Role of Chlorine Promoters in Ethylene Epoxidation over the Ag(110) Surface

摘要

The role of chlorine promoters in Ag catalysts for ethylene epoxidation can be accurately modeled with atomically adsorbed chlorine on Ag(110). Chlorine inhibits both EtO and CO sub 2 production, but CO sub 2 production more strongly, so that an overall promotion in selectivity (up to 85%) results. The major influence develops between the p(2 x 1)-Cl structure at THETA/sub Cl/ = 0.5 and the c(4 x 2)-Cl structure at THETA/sub Cl/ = 0.75. This suggests an ensemble effect. The variation of the steady-state rates, selectivity, and particularly coverage of O/sub a/ with THETA/sub Cl/ indicate that Cl/sub a/ replaces O/sub a/ in the reaction mechanism by creating Ag/sup delta+/ sites for enhanced ethylene adsorption. Adsorbed molecular O sub 2 seems to be the major oxidizing agent in epoxidation. (ERA citation 08:056153)