Theoretical study on formation mechanism of peroxovanadate and the origin of its highly activity for oxidation of sulfide

Abstract

Polyoxovanadates (POVs) show great promise in the catalytic oxidative desulphurisation, an industrially important yet challenging process, in which peroxovanadate generated by the oxidation of POVs is an essential active species. In such reaction, H2O2 is generally used as oxidants because it is environmentally friendly. However, the formation mechanism of peroxovanadate is complicated, and the origin of their high activity in sulfide oxidation remains unclear. Here, we carefully investigate the generation mechanism of peroxovanadate active species formed from the reaction between POVs and H2O2 by density functional theory (DFT) calculations. Results clearly show that POV is oxidized by H2O2 to afford the highly reactive oxidant peroxovanadate intermediate via a proton transfer pathway rather than a radical pathway. Interestingly, the oxidization of VOSO4 by H2O2 affording peroxovanadate intermediate differs with that of POVs, which likely occurs via a HO‒OH bond cleavage (radical) pathway. On the other hand, the high activity of peroxovanadates in sulfide oxidation originates from the lower-energy empty orbitals of the oxygen atoms compared to those in POVs. These findings may provide a new perspective for the application of POV-based materials in the catalytic field.