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, N-2 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 degrees 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 degrees 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.