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New developments in zeolite science and technology
Fuel Processing Technology, 18 (1988) 101-102 Elsevier Science Publishers B.V., Amsterdam - - P r i n t e d in The Netherlands
101
Book Review
New Developments in Zeolite Science and Technology, Proc. 7th International Zeolite Conference, Tokyo, August 17-22, 1986. ( Studies in Surface Science and Catalysis, 28), by Y. Murakami, A. Iijima and J.W. Ward (Eds.), Elsevier, Amsterdam, 1986, ISBN 0-444-98891-1, XXVIII+1092 pages, Dfl. 535.00 (distributed in Japan by Kodansha Ltd., Tokyo). The Seventh International Congress in Tokyo, August 1986, was the first one held in Asia. Because of increasing interest in both the science and the technology of zeolites worldwide, over 260 papers were submitted for oral presentation. This volume presents the full text of 121 accepted papers and 23 invited, introductory, and plenary talks. The volume also lists authors and titles of 180 poster papers. (Texts of these papers were published in a separate volume. ) The science of zeolites embrace a wide range of disciplines. Crystallographers, physical and inorganic chemists, NMR specialists, catalytic chemists, and organic chemists are well represented here. The chapters of the volume cover the geology and mineralogy, the synthesis, the ion exchange and modification, the structure, the adsorption and diffusion, and the applications of zeolites. The meat of the book, the chapter on Catalysis, occupies almost exactly one-third of the volume. The introductory and plenary lectures help specialists because they review most recent developments in their respective fields. However, they are most useful for the uninitiated. The Geology chapter describes a variety of deposits from the Pine-Ridge Indian Reservation in South Dakota to Honshu and Korea in the Far East, Turkey, Yugoslavia, and the remote Yakutia in Siberia. Most zeolites used in industry today are man-made, and perhaps because of this, synthetic zeolites are more thoroughly covered than natural ones. Synthetic zeolites are made by precipitation from supersaturated solutions of various inorganic or organic bases. Many of today's shape selective zeolites are 'built around' organic 'templates', e.g. quaternary ammonium bases. The traditional definition of zeolites ("zeolites are porous aluminosilicates...") breaks down here. In addition to silicon and aluminum, new structures contain phosphorus in place of silicon, and boron, titanium, iron, and many other elements in place of or in addition to aluminum. Once synthesized, the zeolite crystal can be modified to suit divergent needs. Ion exchange and steaming are the most ubiquitous techniques to develop new properties. Acid activity can be introduced by removing alkali ions present at the birth of the crystals. Here again, ion exchange is universally used. Out of the autoclave of the synthesizer come the new materials. These are not simple structures: unit cells are composed of hundreds of atoms. The determination of the structure of some of the new materials can take years. The
102
costs could be over a million dollars. New zeolites are sometimes prepared on a trial-and-error basis. In addition to X-ray crystallography, sophisticated techniques like 27A1 and 29Si N M R are now routinely used to follow the changes during synthesis, thermal activition, and demise caused by severe use. One of the most interesting new techniques is the measurement of the N M R chemical shift of adsorbed 129Xe. The test reveals short-distance crystallinities and electric fields within the void space of the pores of zeolites. Other papers describe the use of "model reactants" to measure void space dimensions. The principle is simple: select a group of hydrocarbons. Each member of the group should be composed of molecules a little wider than those of the molecules next in size. Determine (on an unknown zeolite) which molecules can enter the pores of the zeolite and react there and which cannot. The effective pore size will be between the dimensions of those which could enter the pores and those molecules which could not. Steaming forces aliminum atoms to leave the lattice. The resultant "lowalumina" materials are more resistant to heat than the parent zeolites were, and have unique, and in most cases improved, catalytic properties. Quite a few papers discuss the structural changes occurring during steam activation and the catalytic properties of these modified materials. Acidity is associated with framework aluminum. The number of acid sites is proportional to the number of framework aluminum atoms but the strength of the acid sites is inversely proportional to them. Extremely strong solid acids, approaching the strengths of superacids, may be made by "dealumination". Furthermore, any "bad" hydrocarbon reactions (such as coking and deactivating the catalysts, or those responsible for making low-octane gasolines) require two neighboring acid sites. The new "dealuminated" catalysts last longer and make better products than their predecessors did. Other highlights include the development of a platinum-containing zeolite which can aromatize normal hexane with a much better yield than was previously possible, the discovery that some very strongly acidic zeolites also have considerable hydrogenation activities, and numerous advances in shape selective catalysis. Now, shape selective catalysts differentiate between reactants, products, and reaction intermediates according to shape and size. Only molecules whose dimensions are less than a critical size can enter a pore, react there, and leave after the reaction. Tailoring the environment of catalytically active acid sites to suit certain molecules and reject others according to their shape and size is creating inorganic equivalents of enzymes. The volume will primarily appeal to those active in synthesis, testing, applications, etc., of zeolites and those who work in catalysis. It presents the most recent research and development work. In addition it gives a good overview of this exciting and important field, and therefore, it will also interest the casual reader. The book is neatly printed, well-indexed, and most of the illustrations are clear. SIGMUND M. CSICSERY
101
Book Review
New Developments in Zeolite Science and Technology, Proc. 7th International Zeolite Conference, Tokyo, August 17-22, 1986. ( Studies in Surface Science and Catalysis, 28), by Y. Murakami, A. Iijima and J.W. Ward (Eds.), Elsevier, Amsterdam, 1986, ISBN 0-444-98891-1, XXVIII+1092 pages, Dfl. 535.00 (distributed in Japan by Kodansha Ltd., Tokyo). The Seventh International Congress in Tokyo, August 1986, was the first one held in Asia. Because of increasing interest in both the science and the technology of zeolites worldwide, over 260 papers were submitted for oral presentation. This volume presents the full text of 121 accepted papers and 23 invited, introductory, and plenary talks. The volume also lists authors and titles of 180 poster papers. (Texts of these papers were published in a separate volume. ) The science of zeolites embrace a wide range of disciplines. Crystallographers, physical and inorganic chemists, NMR specialists, catalytic chemists, and organic chemists are well represented here. The chapters of the volume cover the geology and mineralogy, the synthesis, the ion exchange and modification, the structure, the adsorption and diffusion, and the applications of zeolites. The meat of the book, the chapter on Catalysis, occupies almost exactly one-third of the volume. The introductory and plenary lectures help specialists because they review most recent developments in their respective fields. However, they are most useful for the uninitiated. The Geology chapter describes a variety of deposits from the Pine-Ridge Indian Reservation in South Dakota to Honshu and Korea in the Far East, Turkey, Yugoslavia, and the remote Yakutia in Siberia. Most zeolites used in industry today are man-made, and perhaps because of this, synthetic zeolites are more thoroughly covered than natural ones. Synthetic zeolites are made by precipitation from supersaturated solutions of various inorganic or organic bases. Many of today's shape selective zeolites are 'built around' organic 'templates', e.g. quaternary ammonium bases. The traditional definition of zeolites ("zeolites are porous aluminosilicates...") breaks down here. In addition to silicon and aluminum, new structures contain phosphorus in place of silicon, and boron, titanium, iron, and many other elements in place of or in addition to aluminum. Once synthesized, the zeolite crystal can be modified to suit divergent needs. Ion exchange and steaming are the most ubiquitous techniques to develop new properties. Acid activity can be introduced by removing alkali ions present at the birth of the crystals. Here again, ion exchange is universally used. Out of the autoclave of the synthesizer come the new materials. These are not simple structures: unit cells are composed of hundreds of atoms. The determination of the structure of some of the new materials can take years. The
102
costs could be over a million dollars. New zeolites are sometimes prepared on a trial-and-error basis. In addition to X-ray crystallography, sophisticated techniques like 27A1 and 29Si N M R are now routinely used to follow the changes during synthesis, thermal activition, and demise caused by severe use. One of the most interesting new techniques is the measurement of the N M R chemical shift of adsorbed 129Xe. The test reveals short-distance crystallinities and electric fields within the void space of the pores of zeolites. Other papers describe the use of "model reactants" to measure void space dimensions. The principle is simple: select a group of hydrocarbons. Each member of the group should be composed of molecules a little wider than those of the molecules next in size. Determine (on an unknown zeolite) which molecules can enter the pores of the zeolite and react there and which cannot. The effective pore size will be between the dimensions of those which could enter the pores and those molecules which could not. Steaming forces aliminum atoms to leave the lattice. The resultant "lowalumina" materials are more resistant to heat than the parent zeolites were, and have unique, and in most cases improved, catalytic properties. Quite a few papers discuss the structural changes occurring during steam activation and the catalytic properties of these modified materials. Acidity is associated with framework aluminum. The number of acid sites is proportional to the number of framework aluminum atoms but the strength of the acid sites is inversely proportional to them. Extremely strong solid acids, approaching the strengths of superacids, may be made by "dealumination". Furthermore, any "bad" hydrocarbon reactions (such as coking and deactivating the catalysts, or those responsible for making low-octane gasolines) require two neighboring acid sites. The new "dealuminated" catalysts last longer and make better products than their predecessors did. Other highlights include the development of a platinum-containing zeolite which can aromatize normal hexane with a much better yield than was previously possible, the discovery that some very strongly acidic zeolites also have considerable hydrogenation activities, and numerous advances in shape selective catalysis. Now, shape selective catalysts differentiate between reactants, products, and reaction intermediates according to shape and size. Only molecules whose dimensions are less than a critical size can enter a pore, react there, and leave after the reaction. Tailoring the environment of catalytically active acid sites to suit certain molecules and reject others according to their shape and size is creating inorganic equivalents of enzymes. The volume will primarily appeal to those active in synthesis, testing, applications, etc., of zeolites and those who work in catalysis. It presents the most recent research and development work. In addition it gives a good overview of this exciting and important field, and therefore, it will also interest the casual reader. The book is neatly printed, well-indexed, and most of the illustrations are clear. SIGMUND M. CSICSERY