Non-radical peroxymonosulfate activation by Co-doped InBO₃: a green route for selective benzyl alcohol oxidation

The selective oxidation of benzyl alcohol (BzOH) to benzaldehyde (BzH) is of significant importance in industry. In this work, Co-doped InBO₃ with oxygen vacancies was successfully constructed for efficient peroxymonosulfate (PMS) activation towards the selective oxidation of BzOH to BzH. The catalytic performance demonstrated that In_0.75Co_0.25BO₃/PMS exhibits exceptional catalytic performance, BzOH with 46.97% conversion and BzH with 85.95% selectivity, significantly outperforming both the undoped InBO₃ and homogeneous Co²⁺ systems. The catalytic mechanism exploration implies that Co doping-induced oxygen vacancies facilitated the interfacial electron transfer, driving a non-radical-dominated oxidation pathway, where reactive oxygen species (¹O₂ and O₂˙^-) and high-valent cobalt-oxo species (Co(IV)O) were identified as the primary reactive species. The generation of ¹O₂ was attributed to the self-reaction of SO₅˙^- radicals derived from PMS activation and the disproportionation of O₂˙^-. Electrochemical analysis elucidated the electron transfer mechanism. The electrons released from benzyl alcohol oxidation were transferred to PMS via the Co²⁺/Co³⁺ redox cycle, promoting its reductive activation to form the intermediate Co(II)-PMS complexes. Besides, the In_0.75Co_0.25BO₃ also demonstrated excellent reusability over five consecutive cycles. This research applies Co-based borates to green organic synthesis via peroxymonosulfate activation and opens a new avenue for designing efficient selective oxidation catalysts.