以长链伯胺为模板剂、正硅酸乙酯和钛酸四丁酯为原料制备了Ti-HMS介孔分子筛,经硅烷化处理后得到Ti-HMS催化剂并将其应用于丙烯环氧化反应.采用XRD、N2吸附-脱附和UV-Vis等表征手段研究了合成母液中水与乙醇的体积比(简称水醇比)、模板剂分子链长度、钛含量等因素对Ti-HMS催化剂结构特性的影响.表征结果显示,合成母液中加入适量水能提高催化剂的介孔有序度并增大比表面积和孔体积,最佳水醇比为0.30 ～0.60.采用分子链较长的模板剂或减少钛含量能促使钛原子进入HMS分子筛骨架中,同时增大比表面积、孔径、孔体积和孔壁厚度.Ti-HMS催化剂上同时存在骨架四配位钛物种和骨架外六配位钛物种,前者是催化丙烯环氧化反应的关键活性位,而后者则会引起氧化剂无效分解.%Mesoporous molecular sieves containing titanium, Ti-HMS, were prepared from tetraethyl orthosilicate and tetrabutyl orthotitanate with long-chain primary amine surfactants as templates, and characterized by means of XRD, N2 adsorption-desorption and UV-Vis techniques. The catalytic performances of the silylanized Ti-HMS in propylene epoxidation were investigated. The effects of H2O/EtOH volume ratio in synthesis mother liquors, chain length of the template molecule and Ti content on the Ti-HMS catalyst structure were studied. It was indicated that, addition of a proper amount of water into the synthesis mother liquors could improve the mesopore ordering in the Ti-HMS catalysts, and increase their specific surface areas and pore volumes. The optimum H2O/EtOH volume ratio was in the range of 0.30 to 0.60. A template with long molecular chain or low Ti content was conducive to the introduction of Ti atoms into the framework of the mesoporous molecular sieves. The specific surface areas, pore diameters, pore volumes and wall thicknesses of the Ti-HMS catalysts increased with the increase of chain lengths in the template molecules. It was testified that, there were two Ti species, tetrahedral-coordinated and octahedral-coordinated Ti atoms, in the Ti-HMS catalysts. The former was the key active sites for the epoxidation while the latter would lead to noneffective decomposition of the oxidant.
展开▼
