The direct epoxidation of propene over gold–titania catalysts—A study into the kinetic mechanism and deactivation

A reaction scheme is presented for the epoxidation of propene over gold–titania catalysts based on information from catalytic experiments and a detailed infrared study. The reaction mechanism involves the formation of a bidentate propoxy species on titania sites by means of a reactive adsorption of propene, which is catalyzed by the gold nanoparticles. The bidentate propoxy species can react with a peroxide species, produced on the gold from hydrogen and oxygen, to produce propene oxide. Catalyst deactivation occurs via a consecutive oxidation of the bidentate propoxy intermediate to strongly adsorbed carboxylate species. A kinetic model including these reaction steps was fitted to a series of catalytic experiments and provided a good description of the measurements and yielded realistic kinetic parameters.