Gas-phase epoxidation of propylene by molecular oxygen over Ag-CuCl2/BaCO3 catalyst with low CuCl2 doping: Catalytic performance, deactivation and regeneration.

Ag-MCl x /BaCO 3 catalysts with different chloride promoters, prepared by reduction-deposition-impregnation method, were investigated for gas-phase epoxidation of propylene to propylene oxide (PO) by molecular oxygen. Ag-CuCl 2 /BaCO 3 catalyst with 360 ppm of Cu and 400 ppm of Cl exhibits the best initial catalytic performance, in which PO selectivity of 71.2% and propylene conversion of 1.3% are achieved, but only PO selectivity of 13.9% is obtained at propylene conversion of 3.2% after reaction for 500 min. The catalytic reaction mechanism over Ag-CuCl 2 /BaCO 3 catalyst follows Rideal-Eley mechanism, in which propylene in the gas phase reacts with molecular oxygen species adsorbed on the surface of Ag at the interface in close contact with CuCl 2 to produce PO, and with atomic oxygen species adsorbed on the surface of Ag nanoparticles to produce CO 2 and H 2 O. One oxygen atom of molecular oxygen species reacts with propylene to form a PO molecule, and the left insufficient oxygen atoms react with propylene to produce oxygen-containing intermediates and then to form coke deposition which covers the active sites and thus results in the catalyst deactivation. The deactivated Ag-CuCl 2 /BaCO 3 catalyst can be completely regenerated by combustion of coke deposition and then impregnation with appropriate amount of Cl. [ABSTRACT FROM AUTHOR]