Liquid phase selective oxidation of toluene and ethylbenzene over V-based catalysts in the presence of hydrogen peroxide

摘要

The selective oxidations of toluene and ethylbenzene using hydrogen peroxide over vanadium-based catalysts such as VPO, VOPO4, V2O5, VO(acac)(2) and NH4VO3 have been studied. These catalysts were found to be active for the oxidation of toluene and ethylbenzene to benzaldehyde and acetophenone as main products in acetonitrile solvent, respectively. The activity and selectivity, however, in a sequence of decrease order, was found to be followed as: VPO > V2O5 > VOPO4 > VO(acac)(2) > NH4VO3. The highest selectivities to benzaldehyde from toluene and acetophenone from ethylbenzene were 58.8% and 66.1% over VPO catalyst with P/V = 1.1 (molar ratio) in acetonitrile solvent, resepectively. The catalytic performance of VPO with (VO)(2)P2O7 phase was affected by the molar ratio of P/V, hydrogen peroxide amount, solvent property and temperature. The active center for the oxidation was believed to be (VO)(2)P2O7 sites (V4+) in combination with dynamic V5+ sites involving a reversible redox cycle.