Abstract: 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.

Key words: SAPO-11 molecular sieve, hydrogen fluoride, crystallization, acidity, synthesis