September 15
@
4:00 PM
–
5:00 PM
J. Will Medlin
Professor
Department of Chemical and Biological Engineering
University of Colorado – Boulder
Near-surface Environment Control for Selective Catalysis
Identifying catalyst materials that are active and selective for specific reactions is important not only for making improvements to existing chemical processes, but also for designing new routes to a sustainable energy economy. For example, improved materials are needed for carbon-carbon coupling reactions that can yield aviation fuel components from biomass or CO2-derived feedstocks. Solid catalysts used in these applications are commonly designed as composite inorganic materials where, for example, active metal nanoparticles are dispersed on a metal oxide support. Much research effort has gone into optimizing these inorganic components for various applications. Under reaction conditions, however, catalytically active surfaces often are heavily covered by “spectator” species. It was often assumed that these species did not participate directly in the reaction, but recent studies have indicated that such spectators can play a major role in enhancing catalytic selectivity and rates. This suggests the possibility that surface organic species can themselves be tuned as key components of a catalyst, opening up a new avenue for catalyst design. In fact, organic ligands are widely employed as surfactants in the synthesis of metal nanoparticles. Numerous studies have shown that leaving these ligands in place can have beneficial effects for catalyst performance, especially related to controlling selectivity toward desired products.
Thus, one approach toward controlling selectivity in catalysis is to systematically design these encapsulating ligands to impart improved activity, selectivity, and stability in reactions such as CO2 hydrogenation, C-C coupling, and the hydrodeoxygenation of biomass-derived oxygenates. This presentation will describe design of different components of the organic ligands—the “head” group that covalently attaches to the support versus the “tail” organic function—to control selectivity in reactions at surfaces. Use of organic promoters for metal catalysts, metal oxides, and interfacial structures including highly dispersed, “single atom” catalysts will be described. Finally, the presentation will explain advantages and limitations for use of organic modifiers in heterogeneous catalysis.