W-SBA-15的直接合成及其对2-丁烯与乙烯歧化制丙烯反应的催化性能

Direct synthesis of W-SBA-15 catalysts and their catalytic performance for metathesis of ethylene and 2-butene to propylene

以Na2WO4为钨源,以正硅酸乙酯为硅源,采用直接水热法合成了W-SBA-15介孔分子筛,并用XRD、N2吸附、HRTEM、UV-VisDRS、NH3-TPD、H2-TPR等手段对合成的分子筛进行了表征。表征结果表明,当分子筛中硅钨摩尔比为44时,钨物种以高度分散的四面体和八面体形式存在于分子筛的骨架中,随着钨含量的增加,当硅钨比为30时,分子筛中出现了微量的骨架外钨物种,当硅钨摩尔比为20时,骨架外钨含量增多。W-SBA-15分子筛在乙烯与2-丁烯歧化制丙烯反应中表现出优异的催化性能,在反应温度300℃、压力3.0MPa、质量空速6.4h-1的实验条件下,反应24h后丁烯的转化率和丙烯的选择性分别高于50%和96%,优于传统的负载型WO3/SiO2催化剂。硅钨摩尔比为44时的W-SBA-15具有最好的钨物种分散性和最佳的烯烃歧化性能。

Tungsten substituted mesoporous molecular sieves W-SBA-15 catalysts with different Si/W ratios were directly synthesized under hydrothermal conditions by using Na2 WO4 as tungsten precursor and tetraethyl orthosilicate （TEOS） as silica precursor. The prepared W-SBA-15 catalysts were characterized by means of XRD, HRTEM, UV-Vis DRS, NH3-TPD and H2-TPR. The characterization data indicated that amorphous tetrahedral and octahedral tungsten species were mainly incorporated into the framework of SBA-15 （Si/W mole ratio of 44）, and further increase of the amounts of tungsten species led to the appearance of WO3in the channels of W-SBA 15 （Si/W mole ratio of 30 and 20） . The metathesis catalytic performance of W-SBA-15 catalysts was better than that of the conventional WO3/SiO2 catalysts prepared by impregnation. Under the conditions of 300℃, 3.0 MPa and 6.4 h-1 , butene conversion was more than 50% with the propylene selectivity exceeding 96% during the 24 h continuous operation, using W-SBA-15 as the catalyst. The W-SBA-15 with the Si/W mole ratio of 44 exhibited the best dispersion of tungsten species inside the SBA-15 and the best catalytic performance of olefin metathesis among the W-SBA-15 catalysts.