Cobalt-nitrogen co-doped porous carbon sphere as highly efficient catalyst for liquid-phase cyclohexane oxidation with molecular oxygen and the active sites investigation

The selective oxidation of cyclohexane to cyclohexanone and cyclohexanol (KA oil) is a challenging issue in the chemical industry. At present the industrial conversion of cyclohexane to cyclohexanone and cyclohexanol is normally controlled at less than 5% selectivity. Thus, the development of highly active and stable catalysts for the aerobic oxidation of cyclohexane is necessary to overcome this low-efficiency process. Therefore, we have developed a cobalt-nitrogen co-doped porous sphere catalyst, Co-NC-x (x is the Zn/Co molar ratio, where x = 0, 0.5, 1, 2, and 4) by pyrolyzing resorcinol-formaldehyde resin microspheres. It achieved 88.28% cyclohexanone and cyclohexanol selectivity and a cyclohexane conversion of 8.88% under Co-NC-2. The results showed that the introduction of zinc effectively alleviated the aggregation of Co nanoparticles and optimized the structural properties of the material. In addition, Co⁰ and pyridinic-N are proposed to be the possible active species, and their proportion efficiently increased in the presence of Zn²⁺ species. In this study, we developed a novel strategy to design highly active catalysts for cyclohexane oxidation.