Dependence of the nature and catalytic performance on the synthesis factors of SAPO-5 molecular sieve

A series of SAPO-5 molecular sieves have been synthesized by varying the silicon source, template and crystallization time. X-ray diffraction (XRD), SEM-EDAX, IR and TPD of ammonia have been employed to characterize their structure and acidity. The results show that the type and the amount of the template has a great effect on the yield of SAPO-5. The silicon source also exerts influence on the morphology of SAPO-5 and its acidity. Prolonging the aging time not only increases the silicon content in SAPO-5, but also decomposes the large crystal into small one and alters the acidity. However, when the aging time is over 48 h, the crystallinity of the molecular sieve decreases and some SAPO-34 intergrows in the product. Brønsted acid sites with medium strength are predominant on the SAPO-5 samples prepared, with which the n-hexane cracking activity at 450°C runs parallel.