直接法制备多级孔HZSM-5分子筛及其MTO催化性能

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

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、n[CO(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%。

In the system of SiO2 - Al2O3 - EDA - CTAB - CO （ NH2 ）2 - H2 O, 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（ A1203 ） = 150 ,hi CO（ 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.