The promotional roles of multivalent metal ions and oxygen vacancies on nitrogen-doped carbon-combined CuMn-based catalysts for cyclohexylbenzene oxidation

In this work, we fabricated nitrogen-doped carbon (NC)-combined CuMn-based catalysts derived from layered double hydroxide and melamine mixture precursor and further explored their activity in the aerobic oxidation of cyclohexylbenzene (CHB) to produce cyclohexylbenzene-1-hydroperoxide (CHBHP) using molecular oxygen as the oxidant. Series of structural characterizations demonstrated that multivalent Cu and Mn species and abundant surface defective oxygen vacancies could form in catalysts, due to comprehensive redox processes between Cu and Mn atoms upon high-temperature calcination of precursors under inert atmosphere, as well as the promotional effect of melamine added on the reduction of metal ions. As-fabricated NC-combined CuMn catalyst bearing a 1:1 Cu:Mn molar ratio showed a higher catalytic oxidation activity, in comparison to other NCdecorated CuMn-based catalysts, NC-free CuMn-based one, and pure single metal oxides (i.e., CuO, MnO2). It was revealed that the presence of favorable multivalent Cu and Mn ions and abundant oxygen vacancies was conducive to the effective adsorption and activation of CHB and oxygen molecules, thus accelerating the selective oxidation of CHB to form CHBHP. Moreover, surface NC overlayer on catalysts could protect surface structures of catalysts during the oxidation. The present study provides deep understanding of the roles of surface-active metal species and oxygen vacancies of CuMn-based catalysts for efficient oxidation of CHB to form CHBHP.