Controlling the morphologies and crystal growth orientations of H-ZSM-5: their impact on the structure-diffusion-performance relationship in the methanol-to-propylene reaction

Abstract

In this study, three typical ZSM-5 catalysts with different morphologies and crystal growth orientations were prepared for methanol-to-propylene (MTP) reactions. Despite having similar acidity, significant differences in lifetimes and selectivity were observed over the three different ZSM-5 catalysts under a high space velocity of 10 h⁻¹. Generally, the lifetime and propylene selectivity were in the order of ZSM-5-NS (300 h, 55.04%) > ZSM-5-NC (168 h, 53.34%) > ZSM-5-NF (78 h, 49.31%). A series of characterization results revealed that the superior performance of ZSM-NS was attributed to its higher ratio of framework Al distribution within the straight and sinusoidal channels favored for the alkene cycle and enhancing C_2–4 olefin selectivity, a higher diffusion rate owing to its thinner (010) crystal plane along the b axis orientation, and higher crystallinity and fewer framework defects within the micropore contributed to an extended lifetime stability because of its lower coking rate. Additionally, the shaped ZSM-5-NS catalyst exhibited impressive stability and regenerability in a single-tube test, enduring an impressive long 2680 h lifespan in a single cycle and a total of 6800 h lifetime across three cycles, suggesting its significant potential for industrial application in the MTP process.