Abstract
Phenol production in the chemical industry is currently carried out through the Cumene process in which three process steps are included and acetone is produced as a byproduct. Direct oxidation of benzene into phenol is desirable because one-step production of phenol is more economical. However the oxygenation of benzene has been known to be one of the most difficult oxidations. We have previously reported the liquid-phase oxidation of benzene to phenol with molecular oxygen under 4 atm at 303 K using V catalyst (V supported Al2O3 , V/Al2O3 ) in the presence of ascorbic acid as a reducing reagent for V species, although the leaching of V ions on Al2O3 was a serious problem of this reaction system. In this study, we have attempted the utilization of V incorporated heteropolyacid (V-HPA) as a catalyst. The V-HPA led to the remarkable decrease in the leaching of V ions and produced the similar amounts of phenol in comparison with that of the V/Al2O3 catalyst. We have also investigated the effect of the changing composition of the V-HPA. i.e., using NH4+, Cs+ and Rb+ as a counter cation, and Mo and W as a polyanion. The V-HPA which is composed of Cs and Mo had the highest activity among the catalysts studied. The yield of phenol increased with the increase in the reaction time up to 1 h using the V-HPA catalyst composed of Cs and Mo, but leveled off with further increase in the reaction time. It seems that the redox cycle of the V species (V4+, V5+) participates during the oxidation of benzene.
