1. Ab Initio Study of Support Effects in the Direct Oxidation of Propylene to Propylene Oxide
Randall Meyer, Department of Chemical Engineering, University of Illinois at Chicago
Direct partial oxidation routes to propylene oxide have been developed using TiO2 supported gold catalysts by co-feeding hydrogen. It has been suggested that the active oxidant in this system is not O2 but rather H2O2 which forms in the reaction of hydrogen and oxygen and then subsequent is available for the epoxidation reaction. We have examined the reaction mechanism for the hydrogenation of O2 over Pd(111) , Pt(111) and Au(221) surfaces in an effort to understand the effect of electronic structure on the reaction. We have found in all cases for monometallic systems that the dissociation of oxygen is easier than the hydrogenation of oxygen, leading us to conclude a successful alloy catalyst must rely on a two site mechanism.
In our continued examination of epoxidation over Ag catalysts, we have found that the barriers for the epoxidation reaction are lower on Ag(111) than on Ag3 clusters (from 1.15 eV to 0.72 eV). In addition, we found that the presence of sub-surface oxygen greatly lowers the barrier for epoxidation (to 0.20 eV). New calculations will focus on the role of the support in the activation of oxygen and hydrogen peroxide.
Pt(111)
Ag/TiO2