Preparation and Characterization of Vanadium Oxide Species Supported on Mesoporous Silica for the Hydroxylation of Benzene

The homogeneous liquid-phase direct catalytic oxidation of benzene to phenol was performed at 60 °C in acetonitrile solvent using various catalysts of VOx supported on aluminum-substituted mesoporous silica (Al-MPS) and hydrogen peroxide as the oxidant. We employed the molecular designed dispersion method to prepare the VOx catalyst supported on Al-MPS. The deposit of monolayer VO(acac)2 complexes (acac:  acetylacetonate) could be achieved by hydrogen bonding or a ligand-exchange mechanism and subsequently decomposition of organic acac ligands in an oxygen atmosphere at elevated temperature, yielding the six coordination of VV center. The octahedral vanadium oxide samples possess much mobile ligands (i.e., H2O or solvent) around the catalytic center that could be easily substituted by hydrogen peroxide and yielded the active peroxo intermediate for the hydroxylation of benzene. From the studies of powder X-ray diffraction, N2 adsorption and desorption isotherms, diffuse reflectance UV−vis, and electron pa...