Green and practical TEMPO-functionalized activated carbon as a durable catalyst for continuous aerobic oxidation of alcohols

The development of robust heterogeneous catalysts that can realize the aerobic oxidation of alcohols in metal-free conditions is a profound challenge. Here, we report a reliable methodology to covalently graft 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) moieties on commercial activated carbons. Catalyst activity and stability are investigated in a continuous micro-packed bed. Notably, the catalytic activity achieved in the aerobic oxidation of benzyl alcohol to benzaldehyde (Turnover frequency: 135.9 h−1, Turnover number: 328.9) is superior to the catalysts reported in the literature (Turnover frequency: 0.5–67 h−1) and the state-of-art commercial catalysts (Turnover number: 205.6). Additionally, the influence of H2O on the benzaldehyde yield indicated that H2O as the only by-product plays a promotional role in TEMPO/TBN catalytic system. Based on these results and previous mechanism analysis, a possible reaction mechanism is proposed. Post-catalytic analysis and regeneration strategy indicated that the cleavage of the amide bond linkages is the main reason for catalyst deactivation.