Chapter 9 - Effect of Support on Ethylene Epoxidation on Ag, Au, and Au-Ag Catalysts

Abstract

Au, Ag, and Au–Ag catalysts on different alumina, titania, and ceria supports were studied for their catalytic activity in the ethylene oxidation reaction. The addition of an appropriate amount of Au to an Ag/γ-Al2O3 catalyst was found to enhance the catalytic activity because Au acts as a diluting agent on the Ag surface creating new single silver sites which favor molecular oxygen adsorption. The Ag catalysts on both titania and ceria supports exhibited very poor catalytic activity toward the epoxidation reaction; so, pure Au catalysts on these two supports were investigated. The Au/TiO2 catalysts provided the highest selectivity to ethylene oxide at a relatively low ethylene conversion, whereas the Au/CeO2 catalysts were found to favor total oxidation even at low temperatures. Among the studied catalysts, the bimetallic Au–Ag/γ-Al2O3 catalyst showed the best activity for the ethylene epoxidation. The catalytic activity of the gold catalysts was found to depend on the support material and the catalyst preparation method that governs the Au particle size and the interaction between the Au particles and the support.