Bi2O3-TiO2复合氧化物光催化环己烷选择氧化

Photocatalytic selective oxidation of cyclohexane with Bi2O3-TiO2 composite oxide

  • 摘要: 环己烷选择性氧化生成的环己醇和环己酮是己内酰胺合成中的重要中间体,在尼龙生产中具有重要作用,但工业路线条件苛刻,效率低。温和条件下环己烷选择性氧化引起极大关注,而光催化在低温环境压力下的饱和C—H活化和氧化具有独特优势。本文采用水热法制备了一系列Bi2O3-TiO2复合催化剂,对其结构、形貌、光学与光电化学性质通过多种方法包括SEM、XRD、N2吸脱附、UV-Vis、光致发光光谱、瞬态光电流响应等进行详细表征。在室温、0.1 MPa氧气为氧化剂、500 W氙灯模拟太阳光条件下比较了纯TiO2、Bi2O3和Bi2O3-TiO2复合物对环己烷选择性氧化的催化性能,结果表明,复合Bi2O3后提高了TiO2的催化活性,其中9%Bi2O3-TiO2的活性最高,在反应条件下,转化率达13.32%;环己酮/醇总选择性为95.5%,其中环己酮的选择性为57.3%、环己醇的选择性为38.2%、酮醇比为1.5。表征结果证实复合催化剂具有更宽的光吸收频率范围,能有效促进光生电子-空穴分离;同时,比表面积表征也表明复合催化剂比表面积比TiO2和Bi2O3更高,有利于增加表面活性中心浓度。

     

    Abstract: 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.

     

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