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14. Nuclear magnetic resonance studies of adsorption on thorium oxide
Classified abstracts 14---26 16 : 19 13. The study of physical adsorption by infra-red spectroscopy.
(France) As a result of physical adsorption, both adsorbant and adsorbed molecules suffer perturbations which are revealed in their corresponding infra-red spectra. The detailed study of these spectra gives information on the nature of the binding forces and adsorption centres. Full interpretation of the results is however limited at present to a few special cases. Thus the spectra of adsorbants of the SiO2 class show the presence of (OH) groups on their surfaces even after most thorough heating. In this case, physical adsorption is accompanied by the formation of hydrogen bonds between the hydroxyl groups. (France) A Savary and S Robin, JPhys, 25 (6), June 1964, 119-124. 16 14. Nuclear magnetic resonance studies of adsorption on thorium oxide. (USA) W S Brey Jr and K D Lawson, J Phys Chem, 68, June 1964, 1474-
1481. 16 15. Interaction of ethane and ethylene with clean iridium surfaces.
( USA ) R W Roberts, JPhys Chem, 68, Sept 1964, 2718-2722. 16 16. An approach to a theory of monolayer permeation by gases.
( USA ) M Blank, JPhys Chem, 68, Oct 1964, 2793-2800. 16 17. The critical surface tension of glass. (USA) D A Olsen and A J Osteraas, J Phys Chem, 68, Sept 1964, 2730-
2732. 16 18. Molecule-wall collisions in porous media at low gas pressure.
(USA) It is shown by applying the cosine law of molecular reflection derived by Knudsen that the expected number of wall collisions experienced by a gaseous molecule chemically produced within a double open-ended pore at low pressure is given approximately for a zero-order reaction by 1/6(L/r) 2, where L is the length of the pore and r the radius. Corresponding results for partially utilized pores, pores closed at one end, and for first-order surface reactions in pores open at both ends are (f(3--f)/12)(L/r) 2, (2/3)(L/r) 2, and (1/2) • (L/r)2(h cosh ( h ) - s i n h (h))/h 2 sinh (h), respectively, where f is the fraction of the pore utilized, h is the dimensionless quantity L~/k2/rd, k is the intrinsic first-order surface reaction rate constant, and D is the gaseous diffusion constant within the pores. (Author) W S Horton, JPhys Chem, 68, Aug 1964, 2278-2281. 16 19. Areas of uniform graphic surfaces. (USA) The previous suggestion that conventional nitrogen areas of uniform surface graphites are too low is confirmed. Area measurements by benzene, n-hexane, and ethyl chloride agree with nitrogen areas if the cross section is taken as 20/~ 2 instead of 16.2A ~. A proposed explanation is that nitrogen molecules are localized at graphite lattice sites, so that each one fills four of the unit hexagons, an area of 21~k2. Isotherms of similar size molecules, oxygen and carbon monoxide, are in agreement with this model. General limitations of surface area measurements by gas adsorption are discussed. (Author) C Pieree and B Ewing, JPhys Chem, 68, Sept I964, 2562-2568. 16 20. Electric monopole and dipole discreteness effects in adsorption.
(USA) Various consequences of element discreteness upon the electrical characteristics of adsorbed systems of monopoles and dipoles are discussed and methods for determining exact local potentials and fields in such systems are outlined in terms suitably general for wide application. (Author) J R MaeDonald and C A Barlow Jr, J Phys Chem, 68, Oct 1964,
2737-2740. 16 21. Rates of surface migration of physically adsorbed gases. (USA) A molecular model of the surface transport rate process is used to develop quantitative rate equations; these, containing one arbitrary 49
parameter, are compared with experimental measurements of the surface migration rates of propane, butane, propylene, perfluoropropane, and dibromodifluoromethane over a wide range of pressures and a moderate range of temperatures on one solid surface, an alumina catalyst support. The agreement between the experimental results and the theoretical equations developed in this study shows an order-of-magnitude improvement over the prior art. As such, the results of this study support the theoretical model used. Further work, directed toward an understanding of the remaining parameter, would clearly be desirable in order to move more closely toward entirely a priori predictions of the transport rates or mobilities of adsorbed molecules. (Authors) R K Smith and A B Metzner, JPhys Chem, 68, Oct 1964, 2741-2747. 16 22. Physical adsorption on low energy solids. II. Adsorption of nitrogen, argon, carbon tetrafluoride, and ethane on polypropolyene.
( USA ) Nitrogen and argon are adsorbed on a solid hydrocarbon surface (polypropylene) as two-dimensional gases, nitrogen failing to show the supermobility previously observed on polytetrafluoroethylene (teflon). Carbon tetrafluoride and ethane are adsorbed with some restriction of mobility, possibly due to their greater energies of self-interaction, the entropy changes in adsorption being intermediate between those associated with localization and with free mobility in two dimensions. Film pressures at a coverage representing one statistical monolayer are 12 to 14 rgse/cm 2 for nitrogen, argon, and ethane, but only 9 ergs/cm ~ for carbon tetrafluoride, reflecting its appreciably lower free energy of adsorption. (Author) D Graham, JPhys Chem, 68, Oct 1964, 2788-2792. 16 23. Molecular orbitalview ofehemisorbed carbon monoxide. (USA) Carbon monoxide chemisorbed on metals is considered in the light of Htickel molecular orbitals for the metal-carbon-oxygen bonds. The Hiickel molecular orbitals predict the existence of a partially filled 7r-molecular orbital which increases the metal-carbon bond strength but decreases the carbon-oxygen bond strength. In this model only effects in the ~-bonding system are considered; i.e., the o-bonds are assumed constant. This model qualitatively explains: (1) the occurrence of several carbon-oxygen stretching frequencies in the infrared spectra of CO adsorbed on metals; (2) differences in spectra of CO adsorbed on evaporated and supported metals; (3) infrared band positions as a function of coverage; (4) the effect of adsorbing other gases in addition to previously chemisorbed CO; and (5) band shifts in going from adsorption on pure Ni to a Ni-Cu alloy. (Author) G Blyholder, JPhys Chem, 68, Oct 1964, 2772-2778. 16 24. The reaction of hydrogen with cerium metal at 25 °. (USA) The rate of absorption of hydrogen by plates of cerium metal was studied at 25.0 ° and pressures from 100 to 600 ram. For a given constant pressure, the plot of hydrogen absorbed as a function of time was sigmoidal. Corresponding to the different segments of the absorption curves were the four reaction stages: (1) induction stage, (2) autoacceleration stage, (3) linear stage, and (4) deceleration stage. The reaction rate was found to be sensitive to gaseous impurities and to the thermal pretreatment of the metal samples. For the linear stage of the reaction, the pressure dependence of the rate could be described with reasonably accuracy by the equation r -kip + k2, where r is the rate in ml (STP)/cm 2 of original surface, kl = 5.0 × 10 4 ml/cm 2 ram-l, and ks varies from sample to sample. Some aspects of the reaction are discussed. (Authors) K H Gayer and W G Bos, J Phys Chem, 68, Sept 1964, 2569-2574. 16 25. The adsorption of oxygen on silver. (USA) The rate of adsorption and desorption of oxygen on silver powder has been measured from 77 to 351 ° at an oxygen pressure of 10 torr employing a vacuum ultramicrobalance. The measurements were made on a silver surface on which both the total uptake and the rate of adsorption were reproducible at any temperature and pressure. Nominal activation energies of 3, 8, and 22 kcal/mole which were measured are believed to correspond to dissociative adsorption, molecular adsorption, and surface mobility of oyxgen adatoms, respectively. Data on thermodesorption, vacuum desorption, and activation energy are combined to propose relative surface coverages of the various adsorption types. (Author) A W Czanderna, JPhys Chem, 68, Oct 1964, 2765-2772.
(France) As a result of physical adsorption, both adsorbant and adsorbed molecules suffer perturbations which are revealed in their corresponding infra-red spectra. The detailed study of these spectra gives information on the nature of the binding forces and adsorption centres. Full interpretation of the results is however limited at present to a few special cases. Thus the spectra of adsorbants of the SiO2 class show the presence of (OH) groups on their surfaces even after most thorough heating. In this case, physical adsorption is accompanied by the formation of hydrogen bonds between the hydroxyl groups. (France) A Savary and S Robin, JPhys, 25 (6), June 1964, 119-124. 16 14. Nuclear magnetic resonance studies of adsorption on thorium oxide. (USA) W S Brey Jr and K D Lawson, J Phys Chem, 68, June 1964, 1474-
1481. 16 15. Interaction of ethane and ethylene with clean iridium surfaces.
( USA ) R W Roberts, JPhys Chem, 68, Sept 1964, 2718-2722. 16 16. An approach to a theory of monolayer permeation by gases.
( USA ) M Blank, JPhys Chem, 68, Oct 1964, 2793-2800. 16 17. The critical surface tension of glass. (USA) D A Olsen and A J Osteraas, J Phys Chem, 68, Sept 1964, 2730-
2732. 16 18. Molecule-wall collisions in porous media at low gas pressure.
(USA) It is shown by applying the cosine law of molecular reflection derived by Knudsen that the expected number of wall collisions experienced by a gaseous molecule chemically produced within a double open-ended pore at low pressure is given approximately for a zero-order reaction by 1/6(L/r) 2, where L is the length of the pore and r the radius. Corresponding results for partially utilized pores, pores closed at one end, and for first-order surface reactions in pores open at both ends are (f(3--f)/12)(L/r) 2, (2/3)(L/r) 2, and (1/2) • (L/r)2(h cosh ( h ) - s i n h (h))/h 2 sinh (h), respectively, where f is the fraction of the pore utilized, h is the dimensionless quantity L~/k2/rd, k is the intrinsic first-order surface reaction rate constant, and D is the gaseous diffusion constant within the pores. (Author) W S Horton, JPhys Chem, 68, Aug 1964, 2278-2281. 16 19. Areas of uniform graphic surfaces. (USA) The previous suggestion that conventional nitrogen areas of uniform surface graphites are too low is confirmed. Area measurements by benzene, n-hexane, and ethyl chloride agree with nitrogen areas if the cross section is taken as 20/~ 2 instead of 16.2A ~. A proposed explanation is that nitrogen molecules are localized at graphite lattice sites, so that each one fills four of the unit hexagons, an area of 21~k2. Isotherms of similar size molecules, oxygen and carbon monoxide, are in agreement with this model. General limitations of surface area measurements by gas adsorption are discussed. (Author) C Pieree and B Ewing, JPhys Chem, 68, Sept I964, 2562-2568. 16 20. Electric monopole and dipole discreteness effects in adsorption.
(USA) Various consequences of element discreteness upon the electrical characteristics of adsorbed systems of monopoles and dipoles are discussed and methods for determining exact local potentials and fields in such systems are outlined in terms suitably general for wide application. (Author) J R MaeDonald and C A Barlow Jr, J Phys Chem, 68, Oct 1964,
2737-2740. 16 21. Rates of surface migration of physically adsorbed gases. (USA) A molecular model of the surface transport rate process is used to develop quantitative rate equations; these, containing one arbitrary 49
parameter, are compared with experimental measurements of the surface migration rates of propane, butane, propylene, perfluoropropane, and dibromodifluoromethane over a wide range of pressures and a moderate range of temperatures on one solid surface, an alumina catalyst support. The agreement between the experimental results and the theoretical equations developed in this study shows an order-of-magnitude improvement over the prior art. As such, the results of this study support the theoretical model used. Further work, directed toward an understanding of the remaining parameter, would clearly be desirable in order to move more closely toward entirely a priori predictions of the transport rates or mobilities of adsorbed molecules. (Authors) R K Smith and A B Metzner, JPhys Chem, 68, Oct 1964, 2741-2747. 16 22. Physical adsorption on low energy solids. II. Adsorption of nitrogen, argon, carbon tetrafluoride, and ethane on polypropolyene.
( USA ) Nitrogen and argon are adsorbed on a solid hydrocarbon surface (polypropylene) as two-dimensional gases, nitrogen failing to show the supermobility previously observed on polytetrafluoroethylene (teflon). Carbon tetrafluoride and ethane are adsorbed with some restriction of mobility, possibly due to their greater energies of self-interaction, the entropy changes in adsorption being intermediate between those associated with localization and with free mobility in two dimensions. Film pressures at a coverage representing one statistical monolayer are 12 to 14 rgse/cm 2 for nitrogen, argon, and ethane, but only 9 ergs/cm ~ for carbon tetrafluoride, reflecting its appreciably lower free energy of adsorption. (Author) D Graham, JPhys Chem, 68, Oct 1964, 2788-2792. 16 23. Molecular orbitalview ofehemisorbed carbon monoxide. (USA) Carbon monoxide chemisorbed on metals is considered in the light of Htickel molecular orbitals for the metal-carbon-oxygen bonds. The Hiickel molecular orbitals predict the existence of a partially filled 7r-molecular orbital which increases the metal-carbon bond strength but decreases the carbon-oxygen bond strength. In this model only effects in the ~-bonding system are considered; i.e., the o-bonds are assumed constant. This model qualitatively explains: (1) the occurrence of several carbon-oxygen stretching frequencies in the infrared spectra of CO adsorbed on metals; (2) differences in spectra of CO adsorbed on evaporated and supported metals; (3) infrared band positions as a function of coverage; (4) the effect of adsorbing other gases in addition to previously chemisorbed CO; and (5) band shifts in going from adsorption on pure Ni to a Ni-Cu alloy. (Author) G Blyholder, JPhys Chem, 68, Oct 1964, 2772-2778. 16 24. The reaction of hydrogen with cerium metal at 25 °. (USA) The rate of absorption of hydrogen by plates of cerium metal was studied at 25.0 ° and pressures from 100 to 600 ram. For a given constant pressure, the plot of hydrogen absorbed as a function of time was sigmoidal. Corresponding to the different segments of the absorption curves were the four reaction stages: (1) induction stage, (2) autoacceleration stage, (3) linear stage, and (4) deceleration stage. The reaction rate was found to be sensitive to gaseous impurities and to the thermal pretreatment of the metal samples. For the linear stage of the reaction, the pressure dependence of the rate could be described with reasonably accuracy by the equation r -kip + k2, where r is the rate in ml (STP)/cm 2 of original surface, kl = 5.0 × 10 4 ml/cm 2 ram-l, and ks varies from sample to sample. Some aspects of the reaction are discussed. (Authors) K H Gayer and W G Bos, J Phys Chem, 68, Sept 1964, 2569-2574. 16 25. The adsorption of oxygen on silver. (USA) The rate of adsorption and desorption of oxygen on silver powder has been measured from 77 to 351 ° at an oxygen pressure of 10 torr employing a vacuum ultramicrobalance. The measurements were made on a silver surface on which both the total uptake and the rate of adsorption were reproducible at any temperature and pressure. Nominal activation energies of 3, 8, and 22 kcal/mole which were measured are believed to correspond to dissociative adsorption, molecular adsorption, and surface mobility of oyxgen adatoms, respectively. Data on thermodesorption, vacuum desorption, and activation energy are combined to propose relative surface coverages of the various adsorption types. (Author) A W Czanderna, JPhys Chem, 68, Oct 1964, 2765-2772.