钒基催化剂在双氧水存在下对甲、乙苯液相选择氧化的研究

研究了若干钒基催化剂在双氧水存在下对甲、乙苯的液相选择性氧化催化性能.结果表明:在乙腈为溶剂的反应体系中,所研究的钒基催化剂包括VPO,VOPO₄,V₂O₅,VO(acac)₂和NH₄VO₃等均表现出以苯甲醛为甲苯选择性氧化主产物和以苯乙酮为乙苯选择氧化主产物的反应结果;从反应活性和主产物选择性来看,按以下顺序递减:VPO＞V₂O₅＞VOPO₄＞VO(acac)₂＞NH₄VO₃.对于具有(VO)₂P₂O₇晶相的VPO催化剂,在双氧水存在下对甲苯选择性氧化主产物苯甲醛的最高选择性为58.8%,乙苯选择性氧化主产物苯乙酮的最高选择性为67.8%;其催化性能与P/V比、焙烧条件、双氧水的使用量、反应溶剂等有关.从已有的实验结果推测,钒基催化剂在双氧水存在下的甲、乙苯选择氧化反应与V⁵⁺/V⁴⁺的"氧化-还原"作用密切相关.

Liquid Phase Selective Oxidation of Toluene and Ethylbenzene over V-based Catalysts in the Presence of Hydrogen Peroxide

The selective oxidations of toluene and ethylbenzene using hydrogen peroxide over vanadium-based catalysts such as VPO, VOPO 4, V 2O 5, VO(acac) 2 and NH 4VO 3 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>V 2O 5>VOPO 4>VO(acac) 2>NH 4VO 3. 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) 2P 2O 7 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) 2P 2O 7 sites (V 4+) in combination with dynamic V 5+ sites involving a reversible redox cycle.