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Herein, we present the preparation by the non-hydrolytic sol-gel route of a mesoporous SiO2-TiO2 epoxidation catalyst with high specific surface area and large pores. This catalyst is active in the catalytic epoxidation of cyclohexene with H2O2 in acetonitrile, showing performances comparable to a TS-1 catalyst. Yet, it is dramatically deactivated when water is used as a cosolvent, which represents an important limitation for the applicability of this catalyst. In order to circumvent the deactivation of the catalyst in the presence of water, we investigate the effect of surface hydrophobization with methyl groups on the catalytic activity and selectivity. Two functionalization methods are investigated: one-pot synthesis with methyltrichlorosilane and post-synthesis silanization with methyltrimethoxysilane. The catalytic performance of the materials are compared to the pristine catalyst and to TS-1 in the presence of an excess of water in the medium. On the one hand, we show that the one-pot methylation does not increase water resistance, in spite of an increased surface hydrophobicity. We interpret this result in the light of a poorer Ti dispersion and lower Ti 4+ surface content in these catalysts. On the other hand, post-synthesis grafting significantly improves the catalytic performances because it combines a hydrophobic surface with a high active site content. At the molecular level, we show that the direct epoxidation pathway is restored thanks to the surface functionalization.

In order to circumvent the deactivation of the amorphous and mesoporous TiO₂–SiO₂ catalyst, we investigated the effect of surface hydrophobization on the catalyst activity in the presence of water for the epoxidation of cyclohexene.

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