ; certain general features of his discussion will be presented here. The rate of a complex multistage heterogeneous catalytic reaction is controlled by the rate of the slowest step. The slowest step may be the adsorption of the reactants, the chemical reactions on the surface, desorption of the products or diffusion of reactants or products through the gaseous phase near the surface of the catalyst. I n the case where the reaction velocity is determined by the activated adsorption of the reactants and no poisoning by the products occurs, the action of a nonuniform surface simulates the behavior of a uniform surface. A similar situation occurs if there is redistribution on the heterogeneous surface after adsorption, assuming that the rate of surface migration is much greater than the rate of adsorption. If the reaction products are irreversibly adsorbed on the surface of the catalyst they may act as very effective poisons by blocking the active centers for the forward reaction. I n this case RoginskiI found that the kinetic equation obtained had a form which was characteristic of an activated adsorption process. The regularities of the kinetics of reaction controlled by the chemical processes occurring on a nonuniform surface have been thoroughly discussed by Roginskil. On a nonuniform surface, different sections will be characterized by different heats, Q, and activation energies, E , of adsorption and the kinetics of the catalytic reaction on each section will be determined by the nature of the relationship between these energetic quantities. If the heats of adsorption Q and activation energies E vary inversely with respect t o one another on the different sections, then the kinetics will be determined predominantly by those sections having small activation energies and high heats of adsorption. If E and Q increase together as one moves from section t o section, the kinetics will be determined by the process occurring on sections with low activation energies and heats of adsorption because of the nature of the relation for the rate of adsorption. Sections with the minimum activation energy will have too few molecules; thus the highest reaction velocity will occur on sections with an optjimal relationship between E and Q. I n treating the kinetics of catalytic reactions ItoginskiI makes use of the concept of the controlling band which was mentioned earlier in connection with adsorption. The cases discussed above indicate that the kinetics of the reaction occurring on the surface are characteristic of a narrow band of sections in the graph of p ( E ) versus E . The controlling

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255

band may remain stationary or move with extent of surface coverage by the reactants. These examples by no means exhaust the multiplicities and diversities of the kinetics of reactions on heterogeneous surface. The poisoning of catalytic reactions by means of foreign substances will be reviewed later in a section devoted to a discussion of catalyst modification. The kinetics of catalytic reactions on a uniform surface have been investigated recently by Antipina and Frost (10). The treatment was devoted in particular t o processes occurring in flow systems which undergo a change in volume during the course of the reaction. T h e rate of a heterogeneous catalytic process of this type cannot be described by the conventional kinetic equations which disregard the change in the volume during the course of the reaction. The change of volume in such reactions is closely related t o the extent of conversion and must be introduced into the initial kinetic equation. In their development, Antipina and Frost assumed that the heat of reaction is zero and that the kinetics are not diffusion controlled. In addition, it was assumed th a t the surface is energetically uniform and that the adsorption coefficients are unaffected by the presence of other substances in the reaction mixture. Analytical expressions resulting from this theoretical kinetic investigation make i t possible to evaluate from kinetics data the adsorption coefficients of reactants and products involved in a heterogeneous catalytic reaction. Comparison of the values of the adsorption coefficients determined kinetically with those determined from the adsorption isotherms indicates whether the adsorption sites are also the catalytically active sites or not. If the adsorption coefficients determined from the kinetic data and from the adsorption isotherms are equivalent, then it is highly probable that the nature of the catalytic and adsorption sites are identical. If, however, the values of the adsorption coefficients determined by the two methods differ greatly then it can be stated unequivocally th a t the catalytic and adsorption centers are of a different nature. The adsorption coefficients of the substances present during the dehydration of ethyl alcohol (i.e., water, ethylene, and ethanol) over alumina were determined kinetically and from the adsorption isotherms. The values of these adsorption coefficients are listed in Table IV. The values of the adsorption coefficients determined from the adsorption isotherms greatly exceed those calculated from the kinetic data; thus the catalytically active centers are characterized by a smaller adsorption capacity for the reaction product, water, than other sections of the surface. Antipina and Frost, therefore, assert that the dehydration of ethyl alcohol occurs on sections possessing a smaller adsorption for water than those upon which water vapor alone is adsorbed.

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J. G. TOLPIN, G. S. JOHN, AND E. FIELD

The kinetic expressions derived by Antipina and Frost have general applicability t o monomolecular heterogeneous catalytic reactions which occur on a uniform surface. The expression can be made t o describe the cracking of synthin or decomposition of octene over silica-alumina as well as hydrogen disproportionation of gasoline and cracking of gas oils over the silica-alumina. Numerous other applications are discussed. TABLE I V Comparison of the Values of the Adsorption Coeflcients Pound from Kinetic Measurements and from Adsorption Isotherms Adsorption Coefficient Substance Water Water Water Water U'a t cr Ethanol Ethanol Ethanol Ethylene Ethylene Ethylene

T"C.

Kinetic

Adsorption isotherm

310 340 380 415 450 108 150 188 380 415 450

4.00 1.82 1.80 1.80 0.50 0.48 0.48

0.023 0,019 0.016

0.021 0.016 0.014

V. MODIFICATION OF CATALYSTS 1. Promoters and Poisons

The mechanism of poisoning of a catalyst can be discussed from several points of view, such as microblocking of the active centers, chemical interaction between the poison and the catalyst itself and/or a n essential promoter. Small amounts of foreign materials which are occluded in the process of preparation of a catalyst may increase the activity of the catalyst many-fold ;however large amounts of these materials may decrease the catalytic activity very markedly. These observations led Roginskii to advance his concept of the dual character of the effect of additives on catalysts. The explanation of this behavior of additives was based by Roginskii upon the fact that the admixtures altered the energy of activation of the catalytic process. Small amounts of the additives reduce the energy of activation while large amounts increase the activation energy, bringing about the poisoning effect. This general phenomenon has been termed modification of catalysts by RoginskiI.

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257

These effects have been observed by Margolis and co-workers in their detailed kinetic study of the catalytic oxidation of hydrocarbons (219222). The extensive oxidation of hydrocarbons to carbon dioxide over catalysts of the spinel type has been studied by a number of investigators. It was possible for Margolis and co-workers to establish the effect of additives upon the basic kinetic constants, namely the activation energy of oxidation and the frequency factor for this rcaction. The reactions studied were the extensive oxidation of isooctane and of ethylene over magnesia-chromia and copper-chromia and of ethylene over tungstic oxide. The catalysts used in the oxidation of isooctane differed greatly with respect to their activities and the observed value of activation energy and frequency factor, as is indicated in Table V. TABLE V Substance Magnesia-chromia Copper-c hromia

Energy of activation E (cal. /mole)

Logarithm of frequency factor

45,000 15,500

17.0 6.0

These catalysts were modified by adding non-volatile inorganic acids and their salts, namely orthophosphoric acid, boric acid, barium sulfate, sodium silicate, barium nitrate, and hydrofluoric acid. The additives were added to the finished catalyst by direct impregnation from solution. The presence of the additives did not alter the specific surface or the geometric structure of the final preparations. The oxidation kinetics of isooctane were studied in detail and the reaction velocity constants determined. The order of the reaction changes gradually from second order for the pure catalyst to first order with increasing concentration of additive. In the cases of some additives the order of the reaction becomes zero a t large concentrations. The studies were restricted to those regions of concentration of the additives which could be described by the first order kinetic equation. The dependence of the yield of COz from the oxidation of isooctane upon the concentration of phosphoric acid or sodium silicate added to magnesia-chromia is depicted in Fig. 9. It is to be noted that a maximum yield of COz is obtained for a specific concentration of the additive. The temperature dependence of the logarithm of the reaction velocity for different concentrations of the additive upon the inverse absolute temperature is depicted in Fig. 10. Let us consider two temperature regions denoted by the vertical lines a and b. At low temperatures, such as b, the pure catalyst is the most active and all the catalysts con-

258

J. G . TOLPIN, G. 5. JOHN, AND E. FIELD

n

I , , , , ,

-0

I 2 3 4 3 CONCENTRATION OF ADDITIVE COMPONENT (WT.X )

6

FIG. 9. Dependence of the yield of COZ upon the concentration of HsPOa or NazSiOs added to magnesia-chromia catalyst. 1. Magnesia-chromia plus HsPO, 2. Magnesia-chromia plus NazSiOs. 2.c

2

3\

Y (3

3

I .(

FIG.10. Dependence of Log K upon 1 / T for different concentrations of the additive component. 1. Pure catalyst 2. Catalyst plus additive 3. Catalyst plus additive (greater concentration than in 2).

CONTRIBUTIONS O F RUSSIAN SCIENTISTS

259

taining the additive are less active. In this region the additive acts a s a poison. On the other hand, a t high temperatures, such as a, the pure catalyst will be the least active, those containing the additive the most active. I n this region the additive acts as a promoter. The dependence of the action of an additive upon temperature is well illustrated (Fig. 11) by the data of Element (96), who studied the catalytic oxidation of carbon monoxide over nickel oxide promoted with barium

c

Y

w

a

w 0.3

> -

3

-

rr 0.2

-

0.1

-

W

0:

I I I I 2 3 CONCENTRATION OF Ba(N03)2 (WTX)

FIG. 11. Dependence of the activity of nickel oxide upon concentrations of Ba(N03)2a t different temperatures.

nitrate. At the highest temperature the dependence of activity upon promoter concentration is expressed by a curve with a minimum; a s the reaction temperature is lowered, the minimum is converted into a maximum. Consequently the catalyst preparations on either side of the critical concentration should require the lowest energy of activation. The influence of the additives upon the reaction velocity, K , is reflected through the changes produced in the frequency factor, KO, and in the activation energy, E. The dependence of activation energy

260

J. G . TOLPIN, G . S. JOHN, AND E. FIELD

and the frequency factor upon the concentration of phosphoric acid upon magnesia chromia and copper chromia is given in Figs. 12 and 13. It is seen from these figures that as the Concentration of the additive increases, the value of E and K Oincrease a t first, simultaneously reach a maximum, and then drop again. The range of values covered by E and K Oare quite extensive and these effects, as pointed out by Cremer, cannot be explained by an exponential distribution of active centers on a surface.

CONCENTRATION OF H3P04(m%)

FIG.12. Dependence of the energy of activation and the frequency factor upon the concentration of &PO4 in rnagnesia-chromia catalysts. 1. Energy of activation 2. Logarithm of the frequency factor K O .

The energy of activation and the logarithm of the frequency factor are linearly related in the case of catalysts with different additives as is indicated in Fig. 14. This relationship has been observed by others and has received numerous interpretations (cf. 458). The significant features of this investigation are (1) that a given concentration of an additive will serve as a promoter in one temperature range and as a poison in another, ( 2 ) that modification cannot be interpreted in terms of blocking of active centers, and (3) that the change in

261

CONTRIBUTIONS OF RUSSIAN SCIENTISTS 30 W

J

0

I

>

-1

a

0 Y

.-C z

F L I-

Y

LL

0

>W

K W

z

W

C O N C E N T R A T I O N OF H 3 P 0 4 ( W T . % )

FIG.13. Dependence of the energy of activation and the frequency factor upon the concentration of HaPo4 in copper-chromia catalysts. 1. Energy of activation 2. Logarithm of the frequency factor KO.

20

0

Y

s (3

10

0

I

10

I

I

20

I

I

30

I

I

I

40

ENERGY OF A C T I V A T I O N in K C A L . / M O L E

50

FIG.14. Dependence of the logarithm of the frequency factor upon the energy of activation when different additive components are combined with magnesia-chromia and copper-chromia catalysts. @ Magnesia-chromia plus H3P04: 1 - 1.0%; 2 - 1.5%; 3 - 2.0%; 4 - 2.5% 0 Magnesia-chromia plus BaSOd: 1 - 1 % ; 2 - 2%; 3 - 3%; 4 - 5%

Copper-chromia plus HaP04: 1 - 2%; 2 - 3%; 3 - 4%; 4 - 6 % 0 Copper-chromia plus H3BOa: I - 0.5%; I1 - 1.0%; I11 - 2.0% X

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J. (3. TOLPIN, Q. 5. JOHN, AND E. FIELD

activity of the catalyst due to change in the energy of activation and the frequency factor were related to the concentration of the additive. I n connection with oxidation, Margolis discussed (218) the selection of catalysts for the extensive and inextensive oxidation of hydrocarbons. The catalysts considered are classified into three major groups: (1) metals, (2) metal oxides, and (3) salts of metals and mixtures of oxides. The theory of selection of catalysts has received considerable attention in the literature. In 1909 Fokin related the activities of oxidation catalysts with their ability to form unstable higher oxides. These early ideas were further developed by the Russian chemists Koboaev, Anokhin, and Zimakov. Roginskii (332) attempted to connect the electronic nature of the catalytic process with electronic structure of the catalyst. These studies have been materially assisted by advances made in the electronic interpretation of the solid state and of elementary chemical mechanisms occurring on the surface of solids. Out of the multiplicity of catalytic processes, Roginskii has segregated two large groups: (1) those processes characterized by electronic transitions and (2) those in which the acidic properties of the catalyst are important. Thus more restrictive conditions on the nature of the process make i t possible to associate the catalytic activity with certain physical attributes such as color, electrical conductivity, and electron affinity. Consequently a number of simple rules for the selection of catalysts can be stated. The following characteristics have been noted : (1) pronounced effects are noted with highly colored compounds; (2) catalysts containing transition elements are exceptionally active; and (3) white compounds do not have a pronounced catalytic effect. Table V I resulted from the work of Elovich, Zhabrova, Margolis, and Boginskii (98) upon the extensive oxidation of hydrocarbons. Nearly all oxidation reactions involve an electronic mechanism, and on this basis Roginskii has proposed certain orienting rules for the selection of extensive oxidation catalysts. As indicated in Table VI, these rules are based largely upon color and other physical properties which reflect upon the electronic properties of the solid catalyst. Up to the present the application of these selection principles to inextensive oxidation catalysts has been unsuccessful. This is due, in part, to the great diversity in opinions concerning the oxidation mechanism on the catalytic surface and its connection with the inextensive oxidation reaction. Charlot (170) has advanced the idea that the reactions of inextensive and extensive oxidation occur independently and with different reaction velocities. This view, however, has been opposed by Marek (217) who finds i t diffcult to conceive of a catalyst which would accelerate the

263

CONTRIBUTIONS O F RUSSIAN SCIENTISTS

TABLE VI Catalytic Activity of Metal Oxides in the Extensive Oxidation of Hydrocarbons Color

White

Chemical Substance Activitya Stabilityb composition lLanthanum oxide Inactive \ Molybdenum oxide Inactive Inactive Lead oxide Inactive, causes Aluminum oxide cracking Inactive Calcium oxide Inactive Magnesium oxide Silicon dioxide Inactive, causes cracking Zinc oxide Inactive Inactive Antimony oxide Inactive CaC03 Inactive MgC03 Inactive XatSO4 Inactive BaS04 Inactive BaO TiOz (BaTi03) CaO TiOz Inactive (CaTi03) Inactive MgO A1203 Inactive ZnO AI2o3 Inactive CaO A1203 Cr203 NiCrz04 NiO MnOZ MnCroOc MnO Crn03 CuCr~04 CuO CrzOa MgCrzOl MgO Cr203 MgO MnFezO4 Fez03 MnO Fez03 Chromium oxide Cr203 coo Cobalt oxide NiO Nickelous oxide ZnCrzOc ZnO CrzOa CoCr2Ol COaOa COO C1-203 CuCrzO4 CuO rCuO CrzO3 CuAlz04 CUO FeAI2O4 Fez03 FeO AL03 nAg20.mMn02 AgzO MnOz nCoO.mMn0z COO MnOz CUO Copper oxide CdO Cadmium oxide Bismuth oxide Neobium oxide ZnCr204 ZnO

+ +

+

+ + + +

+ + +

(

Colored

+

+ + + + +

+++ +++ +++ +++ +++ +++ ++ ++ ++ ++ ++ ++ ++ ++ ++ ++ + + ++ + + 1

+ + + + +

++

+ + + + + + + +

+ + + +

+

+

-L

a The number of signs (+) denotes the relative catalytic activity of the substances with respect to the oxidation reaction. b The denotes B substance possessing considerable stability, while the indicates an unstable substance.

+

-

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J. G. TOLPIN, G. S. JOHN, AND E. FIELD

oxidation of hydrocarbons and not accelerate the oxidation of alcohols, aldehydes, ketones, and acids, to water and carbon dioxide. Charlot’s view is supported by experimental information whirh indicates that aldehydes and ketones are converted t o the corresponding acids over extensive oxidation catalysts, for example platinum and palladium, with little formation of COZ. RoginskiI’s concepts of catalyst modification may potentially be of considerable importance in clarifying the basic concepts of the inextensive oxidation process. The practical utilization and verification of this theory has been tested only in a limited number of cases (98,218). Theoretical investigations of the modification phenomenon have been carried out by Roginskii and Vol’kenshtein (342,418,419,420,421,423). Their work has been based upon the electronic theory of catalysis which utilizes greatly present-day knowledge of quantum chemistry and those theories of the solid state which deal with processes occurring within crystalline materials. On the basis of these concepts it is possible t o treat the problems involved in the conversion of molecules adsorbed on a solid surface. The adsorbed molecule and the solid are treated as a unified system, the electrons of the lattice participating in bonding and subsequently chemical reaction. The velocity of the chemical reaction is dependent upon the electronic properties of the solid and reactants involved. The work of the Russian investigators of the modification phenomenon was recently reviewed by Zhabrova (458) and compared with the studies of non-Russian workers (50,72,284). 2. Selective Poisoning

One aspect of catalyst preparation involving selective poisoning has been mentioned a number of times in connection with specific conversions. Thus, Zelinskii and Borisov (441) described platinized and palladized asbestos catalysts th at were unable t o promote dehydrogenation of cyclohexane after piperidine was dehydrogenated over them a t 250’; after hydrogenation of pyridine at 150”C., platinum still retained its catalytic hydrogenation activity, but palladium was poisoned. The use of phosphorus trichloride for poisoning a platinum catalyst has also been reported by other workers of Zelinskii’s laboratory (281). The authors could thus depress either the dehydrogenating or the hydrogenating properties of their catalyst. They did not explain their observations hut simply referred to similar observations in the non-Russian literature. The possibility that the unpoisoned catalyst as prepared by them could also be active for side reactions, the products of which, for instance carbon, could destroy its activity, was not discussed. Depressing any

CONTRIBUTIONS O F RUSSIAN SCIENTISTS

265

side reaction with the aid of the poison charged, was also not postulated. Subsequent tests of these platinum catalysts at the Zelinskii laboratory gave results at variance with those originally reported, but confirmed the erratic behavior of the catalysts (cf., for instance, 243b). According to Platonov et at!. (309), nickel can be poisoned by H2S,SO2, H2S04, As203, and P20.5, after which it will direct the decomposition of formic acid preferentially in one of three possible ways; above a critical amount of the poison the latter ceased to act selectively and the catalyst was deactivated. In another study (310) Platonov and co-workers demonstrated that over rhenium catalysts, partly poisoned with HzS or AsZ03, methanol was converted to formaldehyde in preference to the complete decomposition which occurred over the unpoisoned catalyst. However, rhenium sulfide itself was later shown to be a good catalyst for the reaction reported and consequently the poisoning phenomenon may not be applicable to this case (308). Addition of small amounts of poison were believed by Khvatov (164) t o destroy the most active regions of a cat'ilyst, as in the case of nickel treat,ed with carbon monoxide. In a study of the effect of thiophene on nickel-magnesia, Rubinshteh et al. (355) observed that 1 mg. sulfur per gram of catalyst was sufficient to completely destroy the initial high activity in the conversion Cs% S CaH12, although the dehydrogenation activity was not much affected. Further addition of sulfur poisoned it also with respect to dehydrogenation. Rubinshtein concluded that the doublets on the catalyst which activated the hydrogen were poisoned by thiophene and that the finer elementary crystals of nickel were more resistant to sulfur poisoning. The results obtained by Freidlin and Ziminova on the poisoning of hydrogenation and dehydrogenation catalysts such as palladium, platinum, nickel, and cobalt indicate that dissolved hydrogen is an essential promoter (114,115). These catalysts can be poisoned by combination with such substances as oxygen, sulfur, selenium, tellurium, phosphorus, arsenic, antimony, bismuth, fluorine, chlorine, bromine, and iodine as well as reactants or reaction products which combine easily with or are reduced by atomic hydrogen. The most active of these metalloids, oxygen, sulfur, fluorine, and chlorine, do not react chemically a t room tempzrature with the metals of the platinum group; however, the least reactive, iodine, was still able to poison the catalysts even at low temperatures. The selectivity of action of the poison is explained by the chemical affinity between the promoter and poison instead of between metal and poison. The interaction between the promoter and poison is largely irreversible since revivication necessitates re-creation of the active centers.

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The relation of the concentration of some poisons (vinyl butyl ether; 1-methyl-1-cyclopentene) to the drop in the activity led the authors to suggest that catalysts of this type can be modified by these means to reduce their activity to a predetermined level. Both the activc and the inactivated nickel had a cubic structure. This enhances the significance of depromotion by extracting the hydrogen dissolved in the catalyst, rather than in other ways. That the hydrogen in question was dissolved and not adsorbed was established by selecting substances which reacted with the adsorbed hydrogen only or with the dissolved hydrogen as well (113). The conventional practice of charging hydrogen before the substance to be hydrogenated, dehydrogenating in a stream of hydrogen and displacing the reactants with hydrogen during interruptions of the process are explainable on the basis of hydrogen activation.

VI. CATALYTIC COXVERSIONS 1. Dehydrogenation-Hydrogenation Continuing the earlier work of Russian chemists, Zelinskii has concerned himself with dehydrogenation of cyclic compounds since 1911. The contributions of Zclinskil and his students have been reviewed a number of times in the Ilussiarl literature arid several articles on the subject appeared on the occasion of his 90th birthday in 1951 (155,351). The dehydrogenation of cyclohexanes to aromatics in the prcsence of platinum or palladium on charcoal was found to take place rapidly a t 300°, in many cases, although it does begin a t considerably lower temperatures. Cyclohexane homologs and decalin mere similarly converted (438); the course of the reaction was not altered by the presence of diluent hydrocarbons. The method was first applied to the analysis of petroleum fractions (371). After 1921, when nickel supported on alumina was shown by Komarewsky to be similarly applicable (444), attention was paid to hydroforming methods whereby aromatics were formed from some naphthenic petroleum fractions a t a higher rate over nickel-alumina than over platinized charcoal. Applications of nickelalumina were extensively studied by Shuikin in Zelinskii's laboratory (371). The losses over nickel-alumina were greater than those over platinum. Commercial use of the dehydrogenation of cyclohexanes is apparently only now being achieved in Russia (351). Dehydrogenation of the cyclohexanes over platinum, palladium, and nickel is selective in the sense that it affects only those compounds which can form aromatics by this reaction. Six-membered rings with substituent groups in positions such that elimination of hydrogen cannot form a benzene ring, for instance, I, 1-dimethylcyclohexatie, undergo dehydrogenation a t 300" with difficulty (442). The multiplet theory explains

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this dehydrogenation by the orientation of the cyclohexane molecules with respect t o the surface of the catalyst in such a way that the reactive atoms form a multiplet with several atoms of the surface. However, the presence of a ring in a molecule does not predetermine its planar position. In certain cases a cyclic molecule may attach itself to the surface sidewise. This requires the formation of a doublet and olefins are formed by nonselective dehydrogenation, as pointed out by Balandin (15,18,19). Such dehydrogenations occur over oxides (titania or chromia) a t higher temperatures (450”) than over platinum, palladium, nickel. This should be recalled in connection with the criticism of Balandin’s multiplet theory by Kagan (145). I n alkylated polynuclear naphthenes or in cycloalkylparaffins the tendency t o form new rings has been demonstrated. Dicyclohexylmethane gives fluorene and dicyclohexylethane gives phenanthrene (438). Cyclohexanes with an inner bridge, such as 2-methylendomethylenecyclohexane remain unchanged under dehydrogenation conditions over palladium, platinum and nickel a t 300°, but when more severe conditions are employed, the bridge is eliminated and dehydrogenation occurs. “Irreversible catalysis” is the term applied by Zelinskii since 1911 t o hydrogen disproportionation of cyclohexene whereby three molecules of the latter form two molecules of cyclohexane and one molecule of benzene. The reaction was found to occur even a t room temperature over platinum and palladium (450); it was later applied to substituted cyclohexanes (304a) and also studied in a n atmosphere of carbon dioxide (451). Hydrogen disproportionation may also take place in fivemembered cycloolefins. It was shown t o occur at 450-500” over vanadia on alumina (304b), and over chromia on alumina (304c), and also on palladium black in a sealed tube a t 180-200°. Although the resulting cyclopentadiene did not amount to more than 1 to 3 5 of the product, it led t o formation of a high molecular film and t o carbon deposition which poisoned the catalyst. Hydrogenation with combined hydrogen was reported by Shuikin ; a mixture of toluene and ethanol was converted by means of hydrogen exchange over nickel or palladium catalysts a t 190°C. t o form acetaldehyde and methylcyclohexane in 26% yields (372). Levina has been reporting cases of irreversible catalysis involving double bonds in a side chain (vinylcyclohexane) (205), ring rupture (445), redistribution of a triple bond (cyclohexylbutyne, butylbenzene, and butylcyclohexane) (204), etc. Balandin and co-workers have examined the cyclohexane-benzenehydrogen system as well as the alkyl substituted cyclohexanes and their adsorption rates on platinum, palladium, and nickel (17,23,24,27). As

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the number of methyl groups on the ring increased, the adsorption coeficient also increased (23). It was concluded th a t ethylbenzene.is bound to the catalyst surface by the alkyl group (29). The following hydrocarbons were found (25) t o have identical adsorption coefficients on the active centers of the catalyst : cyclohexane, benzene, toluene, m-xylene, and isooctane ; possibly also o-xylene, mesitylene, and ethylbenzene. The technique is useful for the study of the mechanism of side reactions which accompany dehydrogenation. Shuikin and co-workers found that olefins have a deactivating effect on platinum used for dehydrogenation of cyclohexanes. However, they found a difference in this effect, depending upon the position of the olefin double bond; 1-heptene, 1-hexene, and cyclohexene were not harmful, while l-ethyl-l-cyclopentene and cyclopentadiene rapidly deactivated the catalyst (374). Dehydrogenation of the six-membered rings in terpenes was studied by a number of Russian students in the past, for instance, by ZelinskiI (438). An interesting application of this process was found during World War 11, when turpentine constituents including a-pinene were converted at 200-500°C. over chromia-alumina t o p-cymene, which was used as a motor fuel constitucnt after proper refining (315). It was stated (178) that an aviation fuel component was developed starting with turpentine. Hydrogen disproportionation of a-pinene to a mixture of p-cymene and pinane was reported years ago by Zelinskii, whereas the dehydrogenation of p-cymene to a p-a-dimethylstyrene over vanadia-alumina and over copper-chromia was reported by Balandin and co-workers (28). I n the last-mentioned study Ralandin and co-workers demonstrated th a t the presence of two methyl groups in ethylbenzene, one of which is attached to the ring and the other to the side chain in a-position, facilitates the dehydrogenation which was carried out a t 625"C., a space velocity of 0.5-0.9 and diluting the charge with 2 moles carbon dioxide per mole cymene. A yield of u p to 63 % based on the cymene feed was obtained. Ruthenium, osmium, and especially iridium on activated charcoal were found t o be effective catalysts for hydrogenation a t 100-150". At 200300" these catalysts decompose six-membered rings rather vigorously, and some of the benzene formed by dehydrogenation of cyclohexane is converted t o methane and hydrogen (359). Attempts were made to use osmium and other platinum group metals as promoters of common metals for hydrogenation and dehydrogenation, for example, oxides of nickel, cerium, and thorium (127,358). Further, a combination of palladium and platinum or platinum itself deposited with certain precautions on platinized charcoal was reported t o increase the activity of the platinized charcoal (280,285,449).

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Catalytic dehydrogenation of paraffins was represented in the Russian chemical literature by a relatively large number of studies before World War 11. Balandin and co-workers investigated dehydrogenation of n-butane over chromia at 550-575" (31) followed by research on dehydrogenation of l-butene over chromia with yields at 592°C. of up to 29 % butadiene based on the butene passed or 82% based on that reacted (33). Dehydrogenation of 1-butene and 2-butene to 1,3-butadiene has been investigated by Balandin and co-workers since 1936, and the catalysts tested by them consisted of oxides of chromium, vanadium, magnesium, either unsupported or supported on alumina or other oxides or mixed with smaller amounts of the oxides of copper, zirconium, and molybdenum. Carbon dioxide or nitrogen was used by them as diluents (32)) and their effect was compared with that of reduced pressure (33). These studies were held to support the multiplet theory of catalysis; the diluent was thought to hinder polymerization and carbon deposition. The applicability of this theory to dehydrogenation of butane, butene, and ethylbenzene was discussed by them in detail in 1942 (16). Dehydrogenation as a method of formation of esters in 40 to 50% yields from alcohols was studied by Dolgov and co-workers over activated copper and by Ivannikov (142) who suggested a method of preparation of copper catalysts suitable for this purpose. Mixed esters, such as a mixture of butyl acetate and ethyl butyrate, were reported by Lel'chuk (193), and the mechanism of the reaction involved was thought to be a Tishchenko condensation of the aldehydes formed. Other studies by Lel'chuk and co-workers (194,195,198) proposed copper-aluminum promoted with cadmium or titanium oxide for the preparation of ethyl acetate or similar conversions of homologs of ethanol. It was stated (195) that the predominating ester from a mixture of alcohols contains the alkyl group of the higher molecular weight and the acid group of the lower molecular weight. These workers surveyed (196) the ability of various promoters of the catalysts used to accelerate the reaction. In this respect, the promoting effect of manganous oxide upon copper was stressed (414). The catalyst promoted by this oxide gave 35% ester per pass and was stable to poieoning with reaction products, while butyraldehyde gave only a 9.52% yield of butyl butyrate which was held t o contradict the mechanism involving intermediate formation of aldehyde; the formation of a hemiacetate intermediate was postulated. Platonov and co-workers have made a significant contribution to the study of alcohol dehydrogenation by means of rhenium catalysts (310). Rhenium disulfide was found to be efficient in promoting dehydrogenation of alcohols to aldehydes or ketones (acetone), and in the dehydrogenation of cyclohexanol to phenol and a small amount of cyclohexanone (308).

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Simultaneous dehydrogenation and dehydration of cyclvhexanol over silica-alumina cracking catalyst a t 340-375" was reported (245) to give a 78 to 95 % yield of hydrocarbons. Subsequent hydrogenation resulted in the formation of 45 yo methylcyclopentane (245). The direct condensation of ethanol to form n-butanol was investigated by Dolgov and Vol'nov in 1933, using titanium oxide promoted with ironaluminum oxides on charcoal as the catalyst (71). They suggest, with insufficient proof, that ethanol is dehydrated t o form ethylene which then reacts with more ethanol t o form the butanol. I n the field of hydrogenation the early work of Russian researchers has been developed further. Thus, S. V. Lebedev is to be credited with establishing the regularities in hydrogenation of substituted olefins and diolefins over platinum and palladium (187). The hydrogenation of acetylenes has been systematized by Zal'kind in a long number of studies (431). The contributions of the Zelinskii school to hydrogenation catalysis have been outlined by A. A. Balandin (15). Ipat'ev, Jr., and co-workers has reviewed (140) critically the literature on hydrogenation of mixtures and found that their own data and those of other students support the view th at the distribution of hydrogen between the components primarily depends upon the free energies involved. I n the case of two simultaneous hydrogenation reactions the hydrogenation constant of the binary mixture a t the moment when the free energies of both reactants become equal is independent of the hydrogen pressure and of the extent of hydrogenation. Preparation of hydrogenat,ion catalysts was the subject of several papers in a 1940 symposium (387). Continuous study of certain catalysts includes also those used for hydrogenation. For instance, Musaev (244) has been reporting since 1939 the selectivity of copper on asbestos in exhaustive hydrogenation of olefins and diolefins before the aromatics are affected, without adding essentially new information in recent publications. Desulfurization of liquid fuel by hydrogenation, destructive hydrogenation of tars, and hydrogenation of vegetable oils deserve mention here. Both platinum and nickel on alumina have been used in desulfurization of petroleum and shale oil fractions (390,393). I n the case of nickel, its sulfide is first formed which is capable of promoting further destructive hydrogenation of sulfur compounds to the extent of about 50% of their initial contents. In treatment of charge stocks with sulfur ranging from 0.66 t o 12.9 % under atmospheric pressure a t 350" in a stream of hydrogen, all sulfur compounds, including thiophenes, are decomposed and the nickel-alumina was then regenerated by air blowing a t 350" followed by reduction with hydrogen. Instead of hydrogen, a n illuminating gas with 8 40% hydrogen content could also be used. The significance

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27 1

of research on desulfurization by hydrogenation, as compared to that of other catalytic methods of desulfurization in Russia (treatment with oxides of aluminum, zinc and iron, bauxite, clay, etc.) can be seen from a review by Frost (121). Destructive hydrogenation of high-molecular-weight components of various tars dates back to the researches of Ipatieff (139b). The subsequent work in this field carried out at the Institute of High Pressures was reviewed by Nemtsov (255). Of the studies by Nemtsov, Rapoport (316), Puchkov (314), Nikolaeva (257), Prokopets (311), and others, the process described by Shenderovich (364) is perhaps illustrative of the present-day applications made of these studies. Polynuclear aromatics such as naphthalene have been converted over a molybdenum catalyst t o tetralin in up to 75% yields a t 380-400°, 200 atm., and a hydrogennaphthalene mole ratio of 5:8, and the tetralin was then decomposed noncatalytically in a second step a t 560°, 200 atm., and a hydrogen feed ratio of 12: 15 with an hourly space velocity of 0.3 to 0.5, whereupon 8 t o 10% benzene, 16 to 20% toluene, and 35-40% ethylbenzene based on the charge were obtained without formation of cyclohexanes and cyclopentanes. I n a book published in 1949, Rapoport surveyed the researches on hydrogenation of fuel carried out both in Russia and elsewhere, including destructive hydrogenation of tars from shale, coal, and peat (316). I n connection with the research on destructive hydrogenation at the Institute of High Pressures, Maslyanskii (224) passed benzene a t 475’ under 200 atm. hydrogen over molybdenum oxide (1 mole C6H6: 16 moles Hz)t o produce 58% methylcyclopentane, 14% cyclohexane, 8% 2-methylpentane, 5 % n-hexane, and 8% unreacted. Over molybdenum sulfide the product distribution was similar. The preparation of these catalysts was described by him in 1940 (223). Isomerization and other conversions accompanying destructive hydrogenation were also pointed out by Prokopets and by others (257,311,314). For industrial hydrogenation of vegetable and animal oils in Russia a Raney type nickel was prepared by Bag and co-workers (64). Preparation of detergents from hydrogenated fats has been reported (11). Reviews of these so-called skeleton catalysts were published by Russian investigators, for instance, by Lel’chuk and co-workers (197). These catalysts have also been discussed with reference to hydrocarbon synthesis from water gas (148). Lel’chuk (197) states th a t Raney nickel is more drastic for water gas synthesis than are the skeleton nickel catalysts prepared by Bag, and that Bag’s copper-nickel skeleton catalysts approach nickel in their activity. Destructive hydrogenation under mild conditions was said to be possible with Bag’s skeleton catalyst as described by Lel’chuk.

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2. Dehydrocyclization Concurrently with the discovery and development in this country of the catalytic conversion of paraffins t o aromatics (131) three different groups in the U.S.S.R. discovered this reaction independently of each other. Moldavskii and co-workers (238,239) showed that paraffins with six or more carbon atoms form aromatics by closure of a six-membered ring. For example, n-octane gives xylene and some ethylbenzene over amorphous chromia at about 470°C. Olefins also undergo this reaction. In subsequent publications, the group headed by Moldavskii demonstrated that molybdenum sulfide, titanium dioxide, and other oxides as well as activated carbon also may be used for dehydrocyclization (237,239). Kazanskii and Plate described a similar reaction over platinized charcoal at 30O-31O0C. (156,157). These workers observed a long catalyst life with this catalyst in reactions with pure hydrocarbons as contrasted t o the short life of chromia and other catalysts used by Moldavskii. Karzhev and co-workers (147) used hydrocarbon mixtures on which they observed the conversions of paraffins to aromatics over chromia. I n a series of papers from the Zelinskii laboratory (152,153,158,160,443) a systematic study was reported of a variety of catalysts for the reaction under discussion, including its application to synthetic (FischerTropsch) gasoline. Chromia-alumina or silica gel was apparently preferred. Plate reviewed the field of Russian and non-Russian work u p t o 1940 (304), and ShuIkin published another review in 1946 in which dehydrogenation of cyclohexanes as a source of aromatics is considered to be a t least equal in value to dehydrocyclization (371). Kazanskii and Plate made their first observation of aromatization over platinized charcoal using butylcyclopentane and isoamycyclopentane (307). The major conversion was a six-membered ring closure by the side chain, dehydrogenation of the latter, and rupture of the original cyclopentane ring; the minor conversion involved isomeriz&tion of the five-membered ring t o a six-membered ring and dehydrogenation of the latter t o an aromatic compound. These reactions have received much attention in subsequent publications of Kazanskii’s laboratory. Cyclohexylcyclopentane was converted over platinized charcoal chiefly t o the expected three isomeric amylbenzenes (235). Isoamylcyclopentane when passed over nickel-alumina or platinized charcoal in a hydrogen atmosphere gave aromatics as well as 2,5-dimethyloctane, while in the presence of nitrogen instead of hydrogen, some naphthalene was obtained. Secondary butylcyclopentane when passed over chromia-

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alumina gave 16 to 18% yield of olefins and 11 to 13%yield of aromatics at 425°C. Hydrogenolysis of lower naphthenes which may be involved in gasoline reforming was reported, affecting cyclopropanes, cyclobutanes, and cyclopentanes, alkylated cyclopentanes, or those connected t o other cyclic compounds. Ring scission is brought about in a hydrogen atmosphere a t the proper temperature over platinized charcoal (15). Hydrogenolysis of cyclobutane requires a temperature of 200-250" (154), while that of cyclopentane reaches 90% a t 300". Kazanskii, who has contributed much to this field, has recently reviewed the regularities in ring scission of substituted cyclopentanes (149a). The approximate rates of ring scission are related as follows: 1,2,3-Trimethylcyclopentane 1,3-Dimethylcyclopentane 1,2-Dimethylcyclopentane 1,l-Dimethylcyclopentanc Methylcyclopentane Cyclopentane

1 4 8

30 28 46

Alkyl groups other than met,hyl apparently exert the same effect on the rates of decomposition as does methyl. The point of rupture of the ring is also affected by the substituents and 1,2,3-trimethylcyclopentane gives predominantly 2,3,4-trimethylpentane (155). The effect of hydrogen pressure on the scission of the cyclopentane ring has been investigated by several Russian authors. Molybdenum oxide and sulfide and cobalt sulfide gave mostly paraffins at 450-5OO0C., but they also promoted some isomerization of the cyclopentanes t o cyclohexane and dehydrogenation t o benzene as well a s decomposition t o gaseous compounds (311,313). In the presence of nickel-alumina under 250 t o 300 atm. hydrogen, temperatures in excess of 400" were needed t o cause ring scission; the products were of similar composition. At higher pressures (370 atrn.) the destruction of cyclopentane reached 56% (243a). Kazanskii and Terent'eva showed (149b) that in the presence of platinized carbon or nickel on kieselguhr the temperature required for the scission increased with the pressure. Platinum promoted the formation of normal pentane from cyclopentane a t 25 to 50 atm. and 27O-39O0C., while nickel a t 16 to 56 atm. and 320-380" gave yields of normal pentane which decreased with rise of the hydrogen pressure since the hydrogenolysis was complicated by decomposition t o methane. The effectof platinum in scission of cyclopentanes is specific under atmospheric and elevated pressures; the scission over palladium and nickel is accompanied by side reactions (149a,b).

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The proportion of cyclohexanes to cyclopentanes in the naphtha to be treated is of significance not only because of the amount of hydrogen available through liberation from the cyclohexanes, but also because above a certain proportion of cyclohexanes the latter compete with cyclopentanes for a fraction of the platinum catalyst surface and thus the extent of conversion of cyclopentanes may be diminished (149a). Novikov showed (259,260) th at oxygen-containing substituents of cyclopentanes are preferentially adsorbed on the hydrogenation catalyst. This results in the displacement of molecules adsorbed on the surface by their carbon-to-carbon bond in consequence of which cyclopentanes with oxygen-containing side chains do not readily undergo scission. The difference between platinum and nickel in the rupture of a cyclopropane ring was established on the example of 1,l-dimethylbicyclo-[O, 1,3]-hexane over nickel (447). The three-membered ring was ruptured by hydrogenation at 179" forming 1,l-dimethylcyclohexane, while over platinum a t 155" isopropylcyclopentane was formed, and with rise of the temperature the cyclopentane ring was ruptured, and this was followed by partial dehydrocyclization giving about 12% aromatics at 310". It is not entirely clear whether the difference in the catalyst was of more significance than the difference in the temperature employed. In his 1940 review Plate subjected the experimental material on dehydrocyclization of paraffins published to that time to a critical analysis (304) and concluded that aromatization of paraffins a t the temperatures employed will depend upon the selection of proper catalysts in order to suppress the competing reactions, that the multiplet theory satisfactorily explains the mechanism of cyclization, and th a t intermediate formation of olefins is conceivable on oxide catalysts but can hardly occur on platinum. More recent work of Kazanskii and Liberman (150,151) amends the view of the Zelinskii school that gem-substituted cyclohexanes are inert under dehydrogenation conditions over platinum. They established the conversion of 3,3-dimethylhexane into 1,l-dimethylcyclohexane under dehydrocyclization conditions as an intermediate step in the formation of aromatics (toluene and m-xylene) from that paraffin. Furthermore 1,ldimethylcyclohexane was directly converted t o aromatics, although at a lower rate than cyclohexanes with substituents attached t o different carbon atoms. The mechanism of aromatization of paraffins on platinum was thus shown t o involve the intermediate formation of a cyclohexane. Other Russian workers have also contributed to the research on aromatization. Thus, Nametkin and co-workers (250,344) dehydrogenated butylcyclohexane over chromia-alumina a t 520" and obtained

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naphthalene in yields u p to 40 % ; butylbenzene reacted similarly. Indan gave 55% yield of indene over chromia. Petrov and Shchekin (297) showed th at below the cracking temperature (250-316°C.) cyclohexene undergoes over silica-alumina hydrogen disproportionation and dimerization. Identical results were obtained from I-methyl-1-cyclopentene. Ring expansion of lower alkylated cyclopentanes occurs simultaneously with polymerization. However, no bicyclic compounds with similar rings were formed. Maslyanskii has been actively engaged in research on catalytic reforming of naphthas. He has reported (225,227) th a t methylcyclohexane underwent much more cracking and dehydrogenation than did cyclohexane at 515" over silica-alumina (225,227) ; cyclohexane at 515560" when passed over silica-alumina gave negligible quantities of methylcyclopentane, but largely formed aromatics including toluene, xylenes, and ethylbenzene (225). Methylcyclohexane was more reactive and gave toluene, xylene, ethylbenzene, trimethylbenzene, and benzene. Maslyanskir and co-workers reported pilot plant studies of hydroforming of naphtha over chromia-alumina gel catalyst (228). Optimal conditions were 53O-54O0C., 20 atm., 3 to 6 moles hydrogen per mole charge, a n d a space velocity of 0.9 with recycling of the make gas. Gasoline yields were only 75 Yoand octane levels low (228). I n a comparison of the above catalysts with molybdena, they found th at an increase in the hydrogen pressure merely lowered the chromia activity, whereas the performance of molybdena was improved by decreasing carbon formation (226). Obolentsev (268) found that olefins when passed over chromia a t 480" gave more aromatics and more coke than paraffins of similar carbon number, i.e., CT and Cs compounds. The ratio of disubstituted t o monosubstituted aromatics formed from decane over chromia at 450500°C. was from 1 .2 :l to 1.4:l according to Rozenberg (345); olefins amounted t o 10 to 17 %. All theoretically possible schemes of cyclization were thought t o take place. 3. Theory of Melhylene Radicals

When cyclohexane is dehydrogenated over nickel, partial decomposition occurs a t about 350°C., and according to Zelinskii and Shuikin (453), methylene radicals are formed whic'h cause methylation of benzene. This explanation is in agreement with Zelinskii's view on deformation of reacting molecules on the surface of the catalyst by virtue of the energy of the catalytic surface (352,434). In the course of the conversion far reaching deformation of some of the molecules may break them down to fragments; these recombine, forming carbonaceous films which inactivate the catalyst. The possibility of formation of methylene radicals from

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hydrocarbons on metals as an intermediate step in carbon deposition was also cited by Balandin (26) in referring to previously obtained experimental evidence. This very inconclusive evidence consisted in presumed formation of traces of toluene when benzene was introduced into the reaction zone of carbon monoxide with hydrogen subjected to a conversion under the Fischer-Tropsch conditions; the presence of toluene was shown only by a colorimetric nitration test (89). I n the discussion of the subject Balandin mentions (15) th a t Fischer previously postulated that methylene radicals may be produced as a n intermediate in the formation of hydrocarbons by his method (116). This mechanism of carbon deposition on platinum supported on oxides of nickel and chromium (oxidized nichrome) through the intermediate formation of methylencs was thought by Balandin t o be similar to the mechanism of dehydrogenation over this type of catalyst in that both occur on the boundaries of platinum-nickel and of platinum-chromia and were brought in agreement by him with his multiplet theory (26). Mention of the methylene radical theory has been repeatedly made by the investigators working a t the Institute of Organic Chemistry. I n addition to hydrocarbon synthesis, a peculiar part has been ascribed by Eidus and Zelinskii to the methylene radicals in polymerization and hydrogenation (hydropolymerization) of ethylene which is discussed in the next section. It will be interesting to see whether further reports with more precise analytical data than those heretofore offered (89,90) will be forthcoming. Evidence ruling out the possibility of toluene formation by chain growth in Fischer-Tropsch synthesis followed by dehydrocyclization would also be necessary for a confirmation of the methylation of benzene as suggested by Eidus (89).

4, Hydrogenation

of Carbon Monoxide

Interest in the Fischer-Tropsch synthesis was manifested by Russian investigators soon after the first information about it was published; the synthesis was discussed a t the Mendeleev Chemical Congress in 1934, and revicws were published both in book (148) and in journal (73,74,75, 82,84,146,234) form. The work has led to pilot plant studies; full-scale industrial development of this process may have been achieved by 1950. There has been considerably more attention given t o the performance of various catalysts and to the reaction mechanism, and, recently, t o related processes, such as the hydropolymerization, mentioned above, and the hydrocondensation of olefins, rather than to such aspects of this process as preparation of synthesis gas. Eidus is probably the most active Russian workcr in the field. His

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work has involved tests of a variety of cobalt, nickel, and iron catalysts. A kieselguhr from Georgia was found by him to be a very satisfactory support for nickel promoted with oxides of manganese and aluminum (87). Concerning iron catalysts, a study of the reaction velocities by the method developed by Eidus (77) and comparison of the kinetics of carbide formation of hydrocarbons on various components of these catalysts (78) yielded data which were interpreted t o show that iron catalysts are active only when promoted with copper and thoria or potash; the latter is preferable. Iron-copper catalysts are rated by Eidus t o be low in stability (85,86). Catalysts prepared by precipitation are more active than those resulting from thermal decomposition of various compounds. I n agreement with Balandin’s theory it was assumed by Eidus (79,80) that methylene radicals adsorbed on two adjacent centers of the catalyst are dimerized t o ethylene which remains adsorbed on a doublet; subsequently a new rnethylene group is added t o one of the carbon atoms with a hydrogen atom migrating t o the carbon atoms of the ethylene which is then desorbed; further growth with formation of l-olefins proceeds similarly; a shift of the double bond inside of the molecule may occur. The view of Craxford and co-workers th at all polymerizing methylene radicals remain adsorbed t o the surface was contradicted by Eidus as inconsistent with experimental evidence (84b). The hypothesis of formation of oxygenated compounds as intermediate products was rejected by Eidus on the basis of experiments on the conversion over cobalt of methyl and ethyl alcohols and formic acid which were found to form carbon monoxide and hydrogen in a n intermediate step of the hydrocarbon synthesis (76). Methylene radicals are thought t o be formed on nickel and cobalt catalysts (76) by hydrogenation of the unstable group CHOH formed by interaction of adsorbed carbon monoxide and hydrogen] while on iron catalysts methylene radicals are probably formed by hydrogenation of the carbide (78,81). Carbon dioxide was found to interact with the alkaline promoters on the surface of iron catalysts; as little as 1% potassium carbonate was found to occupy 30 to 40% of the active surface area. The alkali also promotes carbide formation and the synthesis reaction on iron (78). According t o Eidus (90) carbides formed on cobalt or nickel catalysts are neither intermediate products nor catalysts promoting the formation of hydrocarbons from carbon monoxide and hydrogen. I n the absence of hydrogen carbon monoxide poisoned the cobalt catalyst. Despite Eidus’ results, Braude and Bruns (42) supported Craxford’s assumption that the carbide is formed by reaction of the metal (iron) with carbon monoxide and hydrogen. It was pointed out by Eidus (84a) that Braude and Bruns did not clearly distinguish between the carbide and free carbon

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that could be present on the surface. According t o some authors the experiments of Eidus are vitiated by the use of fresh catalysts, which cannot be considered the same as those which have operated for several days. Discussing the work of Weller (424), Eidus remarks (83) that this criticism leaves out of account his more recent work (81) which supports his earlier conclusions on the basis of the relative velocities of carbide formation and hydrocarbon formation over nickel and cobalt at the beginning of the process and after a 3-hour period. Karzhavin expressed (146) the view, on the basis of his experiments with nickel and cobalt catalysts, that methylene radicals of limited mobility are adsorbed on the surface and that the chance of their uniting to form larger hydrocarbons is determined exclusively by the character of the surface. The shortest distance between the atoms in the lattice of nickel and cobalt being 2.49 to 2.51 A. is thus in excess of the carbon-tocarbon bonds in hydrocarbons (1.5 A.). The attachment of the carbon atoms of methylene radicals to nickel atoms would place them a t too great a distance for the formation of a bond. Eidus contradicted Karzhavin (84a), as did the editors in publishing Karzhavin’s article (146) on the basis that Karzhavin overlooked the requirement of Balandin’s and Eidus’ theory of preservation of the valerice angle (20). According t o this theory, a distance of 2.47 A. makes the joining of two methylene radicals a t a carbon-to-carbon bond of 1.52 A. quite plausible because the valence angle of 109’28’ makes this combination free of Baeyer strain. The valence angle preservation principle was also seen by Eidus as an additional argument against Craxford’s mechanism of condensation of methylene radicals (84a’b). Bashkirov and eo-workers charged water into the synthesis zone and found that carbon monoxide was converted to carbon dioxide simultaneously with the formation of hydrocarbons (35). According t o this group the synthesis reaction over any catalyst involved CO 2Hz + =CH2 H 2 0 with H 2 0 CO --+ COz H2 as a secondary reaction. This reaction of water with carbon monoxide over iron, cobalt, nickel, and other metals was reported simultaneously (1949) by Koelbel and Engelhardt (174a) who also patented (17410) a process for hydrogenation of carbon monoxide over cobalt occurring predominately according t o 2CO H2---f (CH,) C 0 2 . Eidus commented (84a) that the reaction CO H,O g CO, H, is more likely to occur on iron than on cobalt, which stresses the difference in these catalysts. From their sclheme of dimerization of methylene radicals, Eidus and co-workers assigned exceptional importance to ethylene in the mechanism of hydrocarbon synthesis. Because both of its carbons can add new methylene radicals, its conversion is expected to occur a t a high rate,

+

+

+

+

+ +

+

+

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which is supported by the negligible content of ethylene in the reaction products reported by Storch and others (210,383), despite the fact th a t thermodynamically its formation is thought to be favored (246). The hydrocondensation of carbon monoxide with olefins under atmospheric pressure described by Eidus (88,93,94,440) and the hydropolymerization of olefins under the action of carbon monoxide (91,258) are held t o be in agreement with the general mechanism of polymerization of methylene radicals in the presence of hydrogen involving addition of methylenes t o ethylene adsorbed on a doublet. A feed composed of lCO:2H2:3CzHa yielded a t 110" under atmospheric pressure and a n hourly space velocity of 100 a product of addition of carbon monoxide and hydrogen to ethylene in amounts of 30 to 40 ml. liquid per liter per hour. From 15 to 20% of the ethylene was hydrogenated to ethane (93). The major product was a complex mixture of saturated and unsaturated hydrocarbons with both odd and even numbers of carbon atoms (94). This was reported to have been developed independently of the OX0 synthesis (82). In subsequent work (92,95) a reaction mixture containing 4 to 7 % carbon monoxide was converted, and a liquid boiling at 27-300" containing over 70% unsaturated compounds was obtained in addition to the Cs and C4 compounds. Some branched chain hydrocarbons and a small amount of oxygenated compounds were also formed. All three reaction components were found t o be essential for the synthesis and the process could not be visualized, according t o the authors, as two independent reactions, one involving polymerization or hydropolymerization of ethylene, and the other hydrogenation of carbon monoxide. The catalyst used in hydrocondensation and hydropolymerization was not disclosed, but it may be assumed to be a cobalt catalyst. 5 . Hydration-Dehydration

Although hydration of olefins (isobutylene) by the action of sulfuric acid was reported in the Russian literature as early as 1873 (44), and Kucherov (181) hydrated acetylene over mercury salts and sulfuric acid in 1881, this old tradition did not stimulate much significant research in recent years. Manufacture of ethanol from ethylene was experimentally studied in the 1930's. Frost demonstrated the stability of silica-alumina for the hydration of propene (320,321,322,323). Zelinskii prepared acetone in 80% yields from acetylene by passing it a t 440°C. in mixture with 10 volumes water vapor over ferric oxide-manganese oxide made u p in a ratio of 7:3. Zelinskii (437) and Platonov and co-workers used catalysts composed of 2ZnO.Vz05 or 2CdO.Vt05 to convert acetylene a t 450" t o a mixture containing 50 to 60% acetone together with acetaldehyde and acetic acid but the catalysts were rapidly inactivated. Hydra-

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tion of vinylacetylene to methyl vinyl ketone over mercury salts was studied by Churbakov (48), who reported yields of u p t o 93% on the converted charge. Formation of alkyl-vinyl ketones by hydration of primary acetylenic alcohols accompanied by dehydration as a side reaction was reported by Danilov and Venus-Danilova (56). Dehydration of alcohols served as the starting point in some early Russian studies of catalytic conversidns (40), such as in the preparation of pentamethylethanol and its dehydration to form triptene (2,3,3-trimethyl-l-butene), which was reported by Butlerov (45), and in the preparation of dioxane by dehydration of ethylene glycol by Favorski1 (102). Reference t o some Russian contributions t o the study of dehydration of alcohols and of the pinacoline rearrangement was made by Dolgov (67). This included work on dehydration of unsaturated alcohols. I n connection with the current studies of Favorskii’s school on vinylacetylene derivatives, the work of Zakharova on dehydration of acetylenylcarbinols to vinylacetylenes should be mentioned (430). The most important contribution in the field of simultaneous dehydrogenation, condensation, and dehydration made b y Russian chemists is the synthesis of butadiene from ethanol over a double oxide catalyst by the method of Lebedev. Much has been published on this process. Lebedev’s interest in rubber synthesis began with his researches on conversions of dienes in 1908 and his method of synthesis of butadiene was reported in 1927. An experimental synthetic rubber plant was founded for research in the field and the studies on the mechanism of formation of butadiene and of polymerization were continued after Lebedev’s death by his students (103,104,105,188,190,378). A survey of the properties and methods of preparation of butadiene was published by Petrov (289). According t o Lebedev, when acetaldehyde was substituted for ethanol, only traces of butadiene were produced, whereas a mixture of acetaldehyde and ethanol combined to form butadiene (189). Among Lebedev’s students, Gorin has been continuing the work on the mechanism of diene formation from alcohols. Gorin has demonstrated that addition of acetaldehyde, aldol, or crotonaldehyde to the ethanol passing over the Lebedev double oxide catalyst gives a proportionate increase in butadiene (128) and that these compounds when used alone give no butadiene. Although he indicated (129,130) a sequence of reactions where the above mentioned compounds are intermediate, he also concluded that the alcohol condensation postulated by him involves the hydrogen of the carbon adjacent t o the carbonyl group, and therefore alcohols above ethanol must yield branched chain dienes. This follows from the aldol condensation assumption; for instance, formation of

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2-ethylhexanol arises from the ,condensation of n-butyraldehyde followed by hydrogenation. He also states th at tertiary alcohols cannot give dienes with conjugated double bonds. I n 1947 Kagan and co-workers (144) showed that the mechanism of formation of butadiene from ethanol according t o Lebedev is similar to that proposed earlier by Ostromyslenskii (278,279) for mixtures of ethanol and acetaldehyde; both involve formation of crotonaldehyde. Specific information on the composition, operation, and efficiency of the compound catalyst used in the Lebedev process for butadiene manufacture is lacking in this country (49). Notes in the Russian literature indicating improvement of the yields t o as high as 70 %, published after Lebedev’s death, support the view th a t the early yields were unsatisfactory, probably around 50%. The catalyst probably had a short life span, and the product contained about 80% butadiene. The significance of the aldol condensation t o crotonaldehyde is low according t o Corson (49). 6. Acetylene Chemistry

Russian writers on organic chemistry have stated th a t the chemistry of acetylene derivatives was developed significantly through the work of Favorskii whose selected works were published in 1940 by the Soviet Academy of Sciences. After his research on isomerization of monosubstituted acetylenes over alcoholic potash, which was published in 1887, a number of similar studies by Favorskii, Favorskaya, Nazarov, Shostakovskii, and many other students of Favorskii followed. Of these, mention is made of Favorskii’s work on the synthesis of isoprene a s a n example illustrative of his many researches in this field (106). Condensation of acetylene with acetone under the action of powdered potassium hydroxide gave dimethylacetylenylcarbinol which was electrolytically hydrogenated t o the corresponding olefinic alcohol and the latter dehydrated to isoprene. Apparently rubber from isoprene and from chloroprene (165) is manufactured in the U.S.S.R. in addition to butadiene rubber . The researches of Zal’kind were concerned with the catalytic hydrogenation of acetylenic compounds; acetylenic glycols add only two hydrogen atoms over palladium and divinylacetylenes add only six hydrogen atoms, the hydrogenation being limited to the formation of olefins (431). Shostakovskii has published research on the synthesis and utilization of vinyl alkyl ethers. Hydrolysis of these ethers t o acetaldehyde is probably commercially used today in the U.S.S.R. (290). Other practical utilizations of this class of compounds have been indicated (106,107,108,176,185,207,283,368). Shostakovskii found that a variety of acid

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catalysts were effective in the polymerization of vinyl alkyl ethers, particularly BF3, FeC13, and A1C13 (208). However, he preferred to use SnC12,at least for laboratory work, because of the ease of control (369). The conversion of the vinyl ether polymer t o polyvinyl alcohol was accomplished by treatment with sodium ethylate (369). The work of Nazarov on vinyl ethynyl carbinols involves condensation of vinylacetylene with ketones in the presence of caustic potash and also their conversions, many of which are catalytic in nature. A review of his work involving polymerization, isomerization, hydrogenation, and other conversions was published by him (252). Hydration of divinylacetylenes in methanol solution in the presence of mercuric sulfate and sulfuric acid gave vinyl alkyl ketones. These can be reacted with hydrogen sulfide, amines, etc., to yield heterocyclic compounds. Substituted vinyl alkyl ketones underwent spontaneous cyclization to cyclopentenones. Nazarov summarized a decade of this research in this field in 1951 (253). His general review of organic syntheses based on acetylene is also of interest in this connection (254).

7. Polymerization Polymerization reactions, in addition to those previously mentioned , have been reported in the Russian literature which involve unsaturated compounds of all kinds. However, recent original work has not exceeded in industrial importance the polymerization of butadiene over metallic sodium as developed by Lebedev. In studies of the effect of temperature on this polymerization, Lebedev established the limits of formation of a cyclic butadiene dimer, vinylcyclohexene, while a lower temperature was necessary for polymer formation. Slobodin and co-workers established that at 300-400" over Florida earth, l13-butadienegave the above dimer as well as dimebhylcyclohexadiene and also trimers and tetramers with fused rings (379,382). Medvedev has reported work on the kinetics of polymerization of diolefins and other compounds, as influenced by the number *of free radicals in the reaction (230). I n the polymerization of styrene, two chain reactions are thought to take place: the reaction of free radicals with oxygen leads to oxidation, and the reaction with styrene t o polymerization (231). ZelinskiI and Kazanskil claimed .rather high yields of aromatics by polymerizing acetylene over activated charcoal a t 600-650" (436) ; a 70 to 75% yield of tarry matter was obtained which contained 35% benzene and 4% toluene. Shorygin initiated research on polystyrenes and polyamide resins in Russia. His work is now continued by some of his students (53).

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Petrov and co-workers polymerized acetylene with simultaneous hydrogenation over nickel or nickel plus zinc chloride and obtained saturated and olefinic products. The ratio of products boiling in the gasoline range t o heavier products depended upon the catalyst as well as the pressure. The liquid obtained from nickel consisted of a gasoline obtained in 50 % yield in the runs under atmospheric pressure, and in 70 % yield under 20 atm. pressure. The rest comprised diesel fuel hydrocarbons (292). The structure of the liquid hydrocarbons formed was unaffected by the presence of phosphoric acid or zinc in the catalyst. The gas contained u p to 80% butenes, depending upon the conditions. This work of Petrov on the synthesis of hydrocarbons is apparently being continued a t the present time. Paushkin, Topchiev, and co-workers have been studying polymerization and alkylation using BFP in combination with H3P04 as a preferred catalyst (287,394,395,397,399,402). The acidity of the component added t o BF3is thought to increase the activity of the catalyst. Propylene and isobutylene were among the olefins which were investigated (398,401). Polymerization of olefins in the presence of sulfuric acid accompanied by hydrogenation and dehydrogenation was reported by S. S. Nametkin in 1934; similar work was also reported by him in 1937 (247). The mechanism of polymerization of propylene, as indicated by the structure of its dimers and trimers, was thought by Antsus and Petrov (293) to be similar t o that of polymerization of isobutylene (apparently over acid catalysts) ; in the first step 2-methyl-l-pentene was formed. Reviews dealing with industrial application of polymerization reactions t o the preparation of high polymers in Russia have been published on several occasions (54,380,415). 8. Isomerization

Two reviews of isomerization reactions should be referred to as sources of information on Russian researches in the field. The book by Petrov (291) on isomerization of paraffins, olefins, diolefins, and acetylenes with up t o 34 carbon atoms gives information based on Russian and nonRussian researches and was written by an author who has carried out with co-workers numerous studies of isomerization of olefins in the presence of various catalysts. The review by Danilov (55) was confined to Russian contributions to the field of isomerization during the period of 1917-1947 and covers isomerization of hydrocarbons of all classes, their halogenated derivatives, oxygenated compounds and heterocyclics. In view of these detailed publications, the discussion below is limited to highlights of the field.

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Isomerization of normal paraffins to branched chain structures is of commercial significance in connection with the use of isobutane in alkylation to make high octane gasoline. Aluminum chloride is almost universally used. Among Russian students of this process Borisov and co-workers (41) reported that Grozny gasoline, rich in paraffins and naphthenes, was resistant to isomeriaation in the presence of the A1C13HC1 catalyst, and suggested that the naphthenes exerted an inhibiting effect. Isagulyants and Golovanova (141) studied the isomerization of isobutylene and normal heptane over 10% AlC1, on a variety of supports at 170-180". They obtained 33% isomerization of the heptane without sludge formation. With isobutane they obtained 68 % products. Some aromatics formed which, they believed, arose from intermediate trimethylpentadiene. The possibility of a hydro-dehydropolymerization, as described by Nametkin for olefins in the presence of sulfuric acid, was suspected. Obolentsev (263) studied n-hexane, n-heptane, and n-octane isomerization under hydrogen pressure in the presence of AlC13, to which a variety of other metal chlorides was added in an attempt to inhibit the extensive cracking which was observed. High yields of branched isomers were obtained. Hexane gave high yields of the gem-substituted hydrocarbon (36%), whereas the C7 and Cs compounds gave very little. Obolentsev proposed a cyclic compound as the reaction intermediate. With Chernyshevskii he studied (265) the kinetics of the isomerization of normal butane batchwise in the liquid phase using AlC&and HC1 as the catalyst. They indicated an induction period for the reaction in the temperature range 55-100' and concluded that the liquid phase reaction was homogeneous. The study of normal butane-isobutane equilibrium by Moldavskii and Nizovkina (240) has been criticized because of the side reactions which occurred, but recent work by Pines (300) showed their data to he in agreement with those of other investigators. Obolentsev and co-workers (269) reported in 1941 the isomerization of butenes obtained by dehydration of fermentation butanol to isobutylene. They employed HaP04 on kieselguhr a t atmospheric pressure and observed a 400-hour lifespan of the catalyst, Optimum conditions were 300°C., 260 g./l./hr., with 20% by volume steam added. About 15% of the product was polymeric material which may be hydrogenated to give an 80 octane number gasoline fraction. A number of pure olefins up to Cs have been studied. Zharkova and Moldavskii studied the equilibrium conversion of 1-butene to 2-butene over silica gel, H3P04 on pumice and other catalysts (9.8% l-butene at 200", 19.4% a t 380"), and of the pentenes at the same temperatures over silica gel (459). Petrov and Chel'tsova in 1937 reported the isomerization of l-hexene a t 300-325" over ZnClz supported on pumice (294), and in 1945 (47) with ZnCL on

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pumice with HC1 at 375" tetramethylethylene was isolated from the product. Petrov and Shchukin (295,296) found that 1-heptene gave 3-methyl-3-hexene and 1-octane gave 2-methyl-2-heptene when contacted with H3P04 at 325°C. Raising the pressure from 75 to 2000 atm. only increased branching by 3%. When operating at low conversions t o avoid polymerization, they observed only single branching, and they concluded that the primary reaction involves shifting of the double bond, following which a shift in the methyl group occurs. Turova-Polyak and co-workers have carried out extensive studies of naphthene isomerization with AlC13, particularly of the substituted cyclopentanes. The conversion of mono- and disubstituted cyclopentanes t o cyclohexanes was reported as an analytical technique for the determination of cyclopentanes in mixture with paraffins (411). Ethylcyclopentane a t room temperature gave an 18-20% yield of cyclohexane derivatives (412). A t 140-145", an 85% yield of 1,3,5-trimethylcyclohexane was obtained. This work was also extended to 1,l-dimethylcyclopentane (410), up to 95% of which was converted to methylcyclohexane a t 115'. Similar conversions of alkylated cyclopentanes were also reported by Shuikin and Plate (375). These researches parallel similar work done in the United States. Zelinskii and Levina studied the shift of double bonds when olefins were passed over oxide catalysts (446). Levina also established that in the presence of chromic oxide on alumina a t 250" the triple bond in a 1-alkyne is shifted, giving a product one half of which consists of the corresponding 2-alkene and one-half of a 1,3-diene (206). She also reported migration of double bonds from side chains into the ring of naphthenes carrying unsaturated side chains. The work of Petrov (288) and of Moldavskil (236) on the isomerization of some paraffins in the presence of aluminum chloride points to the similarity in temperature required for cracking and for isomerization of these paraffins in the presence of the catalyst used. Moldavskil used aluminum chloride-hydrogen chloride for isomerization of butanes and pentanes and observed a redistribution of methyl groups (241). Reactions of various compounds with aluminum chloride were studied by a number of Russian chemists in the nineteenth and twentieth centuries. Menshutkin correlated the activity of certain chlorides in Friedel-Crafts reactions and gave (233) the following series in the order of decreasing activity : AlCls-FeCls-ZnC1~-SnC14-TiC1~ (or ZrC14). In a series of papers on the mechanism of the Friedel-Crafts reaction, Korshak and co-workers attributed the catalytic activity of aluminum chloride to the formation of bipolar compounds and have presented evidence in favor of their mechanism which involves reactions of aro-

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matics with chlorinated olefins and paraffins. mechanism is as yet to be determined (175).

The exact value of the

9. Alkylation Until recently, information on alkylation studies reported in the Russian chemical literature was limited to laboratory work. The work of Butlerov and his students on triptene induced one member of their group, El'tekov, to study alkylation as a method of preparation of triptene from lower olefins (99,100). Moldavskii and co-workers recently improved this method in an apparent effort at commercial preparation of triptene which is readily hydrogenated t o the high antiknock fuel, triptane (242). The alkylation of pentene was accomplished by El'tekov with methyl iodide over lead oxide, whereas Moldavskii used methyl chloride and magnesia. MoldavskiI's work was probably carried out simultaneously with similar researches in this country. Tsukervanik et al. alkylated aromatics with alcohols and alkyl halides in the presence of aluminum chloride (4091, zinc chloride (182,408), phosphoric acid (407), and anhydrous ferric chloride (406). When the alkylation using n-butyl or isopropyl alcohol saturated with HC1 was carried out under pressure at 180-230°C. in the presence of ZnClz, yields were higher than in the absence of pressure (182). Furthermore, 0.02 mole ZnCL per mole of alcohol was sufficient t o produce a 75% yield of butyltoluene. Research on vapor phase alkylation of aromatic hydrocarbons with olefins, alcohols, and alkyl halides over synthetic silicaalumina was started before 1941 at the Karpov Institute of Physical Chemistry. Some outcomes of this research, including dealkylation and disproportionation of toluene to benzene and xylene, were reported by Natanson and Kagan (251). Dolgov and co-workers (68,69) are currently publishing a series of papers on reactions of alkyl halides catalyzed by A1C13. The AlC13 was prepared by passing dry HC1 into aluminum shavings in benzene (Radziewanowski method). The yield of monoalkyl benzene obtained with 2 to 4% aluminum ranges from 18 t o 57% of theory and decreases with increase of the size of the aliphatic radical. In addition the condensate contained 30 to 50% higher boiling products. Nametkin and Kagan (249) studied the mechanism of methyl transfer in the xylene-benzene-AlC13 system. They used a flow system operating a t 0.252 space velocity, 1 atm., and 250" and 300°, with 20 and 40% AlC1, on charcoal. Benzene in the absence of xylene is not affected. With an equimolar mixture of benzene and xylene, toluene formation reached 25% with 40% AlC13; half as much was obtained with 20% AICla. Benzene disappearance was less than toluene formation so that,

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the reaction involved xylene disproportionation as well as exchange with benzene. Shuikin (370) passed methyl and dimethyl cyclohexanes over nickel a t 330-350". I n addition to the usual demethylation and dehydrogenation reactions, he found evidence of methyl transfer; methylcyclohexane gave some p-xylene, while dimethylcyclohexane gave some trimethylbenzene. Platinum a t these temperatures did not cause this methyl transfer. Plate and 0. A. Golovina (306) reported that appreciable demethylation of 2,2,4-trimethylpentane took place over molybdena-alumina at 150250°C. and was accompanied by the formation of small amounts of aromatics. In 1945 Mamedaliev published a book in Baku (213) reporting the research carried out in his laboratory on the alkylation of aromatics and isoparaffins with olefins in the presence of a number of catalysts. Subsequent information indicates that Mamedaliev has developed a continuous process of alkylation of benzene with olefins. He also described alkylation of benzene with propylene in the presence of activated clay (214). Other workers also report studies on alkylation of aromatics over silica-alumina (63). Ivanov et al. alkylated coal-tar aromatics with olefins in the presence of aluminum chloride-hydrogen chloride and obtained a product suitable for use as a lubricating oil (143). Topchiev and Paushkin have reported high yields in the alkylation of isopentene with propylene in the presence of a catalyst containing phosphoric acid and boron trifluoride (395). Benzene was alkylated with crude propylene, using HzS04 of strength from 75 to 97 %. The spent acid was recycled in part. With equal moles of benzene and propylene, 25% by weight of acid based on benzene gave 35 % isopropyl and 35 % polyisopropyl benzene, while 100% acid gave 40% isopropyl and 50% polyisopropyl benzene. With 0.5 mole propylene per mole benzene, all the propylene was consumed and the ratio of mono- to polypropyl benzenes was independent of the acid ratio. Paushkin and Topchiev also used HsP04.BF3 a t room temperature to alkylate benzene with olefins (287,402). For alkylation of benzene with alcohols, temperatures of 90-97" and a feed mole ratio of 0.5 alcohol: 1.0 benzene:0.5 catalyst were recommended (394). In a recent study (400a) these authors supplemented their previously published views (396) concerning the properties of boron fluoride complexes with phosphoric acid, alcohols, and sulfuric acid as catalysts. Data on the electroconductivity of these catalysts was correlated with their activity in alkylation of isobutane and it was concluded (400a) that the acid ion concentration did not affect the alkylation or polymerization reactions over these catalysts, and therefore the carbonium ion mechanism was not applicable.

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Dilution of the catalyst with reaction by-products may reduce the conductivity and the activity of the catalyst, but this has no bearing on the carbonium ion theory (400b). They preferred a mechanism postulating the similarity of these catalysts t o aluminum chloride. 10. Cracking

Russian chemists and technologists have evinced interest in catalytic cracking in early publications. In addition t o studies such as those by Gustavson on decomposition of petroleum hydrocarbons in the presence of aluminum chloride (133), the work of Zelinskii initiated in 1922 on cracking kerosenes and heavier oil fractions with aluminum chloride has been frequently mentioned (435,448). Early Russian and nonRussian work on cracking in the presence of catalysts was reviewed by Dobryanskii (61). Dobryanskii doubted that aluminum chloride was a true catalyst in cracking and in general was skeptical of the possibilities of catalytic cracking in 1935. A review of aluminum chloride reactions involving cracking was also published by the same author in 1938 (62). Shorter monographs on catalytic cracking have been subsequently published by other writers, for instance, by Obryadchikov (272,273,274,275) and by others. I n 1940 Frost demonstrated (120) that many silica-alumina catalysts were able t o produce the same cracking reactions as aluminum chloride. This information was correlat,ed with Zelinskili's early views concerning !,he origin of petroleum (122). ZelinskiI and co-workers have stated that organic matter can be converted into petroleum by catalytic conversions a t temperatures not exceeding 200" (277). A variety of materials of vegetable and animal origin including cholesterol were tested by Zelinskil in the presence of aluminum chloride. When cycloolefins or oxygenated compounds were treated with natural clays under conditions where hydrogen disproportionation was t o be expected, an equilibrium mixture of cyclohexane with methylcyclopentane was obtained. On the basis of his own work of this type, Frost concluded that the conversion could have occurred a t temperatures from 90 to 340°C. since all data on the concentrations of these compounds in oil reported in the literature corresponded t o equilibria attainable a t these temperatures. A further support of this view was derived by Frost from his experiments establishing th a t clay from the Askan deposit converts Z-cholesterol into a mixture of the latter with d-rotatory products, which was related to Engler's and Rakuzin's research on the subject at the beginning of the twentieth century. Saturated d-rotatory hydrocarbons (menthane isomers) were obtained by

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the action of activated clay on natural vegetable stock (1-menthol) ( 123,123). In a critical review of the nature of the catalyzing effect of silicaalumina, Ballod and Topchieva (34) quoted evidence from the Russian and non-Russian literature to the effect that silica-alumina catalysts constitute distinct chemical compounds, the activity of which is not dependent upon either silica gel or alumina gel. The silica-alumina catalyst is an acid and its activity in hydrogen disproportionation, alkylation, polymerization, and isomerization depends upon the same active centers. The activity parallels that of other acid catalysts, but cannot be ascribed to acids adsorbed on its surface. Hydrogen ions on the surface can be substituted by cations and thus be poisoned (40,404). When the hydrogen ions are substituted by sodium or potassium, total inactivity of the catalyst for cracking results. However, an increase in activity results from substitution for the alkali by the following metals: Ba, Zn, Mg, Al, Th. Adsorption of the last two cations restores the activity to the level of pure silica-alumina (40). The possibility that effective silica-alumina possesses geometrical parameters corresponding t o those of the molecules of the reacting hydrocarbons was again stated by Topchieva in 1951 (403). These characteristics are ascribed to the compound with 30% alumina and 70% silica, which approaches the composition of montmorillonite. In cracking cumene, decalin and cetane it was found that a sample of the above composition was more active than those with either 72 or 50% alumina, although the surface area of all samples was virtually the same. Correlation of the pore size distribution with hydrogen disproportionation data supports this conclusion (403). Paushkin and Lipatov (286) added 10% boron fluoride to silicaalumina and to activated charcoaI for use in cracking a crude oi1 fraction a t 310-510". Over silica-alumina at 400" or higher the amount of olefins was about half that obtained with silica-alumina alone. The amount of gasoline obtained was increased 15% or more. In the case of charcoal, the polymerizing effect of boron fluoride reduced the yield and increased the specific gravity. Qborin (270,271) examined the suitability of alumina-containing catalysts including silica-alumina for the reactions involved in cracking of hydrocarbons and found that the activity of the catalyst could be explained on the basis of structure analysis evidence obtained by him which supported the view that a mixture of silica and alumina rather than an aluminum silicate was present. He also found that the distance between two aluminum atoms was approximately 2.56 A., which is close to the distance between alternate carbon atoms in a hydrocarbon, thus

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supporting the existence of a doublet. In silica-zirconia-alumina a similar doublet may exist made up of aluminum and zirconium; he offered this as support for the Balandin theory. Frost and co-workers studied the kinetics of cracking of paraffins (not pure compounds) over silica-alumina and concluded that consecutive monomolecular reactions were involved. At 400°C. the rate was 1700 times higher than in the thermal reaction. At 500" it was 27 times as fast (216). Cracking of a topped crude oil (sp. gr. 0.91-0.93, 45% boiling below 300°C.) over silica-alumina a t 310-355°C. was reported by the Institute of Mineral Fuels (186). A 20% yield of gasoline boiling below 200°C. was obtained. The catalyst was prepared from a natural mineral and resembled aluminum chloride in its action. Pure sulfur compounds containing 9 or 10 carbon atoms were examined in the presence of silica-alumina a t 250-300" (391). Liberation of hydrogen sulfide, destructive hydrogenation and hydrogen disproportionation took place forming disulfides, mercaptans, and olefins. Obolentsev (264) has published researches on the conversions of individual hydrocarbons over silica-alumina. Depolymerization of triisobutylene as the temperature was raised from 200 to 365" resulted in a decrease of the liquid products from 45 to 60% progressively to 24 to 26% with a corresponding increase in the yield of the gaseous products; the dimer was also depolymerized, although other workers reported it to be stable. A mechanism was postulated which involved the intermediate formation of an alkylated cyclobutane (264). Isopropylbenzene was dealkylated with simultaneous disproportionation to diisopropylbenzene a t 350-450" (266). Disproportionation may become the principal reaction a t the higher temperature (267).

11. Oxidation Oxidation of individual hydrocarbons may be exemplified by the work of Medvedev (232) who has been studying these reactions for a number of years and has more recently investigated the effect of oxygen on polymerization reactions. Neutral phosphates of aluminum, tin or iron, tin borate, etc., were found to be suitable for the conversion of methane to formaldehyde a t 500°C. A practical aspect of this research is represented by the homogeneous oxidation of petroleum stocks in the presence of naphthenates which was developed by Petrov into an industrial process to supply fatty acids for the soap making and grease making industry (298,299). Kreshkov oxidized methane to formaldehyde in the presence of chlorine and steam over chlorides of copper or barium or over vanadium pentoxide on carbon (179), but his yields were low.

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The catalytic oxidation of ethylene to ethylene oxide was apparently developed into a commercial process by Zimakov (460). Zimakov assumes that ethylene is first activated by migration of an electron, then converted to a peroxide radical which initiates a chain reaction. His use of silver on corundum promoted with BaOz and modified by dichloroethane is similar to that disclosed in patents of Carbide and Carbon Chemical Corporation. In the oxidation of alcohols a variety of catalysts have been tested by Russian investigators (1 17,276) including gold, silver, copper, nickel, manganese, and cobalt. A two-stage oxidation using platinized asbestos followed by copper was used by Orlov (276); the second catalyst was heated to the desired temperature by the heat of the reaction of platinum. Dolgov produced a mixture of 18% formaldehyde and 40% acetaldehyde by blowing air at room or slightly higher temperature through aqueous methanol and ethanol containing a suspension of platinum or palladium (65) * From the results of extensive oxidation of hydrocarbons, alcohols, and aldehydes over catalysts such as platinum black, together with results from the oxidation of aldehydes and ketones over chromites of magnesium and copper and on silver (52,139a,209,221,282,312,377), Margolis concluded (218) that aldehydes cannot constitute intermediate products of oxidation. The nature of the actual oxidation intermediates has not yet been determined. In the oxidation of carbon monoxide, an intermediate compound formed by surface molecules of manganese dioxide with carbon monoxide and oxygen was postulated by Roginskii and Elovich (335). This scheme is thought to agree with the general view concerning participation of the electrons of the solid in the catalytic process. These workers rejected (97) the mechanism of oxidation-reduction effects of manganese dioxide postulated by Benton (39). Margolis and Todes (221) regarded oxidation of normal paraffins, olefins, and aromatics on the above catalysts (chromites, platinum) as first order reactions, but branched chain paraffins and naphthenes undergo oxidation described as a second order reaction with respect to the hydrocarbon. The catalyzed complete combustion of individual hydrocarbons has been investigated by Todes in an attempt to establish the combustion characteristics of these hydrocarbons (220), while other workers have attempted t o improve the techniques of catalyzed combustion (457). At the Power Institute Ravich has been working on the development of catalysts promoting complete combustion of gaseous and solid fuels with the aid of naturally occurring and synthetic minerals containing oxides of iron, chromium, nickel, potassium, aluminum, and manganese (317,318,319). Industrial application of this process has been mentioned.

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12. Other Reactions

In the field of halogenation, the practical aspects of the work were stressed by a number of Russian workers. Thus, in 1940 and later Mamedaliev reported (215) on the chlorination of methane over cupric chloride, pumice, iron, or aluminum shavings. Yields of 75 to 80% of products ranging from methyl chloride to carbon tetrachloride with small amounts of hexachloroethane were obtained. Similar work on the continuous chlorination of hydrocarbons such as isopentane, unsaturated compounds, oxygenated compounds, and on the mechanism of chlorination has been reported by Russian researchers from time to time (180,248,366,367,389). From the review of the literature on polyethylene and its halogenated derivatives (60) one may conclude that research on teflon and similar halogenated polymers is in the initial stage of research in Russia at the present time. Hydrolysis of chlorobenzene and the influence of silica gel catalysts on this reaction have been studied by Freidlin and co-workers (109). Pure silica gel gave up to 45% phenol from chlorobenzene a t 600°C. When the silica gel was promoted with 2 % cupric chloride, up to 75% phenol was obtained (381). A number of other salts were tested by Freidlin and co-workers as promoters, but they exerted an adverse effect on the activity or selectivity of the catalyst. With 0.2% cupric chloride and 6% metallic copper, the activity of silica-gel was doubled (389). At 500" under the above conditions, the halides were hydrolyzed a t rates decreasing in the following order: chloride, bromide, iodide, fluoride (110). The specific activation of aryl halides by cupric chloride was demonstrated by conversion of chlorobenzene to benzene and of naphthyl chloride to naphthalene when this catalyst was supported on oxides of titanium or tin (111). The silica promoted with cupric chloride was also found to be suitable for hydrolysis of chlorophenols and dichlorobenzenes; however, side reactions were too prominent in these cases (1 12). A number of catalytic reactions studied by Russian authors are necessarily left out of this review. These include nitration and sulfonation (138). As an example; the use of alumina in the synthesis of heterocyclic compounds may be mentioned. Ethylene oxide with ammonia gave pyridine; with hydrogen sulfide about 20% thiophene was formed a t 300-450" (211). A t 200°C. ethylene oxide and hydrogen sulfide gave thioxane and dithiane (212,429). Yurlev developed conditions under which the hetero atom of furan, thiophene, and pyrrole could be interchanged (425,426,427,428). Although emphasis in the Russian chemical research is today on the

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practical aspects, studies of the theory of catalysis are not neglected; however, our information on them may become less complete in the near future than it has been in the recent past.

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54. Danilov, S. N., Zhurnal Prikladnoz K h i m i i ( J . Applied Chem. (U.S.S.R.)) 16, 396 (1942). 55. Danilov, S. N., Zhurnal Obshchei K h i m i i ( J . Gen. Chem. (U.S.S.R.)) 17, 1925 (1947). 56. Danilov, S. N., and Venus-Danilova, E. D., Zhurnal Obshchei K h i m i i ( J . Gen. Chem.(U.S.S.R.)) 12, 645 (1932). 57. Dankov, P. D., Zhurnal FizicheskoZ K h i m i i ( J . Phys. Chem. (U.S.S.R.)) 4, 326 (1933). 58. Dankov, P. D., Uspekhi Fizicheskikh N a u k (ProgressPhys. Sci. (U.S.S.R.)) 14,63 (1934); Catalytic Activity and Structure of Thin Layers of Metal. Dissertation, 1936. (See also 343.) 59. Dankov, P. D., and Kochetkov, A. A., Doklady Akad. N a u k S.S.S.R. (Rept. Acad. Sci. U.S.S.R.), 2, 359 (1934). 60. Dintses, A. I., and Losev, I. P., Uspekhi K h i m i i (Progress Chem. (U.S.S.R.))20, 430 (1951). 61. DobryanskiI, A. F., Nauchnye osnovy krekinga nefti (Scientific Principles of Petroleum Cracking). ONTI, Leningrad-Moscow, 1935, 264 pp., pp. 110-124. 62. DobryanskiI, A. F., Kreking s Khloristym Alyuminiem (Cracking with Aluminum Chloride). ONTI, Leningrad, 1938, 129 pp. 63. Doladugin, A. I., et al., Nejtyanoe Khozya'lstvo (Petroleum Znd. (U.S.S.R.)) No. 3-4, 44 (1946). 64. Dolgov, B. N., Kataliz v organicheskol khimii (Catalysis in Organic Chemistry). Moscow-Leningrad, 1949, 560 pp. 65. Dolgov, B. N., Kataliz v organicheskol khimii (Catalysis in Organic Chemistry). Moscow-Leningrad, 1949, 560 pp,, p. 143. 66. Dolgov, B. N., Kataliz v organicheskol khimii (Catalysis in Organic Chemistry). Moscow-Leningrad, 1949, 560 pp., p. 258. 67. Dolgov, B. N., Kataliz v organicheskol khimii (Catalysis in Organic Chemistry). State Chem. Publ. House, 1949, 560 pp., pp. 339 ff. 68. Dolgov, B. N., and Kuchumova, N. A., Zhurnal ObshcheZ K h i m i i ( J . Gen. Chem. U.S.S.R.)) 20,469 (1950). 69. Dolgov, B. N., Sorokin, N. S., and Cherkasov, A. S., Zhurnal ObshcheI K h i m i i ( J . Gen. Chem. (U.S.S.R.)) 21, 509 (1951). 70. Dupont, G., and Piganiol, P., Bull. SOC. chim. France 6, 322 (1939). 71. Dolgov, B. N., et al., Zhurnal Obshchei K h i m i i ( J . Gen. Chem. (U.S.S.R.))3, 313 (1933). 72. Dowden, D. A., J . Chem. SOC.1960, 242. 73. EIdus, Ya. T., Uspekhi K h i m i i (Progress Chem. (U.S.S.R.)) 7, 1714 (1938). 74. Eldus, Ya. T., Uspekhi K h i m i i (Progress Chem. (U.S.S.R.)) 7, 1801 (1938). 75. Eldus, Ya. T., Uspekhi K h i m i i (Progress Chem. (U.S.S.R.)) 9, 673 (1940). 76. Eldus, Ya. T., Zzvestiya Akad. Nauk S.S.S.R., Otdelenie Khimicheskikh N a u k (Bull. Acad. Sci. U.S.S.R., Dept. Chem. Sci.) 65 (1943). 77 Efdus, Ya. T.,Zzvestiya Akad. Nauk S.S.S.R., Otdelenie Khimicheskikh N a u k (Bull. Acad. Sci. U.S.S.R., Dept. Chem. Sci.) 255 (1944). 78. E'Idus, Ya. T., Zzvestiya Akad. N a u k S.S.S.R., Otdelenie Khimicheskikh N a u k (Bull. Acad. Sci. U.S.S.R., Dept. Chem. Sci.) 349 (1944); 62 (1945). 79. EIdus, Ya. T., et al., Zzuestiya Akad. N a u k S.S.S.R., Otdelenie Khimicheskikh N a u k (Bull. Acad. Sci. U.S.S.R., Dept. Chem. Sci.) 110, 263 (1949); 98, 377 (1950). 80. EIdus, Ya. T., et al., Doklady Akad. N a u k S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 64,35 (1946); 60, 599 (1948).

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107. FavorskiI, A. E., Onishchenko, A. S., Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 11, 1111 (1941). 108. Favorskil, A. E., ShostakovskiI, M. F., and Burmistvova, M. S., Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 13, 1-20 (1943). 109. Freidlin, L. Kh., et al., Zzvestiya Akad. Nauk S.S.S.R., Otdelenie Khimicheskikh Nauk (BuZl. Acad. Sci. U.S.S.R., Dept. Chem. Sci.) 439 (1946). 110. FreIdlin, L. Kh., Balandin, A. A., and Fridman, G. A., Izvestiya Akad. Nauk S.S.S.R., Otdetenie Khimicheskikh Nauk (Bull. Acad. Sci. U.S.S.R., Dept. Chem. Sci.) 655 (1945). 111. Freidlin, L. Kh., Balandin, A. A., Fridman, G. A,, and Lebedeva, A. I., Zzvestiya Akad. Nauk S.S.S.R., Otdelenie Khimicheskikh Nauk (Bull. Acad. Sci. U.S.S.R., Dept. Chem. Sci.) 439 (1946). 112. Freidlin, L. Kh., and Fridman, G. A., Izvestiya Akad. Nauk S.S.S.R., Otdelenie Khimicheskikh Nauk (Bull. Acad. Sci. U.S.S.R., Dept. Chem. Sci.) 317 (1949). 113. FreIdlin, L. Kh., and Ziminova, N. I., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 74, 955 (1950). 114. Freldlin, L. Kh., and Ziminova, N. I., Zzvestiya Akad. Nauk S.S.S.R., Otdelenie Khimicheskikh Nauk (Bull. Acad. Sci. U.S.S.R., Dept. Chem. Sci.) 145 (1951). 115. FreIdlin, L. Kh., and Ziminova, N. I., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 76, 551 (1951). (See also the preceding studies in this series.) 116. Fischer, F., Brennstoff-Chem. 11, 589 (1930). 117. Fokin, S. A., J . Russ. Phys.-Chem. SOC.46, 288 (1913). 118. Fricke, R., and Meyer, F., 2 . physik. Chem., A183, 177 (1938). 119. Fricke, R., and Schweckendick, W., Z . Elektrochem. 46, 90 (1940). 120. Frost, A. V., Zhurnal Fizicheskoi Khimii ( J . Phys. Chem. (U.S.S.R.)) 14, 1313 (1940). 121. Frost, A. V., Uspekhi Khimii (Progress Chem. (U.S.S.R.)) 12, 209 (1943). 122. Frost, A. V., Uspekhi Khimii (Progress Chem. (U.S.S.R.)) 14, 501 (1945). 123. Frost, A. V., Bull. Moscow State Univ. No. 3-4, 111 (1946); Antipina, T. V., and Frost, A. V., Zhurnal Fizicheskoi Khimii ( J . Phys. Chem. (U.S.S.R.)) 24, 860 (1 950). 124. Frost, A. V., et al., Bull. Moscow State Univ. No. 9, 71; No. 10, 99 (1949). 125. Frumkin, A. N., and Shlygin, A. I., Acta Physicochim. U.R.S.S. 3, 791 (1935). 126. Gershenovich, M. S., and Kotelkov, N. Z., Zhurnal Prikladnoi Khimii ( J . Applied Chem. (U.S.S.R.)) 11, 253 (1938). 127. Ginzberg, A. S., and Ivanov, A. P., J . Russ. Phys.-Chem. SOC.62,1991-9 (1930). 128. Gorin, Yu. A., Zhurnal Obshchei Khimii ( J . Gen. Chem. (U.S.S.R.)) 16, 283 (1946). 129. Gorin, Yu. A., Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 19, 877 (1949). 130. Gorin, Yu. A., and Gorin, I. K., Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 19, 664 (1949). 131. Grosse, A. v., MorreI1, J. C., and Mattox, W. J., Ind. Eng. Chem. 32, 528 (1940). 132a. Gryaznov, V. M., Korobov, V. V., and Frost, A. V., Compt. rend. (Doklady) acad. sci. U.R.S.S. 48,339 (1945). 132b. Lapin, Ya. P., and Frost, A. V., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 63,801 (1946) ; Bestnik Moskovskogo Universiteta (Bull. Moscow Univ.) 1946,No. 1, 95. 133. Gustavson, G. G., J . Russ. Phys.-Chem. SOC.16, 244 (1884). 134. Halsey, G. D., and Taylor, H. S., J. Chem. Phys. 16, 624 (1947). 135. Herington, E. F. G., Trans. Faraday SOC.37, 361 (1941).

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136. Huttig, G. F., Z. Elektrochem. 44, 571 (1938).

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137b. Ioffe, A. F., Fizika Kristallov (Physics of Crystals), 1929. 138. Ioffe, I. S., Sulfonation of Organic Substances, Vol. 1. Naval Medical Academy, Leningrad, 1944. 139a. Ipatieff, V. N., Ber. 40, 128 (1907). 139b. Ipatieff, V. N., Catalytic Reactions at High Temperatures and Pressures. The Macmillan Company, New York, 1936. 140. Ipat‘ev, V. V., Jr., Levina, M. I., and Karlblom, A. I., Uspekhi Khimii (Proyress Chem. (U.S.S.R.)) 8, 481 (1939). 141. Isagulyants, V. I., and Golovanova, M. V., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 67, 275 (1949). 142. Ivannikov, P. Ya., Zhurnal PrikladnoZ Khimii ( J . Applied Chhem. (U.S.S.R.)) 13, 118 (1940). 143. Ivanov, K. I., et al., Zhurnal PrikladnoZ Khimii ( J . Applied Chem. (V.S.S.R.)) 18, 158 (1945). 144. Kagan, M. Ya., LyubarskiI, R. D., and Podurovskaya, 0. M., Zzvestiya Akad.

Nauk S.S.S.R., Otdelenie Khimicheskikh Nauk (Bull. Acad. Sci. U.S.S.R., Dept. Chem. Sci.) 173 (1947). 145a. Kagan, M. Ya., and Shcheglova, N. A., Zhurnal Fizicheskot Khimii ( J . Phys. Chem. (U.S.S.R.))23,1203 (1949); Kagan, M. Ya., Doklady Akad. NaukS.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 74, 61 (1950); Flid, P. M., and Kagan, M. Ya., Zhurnal Fizicheskot Khimii (J.Phys. Chem. (U.S.S.R.)) 24, 1409 (1950); Fridman, S. D., and Kagan, M. Ya., Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 21, 874 (1951). 145b. Kagan, M. Ya., Erivanskaya, L. A., and Trofimova, I. V., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. 7J.S.S.R.) 82,913 (1952). 146. Karzhavin, V. A., Uspekhi Khimii (Proyress Chem. (U.S.S.R.)) 16, 327 (1947). 147. Karehev, V. I., Severyanova, M. G., and Siova, A. N., Khimiya Tverdogo Toplira (Chem. Solid Fuel) 8, 559 (1936). 148. Kazanskii, B. A., Sintea shidkogo topliva is okisi ugleroda i vodoroda (Synthesis of Liquid Fuel from Carbon Monoxide and Hydrogen). GNTI, Moscow, 1940, 208 pp. 149a. XazanskiX, B. A., Uspekhi Khimii (Progress Chem. (U.S.S.R.)) 17, 641 (1948). 149b. Kazanskii, B. A., and Terent’eva, E. M., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 72, 511 (1950). 150. Kaeanskif, B. A., and Liberman, A. L., Izvestiya Akad. Nauk S.S.S.R. (Bull. Acad. Sci. U.S.S.R.) 265 (1947). 151. KazanskiI, B. A., Liberman, A. L., and Batuev, N. I., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 61, 67 (1948). 152. Kazanskil, B. A., Liberman, A. L., Plate, A. F., Sergienko, S.R., and Zelinskil, N. D., Doklady Aka. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 27, 447 (1940). 153. Kazanskil, B. A., Losik, I. B., and ZelinskiI, N. D., Doklady Aka. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 27, 565 (1940). 154. Kazanskil, B. A., and Lukina, M. Yu., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 74, 263 (1950). 155. Kazanskif, B. A., Nesrneyanov, A. N., and Plate, A. F., Uspekhi Khimii (Proyress Chem. (U.S.S.R.)) 20, 18 (1951).

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156. KasanskiI, B. A,, and Plate, A. F., Ber. 69, 1862 (1936). 157. Kazanskii, B. A , , and Plate, A. F., Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 7, 328 (1937). 158. KasanskiI, B. A., Plate, A. F., Bulanova, T. F., and ZelinskiI, N. D., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 27, 658 (1940). 159. Kazanskif, B. A,, and Sergienko, S. R., Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 9, 447 (1939). 160. KaaanskiI, B. A., Sergienko, S. R., and ZelinskiI, N. D., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 27, 664 (1940). 161. KeIer, N . P., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 73, 1071 (1950). 162. KeIer, M. P., and Roginskii, S. Z., Doklady Akad. Nauk S.S.S.R. (Repl. Acad. Sci. (U.S.S.R.)) 67, 157 (1947). 163. Keler, M. P., and Roginskii, S. Z., Izvestiya Akad. Nauk S.S.S.R., Otdelenie Khimicheskikh Nauk (Bull. Acad. Sci. U.S.S.R., Dept. Chem. Sci.) (1950). 164. Khvatov, A. D., ZhurnaZ ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 9, 819 (1939). 165. KlebanskiI, A. L., Symposium on the 20th Anniversary of the State Institute of Applied Chemistry. 1939, pp. 359-83. 166. Klyachko-Gurvich, L. L., and Kobozev, N. I., Zhurnal FizicheskoZ Khimii ( J . Phys. Chem. (U.S.S.R.)) 14, 650 (1940). 167. Kobozev, N. I., Acta Physicochim. U.R.S.S. 9, 805 (1938). 168. Kobozev, N. I., Zhurnul FizicheskoZ Khimii ( J . Phys. Chem. (U.S.S.R.)) 13, 1, 27 (1939); 14, 663 (1940); 19, 48 (1945); 21, 1413 (1947); Acta Physicochim U.R.S.S. 9, 469, 805 (1940). 169. Kobozev, N. I., Zhurnal Fizicheskd Khimii ( J . Phys. Chem. (U.S.S.R.)) 16,882 (1941); 19, 142 (1946). 170. Kobozev, N. I., Zhurnal Fizicheskoi Khimii ( J . Phys. Chem. (U.S.S.R.)) 23, 388 (1 949). 171. Kobozev, N. I., Nikolaev, N. A., Zubovich, I. A., and Gol’dfel’d, Ya. M., Zhurnal FizicheskoZ Khimii ( J . Phys. Chem. (U.S.S.R.)) 19, 142 (1946). 172a. Kobozev, N. I., and Reshetovskaya, N. A., Zhurnal FizicheskoZ Khimii ( J .Phys. Chem. (U.S.S.R.)) 23, 388 (1949). 172b. Kobosev, N. I., and Lebedev, V. P., Zhurnal Fizicheskd Khimii ( J . Phys. Chem.) 23, 1483-94 (1949). 173. Kobozev, N. I., and Zubovich, I. A., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 62, 131 (1946). 174a. Koelbel, H., and Engelhardt, F., Brennstofl-Chem. 32, No.9/10, 150 (1951). 174b. German Patent (12’, 1/03). 175. Korshak, V. V., et al., Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 19, 690 (1949). (See also preceding articles of this series.) 176. Korshak, V. V., and Zamyatina, V. A., Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 16, 947 (1945). 177. Kotelkov, N. Z., Zhurnal AnalilicheskoZ Khimii ( J . Anal. Chem.) 6, 48 (1950). 178. Kozlov, B. A., and Rastsvetaev, M. K., Vestnik Akad. Nauk S.S.S.R. (Bull Acad. Sci. U.S.S.R.) NO. 4-5, 63 (1943). 179. Kreshkov, A. P., Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 10, 1605 (1940). 180. Kreshkov, A. P., Zhurnal Prikladnoi Khimii ( J . Applied Chem. (U.S.S.R.)) 14, 800 (1941); also previous studies by this author.

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181. Kucherov, M. G., Ber. 14, 1540 (1881); 17, 13 (1884). 182. Kuchkarov, A. B., and Tsukervanik, I. P., Zhurnal ObshcheZ Khirnii ( J . Gen. Chem. (U.S.S.R.))20,485 (1950). 183. Kukina, A. C., Bull. Moscow Unin. No. 10, 87-97 (1949); Balandin, A. A., and Kukina, A. C., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 64, 65 (1949). 184. Kummer, J. T., and Emmett, P. H., J. Chem. Phys. 19, 289 (1951). 185. Kusakov, M., Zzvestiya Akad. Nauk S.S.S.R., Otdelenie Khimicheskikh Nauk (Bull. Acad. Sci. U.S.S.R., Dept. Chem. Sci.) 672 (1944). 186. Larin, A. Ya., Zzvestiya Akad. Nauk S.S.S.R., Otdelenie Tekhnicheskikh Nauk (Bull. Acad. Sci. U.S.S.R., Dept. Tech. Sci.) 724 (1944). 187. Lebedev, S. V., et al., Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 6, 1422 (1935). (See also preceding articles by Lebedev on this subject.) 188. Lebedev, S. V., Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 3, 698 (1933);Lebedev, S. V., et al., Trans. Exptl. Plant B 3, (1933). 189. Lebedev, S. V., Gorin, Yu. A., Khutoretskaya, S. N., Charskaya, K. N., and Kogan, F. N., SinteticheskiZ Kauchulc (Synth. Rubber) No. 1, 8 (1935). 190. Lebedev, S. V., VolshinskiI, I. A., Gorin, Yu. A., Gulyaeva, A. I., Kogan, 0. M., KoblyanskiI, G. G., Karpyshev, M. A., Livshits, I. A., Orlov, S. M., Slobodin, Ya. M., Subbotin, S. A., Khokhlovkin, M. A,, Reshetov, A. N., and Tatarnikov, A. M., Trans. Exptl. Plant B 3, 16 (1934). 191. Le Clerc, G., and Lefebre, H., Compt. rend. 208, 1650 (1939). 192. Le Clerc, G., and Michel, R., Compt. rend. 208, 1583 (1939). 193. Lel’chuk, S. L., et al., Promyshlennost’ Organicheskoi Khimii (Org. Chem. Ind. (U.S.S.R.)) 6, 657 (1939). 194. Lel’chuk, S. L., et al., Zhurnal PrikladnoZ Khimii ( J . Applied Chem. (U.S.S.R.)) 17, 60 (1944). 195. Lel’chuk, S. L., Khimicheskaya Promyshlennost’ (Chem. Ind.) No. 4, 7 (1945). 196. Lel’chuk, S. L., Compt. rend. (Doklady) acad. sci. U.R.S.S. 49, 652 (1945). 197. Lel’chuk, S. L., Balandin, A. A., and Vaskevich, D. N., Uspekhi Khimii (Progress Chem. (U.S.S.R.)) 14, 185 (1945). 198. Lel’chuk, S. L., Vaskevich, D. N., Belen’kaya, A. P., and Dashkovskaya, F.A., Izvestiya Akad. Nauk S.S.S.R., Otdelenie Khimicheskikh Nauk (Bull. Acad. Sci. U.S.S.R., Dept. Chem. Sci.) 191 (1946). 199. Lennard-Jones, J. E., Trans. Faraday SOC.28, 333 (1932). 200. Levin, V. I., Problems of Kinetics and Catalysis edited by S. Z. Roginskil. Vol. VII, pp. 205-37. 201. Levin, V. I., Uspekhi Khimii (Progress Chem. (U.S.S.R.)) 17, 174 (1948). 202. Levin, V. I., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 69, 269 (1948). 203. Levina, R. Ya., and Gladshteh, B. M., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 71,65 (1950). 204. Levina, R. Ya., and Potapova, Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.8.S.R.)) 7, 353 (1937); Levina, R. Ya., and Trakhtenberg, D. M., ibid. 6, 764 (1936). 205. Levina, R. Ya., and Tsurikov, F. F., Zhurnal ObshcheX Khimii ( J . Gen. Chem. (U.S.S.R.)) 4, 1250 (1934); Levina, R. Y., Petrov, D. A., and Trakhtenberg, D. M., ibid. 6, 1496 (1936); Levina, R. Ya., and Cherniak, M. I., ibid. 7, 402 (1937) ; and subsequent papers by Levina and co-workers. 206. Levina, R. Ya., and Viktorov, E. A., Zhurnal Obshchei Khimii ( J . Gen. Chem. (U.S.S.R.)) 20, 713 (1950).

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207. Losev, I. P., et al., Zhurnal Obshchel Khimii ( J . Gen. Chem. (U.S.S.R.)) 16, 353 (1945). 208. Losev, I. P., Fedotova, 0. Ya., and ShostakovskiI, M. F., Zhurnal ObshcheZ Khimii (J.Gen. Chem. (U.S.S.R.)) 14, 889 (1944). 209. Lowdermilk, Day, J . Am. Chem. SOC.62, 3535 (1930). 210. Lowry, H. H., Chemistry of Coal Utilization 2, 1797 (1945). 211. MalinovskiI, M. S.,and Moryganov, B. N., Zhurnal PrikladnoZ Khimii ( J . Applied Chem. (U.S.S.R.)) 21, 995 (1948). 212. MalinovskiI, M. S.,and Moryganov, B. N., Zhurnal Prikladno‘l Khimii ( J . Applied Chem. (U.S.S.R.)) 23, 853 (1950). 213. Mamedaliev, Yu. G., Alkylation Reaction in the Production of Aviation Fuels, Aznefteizdat, Baku, 1945, 103 pp. 214. Mamedaliev, Yu. G., Izvestiya Akad. Nauk S.S.S.R. Otdelenie Khimicheskikh Nauk (Bull. Acad. Sci. U.S.S.R., Dept. Chem. Sci.) 458 (1946); 197 (1947). 215. Mamedaliev, Yu. G., Dement’eva, V. V., Kuliev, A. M., and Bakhshiev, A. A., Zhurnal Prikladnoi Khimii ( J . Applied Chem. (U.S.S.R.)) 12, 1826 (1939). 216. Mankash, E. K., Borisova, G. P., Orochko, D. L., and Frost, A. V., Neftyanoe Khozyaistuo (Petroleum Ind.) No. 6-7, 26 (1946). 217. Marek, L. F., and Hahn, D. A., Catalytic Oxidation of Organic Compounds. (Russ. transl.) ONTI, 1936, pp. 184, 450, 480, 529. 218. Margolis, L. Ya., Uspekhi Khimii (Progress Chem. (U.S.S.R.)) 20, 176 (1951). 219. Margolis, L. Ya., and Krylov, 0. V., Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 20, 1991 (1950). 220. Margolis, L. Ya., and Todes, 0. M., Izvestiya Akad. Nauk S.S.S.R., Otdelenie Khimicheskikh Nauk (Bull. Acad. Sci. U.S.S.R., Dept. Chem. Sci.) 44 (1937). 221. Margolis, L. Ya., and Todes, 0. M., Zhurnal Obshche’l Khimii ( J . Gen. Chem. (U.S.S.R.)) 18, 1043 (1948). 222. Margolis, L. Ya., and Todes, 0. M., Zhurnal ObshcheZ Khimii (J.Gen. Chem. (U.S.S.R.)) 20, 1981 (1950). 223. MaslyanskiI, G. N., Zhurnal Fizicheskol Khimii ( J . Phys. Chem. (U.S.S.R.)) 14, 1301 (1940). 224. MaslyanskiI, G. N., Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 14, 148 (1944). 225. Maslyanskil, G. N., and Berlin, T. S., Zhurnal ObshcheZ Khimii ( J . Gem. Chem. (U.S.S.R.)) 16, 1643 (1946). 226. MaslyanskiI, G. N., Meshebovskaya, E. I., and Kholyavko, V. S., Trans. T s I A T I M 4, Moscow-Leningrad, 1947 pp. 98-117. 227. MaslyanskiI, G. N., Mezhebovskaya, E. I., and Berlin, T. S., Zhurnal Obshchet: Khimii (J.Gen. Chem. (U.S.S.R.)) 16, 1823 (1946). 228. MaslyanskiI, G. N., Mezhebovskaya, E. I., and Kholyavko, V. S., Neftyanaya Promyshlennost’ S.S.S.R. (Petroleum Ind. U.S.S.R.) No. 9-10, 40 (1946). 229. McGreer, T. P., Doctoral Thesis, Princeton Univ. (1949). 230. Medvedev, S., Zhurnal FizicheskoZ Khimii ( J . Phys. Chem. (U.S.S.R.)) 17, 391 (1943). 231. Medvedev, S., and TseItlin, P., Acta Physicochim. U.R.S.S. 20, 3 (1945). 232. Medvedev, S., Trans. Karpov Inst. 3, 54 (1924); 4, 126 (1925). 233. Menshutkin, B. N., Izvestiya Politekh. Inst. (Bull. Polytech. Inst.) 22,443 (1914). 234. Metody Khimicheskogo Ispol’zouaniya Okislov Ugleroda (Methods of Chemical Utilization of Carbon Oxides). 1936. 235. Minachev, Kh. M., ShuIkin, N. I., and Roshdestvenskaya, Doklady Akad, Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 76, 543 (1951).

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262. Nyrop, J. E., J. Phys. Chem. 39, 643 (1935); Phys. Rev. 39, 967 (1932); The Catalytic Action of Surfaces. Copenhagen: Levin and Munksgaard, 1937. 263. Obolentsev, R. D., Zhurnal ObshcheZ Khirnii ( J . Gen. Chem. (U.S.S.R.)) 16, 77 (1946). 264. Obolentsev, R. D., Zhurnal PrikladnoZ Khimii ( J . Applied Chem.) 22, 157 (1949). 265. Obolentsev, R. D., Chernyshevskil, N. G., Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.8.S.R)) 21, 79 (1951). 266. Obolentsev, R. D., and Gryazev, N. N., Doklady Akad. Nauk S.S.S.R. (Rep!+ Acad. Sea, U.S.S.R.) 73, 121 (1950). 267. Obolentsev, R. D., and Gryaseu, N. N., Zhurnal Obshcher Khimii (J.Gen. Chem. (U.S.S.R.)) 21, 860 (1951). 268. Obolentsev, R. D., and Usov, Yu. N., Zhurnal Obshchd Khimii ( J . Gen. Chem. (U.S.S.R.)) 17, 897 (1947); 21, 1438, 1567 (1951). 269. Obolentsev, R. D., Pazhetnov, B., Rutkovski'l, D., and Trifel, A., Nejtyanoe KhozyaZstvo (Petroleum Znd. U.S.S.R.), No. 1, 93 (1941). 270. Oborin, V. I,, Neftyanoe KhozyaZstoo (Petroleum Znd.) 26, No. 11, 50 (1947). 271. Oborin, V. I., Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 18, 612 (1948). 272. Obryadchikov, S.N., Mechanism and Chemistry of Catalytic Cracking. Moscow-Leningrad, 1946. 273. Obryadchikov, S. N., Selective Catalysis in Treatment of Oil. Moscow-Leningrad, 1946. 274. Obryadchikov, S. N., Trans. Z. M . Gubkin Petroleum Znst., Moscow, No. 4, 118. 275. Obryadchikov, S. N., Neftyanoe KhozyaZstvo (Petroleum Znd. U.S.S.R.), No. 11, 36 (1946). 276. Orlov, E. I., J . Russ. Phys.-Chem. SOC.40, 656 (1908). 277. Osnitskaya, L. K., and Frwt, A. V., Uspekhi Khimii (Progress Chem. (U.S.S.R.)) 20, 360 (1951). 278. Ostromyslenskil, I. I., J . Russ. Phys.-Chem. SOC.47, 1472 (1915). 279. OstromyslenskiI, I. I., J . Russ. Phys.-Chem. SOC.47, 1494 (1915). 280. Packendorf, K., Ber. 67, 905 (1934). 281. Packendorf, X., and Leder-Packendorf, Ber. 67, 1388 (1934). 282. Palmer, W. G., Proc. Roy. SOC.(London) A99, 412 (1921). 283. Panov, V. V., Nejtyanoe KhozyaZslvo (Petroleum Ind.) No. 10, 45 (1947). 284. Patat, F., Z. Elektrochem. 63, 216 (1949). 285. Patrikeev, V. V., and Liberman, A. M., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 62, 87 (1948). 286. Paushkin, Ya. M., and Lipatov, Yu. S., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 76, 547 (1950). 287. Paushkin, Ya. M., and Topchiev, A. V., Zhurnal PrikladnoZ Khimii ( J . Applied Chem. (U.S.S.R.)) 21, 1065 (1948). 288. Petrov, A. D., Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 5, 973 (1935). 289. Petrov, A. A., Trans. Voronezh State Univ. 10,No. 2, 101 (1938). 290. Petrov, A. D., Development of Organic Synthesis. Acad. of Sciences, MoscowLeningrad, 1943, p. 87. 291. Petrov, A. D., Sintes i isomernye prevrashcheniva alifaticheskikh uglevodorodov (Synthesis and Isomeric Conversions of Aliphatic Hydrocarbons) Publ. Acad. 8ci. U.S.S.R., Moscow-Leningrad, 1947, 298 pp.

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292. Petrov, A. D., and Antsus, L. I., Izuestiya Akad. Nauk S.S.S.R., Otdelenie Khimicheskikh Nauk (Bull. Acad. Sci. U.S.S.R., Dept. Chem. Sci.) 271 (1940). 293. Petrov, A. D., and Antsus, L. I., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 70,425 (1950). 294. Petrov, A. D., and Shchukin, V. I., Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 9, 506 (1939). 295. Petrov, A. D., and Shchukin, V. I., Zhurnal ObshcheZ Khimii ( J . Gen. Chem, (U.S.S.R.)) 11, 1092 (1941). 296. Petrov, A. D., and Shchukin, V. I., Zhurnal Obshchei Khimii ( J . Gen. Chem. (U.S.S.R.)) 11, 1092 (1941). 297. Petrov, A. A., and Shchekin, V. V., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 78, 913 (1951). 298. Petrov, G. S., Trans. Karpov Inst. 157 (1924); 126 (1928). 299. Petrov, G. S., Synthetic Fatty Acids. Moscow, Pishchepromizdat, 1944. 300. Pines, H., Advances in Catalysis, 1, 201 (1948). 301. Pisarzhevskir, L. V., Report at the Meeting on Physical Chemistry 1928, p. 135; quoted from P. D. Dankov, Uspekhi Fizicheskikh Nauk (ProgressPhys. Sci. (U.S.S.R.)) 14, 63 (1934). 302. Pisarzhevskil, L. V., Ukrainskii Khemichnyl Zhurnal (Ukrainian Chem. J.) 1-18 (1925); Acta Physicochim. U.R.S.S. 6, 555 (1937). 303. PisarzhevskiI, L. V., Kataliz. Trudy Vsesoyuznogo Soveshchaniya Posvyashchennogo Pamyati L. V. Pisarzhevskogo (Catalysis. Trans. AII-Union L. V. PisarzhevskiI Memorial Meeting), A. I. Brodskir, editor, Kiev, 1950. 304a. Plate, A. F., Uspekhi Khimii (Progress Chem. (U.S.S.R.)) 9, 1301 (1940). 304b. Plate, A. F., Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 16, 156 (1945). 304c. Plate, A. F., and Batuev, M. I., Zhurnal ObshcheZ Khirnii ( J . Gen. Chem. (U.8.S.R.)) 16, 805 (1946). 305. Plate, A. F., Kataliticheskaya aromatizatsiya parafinovykh uglevodorodov (Catalytic Aromatization of Parafinic Hydrocarbons). Akad. Sci. U.S.S.R., Moscow, 1948, 262 pp. 306. Plate, A, F., and Golovina, 0.A., Zhurnal ObshcheZ Khimii (J. Gen. Chem. (U.S.S.R.)) 20, 2242 (1950). 307. Plate, A. F., and KazanskiI, B. A., Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 7, 328 (1937). 308. Platonov, M . S., Zhurnal ObshcheE Khimii (J.Gen. Chem. (U.S.S.R.)) 11, 683 (1941). 309. Platonov, M. S., and Tomilov, V. I., Zhurnal Obshchel Khimii ( J . Gen. Chem. (U.S.S.R.)) 8, 346 (1938). 310. Platonov, M. S., Tomilov, V. I., and Tur, E. V., Zhurnal ObshcheZ Khimii (J.Gen. Chem. (U.S.S.R.)) 7, 1803 (1937). 311. Prokopets, E. I., and Filaretov, A. N., Zhurnal PrikladnoZ Khimii ( J . Applied Chem. (U.S.S.R.)) 11, 1631 (1938), and other papers in this series. 312. Pshezhetskil, S. Ya., and Kamenetskaya, S. A., Zhurnal Obshchel Khimii ( J . Gen. Chem. (U.S.S.R.)) 19, 136 (1949). 313. Puchkov, P. V., and Nikolaeva, A. F., Zhurnal Obshche?:Khimii ( J . Gen. Chem. (U.S.S.R.)) 8, 1151, 1159 (1938). 314. Puchkov, P. V., and Nikolaeva, A. F., Zhurnal ObshcheZ Khimii (J.Gen. Chem. (U.S.S.R.)) 9, 280 (1939), and related studies by these authors. 315. Rannak, E. D., Rudakova, M. P., and Titova, 2. M., Zhurnal PrikladnoZ Khimii ( J . Applied Chem. (U.S.S.R.)) 18, 425 (1945).

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316. Rapoport, I. B., “Iskusstvennoe zhidkoe toplivo. Cidrogenizatsiya topliv I’ (Synthetic Liquid Fuel, Part I, Hydrogenation of Fuels) Moscow-Leningrad, 1949, 332 pp. 317. Ravich, M. B., Bull. G . M . KrzhizhanovskiZ Energetics Inst. 9, 23 (1940). 318. Ravich, XI. B., Izvestiya Akad. Nauk S.S.S.R., Otdelenie Tekhnicheskikh Nauk (Bull. Acad. Sci. U.S.S.R., Dept. Tech. Sci.) 833 (1946). 319. Ravich, M. B., FlameIess Combustion. Acad. Sci. U.S.S.R., Moscow-Leningrad, 1949, 354 pp. 320. Remiz, E. K., and Frost, A . V., trans. “Khimgaz” plant 3, 297 (1936). 321. Remiz, E. K., and Frost, A. V., Zhurnal Prikladnol Khimii (J.Applied Chem. (U.S.S.R.)) 9, 703 (1936). 322. Remiz, E. K., and Frost, A. V., Zhurnal ObshcheZ Khimii ( J . Gen. Cheni. (U.S.S.R.)) 7, 65 (1937). 323. Remiz, E. K., and Frost, A. V., Zhurnal Prikladnoz Khimii (J.Applied Chem. (U.S.S.R.)) 13, 210ff. (1940). 324. Roginskii, S. Z., Teoreticheskie osnovy geterogennogo kataliza (Theoretical Principles of Heterogeneous Contact Catalysis) 2, Moscow, 1935. 325. RoginskiI, S. Z., Acta Physicochim. U.R.S.S. 4, 729 (1936). 326. RoginskiI, S. Z., Zhurnal FizicheskoZ Khimii ( J . Phys. Chern. (U.S.S.R.)) 12, 427 (1938). 327. RoginskiI, S. Z., Trans. Faraday SOC.34, 959 (1938). 328. RoginskiI, S. Z., Zhurnal FizicheskoZ Khimii ( J . Phys. Chem. (U.S.S.R.)) 16, 708 (1941). 329. RoginskiI, S. Z., Zhurnal PrikladnoZ Khimii ( J . Applied Chem. (U.S.S.R.)) 17, 3, 97 (1944). 330. RoginskiI, S. Z., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 47, 439 (1945). 331. RoginskiI, S. Z., Adsorhtsiya i katdiz na neodnorodnykh poverkhnostyakh (Adsorption and Catalysis on Non-uniform Surfaces). Acad. Sci. U.S.S.R. 1948. 332. RoginskiI, S. Z., Doklady dkad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 67, 97 (1949). 333. RoginskiI, S. Z., editor, Problemy kinetiki i kataliza (Problems of Kinetics and Catalysis) Vol. 7 , Statistical Phenomena in Heterogeneous Systems. Acad. Sci. U.S.S.R., Moscow-Leningrad. 334. RoginskiI, S. Z., Problemy kinetiki i kataliza (Problems of Kinetics and Catalysis) Vol. 7, Statistical Phenomena in Heterogeneous Systems. Academy of Sciences U.S.S.R., Moscow-Leningrad, 452 pp.; pp. 72-88. 335. RoginskiI, S. Z., and Elovich, S. Yu., Byull. In-ta Azota (Bull. Nitrogen Inst.) 7, 25 (1938). 336. RoginskiI, S. Z., and KeIer, N. P., Zhurnal FizicheskoZ Khimii ( J . Phys. Chem. (U.S.S.R.)) 21, 539 (1947). 337. Roginskil, S. Z.,and Schulz, E., Z. physik. Chem. A138, 21 (1928). 338. Roginskii, S. Z.,and Todes, 0. M., Acta Physicochim. U.R.S.S. 21, 519 (1946). 339. Roginskil, S. Z., and Tsellinskaya, T. F., Zhurnal FizicheskoZ Khimii ( J . Phys. Chem. (U.S.S.R.)) 21, 919 (1947). 340. Roginskil, S. Z., and Tsellinskaya, T. F., Zhurnal FizicheskoZ Khimii ( J . Phys. Chem. (U.S.S.R.))22, 1360 (1948). 341. Roginskiy, S. Z., and Vol’kenshteln, F. F., Kataliz. Trudy Vsesoyuznogo Soveshchaniya Posvyashchennogo Pamyati L. V. Pisarzhevskogo (Catalysis. Trans. All-Union L. V. PisarzhevskiI Memorial Meeting). A. I. Brodskil, editor, Kiev, 1950, pp. 9-38.

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342. RoginskiI, S. Z., and Vol’kenshteh, F. F., Kataliz. Trudy Vsesoyuznogo Soveshchaniya Posvyashchennogo Pamyati L. V. Pisarzhevskogo (Catalysis. Trans. All-Union L. V. Pisarzhevskii Memorial Meeting). A. I. Brodskil, editor, Kiev, 1950, p. 34. 343. Roginskil, S. Z., and Zhabrova, G. M., editors, Metody izucheniia katalizatorov (Methods of Investigation of Catalysts). Akad. Nauk S.S.S.R., 1948; cf. P. D. Dankov, pp. 45-57 (scc also 58). 344. Rozenberg, L. M., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 66, 401 (1949). 345. Rozenherg, L. M., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 73, 719 (1950). 346. Rubinshteh, A. M., Izvestiya Akadeinii Nauk S.S.S.R., Seriya Khimicheskaya (Bull. Acad. Sci. U.S.S.R., Chem. Series) 4, 815 (1938) and subsequent studies; Zhurnal Fizicheskot Khimii (J.Phys. Chem. (U.S.S.R.)) 13, 1271 (1939). 347. Rubinshtein, A. M., Izvestiya Akad. Nauk S.S.S.R., Seriya Khimicheskaya (Bull. Acad. Sci. U.S.S.R., Chem. Series) 135 (1940). 348. RubinshteIn, A. M., Izvestiya Akad. Nauk S.S.S.R., Seriya Khimicheskaya (Bull. Acad. Sci. U.S.S.R., Chem. Series) 144 (1940). 349. Rubinshteln, A. M., Zzvestiya Akad. Nauk S.S.S.R., Seriya Khimicheskaya (Bull. Acad. Sci. U.S.S.R., Chem. Series) 427 (1943). 350. Rubinshteh, A. M., Metody izucheniya katalizatorov (Methods of Study of Catalysts). Edited by S. 2. RoginskiI and G. M. Zhahrova. Moscow, 1948, p. 11. 351. Rubinshtein, A. XI., Uspekhi Khimii (Progress Chem. (U.S.S.R.))20, 393 (1951). 352. Rubinshteln, A. M., Uspekhi Khimii (Progress Chem. (U.S.S.R.)) 20,395 (1951). 353. Rubinshtch, A. M., Minachev, Rh. M., and ShuIkin, N. I., Dokladg Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 62, 497 (1948). 354. Rubinshteh, A. M., Minachev, Kh. M., and ShuIkin, N. I., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 67, 287 (1949). 355. Rubinshteh, A. M., and Pribytkova, N. A . , Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 61, 285 (1948). 356. Rubinshteh, A. hi., and Pribytkova, N. A., Zzvestiya Akad. Nauk S.S.S.R., Otdelenie Khinzicheskikh Nauk (Bull. Acad. Sci. W.S.S.R., Dept. Chem. Sci.) 70 (1951). 357. Russel, A. S., Nature 117, 47 (1026). 358. Sadikov, S. V., and hlikhallov, A. G., Ber. 61, 1792 (1928). 359. Uchenye zapiski M . G . V . (Sci. Rept. Moscow State Univ.) No. 6, 347-52 (1936). 360. Schmidt, O . , Z. physik. Chem. 118, 1% (1925). 361. Schmidt, O . , Chem. Revs. 12, 363 (1933). 362. Semenov, N . N., et al., Sovetskaya khimiya 2% dvadtsat’ pyat’ let (Twenty-Five Years of Sovict Chemistry). Acad. Sci. U.S.S.R., Moscow-Leningrad, 1944, 288 pp. 363a. Shekhter, A. S., RoginskiK, S. Z., and Isaev, B. M., Zzvestiya Akad. Nauk S.S.S.R., Otdelenie Khimii (Bull. Acad. Sci. U.S.S.R., Dept. Chem.) 322 (1945). 36313. Shekhter, A. B., Echeistova, A. I., and Tret’yakov, I. I., Zzvestiya Akad. Nauk S.S.S.R., Otdelenie Khimicheskikh Nauk (Bull. Acad. Sci. U.S.S.R., Dept. Chem.) 465, 1960; 42, 1961. 363c. Shekhter, A. B., and Tret’yakov, I. I., Doklady Akad. Nauk S.S.S.R. (Rept. Acad. Sci. U.S.S.R.) 72, 551 (1950). 363d. Shekhter, A. B., and MoshkovskiK, Yu. Sh., Doklady Akad. Nauk S.S.S.R. Rept. Acad. Sci. U.S.S.R.) 72, 339 (1950).

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364. Shenderovich, F. S., Aromatics from Petroleum. Trans. of TsIATIM 4, 151-9, Moscow-Leningrad, 1947. 365. Sherburne, R.K., and Farnsworth, H. E., J . Chem. Phys. 19, 387 (1951). 366. Shilov, E. A,, Zhurnal ObshcheZ Khimii ( J . Gen. Chem. (U.S.S.R.)) 16,135 (1945);

Godnev, I. N., and Filatova, N. N., Doklady Akad. Nauk S.S.S.R. (Rept. Acad.

Sci. U.S.S.R.) 62, 43 (1946); Ushakov, S. N., and Matuaov, P. A., Zhurnal PTikladnoZ Khimii (J. Applied Chem. (U.S.S.R.)) 17, 538 (1944); loffe, I. I., and Yampol’skaya, E. S., i b i d . 18, 50 (1945). 367. Shilov, E. A., Compt. rend. (Doklady) acad. sci. U.R.S.S. 46, 64 (1945).

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this series.

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