Electron transfer and back-transfer in the partial oxidation of ethylene on an Ag surface: dipped adcluster model study

The crucial step in catalyst design to increase the overall selectivity of epoxidation of ethylene on a silver surface is the reaction of atomically adsorbed oxygen with ethylene to give ethylene oxide, as shown previously. The energy diagram is recalculated using the dipped adcluster model combined with MP2 geometry optimizations. The previous result is confirmed. At the key transition state (TS), one-electron is back-transferred from the admolecule to the bulk Ag surface. The energy barrier is calculated to be 41 kcal/mol, comparable with the energy barrier of 39 kcal/mol in the complete oxidation path. The energy barrier of this electron-transfer type TS must be lowered to obtain a higher overall selectivity of ethylene oxide.