Enhanced productivity toward propene oxide in the direct propene epoxidation with hydrogen and oxygen over gold nanoparticles supported on titanium‐grafted silica was achieved by adjusting the gold–titanium synergy. Highly isolated titanium sites were obtained by lowering the titanium loading grafted on silica. The tetrahedrally coordinated titanium sites were found to be favorable for attaining small gold nanoparticles and thus a high dispersion of gold. The improved productivity of propene oxide can be attributed to the increased amount of the interfacial AuTi sites. The active hydroperoxy intermediate is competitively consumed by epoxidation and hydrogenation at the AuTi interface. A higher propene concentration is favorable for a lower water formation rate and a higher formation rate of propene oxide. Propene hydrogenation, if occurring, can be switched off by a small amount of carbon monoxide.

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.

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