Hierarchical SAPO-34: Synthesis and Catalytic Performances in Methanol to Olefins

SAPO-34 is prone to losing its activity during methanol to olefins (MTO). Hierarchical SAPO-34 with different particles size was synthesized in a hydrothermal procedure. The factors controlling the size of SAPO-34 zeolite such as aluminum species and silicon species, and the effect of secondary template on the synthesis of hierarchical SAPO-34 were investigated in details. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, N-2 adsorption-desorption, transmission electron microscopy (TEM), and NH3TPD techniques. The results displayed that the different silicon species can tailor the crystalline size effectively, Secondary template can give the as synthesized SAPO-34 a mesopore structure with crystalline walls, which contributes to enhancing the thermostability, especially the hydrothermal stability during the MTO process. The catalytic performance of the as-synthesized SAPO-34 was investigated during the MTO, as compared with the referenced SAPO-34-R, hierarchical SAPO-34 displayed an excellent catalytic performance during the MTO by giving a prolonged catalytic life and an elevated selectivity for oil while a depressed olefins selectivity because of the shortened microporous channel length caused by the nanocrystallization or the introduced mesopore system.