Fundamentals of catalysis: Structure of catalytic particles and elucidation of active sites and reaction mechanisms

This dissertation covers three subjects: the composition distribution of bimetallic nanoparticle catalysts, the catalytic active site of the Au/TiO 2 catalyst used in low temperature CO oxidation, and the mechanism of CO oxidation-assisted propene epoxidation.;The potential of bimetallic catalysts to out-perform current monometallic catalysts, coupled with their tendency to undergo in-situ changes in the bulk and surface compositions, necessitates a high-level understanding of structure-function relationships. To achieve this goal, better characterization methods are needed. The first part of the work describes the successful application of X-ray Absorption Spectroscopy (XAS) and Pair Distribution Function (PDF) to this problem. The XAS/PDF study accurately described the Cu surface enrichment and the PtCu alloy core of Al2O3 supported PtCu particles, as well as the increased surface concentration of Pt upon treatment in CO. Similar success was achieved with a PdAu/TiO2 catalyst. Thus, a versatile technique for better understanding bimetallic particles, with particular applicability to in-situ studies, is demonstrated.;Bulk gold is chemically inert, but supported nanoparticle gold catalyzes a number of interesting reactions, such as CO oxidation. Several unknowns remain despite extensive study, including the identity of the catalytic active site and the method by which oxygen is activated. In this portion of the work, a combination of in-situ XAS, FTIR, chemisorption, and catalytic measurements was used to probe the effect of halide poison on the properties of an Au catalyst. Comparison of the results to computational models of Au particles suggested that the catalytic active site is the metal-support interface. Based on this discovery, some speculation on oxygen activation is provided.;Propene oxide is an important chemical intermediate that is currently produced by environmentally unfriendly processes. In this final section, a process that requires only CO, O2, and propene as inputs, and only produces CO2 and propene oxide, is described. The propene oxidation reaction is facilitated by the in-situ formation of H2O2 during CO oxidation on Au/TiO2. Isotopic labeling studies revealed that of the two possible oxygen sources, O 2 and H2O, O2 is the ultimate oxidant. There were two possible oxygen transfer mechanisms, and alkylperoxide was shown to be the more likely candidate.