LBL-32877 UC-404 Center for Advanced Materials ©L%~===== Model Heterogeneous Acid Catalysts and Metal-Support Interactions: A Combined Surface Science and Catalysis Study I. Boszormenyi (Ph.D. Thesis) May 1991 --- I o..... ....0 r '1'10 n >- ~c::z.... CillO l'Dr+o I'D I'D ." ~[QO< --[Q - ....ttl Materials and Chemical Sciences Division a. IQ. U1 Lawrence Berkeley Laboratory 0 University of California I IS.) r r ttl ONE CYCLOTRON ROAD, BERKELEY, CA 94720 • (415) 486-4755 .... r D"O I '1 0 W 111'0 tv Prepared for the u.s. Department of Energy under Contract DE-AC03-76SF00098 '1'< (» '< -...J . tv -...J DISCLAIMER This document was prepared as an account of work sponsored by the United States Government. 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LBL-32877 UC-404 MODEL HETEROGENEOUS ACID CATALYSTS AND METAL - SUPPORT INTERACTIONS: A COMBINED SURFACE SCIENCE AND CATALYSIS STUDY ISTVAN BOSZORMENYI Ph.D. Thesis DEPARTMENT OF CHEMISTRY University of California and MATERIALS SCIENCE DNISION Lawrence Berkeley Laboratory University of California Berkeley CA 94720 MAY 1991 ",", This work was supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Materials Sciences Division, of the U.S. Department of Energy under Contract No. DE-AC03-76SFOOO98. Model Heterogeneous Acid Catalysts and Metal - Support Interactions: A Combined Surface Science and Catalysis Study by Istvan Boszormenyi Abstract Thin « 100 A) silica-alumina layers have been prepared, characterized and tested as potential model heterogeneous acid catalysts for combined surface science and catalysis studies. Three methods have been developed for their preparation: 1) Oxidation of r3xr3 R30 Al/Si(1l1) structure in ultra-high vacuum (URV) using water and oxygen. 2) Deposition on Si(1l1) from aqueous solution. 3) Argon ion beam sputter deposition in UHV. The homogeneous thin layers are amorphous by LEED and XRD. Based on XPS, the chemical environment of surface atoms in the thin films is similar to that of silicon, aluminum and oxygen atoms on high surface area acid catalysts. Since the ion beam deposited thin layer of silica-alumina has the same composition as the target zeolite, and the chemical shifts in XPS indicate similar atomic environments on both surfaces this deposition method appears to be a promising tool to prepare model catalysts using practical catalyst targets. The silica-alumina layers are active in cumene cracking, a typical acid catalyzed reaction. In order to clearly distinguish background reactions taking place on the reactor walls and the acid catalyzed reaction occurring on the model acid catalyst, at least 20 cm2 catalyst surface area is needed. The interaction of platinum and alumina has also been studied. Two series of model platinum-alumina catalysts have been prepared in a combined URV - high pressure reactor cell apparatus by 1) depositing alumina on a polycrystalline platinum foil and by 2) vapor depositing platinum on a thin layer of alumina on gold. Both model surfaces have been prepared in the presence and in the absence 11 of chlorine. Auger electron spectroscopy, temperature programmed desorption of CO, as well as methyl cyclopentane (MCP) hydrogenolysis studies indicate that the platinum surface area is always higher if the catalyst preparation and regeneration involved a chlorination step. This observation can be explained in terms of chlorine assisted redispersion of platinum. The selectivity patterns in MCP ring opening on 'platinum-on-alumina' and on 'alumina-on-platinum' are different, and only the former can be described as a linear combination of selective and statistical ring opening. The product distribution, however, changes with coverage and reaction time. The properties of the two model catalyst systems and the role of chlorine, as a source of Lewis acidity at the platinum alpmina boundary, in MCP hydrogenolysis are also discussed. III Acknowledgements There are many people I would like to thank for their help during these years in Berkeley. It has been a great experience to work with Professor Gabor Somorjai and his international group. I am thankful for his guidance, enthusiasm and patience throughout my stay. He has been a constant source of ideas and encouragement. I would also like to thank Professor Laszl6 Guczi for his understanding and support. Without Gabor and Laszl6 my coming to Berkeley would never have realized. My deepest thanks go to Judit Boszormenyi for the sacrifices she has made, for her efforts to help me through difficulties and for her willingness to have put up with me despite my cranky moods when nothing seemed to work. I am also grateful for all the great times we have had together. I thank Dr. Miquel Salmeron and Dr. Michel Van Hove who were always available for valuable discussions. Then I would like to thank past and present members of the Somorjai group for their help and for valuable scientific and not so scientific discussions. I feel very fortunate to have been able to work with this distinguished group of people. Because of limited space here, I cannot acknowledge everyone who directly or indirectly contributed to this work. But I wold like to mention a few of them. Brian Naasz, Brian Bent, Ken Lewis and Greg Blackman helped me go through the first confusing weeks, perhaps months, here in Berkeley. Bruno Marchon and Brian Naasz taught me the UHV basics and I inherited their chambers. Discussions with Dr. Jule Rabo of UOP and Dr. Juan Garces of DOW lead to the development of both aqueous and ion beam depositions. The zeolite targets for the sputter deposition were kindly provided by them. Gil Vandentop helped me take electron microscopy pictures of thin silica-alumina films prepared in aqueous solution. Some of these films were carefully prepared by Yusing Ko. The time consuming ion beam sputter deposition work could not have been completed v without the devoted assistance of Brian McIntyre and Dr. Taisei Nakayama. Dave Kelly and Dave Jentz, saved me trips by turning off the bake-out at ungodly hours. When I had problems related to catalysis I could always turn to Pedro Pereira for ideas and suggestions. The first attempts to study the alumina on platinum system were made with the help of Gerard Vurens during a Christmas break. I have learned a great deal from stimulating conversations with Sabrina Fu, v Michael Quinlan and Colette Knight. I will miss them with all their spicy humor and sarcasm. The electrical problems were handled by Jim Severens and Bob Ybarra in electronic shop on the Hill. The new manifold, numerous small UHV parts and the differentially pumped manipulator were built by Bob Wright and Dan Colomb in the Hill machine shop. Forgiving advice on rewiring the entire system, the Instrument Repair Shop on campus needs to be thanked. I also wish to thank Brigid Tung for making her printer available for printing this manuscript, for the delicious treats, and, in general, for her kind support over the years. Outside the lab, Leslie and Greg, Sue and Ken, Pamela and Mike, Pauline and Bruno, Marinella and Roberto, Chin-Chi and Peter, Karina and Albert, Marti and Lennon, Satomi, Patti, and Mark have been great to go out with. We could always count on them to do some hiking, camping, gardening, mushroom hunting or anything relaxing at home. This work was supported in part by the Director, Office of Energy Research, Office of Basic Energy Sciences, Materials Sciences Division, of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098. VI Contents List of Figures IX '. 1. Introduction . 1 1.1 Acid Catalysis 2 1.2 Typical High Surface Area Catalysts . 4 1.2.1 Alumina 4 1.2.2 Silica-alumina .......... 6 1.2.3 Zeolites 9 1.3 Characterization of High Surface Area Acid Catalysts .........