Photothermal Oxidation of Cyclohexane Over CeO2/g-C3N4 Composite with S-Scheme Heterojunction in Solvent-Free Conditions

The selective oxidation of saturated C-H bonds has long been a significant challenge in chemical research, with the partial oxidation of cyclohexane (Cy) to KA oil (a mixture of cyclohexanol and cyclohexanone) using molecular oxygen (O₂) recognized as one of the most important reactions. In this study, we demonstrate the selective oxidation of cyclohexane via photothermal synergism under solvent-free conditions and in the presence of a co-catalyst system. We have elucidated the synergistic effect of the CeO₂/g-C₃N₄ composite catalyst in the photothermal oxidation of cyclohexane. The CeO₂/g-C₃N₄ composite achieved a cyclohexane conversion of 13% and a KA oil selectivity of 97.5%, surpassing the simple additive effects of photocatalysis and thermal catalysis. Through extensive characterization techniques, we present a detailed mechanistic study. Photo-generated electron–hole pairs facilitate the valence cycling of metals during thermal processes, while heat promotes the efficient utilization of these carriers. Furthermore, lattice oxygen can trap holes, reducing the recombination probability of photo-generated charge carriers. This interaction results in a synergistic effect between light and heat, elucidating the phenomenon of photothermal cooperative catalysis in the composite catalyst. These findings suggest that photothermal co-catalysis holds considerable potential for widespread application in green industrial catalytic processes, offering high selectivity and efficiency in organic transformations.

Graphical Abstract

Herein, we synthesized a CeO2/g−C3N4 composite with S−scheme heterojunction as a photothermal catalyst, and employed it for the oxidation of Cy to K−A oil in a solvent−free system. CeO2 demonstrates prominent photothermal synergy, and the addition of g−C3N4 can enhance the utilization of electron–hole pairs. This method significantly improves cyclohexane conversion and KA oil selectivity and exceeds the sum of generations of pure photocatalysis and thermal catalysis. The results provide a mechanistic description for photothermal co−catalysis and demonstrate its potential for widespread use in green industrial catalysis