Progress in photocatalytic selective oxidation of cyclohexane to cyclohexanone/cyclohexanol

The selective oxidation of cyclohexane to cyclohexanone/ol is an industrially important process. The industrial thermal oxidation route has some disadvantages such as harsh reaction conditions, inevitable side reactions, low conversion of cyclohexane and low selectivity of cyclohexanone and cyclohexanol, which demands the development of alternative route that is more mild and environmentally friendly. The photocatalytic cyclohexane oxidation driven by sunlight can take place at normal temperature and pressure, and hence has attracted great attention. In this paper, the progress on the catalytic system, reaction mechanism and influencing factors of the photocatalytic selective oxidation of cyclohexane in last decade are reviewed. The research results on the element procedures of cyclohexane activation, cyclohexanone/ol formation and active radical regeneration as well as on the deactivation mechanism of catalysts were summarized and analyzed. In addition, the reaction parameters affecting the photocatalytic selective oxidation of cyclohexane were also analyzed and discussed in depth. It was found that •OH was the main active radical, and cyclohexyl peroxide was the important intermediate. Cyclohexanone/alcohol was formed mainly through the photocatalytic decomposition of cyclohexyl peroxide. The light radiation parameters (incident light intensity and wavelength range), solvent and the structural and surficial properties of the catalysts are important factors affecting the reaction efficiency. Finally, it is pointed out that the key to the large-scale application of photocatalytic cyclohexane oxidation is to further improve the life and stability of the photocatalyst and to design a photocatalytic reaction device with reasonable structure and highly efficient utilization of light energy. © 2020, Chemical Industry Press Co., Ltd. All right reserved.