Silylation enhances the performance of Au/Ti-SiO2 catalysts in direct epoxidation of propene using H2 and O2

The effect of silylation on a series of Au/Ti-SiO2 catalysts for the direct epoxidation of propylene in the presence of H-2 and O-2 was studied. It was found that silylation significantly improved catalyst performance: propylene conversion, propylene oxide (PO) selectivity, and H-2 efficiency increased. The extent of improvement depended on the Au and Ti content of the catalysts. The catalyst showing the best activity (Au(0.1)/Ti(1)-SiO2) exhibited an average PO formation rate of 121 g(po) kg(cat)(-1) h(-1) and a PO selectivity of 92% at 473 K, while the catalyst having the maximum Au and Ti loading (Au(1)/Ti(5)-SiO2) showed the most significant improvement in performance with a 78% increase in the rate of PO formation upon silylation. The catalysts were characterized by contact angle measurements, FTIR, TGA, TEM, ICP-OES and these observations were used to elucidate the key factors governing the enhanced catalytic performance upon silylation. It was found that the silylated catalyst exhibited superior performance due to increased hydrophobicity, which aids product desorption, a decrease in acidic sites that are responsible for side product formation, and a possible redistribution of the Au particles. (C) 2016 Elsevier Inc. All rights reserved.