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Analysis of Adsorption Induced Surface Composition Changes In CuPt/Al2O3

Sean Oxford1, Peter L. Lee2, Jeffrey T. Miller3, Mayfair C. Kung1, and Harold H. Kung1. (1) Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208-3120, (2) Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, (3) BP, Naperville, IL 60563-7011

Bimetallics nanoparticles are technologically important catalysts with unique properties and a variety of potential applications. To enhance understanding of bimetallics, quantitative information about the metal distribution and how it is affected by reactant adsorption is needed. Spatial composition distribution information is crucial for understanding catalyst longevity and structure-activity relationships. Here we report the results of an investigation into the composition changes induced in a CuPt/Al2O3 catalyst by treatment in a flowing stream of CO at 225C using a combination of FTIR spectroscopy, x-ray absorption spectroscopy (XAS), and pair distribution function analysis (PDF).

After reduction, monometallic particles adsorb CO, which exhibit a 2065 cm-1 (adlinear) and 1812 cm-1 (bridged) peak on Pt/Al2O3 and a 2090 cm-1 (adlinear) peak on Cu/Al2O3. However, CO on CuPt/Al2O3 has a peak at 2106 cm-1 and a broad peak at ~1994 cm-1, which shift to 2114 cm-1 and ~2019 cm-1, respectively, with time on stream in flowing CO at 225C, suggesting a slow redistribution of the metal components in the nanoparticles. The dependence of this redistribution on temperature, particle composition, and adsorbate molecule using results from a combination of FTIR, XAS and PDF analyses will be presented.