MgAl and ZnAl layered double hydroxides modified with molybdate and tungstate anions as catalysts for oxidation of cyclohexane

Abstract

Catalytic oxidation of cyclohexane to cyclohexanol and cyclohexanone with H2O2 was performed at a mild temperature of 40 °C and atmospheric pressure, using ZnAl (ZA) or MgAl (MA) layered double hydroxides (LDHs) modified with tungstate and molybdate anions as catalysts in heterogeneous medium. The catalysts were prepared by direct anion exchange reactions of tungstate and molybdate on LDHs intercalated with chloride/carbonate anions. All the solids showed catalytic activity in the cyclohexane oxidation, with slight selectivity for the ketone product. The catalytic efficiency was sensitive to the M2+ present in the composition of the LDH as well as to the anions. ZnAl-modified with WO42- was more active and more selective for ketone than the MgAl-modified WO42- or any molybdate-based LDH catalysts.