单金属双中心Ti-MCM-41分子筛催化剂的光催化性能

Photocatalytic Performance of Ti-MCM-41 Molecular Sieve Containing both Framework and Extra-framework Ti Sites in Hydroxylation of Benzene

制备了单金属双中心Ti MCM 41分子筛催化剂 ,通过XRD、低温N2 吸附 脱附、XPS及原子吸收光谱等对催化剂进行了表征 .结果表明 ,单金属双中心Ti MCM 41分子筛催化剂具有良好的长程有序结构和孔结构 ,其比表面积大于 10 0 0m2 g ,孔径分布窄 ,最可几孔径为 2 7nm ;Ti的电子结合能为 45 8 6eV ,介于骨架Ti(选择性氧化活性中心 )和非骨架Ti(光催化活性中心 )之间 .以H2 O2 和·OH的生成量为基准 ,考察了Ti MCM 41对苯羟化反应的催化性能随光照时间、催化剂用量、加水量、反应温度和空气流速等条件的变化 ,得出了光催化反应的最佳条件 .在无外加氧化剂的情况下 ,单金属双中心Ti MCM 41上苯的转化率为 0 2 % ,表明其确实具有一定的光催化性能 ,可实现光催化 选择性氧化的反应 反应耦合 .与骨架取代Ti MCM 41和MCM 41负载TiO2 催化剂相比 ,单金属双中心Ti MCM 41的催化活性最高 .这主要是由于它既具有光催化活性中心 。

Using redox molecular sieves as catalysts and using H_2O_2 in aqueous solution as oxidant, the organic compounds can be transformed without production of environmentally unfriendly by-products. The high cost and low efficiency of H_2O_2, however, limit the application of redox reactions in liquid phase on an industrial scale. We investigate whether it is feasible to achieve the reaction-reaction coupling between photocatalytic reaction and selective oxidation. The Ti-MCM-41 containing both framework and extra-framework Ti sites (also denoted as used Ti-MCM-41) as well as possessing well ordered long-range and pore structures with specific surface area higher than 1?000 m 2/g and narrow distribution of pore diameters, supported by XRD, XPS and low temperature N_2 adsorption-desorption, are prepared. The variation of photocatalytic performance in hydroxylation of benzene as a function of reaction conditions, such as radiation time, catalyst amount, reaction temperature, water amount and air flow rate, is investigated according to the production of H_2O_2 and ·OH. The conversion of benzene on used Ti-MCM-41 under irradiation of UV-light is 0.2%, indicating that it is feasible to achieve the reaction-reaction coupling. The photocatalytic performance of used Ti-MCM-41 is higher than that of fresh Ti-MCM-41 and TiO_2/MCM-41, probably because that the used Ti-MCM-41 contains both photocatalytic centers and selective oxidation centers.