Abstract
The gold-silver alloy system was chosen for a study of the effect of the geometric factor in the silver-catalyzed oxidation of ethylene because of the known promoting ability and inertness for oxygen chemisorption of metallic gold. Alloys with gold contents of 0, 5, 15, 30, 45, 60, and 80 atom % were prepared by a chemical reduction technique and examined for catalytic activity for ethylene oxidation in a microreactor assembly coupled to a gas chromatography unit. Dynamic adsorption measurements and lattice parameter measurements were also performed on the alloy samples. The results of these studies show that activity for overall ethylene oxidation over gold-silver alloys is dependent on lattice spacing, and that gold, at low concentrations, is a promoter for ethylene oxide formation, markedly improving ethylene oxide selectivity even though conversion falls off somewhat. Activation energy values indicate that the number of active sites decreases as gold concentration increases. Oxidation activity appears to be related to surface sites having fairly low adsorption energies for oxygen. Ethylene adsorption was found to be relatively unimportant.
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