Abstract: 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 ofX-raydiffraction, scanning electron microscopy,X-rayfluorescence 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.

Key words: SAPO-34 molecular sieve, hydrogen fluorine, Si(4Al) coordination environment, methanol-to-olefins reaction