Atomically Dispersed Copper Sites on Nitrogen-Doped Mesoporous Carbon for Efficient Ammoxidation of Aromatic Alcohols to Nitriles

Catalytic ammoxidation of alcohols has emerged as a preeminent technology for nitrile synthesis, distinguished by its utilization of low-cost, readily accessible alcohols and the circumvention of highly toxic cyanide-based reagents. Herein, we report for the first time a nitrogen-doped mesoporous carbon-supported Cu-based single-atom catalyst that enables the efficient conversion of alcohols and aqueous ammonia to nitriles in the aqueous phase with molecular oxygen as the oxidant. This catalytic system exhibits a wide range of substrates, including various benzylic, allylic, and heterocyclic alcohols. Most substrates can be efficiently converted into the corresponding nitriles in moderate to excellent yields under mild conditions. Furthermore, the catalyst features robust stability, enabling 13 consecutive catalytic cycles with no notable attenuation in catalytic activity. Gram-scale experiments validate the excellent practical feasibility of the catalyst. XPS, aberration-corrected HAADF-STEM, and XAFS characterizations verified the existence of atomically dispersed Cu sites coordinated with nitrogen atoms. The potassium thiocyanate poisoning experiment, DFT calculations, as well as the comparison of the performance of Cu or CuO nanoparticle-based catalysts, suggested that Cu-Nx sites are the main contributors to the ammoxidation of alcohols to nitriles. Mechanism investigation revealed that the reaction proceeds through a radical-mediated pathway, and the oxidation of alcohol to aldehyde is identified as the rate-determining step.