Density functional study of ethylene oxidation on an Ag(111) surface

The mechanism of ethylene epoxidation on Ag surfaces has been investigated using the density functional method and Ag-n clusters (n = 3 to 10) modelin g the Ag(lll) surface. The adsorption energy of O-2 to the Ag clusters was strongly dependent on the HOMO level of the cluster, and the clusters with higher HOMO levels afforded larger O-2 adsorption energies. The energetics was investigated for both the molecular and atomic oxygen epoxidation mecha nisms. For the atomic oxygen mechanism, epoxidation was found to proceed wi thout an activation energy, whereas a small amount of activation energy (ab out 5 kcal/mol) was calculated for the molecular oxygen mechanism.