Abstract: The effect of cage size on the catalytic performance of SSZ-13 with CHA structure and RUB-50 with LEV structure has been comparatively investigated in the methanol-to-olefin (MTO) reaction. The zeolite structure and coke deposit were characterized by X-ray diffraction, N₂ adsorption-desorption, solid-state NMR, thermogravimetry and UV-Vis spectroscopy. It is found that SSZ-13 zeolite with larger cage size has better stability and higher propylene selectivity in the MTO reaction, while RUB-50 zeolite with smaller cage size has higher ethylene selectivity. Most of nonframework Al can be extracted, and the acidity is altered to some extent after the zeolites were washed with dilute acid. However, this would not obviously change the ratio of propylene to ethylene in the products. In addition, the volume of carbonaceous species is dependent on the zeolite cage size. More ethylene would be produced in the zeolite with smaller cage size. Thus, the zeolite cage size is very important in altering the ethylene and propylene selectivity in the MTO reaction.

Key words: methanol, olefin, ethylene, propylene, SSZ-13 zeolite, RUB-50 zeolite, cage size