Transformation of Superoxo-to-Peroxo over Dual Mo–Co-Doped g -C3N4 Enables Efficient Aerobic Oxidative Desulfurization

Aerobic oxidative desulfurization is a promising technology to reduce benzothiophene (BT) in commercial diesels or gasolines, which is primarily constrained by the inertness of O2 under mild conditions. In this study, a series of Mo–Co-doped g-C3N4 (Mo–Co–UCN) catalysts have been successfully synthesized, and 2–Mo–Co–UCN achieves a complete conversion of BT and 100% selectivity toward benzothiophene sulfone (BTO2) under 0.2 MPa O2 at 50 °C for 4 h and maintains high catalytic reactivity after five-cycle experiments. The apparent rate constant (k) of 2–Mo–Co–UCN (1.57 h–1) is higher than those of Mo–UCN (0.30 h–1) and Co–UCN (0.42 h–1) with an apparent activation energy of 95.8 kJ mol–1. XPS analysis indicates that the doped Co(II) promotes the generation of Mo(IV,V), and both Co(II) and Mo(IV,V) sites are reactive sites for O2 activation on 2–Mo–Co–UCN. Quenching experiments and EPR and Raman analyses indicate that although both ≡Co–OO● superoxo and ≡Mo-η2-O2 peroxo have been detected on 2–Mo–Co–UCN, ≡Mo-η2-O2 peroxo is indeed the primary oxidizing species in the oxidation of BT. Operando Raman confirms the gradual transformation of ≡Co–OO● superoxo to ≡Mo-η2-O2 peroxo. DFT calculations further reveal that O2 is preferentially activated at Co(II) sites to ≡Co-OO● superoxo, which then reacts with Mo(IV,V) sites to generate ≡Mo-η2-O2 peroxo, and the generated ≡Mo-η2-O2 peroxo subsequently oxidizes BT to BTO2 via the oxygen atom transfer (OAT) pathway. This study enriches our understanding of the important transformation of surface superoxo and peroxo in OAT reactions.