Insight into the role of mesoporosity in the selective production of propene from methanol

Microporous ZSM-5, hierarchical ZSM-5, and hierarchical ZSM-11 zeolites with different crystalline sizes were prepared to determine the relations of mesoporosity with catalytic performance in methanol-to-propene reaction. The physicochemical properties were investigated by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy, Temperature-Programmed Desorption, and sorption techniques. It was shown that the low pore tortuosity, hierarchical structure, and the reduction of the crystal size all can shorten the diffusion path and reduce the diffusion resistance, leading to the increase of propylene yield. By comparison, the propene yield increase to the increment of mesoporous volume due to the tortuosity is more effective than other aspects. For silica–alumina zeolites, the effective way to reduce the diffusion resistance and increase the selectivity of propylene is to lower the pore tortuosity degree, and then introduce the mesoporous structure and reduce the grain size.