J. Phys. Chem. 1996, 100, 9929-9934
9929
Surface Characterization Study of Au/r-Fe2O3 and Au/Co3O4 Low-Temperature CO Oxidation Catalysts William S. Epling, Gar B. Hoflund,* and Jason F. Weaver Department of Chemical Engineering, UniVersity of Florida, GainesVille, Florida 32611
Susumu Tsubota and Masatake Haruta Osaka National Research Institute, AIST, 1-8-31 Midorigaoka, Ikeda, Osaka 563, Japan ReceiVed: February 27, 1996; In Final Form: April 16, 1996X
Au/R-Fe2O3 and Au/Co3O4 catalysts prepared by coprecipitation with a nominal 10 atom % Au are active for CO oxidation even at temperatures below 0 °C. The surfaces of these as-prepared, powdered catalysts have been examined using X-ray photoelectron spectroscopy (XPS) and ion-scattering spectroscopy (ISS) to gain information about the composition, morphology, and chemical states of the species present at these surfaces. The nature of the Au is complex. The near-surface region of the Au/R-Fe2O3 catalyst contains more Au than that of the Au/Co3O4 catalyst. The Au is present as crystallites, and small amounts of Au(OH)3 are also present on the Au/Co3O4 catalyst. The ISS data indicate that a thin layer of metallic Au, which covers most of the iron oxide substrate, is present on the Au/R-Fe2O3 catalyst surface. This layer is removed rapidly by ion sputtering, leaving the larger Au crystallites on the surface.
Introduction Low-temperature (
