(58c) Understanding Zeolite Catalyst Compositions and Structures At a Molecular Level

Heterogeneous catalysts exhibit chemical reaction activities and/or selectivities that depend strongly on the local compositions and structures near active-site moieties. Such catalytically active species are formed or can be modified during synthesis/processing treatments or subsequent reactor operation. The reactive moieties are generated or influenced by interrelated physicochemical processes, including precipitation, self-assembly, crystallization, ion-exchange, calcination, reduction, and/or surface reactions. These processes and their compositional and structural influences on the resulting catalysts are challenging to elucidate and control, in part because of the absence of long-range atomic ordering, distributions of local environments, or complexity of surface interactions. Such processes and features can nevertheless be monitored and understood by combining spectroscopic, scattering, modeling, and macroscopic property analyses to correlate the compositions, structures, and properties of heterogeneous catalysts across multiple length scales. This includes understanding the molecular-level interactions, distributions, and roles of organic structure-directing or surface-modifying species with respect to their influences on the generation or stabilities of active-site moieties. Recent results will be presented on local compositions, structures, and surface interactions in zeolitic catalysts, taking advantage especially of new methodologies and insights provided by solid-state nuclear magnetic resonance (NMR) spectroscopy. The analyses are expected to provide criteria and new opportunities for rational design of heterogeneous catalysts with improved transport, adsorption/reaction, or structural properties for diverse engineering applications.