The oxidation of ethylene over silver-based alloy catalysts: II. Silver-cadmium alloys

Abstract

Silver-cadmium-supported alloy catalysts were prepared by impregnation of α-alumina with mixed silver nitrate and cadmium nitrate solutions. They were characterized in terms of exposed metallic area and surface composition employing selective chemisorption of oxygen and hydrogen. Surface enrichment in cadmium was observed which increased after the catalysts had been exposed to reaction conditions. Turnover frequencies of ethylene epoxidation and combustion reactions were determined. The former was found to increase significantly with increasing cadmium content of the surface while the latter was found to remain constant or slightly increase, resulting in improved selectivities. Activation energies were found to decrease with increasing cadmium content. The results are discussed in terms of geometric and electronic considerations of the alloy surfaces and it is concluded that electronic interactions between silver and cadmium atoms, affecting the rate-controlling step of the reactions, are primarily responsible for their observation.