Selective hydroxylation of benzene to phenol over supported vanadium oxide catalysts

Investigations of the one-step liquid-phase hydroxylation of benzene to phenol by hydrogen peroxide on vanadium oxide catalysts are described. The vanadium oxide catalysts have been prepared using mesoporous siliceous structures of MCM-type, silica of Aerosil® 300 type and amorphous siliceous microporous mixed oxides as supports. Characterization of composition, surface area, and reducibility of the catalysts showed that the vanadium oxide species were highly dispersed on the silica surfaces. In a broad screening, the catalytic performances were determined in different solvent systems such as acetic acid, acetone, methanol, acetonitrile as well as in the solvent-free so called "triphase" system. The influence of vanadium content of the catalyst on the hydroxylation was studied. Best results were obtained on a low vanadium-containing VOx/SiO2 catalyst (0.14 wt.% V) in acetonitrile as solvent. The drastic influence of dispersion of vanadium sites on the catalytic performance has been demonstrated.