Effect of heat treatment on the structure, acidity and catalytic performance of HZSM-5 zeolites in ethanol dehydration

Heat treatment at high temperature was used to modify HZSM-5 zeolites. The HZSM-5 samples before and after heat treatments were characterized by X-ray diffraction (XRD), ²⁷Al-MAS NMR, N₂ adsorption, inductively couple plasma emission spectroscopy (ICP-AES), temperature-programmed desorption of ammonia (NH₃-TPD), and Fourier transform infrared (FT-IR) spectroscopy of adsorbed pyridine. The effects of heat treatment conditions on the structure, acidity, and catalytic performance of HZSM-5 zeolites in dehydration of ethanol to ethylene were investigated. The results showed that the heat treatment leads to dealuminization from the zeolite framework and channels, which may decrease the amount of Bronsted acid sites, increase the Lewis acid sites and the pore volume, and form new mesopores. When the heat-treated HZSM-5 is used as the catalyst in ethanol dehydration, owing to its appropriate acidity and binary meso/micro porous structure, the side reaction is reduced and the selectivity to ethylene and the catalyst life time are increased significantly.