Effect of tetrahedral Ti in titania–silica mixed oxides on epoxidation activity and Lewis acidity

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Abstract
The states of Ti in titania–silica mixed oxides have been studied by varying the Ti content. EXAFS analyses indicated that the amount of tetrahedral Ti species increased with a decrease in the Ti content reaching a maximum at 10 to 20 mol% of Ti while octahedrally coordinated Ti predominated in the high Ti content region (Ti 50 mol%). Tetrahedral Ti species catalyse the eposidation of oct-1-ene and cyclohexene using tert-butyl hydroperoxide as an oxidant. Lewis acid sites of the titania–silica also originated from the tetrahedral Ti species. Both epoxidation activity and Lewis acidity of the titania–silica were well explained by the coordinative unsaturation of the tetrahedral Ti site.