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ACS S Y M P O S I U M S E R I E S 368 Perspectives in Molecular Sieve Science William H. Flank, EDITOR Union Carbide Corporation Thaddeu The PQ Corporation Published in advance of a symposium cosponsored by the Divisions of Industrial and Engineering Chemistry, Inc., Petroleum Chemistry, Inc., and Fuel Chemistry at the Third Chemical Congress of North America (195th National Meeting of the American Chemical Society), Toronto, Ontario, Canada June 5-11, 1988 American Chemical Society, Washington, DC 1988 In Perspectives in Molecular Sieve Science; Flank, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988. Library of Congress Cataloging-in-Publication Data Perspectives in molecular sieve science. (ACS symposium series, ISSN 0097-6156; 368) Published in advance of a symposium cosponsored by the Divisions of Industrial ana Engineering Chemistry, -Inc., Fuel Chemistry, and Petroleum Chemistry, Inc., at the Third Chemical Congress of North America (195th Meeting of the American Chemica Ontario, Canada, June 5-11 Includes bibliographies and indexes. 1. Molecular sieves—Congresses. I. Flank, William H. II. Whyte,Thaddeus E., 1937- . III. American Chemical Society. Division of Industrial and Engineering Chemistry. IV. Series TP159.M6P47 1988 660.2'842 88-6268 ISBN 0-8412-1476-X Copyright © 1988 American Chemical Society All Rights Reserved. The appearance of the code at the bottom of the first page of each chapter in this volume indicates the copyright owner's consent that reprographic copies of the chapter may be made for personal or internal use or for the personal or internal use of specific clients. This consent is given on the condition, however, that the copier pay the stated per-copy fee through the Copyright Clearance Center, Inc., 27 Congress Street, Salem, MA 01970, for copying beyond that permitted by Sections 107 or 108 of the U.S. Copyright Law. This consent does not extend to copying or transmission by any means—graphic or electronic—for any other purpose, such as for general distribution, for advertising or promotional purposes, tor creating a new collective work, for resale, or for information storage and retrieval systems. The copying fee for each chapter is indicated in the code at the bottom of the first page of the chapter. The citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by ACS of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance of any right or permission to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related thereto. Registered names, trademarks, etc., used in this publication, even without specific indication thereof, are not to be considered unprotected by law. PRINTED IN THE UNITED STATES OF AMERICA In Perspectives in Molecular Sieve Science; Flank, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988. ACS Symposium Series M. Joan Comstock, Series Editor 1988 ACS Books Advisory Board Paul S. Anderson Vincent D. McGinniss Merck Sharp & Dohme Research Battelle Columbus Laboratories Laboratories Harvey W. Blanch University of Iowa University of California—Berkeley Malcolm H. Chisholm James C. Randall Exxon Chemical Company Indiana University Alan Elzerman E. Reichmanis Clemson University AT&T Bell Laboratories John W. Finley C. M. Roland Nabisco Brands, Inc. U.S. Naval Research Laboratory Natalie Foster Lehigh University W. D. Shults Oak Ridge National Laboratory Marye Anne Fox The University of Texas—Austin Geoffrey K. Smith Rohm & Haas Co. Roland F. Hirsch U.S. Department of Energy Douglas B. Walters National Institute of G. Wayne Ivie Environmental Health USDA, Agricultural Research Service Michael R. Ladisch Wendy A. Warr Purdue University Imperial Chemical Industries In Perspectives in Molecular Sieve Science; Flank, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988. Foreword The ACS SYMPOSIUM SERIES was founded in 1974 to provide a medium for publishing symposia quickly in book form. The format of the Series parallels that of the continuing ADVANCES IN CHEMISTRY SERIES except that, in order to save time, the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form. Papers are reviewed under the supervision of th Editor with th assistanc f th Serie Advisory Board and symposia; however, verbatim reproductions of previously pub lished papers are not accepted. Both reviews and reports of research are acceptable, because symposia may embrace both types of presentation. In Perspectives in Molecular Sieve Science; Flank, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988. Preface THIS STATE-OF-THE-ART book began with some exploratory discussions we had almost three years ago at an executive committee meeting of the Division of Industrial and Engineering Chemistry, Inc., of the American Chemical Society. It gathered support from discussions with peopl Inc., and Fuel Chemistry after several brainstorming sessions face-to-face and over the phone. The result, Perspectives in Molecular Sieve Science, provides much satisfaction to us as editors. A unique aspect in which we take some pride is the arrangement with the Books Department of the American Chemical Society to have this book published in time for the meeting at which the symposium sessions will be held. This was made possible by the cooperation of our authors and reviewers, who met the necessary deadlines, as well as some fancy footwork by the editors. The timing we chose for this book, coming between meetings of the International Zeolite Association during a period of high research activity, has resulted in comprehensive coverage and high quality. We have included a number of reviews that provide some background and introduction to the field of molecular sieves and related materials for those who have entered the field recently. At the same time, significant new work in a number of areas is reported to keep those with experience abreast of new developments and to stimulate discussions which we hope will lead to further progress. A lot of work went into putting this book and the symposium together as coherent packages. We acknowledge the important contributions of John-Pierre Gilson of Shell Research B.V., who compiled comprehensive lists of reviewers for the draft manuscripts, and of V. Udaya S. Rao of the U.S. Department of Energy, who organized the scheduling details for the symposium program. We were especially pleased to have George T. Kerr write an introduction to the book. We also thank Lillian De Lello and Charlotte Reynolds for their extra effort in helping to make it all xi In Perspectives in Molecular Sieve Science; Flank, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988. happen. Organizing this book has been a rewarding, if sometimes hectic, experience for us, and we hope our audience will be satisfied with the results. WILLIAM H. FLANK Molecular Sieve Department Union Carbide Corporation Tarrytown, NY 10591 THADDEUS E. WHYTE, JR. The PQ Corporation Lafayette Hill, PA 19444 February 2, 1988 xii In Perspectives in Molecular Sieve Science; Flank, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988. Introduction by George T. Kerr Past President, International Zeolite Association A Brief History THE TERM "MOLECULAR McBain to describe the selective adsorption of molecules of relatively small size over molecules of larger size by chabazite, a mineral zeolite, which had been purged free of adsorbed water. At that time, zeolite science or molecular sieve science was rudimentary at best, and zeolite technology was nonexistent. Starting about 1940, R. M. Barrer published a number of papers on the synthesis and adsorptive properties of zeolites, some of which had neither structural nor naturally occurring (mineral) counterparts. Barrer's work attracted the attention of researchers at Union Carbide's Linde Division, who initiated a program in 1949 on the synthesis of zeolites because they hoped to use the selective sorptive or molecular sieve properties of zeolites for the fractionation of air. Fractional distillation of liquid air was a longstanding commercial activity of the Linde Division. About the same time, many coals were reported to be ultramicroporous, similar to zeolites, a fact that led to the preparation of amorphous molecular sieve carbons by the charring of organic polymers. In 1955 Union Carbide announced the commercial availability of a number of cationic forms of two synthetic zeolites designated A and X, the latter a synthetic form of the rare mineral faujasite. At this announcement, Mobil Research and Development Corporation, as well as the research and development laboratories of other major petroleum companies, hastened to obtain samples from the Linde Division. In 1955 and 1956 Mobil began to explore the potential use of these materials as adsorbents and catalysts and also began its own program on zeolite synthesis. In 1962 Mobil began using the rare-earth form of zeolite X as a gas-oil cracking catalyst, the first commercial use of a zeolite as a catalyst. By this time a flurry of activity was underway throughout xiii In Perspectives in Molecular Sieve Science; Flank, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988. the world on zeolite research and development. Barrer, at Imperial College of Science and Technology in London, realized the extent of this activity and organized the first international meeting on molecular sieves in 1967 in London. At the end of this meeting, the participants enthusiastically recommended that another meeting be held in 1970. In that year the Second International Conference on Molecular Sieves was held in Worcester, Massachusetts, and the London meeting has since become known as the First International Conference on Molecular Sieves. The Third International Conference on Molecular Sieves convened in Zurich in 1973 and the fourth in Chicago in 1977. At the Chicago meeting, the participants approved the formation of the International Zeolite Association, which was incorporated in 1982 Since that time the triennial international meetings Conferences, and the numeration already in use for the International Conferences on Molecular Sieves has continued. The Fifth International Zeolite Conference was held in Naples, Italy, in 1980; the sixth in Reno, Nevada, in 1983; and the seventh in Tokyo in 1986. I hope that this historical review is of interest to newcomers in the zeolite or molecular sieve fields. What Is a Zeolite? No permanent majority agreement has been reached among workers in these fields as to which term is preferable, zeolite or molecular sieve. "Molecular sieve" is all-inclusive in that it embraces all materials that exhibit shape selectivity, regardless of composition or degree of crystallinity. Traditionally, everyone has agreed that zeolites are crystalline aluminosilicates that have cation-exchange capacities and can reversibly sorb and desorb guest molecules small enough to enter the zeolite pores or channels. In addition, zeolites were recognized as three-dimensional framework structures composed of silicon and aluminum tetrahedra bound to one another by oxygen. The recent syntheses of zeolitelike crystalline silicas, which contain infinitesimal amounts of aluminum, and the more recent syntheses of zcolitelike crystalline aluminum phosphates, chemical analogues of crystalline silica, have further confused the "zeolite" versus "molecular sieve" question. The conservative position contends that these molecular sieve crystals are not zeolites on two counts: They are not aluminosilicates, and they do not contain exchangeable cations. Furthermore, some of the relatively high silicon-containing materials have an average of less than one xiv In Perspectives in Molecular Sieve Science; Flank, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988. aluminum per unit cell, which disqualifies them as zeolites. The liberal view is that the traditional zeolite definition should be updated to state simply that zeolites are crystalline molecular sieves consisting of three-dimensional frameworks composed of tetrahedrally coordinated atoms or ions bound to one another by oxygen. Many of these new substances have frameworks that are isostructural with conventional zeolites. Also, some people argue that some of the high silicon-containing crystals, whose average aluminum contents amount to less than one aluminum per unit cell, have been shown to have aluminum concentration gradients such that some portions of the crystals have at least one aluminum per unit cell, whereas other regions within the same crystal are essentially aluminum-free. Are such crystals both zeolites and nonzeolites? The resolution of this disagreemen participants of a future International Zeolite Conference. About the Book Although the title of this book, Perspectives in Molecular Sieve Science, avoids the zeolite definition controversy, a large majority of the research reported here centers on traditional zeolites. Only three of the 39 chapters comprising the book deal with materials that are clearly nonzeolitic: Two cover clay-type derivatives, and one deals with carbon molecular sieves. Not surprisingly, interest in these materials lies in their possible use as catalysts. Only four chapters present work on mineral zeolites and three on aluminum phosphate- type molecular sieves. Two of those chapters are by workers from Union Carbide, the laboratory that did the pioneering work in this field. It is surprising that other workers have not submitted papers on the aluminum phosphates, but perhaps this situation indicates that although much activity may be underway, laboratories hesitate to publish until patent positions are established in this potentially lucrative area. Union Carbide's synthetic faujasites (zeolites X and Y) and zeolite A receive the most attention, while ZSM-5-class materials are accorded more attention than zeolite A alone. This reflects the important roles that zeolites X and Y and ZSM-5 materials have already played as catalysts. Of the phenomena discussed in this book, catalysis and acidity head the list, with sorption a relatively close second, followed by ion exchange. This situation has been the order of activity for the past 20 to 25 years. Studies of crystal structure, crystal and solution chemistry, and crystal growth are presented, indicating that efforts are still underway to make zeolite synthesis a more predictive science than it is at present with only a collection of empirically xv In Perspectives in Molecular Sieve Science; Flank, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988. derived recipes available. That about a dozen known mineral zeolites have not yet been synthesized is a great challenge to zeolite synthesis scientists. Among relatively new instrumental techniques, magic-angle spinning-nuclear magnetic resonance (MAS-NMR) is the most popular, having already proven its value in confirming earlier research on the mechanism of dealumination and the crystal chemistry of dealuminated zeolites. Several interesting papers in this book deal with recent results using 27A1 and 29Si MAS-NMR in further elucidating zeolite crystal and solution chemistry. One of the most interesting chapters in this book announces the synthesis of a silica that is isostructural with AlPO^-5. This is the first example in which synthesis of a unique aluminum phosphate structure preceded the synthesis of other isostructural chemical analogues. Perhaps th synthesis of an aluminosilicate that has this structure. What will be the conservative point of view regarding the classification, zeolite or nonzeolite, of a substance whose "parent" is not a traditional zeolite? February 2, 1988 xvi In Perspectives in Molecular Sieve Science; Flank, W., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.
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