The effect of silylation on titanium-containing silica catalysts for the epoxidation of functionalised molecules

The epoxidation of functionalised substrates of interest as fine chemicals using mesoporous titanium-containing silicas is here reported and the role of silylation in changing the surface hydrophilic character of these catalysts is investigated. The silylation procedure was carried out on two titanium-grafted silicas with different morphologies. An ordered MCM-41 and a non-ordered commercial mesoporous silica were used as supports. The reactivity of bulky substrates with different characteristics (limonene, -terpineol, carveol and methyl linoleate) is studied and compared. The effect of silylation is more pronounced on Ti–MCM-41 than with low-surface area Ti–SiO₂ and it is shown that the catalytic performances are strongly dependent on the nature of the reactant. Purely alkenic molecules show better reactivity over silylated catalysts than over non-silylated ones. On the other hand, a hydrophilic environment around the titanium active sites has often a beneficial effect in the epoxidation of richly functionalised substrates.