TRANSIENT-RESPONSE AND INFRARED STUDIES OF ETHYLENE-OXIDE REACTIONS ON SILVER CATALYSTS AND SUPPORTS

Secondary reactions of ethylene oxide on silver powder, catalysts Ag/alpha-Al2O3, Ag/SiO2 and support alpha-Al2O3 have been studied by using transient response technique and IR spectroscopy. Three possible routes of ethylene oxide conversion on the surface of the silver catalysts and supports have been elucidated: (1) ethylene oxide decomposition to ethylene and adsorbed oxygen; (2) ethylene oxide isomerization to acetaldehyde; (3) formation of glycol-like species on the support surface and their further oxidation on silver particles. The first two processes occur mainly on silver powder and catalyst Ag/SiO2. Deep ethylene oxide oxidation rates on Ag/alpha-Al2O3 with small silver particles exceed those on the catalysts with larger silver particles. Ag/alpha-Al2O3 promotion with cesium or water vapour addition to the reaction mixture decelerate isomerization and accelerate the deep oxidation of ethylene oxide. Formation of glycol-like species on the support surface was found to involve basic hydroxyl groups of the support. The contribution of secondary ethylene oxide reactions via this pathway can be dominating, especially for alumina surface modified with alkali additives and/or water vapour.