Direct epoxidation of propene on silylated Au–Ti catalysts: a study on silylation procedures and the effect on propane formation†
Silylation was employed on an active Au/Ti–SiO2 catalyst, in order to enhance catalyst performance for the direct epoxidation of propene to propene oxide (PO) using H2 and O2. The effect of using different silylating agents and procedures on surface hydrophobicity and subsequently on catalytic activity was systematically investigated. The best performing catalysts were found to be those prepared by gas phase silylation after Au deposition, using hexamethyldisilazane (HMDS) and tetramethyldisilazane (TMDS) as silylating agents. The time of silylation was found to be critical for obtaining enhanced catalyst performance. An increase in the PO yield, selectivity and H2 efficiency was observed on silylation. Interestingly silylation also led to suppression of propene hydrogenation which is a major drawback of the process. The enhancement in catalytic performance is attributed to an increase in hydrophobicity and to blocking of unwanted Ti–OH sites that are potential sites for propane formation.