Consequences of Acid Strength and Solvation in Catalysis Mediated by Ion-pair Transition States

2012 Spring Symposium

Enrique Iglesia
Department of Chemical Engineering
University of California at Berkeley and Chemical Sciences Division
E.O. Lawrence Berkeley National Laboratory

Abstract – The rate and selectivity of reactions catalyzed by acids depend on the stability of ion-pairs at transition states that mediate kinetically-relevant steps. Rates and selectivities for alkanol dehydration and homologation, alkene and cycloalkene isomerization, and alkoxide scission and hydrogen transfer on polyoxometalate and zeolitic acids show that sensitivity to acid strength reflects differences in the amount and diffuseness of the charge in the relevant precursors and the transition states. The effects of solvation by confinement on rates and selectivities depend, in turn, on their respective differences in size. The known structures of these acids allow rigorous comparisons between experiment and theory, which confirm the mechanistic interpretations of rate data and the relevance of deprotonation energies as theoretical proxies of acid strength. These studies and insights suggest a rigorous reactivity-based ranking of acid strength that can be used to assess the strength of solid acids with uncertain or non-uniform structures.

Speaker’s Biography – Enrique Iglesia is the Theodore Vermeulen Chair in Chemical Engineering at the University of California at Berkeley and a Faculty Senior Scientist in the Lawrence Berkeley National Laboratory. He received his B.S. from Princeton University and his Ph.D. degree from Stanford University with Professor Michel Boudart and joined the Berkeley faculty in 1993 after 12 years in research and leadership positions at the Corporate Research Labs of Exxon. He has served as Editor-in-Chief of Journal of Catalysis and is the President of the North American Catalysis Society and the Director of the Berkeley Catalysis Center. He has co-authored more than 300 articles in the leading journals in chemistry and chemical engineering and is a co-inventor in 38 U.S. patents. He is a member of the National Academy of Engineering and a Fellow of the American Chemical Society. His research has been recognized with the Somorjai and Olah Awards of the American Chemical Society, the Award for Excellence in Natural Gas Conversion, the Alpha Chi Sigma and Wilhelm awards of the American Institute of Chemical Engineers, the Emmett and Burwell Awards of the Catalysis Society, the Tanabe Prize in Acid-Base Catalysis, the Canadian Chemical Society Cross Canada Lectureship, and the Francois Gault Award of the European Federation of Catalysis Societies. His research interests include the synthesis and structural and mechanistic characterization of novel inorganic solids useful as catalysts in chemical reactions of critical importance in energy conversion, sustainable synthesis of energy carriers and petrochemicals, and pollution prevention and environmental control.