Atomically dispersed Co/C3N4 for boosting aerobic cyclohexane oxidation

Abstract

The atomically-dispersed and high-loading Co on graphitic carbon nitrogen (Co/C3N4-w, w representing the molar ratio of Co to melamine in the synthesis recipe) was synthesized by coupling the one-pot strategy with the electrostatic adsorption method and used for the solvent-free aerobic oxidation of cyclohexane. The characterization results of Co/C3N4-w revealed that the single-atom Co with the positive charge existed in the sixfold cavities of C3N4 and was stabilized by the CoN interaction along with the electron transfer from Co atoms to C3N4. The catalytic activity of Co/C3N4-w presented the positive correlation with the loading of the single-atom Co, and the superior catalytic performance with 21 % conversion and 95 % overall selectivity was obtained over Co/C3N4-0.02, which also exhibited the excellent universality to the aerobic oxidation of other cycloalkanes and alkyl aromatics. Experiments combined with density functional theory calculations demonstrated that the favored O2 dissociation and intermediate cyclohexylhydroperoxide decomposition on the low-coordinated single-atom Co, and the promoted adsorption of cyclohexane on the electron-rich C3N4 surface, synergically boosted the cyclohexane oxidation. Distinctively, the high stability of Co/C3N4-0.02 in the cyclohexane oxidation originated from the robust single-atom Co structures and hydrophobic C3N4 surface.