A theoretical study on the formation mechanism of peroxovanadate and the origin of its high activity for oxidation of sulfide

Abstract

Polyoxovanadates (POVs) show great promise in 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 an oxidant because it is environmentally friendly. However, the formation mechanism of peroxovanadate is complicated, and the origin of its high reactive activity in sulfide oxidation remains unclear. Herein, we carefully investigate the generation mechanism of peroxovanadate active species formed from the reaction between POVs and H₂O₂ by density functional theory (DFT) calculations. The 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 oxidation of VOSO₄ by H₂O₂ affording a peroxovanadate intermediate differs from 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.