Collaborative Research: Integrated Measurement and Predictive Modeling of Adsorbate Coverage and Compositional Effects on Catalytic Activity

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ABSTRACTHeterogeneous, solid catalysts are widely used to promote desirable chemical reactions. One very common example is the automotive catalytic converter, which catalyzes the chemical conversion of the environmentally hazardous components of engine exhaust into benign products. The ?active? catalysts in the catalytic converter contain expensive precious metals, like platinum, palladium, and rhodium as the active metal sites. Other processes critical to society, like the production of ammonia for fertilizer or of gasoline for fuel, all depend on catalysts to promote the key chemical reactions. In many of these cases the available catalysts are expensive, perform less than perfectly, or seriously degrade in performance over time. Further, there are many reactions for which good catalysts are simply unknown. In most cases, heterogeneous catalytic reactions happen at the surface of the catalyst. This interface has traditionally been studied under ultra-high vacuum, where it is relatively easy to tease out the various chemical events. Quantum mechanical, density functional theory (DFT), molecular models are well suited to studying these interfaces and processes in the high vacuum limit. There remains however a gap between these traditional approaches and the real conditions of catalytic interest. It is now well understood that at operating conditions, a catalyst surface is often crowded with lots of molecules and that these molecules can even cause the catalyst surface to change shape or chemical form. To understand and improve heterogeneous catalysts, one must study and model them at these more realistic conditions. The National Science Foundation Catalysis & Biocatalysis Program is awarding three researchers, Professors William Schneider and Franklin Tao of Notre Dame University and Christopher Wolverton of Northwestern University to collaboratively tackle the high-pressure challenge through a combination of advanced computer models and ambient pressure experiments. By combining the expertise of Schneider at Notre Dame in molecular-level modeling of catalytic reactions with the expertise of Wolverton at Northwestern in multi-scale cluster expansion models, tools will be developed to predict the behavior of a metal surface under reaction conditions. The tools will be developed and validated initially against the ambient pressure experiments of Tao at Notre Dame. The workers will study in particular the reactions of CO and NO at platinum and rhodium surfaces, reactions relevant to environmental protection. The students will be exposed to an interdisciplinary, multi-institutional collaborative research program which will lead to cross-fertilization of ideas. Three graduate students advised by the principle investigators will work together on the theory and experiments. The models will be disseminated to the catalyst community, and have the potential to advance both the application of existing catalysts and discovery of design principles for new ones.