Realumination of dealuminated HZSM-5 zeolites by acid treatment, the impact of AlF distribution and its catalytic cracking performance of alkanes

Realumination of dealuminated HZSM-5 zeolites by acid treatment has always been controversial and puzzling. Through characterizations of XRD, nitrogen adsorption, NH 3 -TPD, IR, XPS and 27 Al MAS NMR, this work confirmed realumination of dealuminated HZSM-5 zeolites could indeed be achieved after treated with HCl solution. And it was found mainly a portion of the penta-coordinated extra-framework aluminia (EFAl) were reinserted into the framework during the process of realumination. Moreover, the characterizations of ICP-AES and UV–Vis-DRS of Co 2+ -exchanged zeolites indicated the realumination capacity was closely related to the distribution of framework Al (Al F ). Realumination was more likely achieved when there was lower content of Al pairs and less Al F located in the channel intersections in HZSM-5. Finally, realuminated zeolites exhibited a higher conversion of n -octane due to its more Brønsted acid sites than dealuminated HZSM-5 in catalytic cracking reaction. The significantly lower content of Al pairs in realuminated zeolites compared to parent HZSM-5 inhibits the hydride transfer process to a certain extent, resulting in a higher selectivity of propylene. • Realumination of dealuminated HZSM-5 zeolites achieved by treatment with the aq HCl solution. • A portion of the penta-coordinated EFAl reinserted into the framework during realumination. • Realumination capacity is strongly dependent on the distribution of Al F in HZSM-5 zeolites. • Fewer Al pairs and more Al F located in the straight and sinusoidal channels are easier for realumination.