Solvating molecules and the environment that surround catalytic sites provide interactions that change rates and selectivities of catalytic events by orders of magnitude. Although heuristics exist for many homogeneous reactions, the interactions among solvent molecules and reactive surface intermediates remain challenging to describe. These challenges are compounded when solvents not only restructure about intermediates at active sites but also sense the presence and functionality of solid-liquid interfaces that extend beyond active sites. Understanding and exploiting these phenomena requires a conceptual framework, rooted in familiar principles, and informed by experimental methods that probe the reactivity of intermediates, the structure of the catalyst, and changes in the solvent at the reactive interface during catalysis.<br/>Catalytic epoxidations of alkenes proceed at early transition metal active sites stabilized within the framework of zeolites. These epoxidation reactions depend on multiple factors including the dimensions and polarity of surrounding voids. The topology of the support changes the structure of the solvation shells that form about reactive species and evolve along with the reactants. Comparisons of results from kinetic, thermodynamic, spectroscopic, and synthetic experimentation provide insight to the coupled molecular interactions between catalyst surfaces, solvating molecules, and reactive species from which we can extract principles to design solid-liquid interfaces for catalysis. Experimental measurements of activation barrier, adsorption enthalpies, and intrapore solvent composition agree closely with predict quantities from DFT and GCMC calculations, which then provide the basis to examine how solvent structure evolves to accommodate reactive species. These changes depend strongly upon the local concentration and hydrogen bonding of water molecules.<br/>These findings show that individually weak but collectively significant interactions among critical transition states, solvent molecules, and the extended surface of solid catalysts present opportunities for catalyst design and reaction engineering particularly in microporous materials.

Solvent-mediated interactions and catalysis within confined liquids

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.