A transient kinetic study of ethylene epoxidation over Ag/SiO2

Transient kinetics of ethylene epoxidation over a Ag/SiO₂ catalyst has been studied at relatively low temperatures (110-130‡C) using an automated square pulse cyclic reactor. It is observed at this low temperatures that the formation of CO₂ and H₂O was retarded compared to epoxide formation. The 100% selectivity toward ethylene oxide was obtained after hydrogen treatment of the catalyst surface. It indicates that maximum selectivity of 6/7 based on classical molecular oxygen hypothesis should be carefully reviewed. The participation of both atomic and molecular oxygen to epoxide formation was posiulated, but the former probably after recombination with subsurface oxygen.