Abstract

Catalytic reactions on solid materials form the foundations of chemical manufacturing, yet many phenomena that impact catalysis within microporous zeolites and on metal nanoparticles challenge current understanding. As society transitions toward more sustainable methods of producing platform chemicals and fuels, clear insight to dynamics of active sites and the structural evolution of catalytic materials will only become more important for design of processes that harness electrocatalytic reactions, valorize renewable feedstocks, and develop new catalytic chemistries. This seminar will share insight from select examples that include the discovery of the unexpected roles of solvent molecules in accelerating epoxidations in zeolites and mediating H₂O₂ formation on palladium nanoparticles at solid-liquid interfaces, as well as the identification of oxygen activation pathways and surface sites for ethylene epoxidation on silver catalysts. These three reactions play a central role in reducing the environmental impact (CO₂ emissions, chlorine use) of the largest class of organic intermediates for chemical manufacturing.

Solvent molecules surround and interact with catalytic sites in ways that change reaction rates and selectivities by orders of magnitude. While the importance of solvent effects on organic chemistry is established and heuristics exist for homogeneous systems, interactions among solvent molecules and reactive species remain challenging to describe molecularly especially at surfaces. Within zeolite pores, the catalytic epoxidation of alkenes at framework Ti-atoms exhibits rates and that depend on dimensions and polarity of surrounding voids. As a consequence, rates and selectivities span 10²-10³ fold at active sites with indistinguishable electronic structure. These results indicate the topology of the catalyst changes the structure of the solvation shells that form about reactive species and evolve along with the reactants. During reactions between H_² and O_² on palladium nanoparticles, organic solvents cause changes in the active phase of the metal nanoparticles such that the material possesses a structure distinct from reactions within water. Moreover, the organic residues spontaneously form surface organometallic complexes that act as redox mediators and co catalyze proton electron transfer steps that reduce O₂.

Introduction

David Flaherty is the Thomas C. De Loach Jr. Endowed Professor in the School of Chemical and Biomolecular Engineering at the Georgia Institute of Technology. He leads a group that develops understanding and design principles for the use of solid catalysts to resolve challenges for the sustainable production of chemicals and energy carriers. Research focuses on generating new insight into chemical phenomena that emerge when reactions occur on complex and dynamic catalyst, often solid liquid interfaces. Knowledge of these systems comes from kinetic, spectroscopic, synthetic, and computational perspectives intended to develop principles needed to harness diverse chemical interactions. Flaherty serves as Editor for Journal of Catalysis, Associate Editor of Catalysis Reviews, and the editorial advisory board of multiple other journals. Prof. Flaherty received the Department of Energy Early Career Award; National Science Foundation CAREER Award; the American Vacuum Society, Early Career Research Award; and the Dean's Award for Research Excellence at Illinois. In 2021, he was selected as an Eastman Foundation Distinguished Lecturer in Catalysis at the University of California, Berkeley. He assisted in organizing the 26^th and 29 ^th North American Catalysis Society Meetings in multiple roles of the CATL Division of ACS. He started his independent career at the University of Illinois at Urbana Champaign, where he was promoted to full professor and received numerous campus awards for teaching and scholarship. His group relocated to Georgia Tech in 2023.