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

• We have epoxidation in the presence of redox and monomeric vanadium sites.
• Allylic oxidation was obtained with acidic and/or polymeric vanadium sites.
• This reaction is heterogeneous and vanadium leaching is not observed.
• The results indicate that this material is stable for 4 cycles of the reaction.

VO2–SiO2 based catalysts with V contents between 5 and 20 wt.% were prepared from inorganic precursors via the sol–gel process and subsequently dried, calcined and reduced at 673 K. Structural characterization of these materials was carried out with X-rays diffraction (XRD), ICP, N2 adsorption–desorption at 77 K, 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 22 m2 g−1 with V content. The results of pyridine adsorption followed by FTIR indicated that the 5 wt.% VO2–SiO2 catalyst displays low acid densities. Experimental results pointed out that the 5 wt.% 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.

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