Effect of seed form on the structure and properties of as-synthesized SAPO-34 molecular sieves and their catalytic performance in the conversion of methanol to olefins

A series of SAPO-34 molecular sieves with low Si/Al ratio were synthesized by conventional hydrothermal method as well as adding powder crystal seed and liquid crystal seed containing SAPO-34 precursor. These SAPO-34 molecular sieves were characterized by XRD, SEM, FT-IR and NH₃-TPD and the effects of synthesis method on the structure, morphology, crystal size and acidity of the resultant SAPO-34 molecular sieves as well as their catalytic performance in the conversion of methanol to olefins (MTO) were investigated. The results indicate that although the seed form has little influence on the crystallinity, the silicon distribution in SAPO-34 framework, crystal size, and acidic properties are strongly related to the seed form. In comparison with the SAPO-34 sample synthesized with powder form seed, the SAPO-34 molecular sieves prepared using liquid crystal seed containing SAPO-34 precursor exhibit smaller crystal size, weaker acidic strength, and higher selectivity to light olefins in MTO.