Liquid phase cyclohexene oxidation over vanadia based catalysts with tert-butyl hydroperoxide: Epoxidation versus allylic oxidation

Abstract

VO2–SiO2 based catalysts with V contents between 5 and 20wt.% were prepared from inorganic precursors via the sol–gel process and subsequently dried, calcined and reduced at 673K. Structural characterization of these materials was carried out with X-rays diffraction (XRD), ICP, N2 adsorption–desorption at 77K, UV–vis diffused reflectance spectroscopy (DR UV–vis), FTIR and pyridine adsorption followed by FTIR. Their catalytic activities in the cyclohexene epoxidation with TBHP as oxidant and heptane as solvent were also examined. Results of XRD and DR UV–visible spectroscopy revealed that VO2 species are well dispersed on silica. BET analysis showed that the surface area decreases from 390 to 22m2g−1 with V content. The results of pyridine adsorption followed by FTIR indicated that the 5wt.% VO2–SiO2 catalyst displays low acid densities. Experimental results pointed out that the 5wt.% VO2–SiO2 catalysts offer excellent activity. The obtained cyclohexene conversion and selectivity toward epoxide are 21% and 84% respectively. A reaction mechanism explaining clearly epoxidation versus allylic oxidation is proposed.