The Hβ zeolite was modified with different concentrations of citric acid. The textures of the modified Hβ zeolites were characterized by XRD and Ar adsorption, and the acid properties were characterized by NH3⁃TPD and Py⁃FTIR. In addition, the interaction between the pyridine molecules and the active constituent units of the Hβ zeolite was also analyzed by Py⁃FTIR. The results showed that several active sites, such as the Brønsted acid sites associated with the bridging hydroxyl groups (SiOHAl), the weak Lewis acid sites associated with EFAL hydroxyl groups and the strong Lewis acid sites associated with the three⁃coordinated Al hydroxyl species and AlO+ cations were existed in the Hβ zeolite. The synergistic effect between the EFAL and the adjacent bridging hydroxyl groups was found on the adsorption of pyridine. The pyridine molecule which adsorbed in the Lewis acid site and bonded with the adjacent B acid sites was less likely to desorb at high temperature. Pyridine molecules were preferentially adsorbed on the strong acidic bridging hydroxyls and defect sites associated with the three⁃coordinated Al hydroxyl species. It was only weakly interacted with EFAL hydroxyl groups. After citric acid treatment, EFAL hydroxyl groups were selectively removed while the framework aluminum was not severe damaged. The strong Lewis acid sites were preserved in the modified Hβ zeolite after citric acid treatment, and the strong Lewis acid sites may be related to AlO+ and the three⁃coordinated Al species of defect sites.

Hβ zeolites were modified by hydrochloric acid. The crystal structure, textual properties and total acid content of the Hβ zeolites were characterized by XRD, N ₂ adsorption and NH ₃­TPD. Using thiophene as the probe molecule, the mass transfer behavior of Hβ zeolites modified by hydrochloric acid was studied by Frequency Response. The results showed that hydrochloric acid washed away the non skeleton aluminum which blocked the pore of zeolites, enhanced the permeability of molecular sieve pore and improved the mass transfer performance of the molecular sieve. In the frequency response spectrum, the response intensity of thiophene in the modified Hβ zeolites was obviously greater than that in the unmodified zeolite. The mass transfer performance of modified Hβ zeolites was improved, and the ability to adsorb thiophene was also enhanced obviously, which was significant for catalyzing thiophene reaction and optimizing industrial desulfurization.