Curved Surface of Graphitic Carbon Nitride Boosting Cyclohexane Oxidation over Single-Atom Catalysts

Although single metal sites on graphitic carbon nitride (g-C3N4) are extensively employed in the catalysis field, the related study is based on the flat g-C3N4 surface model, which is far beyond the reality of the curved structure involved in g-C3N4. Herein, g-C3N4 nanorods with diameters of 9.0 and 7.0 nm are synthesized via the hard template approach to support single-atom Co for the catalytic oxidation of cyclohexane. Comprehensive characterizations, combined with theoretical calculations, find that the curved structure would broaden the space of g-C3N4 interlayers, modulate the electronic structure, and reduce the coordination number of atomic Co. The mechanism study reveals that compared with Co atoms on a flat g-C3N4 surface, the low-coordinated Co atoms anchored on a curved g-C3N4 surface are capable of enhancing the reactant adsorption and facilitating the oxygen dissociation, thereby boosting the catalytic cyclohexane oxidation. The cyclohexane conversion on resultant Co/g-C3N4-9 nm reaches up to 22.4% at the overall selectivity of above 95% under mild reaction conditions, outperforming state-of-the-art nonprecious metal-based catalysts. The present work not only offers a synthesis strategy of the effective single-atom metal catalysts for the cyclohexane oxidation but also sheds light on the origin of the enhanced catalytic performance of curved g-C3N4-based catalysts.