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

- Influence of silylation on Au/Ti-grafted SiO2 for propylene epoxidation investigated.
- Extent of performance improvement depends on Au and Ti content.
- Typically increased propylene oxide yield and selectivity, with higher H2 efficiency.
- Silylation increases hydrophobicity, decreases acidity and affects gold dispersion.

The effect of silylation on a series of Au/Ti-SiO2 catalysts for the direct epoxidation of propylene in the presence of H2 and O2 was studied. It was found that silylation significantly improved catalyst performance: propylene conversion, propylene oxide (PO) selectivity, and H2 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 gPO kgcat−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.

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