Kinetic study of propylene epoxidation with H2 and O2 over Au/Ti–SiO2 in the explosive regime

Abstract

A kinetic study of propene epoxidation with hydrogen and oxygen over a Au/Ti–SiO₂ catalyst has been performed in a wide range of reactant concentrations including the explosive region in a micro reactor. The observed rate dependency on the reactants for the epoxidation and the competing direct water formation is discussed in relation to the current mechanistic insights in the literature. The formation rate of propene oxide is most dependent on the hydrogen concentration, in which the formation of an active peroxo species on the gold nanoparticles is the rate determining step. Deactivation is mainly caused by consecutive oxidation of propene oxide. Oxygen favours the regeneration of the deactivated catalytic sites. Water formation and propene epoxidation are strongly correlated. Water is formed via two routes: through the active peroxo intermediate responsible for epoxidation and from direct formation without involving this active intermediate. Improving the hydrogen efficiency should distinguish between these two routes of water formation. The active peroxo intermediate in epoxidation is competitively consumed by hydrogenation and epoxidation. The active gold site is blocked during deactivation.