Structural properties and catalytic oxidation of benzene to phenol over CuO-impregnated mesoporous silica

A series of copper catalysts supported on mesoporous molecular sieves MCM-41 with copper loading varying from 2 wt% to 10 wt% were synthesized by impregnation method using aqueous copper nitrate solution as the precursor. The samples were characterized by nitrogen adsorption–desorption, X-ray powder diffraction, FT-IR, UV-diffuse reflectance spectra and temperature programmed reduction. X-ray diffraction patterns indicate the presence of crystalline CuO phase above 4 wt% copper loading. TPR patterns at low temperatures reveal the presence of highly dispersed copper oxide on the surface of the support and the profiles at high temperatures indicates bulk copper oxide. The catalytic activity of the samples was evaluated towards benzene oxidation using H2O2 as the oxidant in acetic acid solvent at room temperature. The effect of reaction parameters, i.e. time, temperature, catalyst amount, amount of H2O2, solvent and alkyl substitution on the substrate, were also investigated. Among the catalysts studied, 4 wt% copper loaded MCM-41 showed maximum conversion (21%) and selectivity (94%) towards phenol.

Cu/MCM-41 is an efficient catalyst for one-step benzene oxidation to phenol. H2O2 reacts with Cu/MCM-41 to give hydroxyl radical through a redox mechanism, which attacks benzene ring to give phenol. Phenol again oxidized in presence of hydroxyl radical to give hydroquinone and benzoquinone. Figure optionsDownload as PowerPoint slide