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.