Electrocatalytic oxidation of toluene into benzaldehyde based on molecular oxygen activation over oxygen vacancy of heteropoly acid

• Molecular oxygen can be facilely activated on oxygen vacancy under electric field. • Toluene is initially activated to benzyl cation and then oxidized to benzaldehyde. • The benzaldehyde selectivity is 83.5% at the toluene conversion of 83.4%. • O 2 2- ads and O 2 - ads are dominant active species for selective oxidation of toluene. Benzaldehyde is much easier to be oxidized with respect to toluene, making the selective oxidation of toluene to benzaldehyde extremely challenging. Herein, a series of heteropoly acid catalysts with different ratios of molybdenum and vanadium supported on carbon paper (CP) were synthesized. The oxygen vacancy concentration and dispersion of heteropoly acid on CP can be changed by regulating the ratio of molybdenum and vanadium. Due to the suitable oxygen vacancy concentration and most uniform dispersion on CP, HPMoV 2 has the highest electrocatalytic oxidation performance, showing the benzaldehyde selectivity of 83.5% at the toluene conversion of 83.4%. In-situ Raman spectroscopy proved that toluene was initially activated into benzyl cation and further oxidized by active oxygen species (O 2 2- ads , O 2 - ads ) to form benzaldehyde. The active oxygen species generated by electro-activation of molecular oxygen adsorbed on oxygen vacancies of heteropoly acid, mainly contribute to the selective oxidization of toluene into benzaldehyde. This work develops a new electrochemical strategy to achieve highly selective conversion of toluene into benzaldehyde with molecular oxygen under mild conditions.