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 selectivit y of epoxidation of ethylene on a silver surface is the reaction of at omically adsorbed oxygen with ethylene to give ethylene oxide, as show n previously. The energy diagram is recalculated using the dipped adcl uster model combined with MP2 geometry optimizations, The previous res ult is confirmed, At the key transition state (TS), one-electron is ba ck-transferred from the admolecule to the bulk Ag surface. The energy barrier is calculated to be 41 kcal/mol, comparable with the energy ba rrier of 39 kcal/mol in the complete oxidation path. The energy barrie r of this electron-transfer type TS must be lowered to obtain a higher overall selectivity of ethylene oxide. (C) 1997 Elsevier Science B.V.