Catalytic performance of hierarchical H-ZSM-5/MCM-41 for methanol dehydration to dimethyl ether

Micro-mesoporous composite molecular sieves H-ZSM-5/MCM-41 were prepared by the hydrothermal technique with alkali-treated H-ZSM-5 zeolite as the source and characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, N₂ adsorption-desorption measurement and NH₃ temperature-programmed desorption. The catalytic performances for the methanol dehydration to dimethyl ether over H-ZSM-5/MCM-41 were evaluated. Among these catalysts, H-ZSM-5/MCM-41 prepared with NaOH dosage (n_Na/n_Si) varying from 0.4 to 0.47 presented excellent catalytic activity with more than 80% methanol conversion and 100% dimethyl ether selectivity in a wide temperature range of 170-300 C, and H-ZSM-5/MCM-41 prepared with n_Na/n_Si = 0.47 showed constant methanol conversion of about 88.7%, 100% dimethyl ether selectivity and excellent lifetime at 220 C. The excellent catalytic performances were due to the highly active and uniform acidic 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 process was also discussed.