骨架富含Si(4Al)结构的SAPO-34分子筛的合成及其对甲醇制烯烃反应的催化性能

通过在初始凝胶中加入HF合成了骨架富含Si(4Al)配位结构的SAPO-34分子筛. 使用X射线衍射、扫描电镜、X射线荧光和核磁共振等表征手段研究了初始凝胶中HF的加入对合成SAPO-34分子筛的晶体结构、晶体形貌、元素组成以及骨架硅配位环境的影响. 结果表明,在初始凝胶中加入F离子后,合成的SAPO-34分子筛的晶体结构更加规整;随着初始凝胶中F离子含量的提高,合成的SAPO-34分子筛晶体骨架中Si(4Al)配位结构的数量增多, Si(nAl)(n=3～0)配位结构的数量减少. 将合成的SAPO-34分子筛催化剂用于甲醇制烯烃反应,结果显示, SAPO-34分子筛骨架中富含Si(4Al)配位结构可以有效提高反应产物中乙烯的选择性,同时能够延长催化剂的寿命.

Synthesis of SAPO-34 with Rich Si(4Al) Coordination Environment in the Framework and Its Catalytic Performance in Methanol-to-Olefins Reaction

SAPO-34 molecular sieve samples with rich Si(4Al) coordination environment were synthesized by adding HF in the initial gel.The crystalline phase,crystal morphology,elemental composition,and Si coordination environment of the as-synthesized samples were determined by means of X-ray diffraction,scanning electron microscopy,X-ray fluorescence spectroscopy,and nuclear magnetic resonance.The crystallization of SAPO-34 molecular sieve can be adjusted by adding HF in the initial gel,and correspondingly,the Si coordination modeling can be controlled.The proportion of Si(4Al) species in the as-synthesized SAPO-34 increased,and that of Si(nAl)(n=3-0) decreased with increasing fluorine ion content in the initial gel.The catalytic performance of the SAPO-34 catalysts with various Si coordination was investigated in the methanol-to-olefins reaction.The results showed that SAPO-34 catalysts with rich Si(4Al) coordination structure had higher selectivity to ethylene and longer life time.