Photocatalytic selective oxidation of cyclohexane with Bi2O3 - TiO2 composite oxide

The selective oxidation of cyclohexane to cyclohexanol and cyclohexanone is an important process to synthesis of caprolactam, which is an important raw material in the production of nylon. However, the industrial route suffered from the disadvantages such as harsh reaction conditions and low reactivity, therefore, selective oxidation of cyclohexane under mild conditions attracted great attention. Since photocatalysis has unique advantages in saturated C− H activation and oxidation, in this paper, a series of Bi2O3-TiO2 composite photocatalysts were prepared by hydrothermal method. Their structure, morphology, optical and photoelectrochemical properties were characterized in detail by various techniques such as SEM, XRD, N2 physical absorption and desorption, UV-Vis, photoluminescence spectroscopy, and transient photocurrent response. The photocatalytic performance of pure TiO2, Bi2O3 and Bi2O3-TiO2 composites toward selective oxidation of cyclohexane was compared under the reaction conditions of ambient temperature, 0.1 MPa of oxygen, and 500 W xenon lamp simulating solar light source. The results show that the catalytic activities of hybrid Bi2O3-TiO2 composites are higher than that of pure TiO2. Among them, 9%Bi2O3-TiO2 exhibits the highest activity, the conversion is 13.32%, and the total selectivity (cyclohexanone and cyclohexanol) is 95.5%. The selectivity of cyclohexanone and cyclohexanol is 57.3% and 38.2%, respectively, and the ketone to alcohol ratio is 1.5. The characterization results confirm that the composite catalyst has a wider light absorption frequency range and can effectively promote the separation of photogenerated electrons and holes. In addition, the Bi2O3-TiO2 composites possess higher specific surface area than pure TiO2, which is conducive to increasing the concentration of surface active centers. © 2022 Beijing University of Aeronautics and Astronautics (BUAA). All rights reserved.