Vanadium incorporated mesoporous silicates as catalysts for oxidation of alcohols and aromatics

Abstract

Abstract The present paper explores different synthesis conditions (direct hydrothermal synthesis or impregnation) for preparation of vanadium incorporated mesoporous silicate catalysts. Both hexagonal and cubic mesostructures have been obtained by varying the gel composition. All the prepared V-MCM-41 molecular sieves were tested in the oxidation of alcohols (hexanol, cyclohexanol and 1,3-hexanediol) and aromatic hydrocarbons (styrene and benzene) under mild conditions with hydrogen peroxide. The fresh (as-synthesized) and used samples after oxidation reactions were intensively characterized by X-ray diffraction (XRD), N2 adsorption–desorption, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) techniques. The effect of the preparation conditions on the structure, texture, morphology and acidity of samples has been studied. The results show very low activity of all the V-MCM-41 catalysts in the oxidation of alcohols and high activity and selectivity in oxidation of styrene and benzene. It is interesting to note that the catalysts which are active in the oxidation of styrene to benzaldehyde will be less active in the oxidation of benzene to phenol and vice versa, suggesting that active centers for oxidation of styrene might probably be different to those for oxidation of benzene.