An improved dealumination method for adjusting acidity of HZSM-5

An improved dealumination method for adjusting the acidity of HZSM-5 was developed by utilizing the self-adsorbed water in HZSM-5. The parent and treated HZSM-5 were characterized by XRD, FT-IR, 27Al MAS NMR, N2 adsorption, XRF and NH3-TPD. The results showed that HZSM-5 can be dealuminated when treated at above 400 °C. About 80% acidic amount was removed from parent HZSM-5 with 8% adsorbed water and more Lewis acid sites were produced after treated at 500 °C. It is thought that the dealumination was mainly caused by its self-adsorbed water. The comparisons of the acidity in dealuminated HZSM-5 by traditionally steaming and improved methods indicated that the latter was more effective in decreasing the acidity and weakening acid strength, and more environmentally benign and timesaving. The method is also applicable to adjust acidity of other zeolites, such as HY, Hβ.