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Enrique Iglesia

Myths and Challenges in Acid Catalysis within Small Voids

University of California at Berkeley

Event Details:

Monday, April 18, 2022
4:00pm - 5:00pm PDT

Location

(In Person) Room Shriram 104

This event is open to:

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Enrique Iglesia

Enrique Iglesia
Department of Chemical and Biomolecular Engineering
University of California at Berkeley

Abstract: Myths and Challenges in Acid Catalysis within Small Voids
The sieving and confinement phenomena that confer remarkable functional diversity on solids with voids of  molecular size also act to blur the chemical origins of the molecular transformations that they catalyze. The mechanistic conjectures imposed by such barriers to direct observation deserve reconsideration through theory and experiments of increasing precision and fidelity. This lecture focuses on acid catalysis, because it is ubiquitous in practice, but the myths and the challenges are evident for many reactions that occur within small voids. Selectivity and reactivity differences among heterosilicates that differ in void topology are frequently ascribed to their diverse acid strength, but such properties are, in fact, similar for these framework structures. Their different catalytic properties reflect instead confinement and sieving effects that favor specific transition states, and, in some cases, the preferential diffusion of certain molecules thought small apertures based on their size. Acid strength, a precise chemical property, can be estimated from theory for solids with well-defined structure, but cannot be measured. It influences turnover rates when the amount (and distribution) of charge differs between cationic transition states and their relevant precursors. In small voids, the consequences of acid strength are inextricably linked to those brought forth by host-guest interactions, through non-covalent van der Waals contacts that depend on their respective size and shape. The strong preference for terminal methyls in skeletal alkane isomerization within small voids, quaintly ascribed to “pore mouth catalysis”, merely reflects the preferential sieving of such isomers by apertures of molecular dimensions. Despite the prevailing paradigms, the selectivity towards more demanding reactions is not inherently preferred on stronger acids and very strong acids are not essential to activate H2 and CH4 reactants in alkene hydrogenation and alkane alkylation, respectively. The clarity that emerges from dissecting chemistry from transport (and binding from solvation) is enabled by an increasingly seamless theory-experiment nexus; it provides essential guidance in designing solids that exploit synergies between binding sites and their outer sphere environments.  

Biography
Enrique Iglesia is the Theodore Vermeulen Chair in Chemical Engineering at the University of California at Berkeley and a Laboratory Fellow at Pacific Northwest National Laboratory. He holds degrees from Princeton (B.S.) and Stanford (Ph.D) and doctor honoris causa from the Universidad Politecnica de Valencia and the Technical University of Munich  His research addresses the synthesis and the structural and functional characterization of porous inorganic solids as catalysts that enable the efficient production and use of energy carriers and chemicals and the mitigation of their environmental footprints. He has been elected to the National Academy of Engineering, the American Academy of Arts and Sciences, the National Academy of Inventors, and the Real Academia de Ciencias (Spain). His research has been recognized by the American Chemical Society (ACS) with the Olah, Somorjai, Murphree awards, by the American Institute of Chemical Engineering (AIChE) with its Wilhelm, Alpha Chi Sigma, and Walker awards, and by chemical and catalysis societies in North America and Europe with the Emmett, Burwell, Boudart, and Distinguished Service awards, as well as the Francois Gault and Cross Canada lectureships. He has received the ENI Prize and the Kozo Tanabe Prize in Acid-Base Catalysis. He has served as Editor-in-Chief of Journal of Catalysis and as President of the North American Catalysis Society. He is a Fellow of ACS and AIChE and an Honorary Fellow of the Chinese Chemical Society. His teaching has been recognized with several campus awards, most notably the Noyce Prize, the most prestigious teaching award in the physical sciences at Berkeley. In 2012, he presented the David M. Mason Lectures at Stanford.

 

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