Green and selective epoxidation of alkenes catalysed by new TiO2–SiO2 SBA mesoporous solids

Abstract

New catalysts TiO₂–SiO₂ (Ti–SBA) with pore sizes of 37 and 65 Å have been synthesized by grafting titanium on a structured mesoporous SBA15 (SBA for Santa BArbara and 15 for hexagonal structure) by means of titanium tetrachloride in the gas phase. These catalysts have been tested in the selective epoxidation of cyclooctene, cyclohexene, (R)-limonene and α-pinene. Whatever the oxidant, hydrogen peroxide (H₂O₂), tert-butyl hydroperoxide (TBHP) or cumyl hydroperoxide (CHP), the selectivity is 100%. However, the yield is low with H₂O₂ and the catalyst is partially leached out. In the case of TBHP and CHP the epoxide yields can reach practically 100% and no leaching of titanium is observed after four successive reaction cycles. An effect of pore size on the epoxidation kinetics of α-pinene and cyclooctene has been found.