Aerobic oxidation of alcohols over novel crystalline MoVO oxide

Novel crystalline MoVO oxide was employed as the catalyst in the aerobic oxidation of alcohols to the corresponding carbonyl compounds. Reactions were mainly conducted at 353 K in pure oxygen or air (1 atm). The selectivities for benzaldehydes were more than 95% in all cases. The conversions of benzyl alcohols varied from 10% to 99% depending on the substituent. A Hammett plot gave a moderate ρ-value of −0.249 (r2 = 0.98), suggesting that the reaction processes may involve hydride abstraction. The oxidation of primary alkanols afforded aldehydes, and secondary alcohols were mainly dehydrated to olefins. It was found that the conversion of linear alkanols decreased with the length of alkanols. Kinetic analysis showed that catalytic reaction rate was first-order dependent on the concentrations of substrate and of catalyst. The apparent activation energy was estimated to be 45.7 kJ mol−1. Catalytic reactions took place on the 6- or 7-member rings on the a–b basal plane, where highly dense unsaturated metal cation centers and oxygen anion might serve as catalytic active sites.

We report here that the molybdenum and vanadium mixed crystal oxide is an effective heterogeneous catalyst for the selective oxidation of benzyl alcohols to benzaldehydes under mild condition with molecular oxygen as oxidant and without additive. Competitive tests revealed that hydride transfer may be involved in the reaction course. Kinetic analysis shows that the oxidation of benzyl alcohol exhibits first-order dependence on substrate concentration and on catalyst concentration.Figure optionsDownload as PowerPoint slide