An AM1-d study of epoxidation of ethylene on Ag surfaces

摘要

Reactions between ethylene and adsorbed atomic oxygen species on Ag surfaces have been studied using AM1-d in WinMOPAC. Two cases are calculated to investigate the reactions between ethylene with three types of adsorbed atomic oxygen species, i.e. O_((ad))_4-coordinate-site/Ag(110), O_((ad))_3-coordinate-site/Ag(110) and O_((ad))_3-coordinate-site/Ag(111). The first case, case (a), is the one where the reaction proceeds at the center of the C-C double bond in ethylene, and the other, case (b), where the reaction goes on one of the carbon atoms of ethylene. In case (a), the energy minimum path made all the three types of oxygen species react with ethylene to form ethylene oxide (EO) directly. In case (b), O_((ad))_4-coordinate-site/Ag(110) or O_((ad))_3-coordinate-site/Ag(111) reacts with ethylene to form an intermediate which isomerizes to EO or acetaldehyde, which causes total oxidation of ethylene. Side reaction of epoxidation occurs in case (b). In both cases, since O_((ad))_3-coordinate-site/Ag(110) reacts with ethylene to form only EO, it is probably the oxygen species which causes the epoxidation of ethylene.