Photocatalytic Selective Oxidation of Toluene into Benzaldehyde on Mixed-Valence Vanadium Oxide V₆O₁₃ Catalyst with Density Functional Theory

Abstract

The photocatalytic oxidation of toluene to benzaldehyde has attracted wide attention due to its mild condition, low cost and green process. In general, the traditional semiconductor photocatalytic mechanism is an oxidation–reduction reaction between photogenerated carriers and reactants. Recently, the catalyst V₆O₁₃ shows the high photocatalytic activity because of the different photocatalytic mechanism from the oxidation–reduction reaction. The catalyst V₆O₁₃ and aliphatic alcohol would form V₆O₁₃–alkoxide, which could be excited by visible light to effectively activate the C–H bond of α–C. However, it is unknown whether the catalyst V₆O₁₃ could efficiently achieve photocatalytic oxidation of toluene and there is a similar photocatalytic mechanism for toluene by catalyst V₆O₁₃. In this work, the photocatalytic selective oxidation of toluene to benzaldehyde by V₆O₁₃ catalyst is systematically investigated by density functional theory. The results show that V₆O₁₃ catalyst can effectively activate toluene C(sp³)–H bond into benzyl with the activation energy is 14.2 kcal mol⁻¹. The V₆O₁₃–toluene complex has stronger light absorption in the range from 200 to 800 nm than that of the individual V₆O₁₃ clusters. Furthermore, the barrier for the dehydration of C₆H₅CH₂OOH and C₆H₅CHOHOH decreased from 49.0 to 35.0 kcal mol⁻¹ and from 26.3 to 19.5 kcal mol⁻¹, respectively. We trace these surprising results to the novel photocatalytic mechanism that the V₆O₁₃–toluene complex could be excited by light to effectively activate the toluene C(sp³)–H bond. Our work may provides new opportunities and challenges for photocatalytic field.

Graphical Abstract