含HF体系中SAPO-11分子筛的合成与表征

Synthesis and Characterization of SAPO-11 Molecular Sieve in the Presence of Fluoride Ions

在含HF体系中合成了SAPO-11分子筛,并采用X射线衍射、扫描电镜、低温氮物理吸附、红外光谱和吸附氨的程序升温脱附等手段对其进行了表征.结果表明,相对于常规无HF合成体系,在HF体系中合成的SAPO-11分子筛样品结晶度提高,结晶速度加快,分子筛单晶增大,分子筛晶粒聚集体的粒径减小,比表面积降低,孔体积与平均孔径增大.合成体系中加入HF后SAPO-11分子筛上B酸中心的总酸量和弱酸量降低,中强酸中心的比例有所提高,而L酸的酸量和酸强度无明显改变.

The silicoaluminophosphate SAPO-11 molecular sieve was synthesized by the hydrothermal crystallization method in the presence of fluoride ions and characterized by X-ray diffraction, scanning electron microscopy, N2 adsorption, Fourier transform infrared reflectance spectroscopy, and temperature-programmed desorption of adsorbed NH3. The results showed that the addition of HF increased the crystallization rate of SAPO- 11 and decreased the crystallization time considerably, and hence the relative crystallinity of SAPO-11 increased whereas the defects in the crystal lattice decreased. Prismatic crystal aggregates of 1- 3 μm in length were obtained in the presence of HF during the preparation of SAPO-11, whereas spherical aggregates with diameters of 8-10 μm were synthesized without using HF. The SAPO-11 synthesized in the presence of HF possessed lower BET surface area, higher pore volume, and larger mean pore diameter and crystal size than that prepared without HF. The addition of HF into the synthesis system decreased the amount of surface acid sites and increased the acidic strength of B acid sites on SAPO-11, while the amount of L acid sites kept constant.