Highly Selective Oxidation of Benzene to Phenol Mediated by KHCO3 in the Bimetallic Mo–Cu/NC-H2O2 System

Abstract

Although selective oxidation of benzene to phenol (SOBP) by H₂O₂ is an important chemical process, overoxidation of benzene by the produced nonselective ^•OH during the activation of H₂O₂ inevitably reduces the oxidation selectivity. We, therefore, attempt to mediate the oxidation selectively by using electrophilic KHCO₃ in the oxidation system. In this study, Mo–Cu/NC has been successfully synthesized via ball-milling bimetallic Mo–Cu and N-doped carbon, which exhibits high reactivity in SOBP by H₂O₂ and KHCO₃ with a desirable phenol yield of 25.1% and selectivity of 100%. A series of characterizations and DFT calculations reveal that the reaction between H₂O₂ and KHCO₃ produces HCO₄^–, which is then moderately activated on Mo₁Cu₂/NC via the nonradical pathway with the formation of Mo-(η²-O₂) peroxo. Meanwhile, O_v at Mo₁Cu₂/NC facilitates the adsorption of benzene, which is then selectively oxidized by Mo-(η²-O₂) peroxo to phenol via the oxygen atom transfer pathway. This study provides new insights on the importance of Mo-(η²-O₂) peroxo mediated by H₂O₂–KHCO₃ in selective oxidation of aromatic C–H bond via the nonradical pathway.