Highly selective allylic oxidation of cyclohexene over molybdenum-doped manganese oxide catalysts

A facile synthesis of molybdenum-doped manganese oxides was achieved by a single step reflux method. The catalytic activity of molybdenum-doped manganese oxides for the oxidation of cyclohexene was investigated under solvent-free conditions. Various techniques such as X-ray diffraction, transmission electron microscopy, hydrogen temperature-programmed reduction, thermogravimetric analysis and diffuse reflectance infrared Fourier transform spectroscopy of adsorbed pyridine were employed to indentify the features of catalysts as prepared. The characterization results indicate that Mo dopants were successfully incorporated into the crystal structure of manganese oxide and the concentration of Mo dopant had an influence on redox properties as well as the Lewis acid sites of Mo dopant catalysts. Furthermore, 1.0 mol%Mo-MnO2 catalyst exhibited highest total yield (32.4%) and almost 100% selectivity towards allylic oxidation products, which could be attributed to its relative lower redox properties and the highest Lewis acidity. These results thereby provide an insight of catalyst design in selective catalytic oxidation of cyclohexene.