Micro-mesoporous composite molecular sieves H-ZSM-5/MCM-41 for methanol dehydration to dimethyl ether: Effect of SiO2/Al2O3 ratio in H-ZSM-5

Abstract

Micro-mesoporous composite molecular sieves H-ZSM-5/MCM-41 were prepared by the hydrothermal technique with alkali-treated H-ZSM-5 zeolite as source and characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, N2 adsorption and desorption measurement, and NH3 temperature-programmed desorption. The effect of SiO2/Al2O3 ratio in H-ZSM-5 on the structure, surface acidity and catalytic performances of H-ZSM-5/MCM-41 for methanol dehydration to dimethyl ether were investigated. H-ZSM-5/MCM-41 prepared with H-ZSM-5 of different SiO2/Al2O3 ratios as source in which H-ZSM-5 nanoparticles were uniformly dispersed in MCM-41 matrix, had well-ordered micropores and mesopores. The acid amount and strength of moderate acid sites (TP1) of H-ZSM-5/MCM-41 can be controlled by the SiO2/Al2O3 ratio in H-ZSM-5 during the range from 25 to 50. Among these catalysts, H-ZSM-5/MCM-41 presented a comparable catalytic activity to the corresponding pure H-ZSM-5 and 100% dimethyl ether selectivity in a wider temperature range than the corresponding pure H-ZSM-5. The excellent catalytic performances were due to the highly active and uniform strong acid sites and the hierarchical porosity in the micro-mesoporous composite molecular sieves. The catalytic mechanism of H-ZSM-5/MCM-41 for the methanol dehydration to dimethyl ether was also discussed.