双矿化剂对合成ZSM-5分子筛酸性和织构特征及其甲醇转化制丙烯催化性能的影响

Modification of the acidic and textural properties of ZSM-5 zeolite by using double mineralizers in synthesis and its catalytic performance in the conversion of methanol to propene

  • 摘要: 采用静态水热法在F--OH-体系中,以四丙基氢氧化铵为模板剂、偏铝酸钠为铝源、正硅酸乙酯为硅源,合成了纳米SiO2-ZSM-5分子筛,考察了F-/Al2O3物质的量比对所合成的ZSM-5分子筛织构性质和甲醇转化制丙烯催化性能的影响。结果发现,随着初始溶胶F-/Al2O3物质的量比的增大,产物中SiO2的含量增大,ZSM-5分子筛的相对结晶度有所降低;同时,分子筛的比表面积和孔容减小、酸强度降低、酸量减少。对于甲醇转化制丙烯,最佳F-/Al2O3物质的量比为12;此时,丙烯选择性高于45%,丙烯/乙烯(P/E)比值大于10。反应机理分析表明,过渡态择形选择性是控制烯烃选择性的重要因素。

     

    Abstract: A static hydrothermal approach was adopted to synthesize nanosized SiO2-ZSM-5 zeolite in the media of F--OH- with double mineralizers, using tetraethoxysilane, sodium aluminate, and tetrapropylammonium hydroxide as the silicon source, aluminum source, and template agent, respectively. The physical and chemical properties of the synthesized ZSM-5 zeolites were characterized and their catalytic performance was evaluated in the conversion methanol to propene (MTP); the effect of F-/Al2O3 molar ratio on the catalytic performance of synthesized H-ZSM-5 was investigated. The results indicate that an increase in the F-/Al2O3 molar ratio of the synthesis mixture leads to an increase in the surface content of microcrystalline SiO2, accompanying with a decrease in the relative crystallinity, surface area, pore volume, and acid strength and density. With a F-/Al2O3 molar ratio of 12, the SiO2-ZSM-5 zeolite exhibits the best catalytic performance in MTP, with a selectivity of 45% to propene and a propene/ethene (P/E) ratio of greater than 10. It is further hypothesized that the transition state shape selectivity plays an important role in determining the product selectivity in MTP.

     

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