Abstract
Silver-zinc alloy catalysts were prepared by impregnation of α-alumina supports with mixed silver nitrate and zinc nitrate solutions. They were characterized in terms of exposed metallic surface area and surface composition, employing selective chemisorption of oxygen and hydrogen. A dramatic enrichment of the surface with Zn was observed and was not altered after exposure of catalysts to reaction conditions. XPS analysis indicates that surface Zn atoms are in the 2+ valence state. Kinetic parameters of ethylene epoxidation and combustion were found to be nearly unaffected by the presence of Zn atoms on the surface of the catalysts. EXAFS analysis indicates that silver atoms exhibit absorption characteristics which are nearly identical to atoms in a silver foil, which was used as a standard. Thus, silver atoms are coordinated mostly to other silver atoms, indicating that AgZn clusters consist of a central core of primarily silver atoms with Zn atoms primarily on the surface.
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