Hydrothermal synthesis of core-shell ZSM-5/SAPO-34 composite zeolites and catalytic performance in methanol-to-aromatics reaction

A series of core-shell ZSM-5/SAPO-34 composite catalysts with different molar ratios were synthesized using hydrothermal method, and their catalytic performance was tested for the conversion of methanol-to-aromatics. The catalysts were characterized by means of XRD, SEM, NH3-TPD and N-2 adsorption-desorption analysis. The results showed that pristine SAPO-34 showed much lower selectivity to aromatics due to its narrow cage structure and lower acid sites. However, with increasing ZSM-5/SAPO-34M ratio, composite zeolite showed higher selectivity to aromatics. As the molar ratio was up to two, the selectivity to aromatics was even higher than that of pristine ZSM-5, indicating that core-shell composite zeolites with hierarchical structure and moderate acid sites were favored for methanol to aromatics. Meanwhile the optimum reaction condition for high yield of aromatics is determined to be 450 degrees C and 1.5 h(-1)(WHSV).