直接法制备多级孔HZSM-5分子筛及其MTO催化性能

考察SiO_2-Al_2O_3-EDA-CTAB-CO(NH2)2-H2O体系中水热法一步晶化程序合成多级孔HZSM-5分子筛时各因素对产品性能的影响。在投料n(SiO_2)∶n(Al_2O_3)=150、nCO(NH2)2]∶n(SiO_2)=1.5和180℃一步晶化72 h时,合成多级孔HZSM-5分子筛的结晶度为99%。n(SiO_2)∶n(Al_2O_3)从50增至250,多级孔HZSM-5分子筛结晶度先增加后降低;随着n(SiO_2)∶n(Al_2O_3)增加,多级孔HZSM-5分子筛的微孔体积减小,介孔体积逐渐增大,比表面积大于400 m2·g-1。合成的多级孔HZSM-5分子筛对甲醇制烯烃反应具有良好的催化活性,不同n(SiO_2)∶n(Al_2O_3)合成的样品在反应时间80 h前,甲醇转化率均接近100%;n(SiO_2)∶n(Al_2O_3)=150的多级孔HZSM-5上丙烯选择性和乙烯选择性分别为45.11%和11.30%。

Direct synthesis of hierarchical HZSM-5 molecular sieves and research on their properties

In the system of SiO₂-Al₂O₃-EDA-CTAB-CO(NH₂)₂-H₂O,the effects of hydrothermal synthesis parameters on the properties of hierarchical HZSM-5 molecular sieves were investigated.The results showed that the crystallinity of the as-synthesized sample was 99% under the condition of feeding n(SiO₂):n(Al₂O₃)=150,nCO(NH₂)₂]:n(SiO₂)=1.5,crystallization temperature 180 ℃,crystallization time 72 h,and one-step crystallization procedure.When the feeding molar ratio of SiO₂ to Al₂O₃ enhanced from 50 to 250,the crystallinity of synthesized hierarchical HZSM-5 molecular sieves firstly increased and then decreased,the micro-pore volume of the samples reduced and the meso-pore volume increased while the BET specific surface areas were above 400 m²·g^-1.The as-synthesized hierarchical HZSM-5 molecular sieves exhibited excellent activity in the methanol-to-olefins reaction.Methanol conversion was close to 100% over catalysts prepared with different feeding n(SiO₂):n(Al₂O₃) before reaction time was 80 h;the selectivity to propylene and ethylene were 45.11% and 11.30%,respectively,over hierarchical HZSM-5 molecular sieve prepared with n(SiO₂):n(Al₂O₃)=150.