Influence of the post-treatment of HZSM-5 zeolite on catalytic performance for alkylation of benzene with methanol

The porousmaterialHZSM-5 zeolite with micro-mesopore hierarchical porosity was prepared by post-treatment (combined alkali treatment and acid leaching) of parent zeolite and its catalytic performance for benzene alkylation with methanol was investigated. The effect of post-treatment on the textural propertieswas characterized by various techniques (including ICP-AES, XRD, nitrogen sorption isotherms, SEM, NH₃-TPD, Py-IR and TG). The results indicated that the post-treatment could modify the structural and acidic properties of HZSM-5 zeolite. In this procedure, not only additional mesopores were created by selective extraction of silicon but also the acidity was tuned. Consequently, themodified HZSM-5 zeolite showed larger external surface areawith less acid sites as compared to the parent zeolite. Itwas found out that themodified zeolite exhibited a higher benzene conversion and xylene selectivity for alkylation of benzene with methanol as well as excellent life span of the catalyst than conventional ones. This can be explained by the facts that the presence of additional mesopores improved the diffusion property in the reactions. Furthermore, the modified zeolite showed an appropriate Brønsted acidity for effective suppression of the side reaction of methanol to olefins, thus reduced the accumulation of coke on the HZSM-5 zeolite,whichwas favorable for the catalyst stability. In comparison with the parent HZSM-5 zeolite, themodified zeolite by alkali treatment and acid leaching showed better performance for the benzene alkylation with methanol.