A Preliminary Study on the Role of the Internal and External Surfaces of Nano-ZSM-5 Zeolite in the Alkylation of Benzene with Methanol

The catalytic behaviors of the internal and external Bronsted acid sites on HZSM-5 zeolite were investigated in the alkylation of benzene with methanol (MeOH). The external surface passivated HZSM-5 zeolites were prepared by the silanization of tetraethyl orthosilicate, while the internal surface passivated HZSM-5 zeolites were obtained by sodium cation exchange followed by tetrapropylammonium cation re-exchange. Ammonia temperature-programmed desorption (NH3 -TPD) and pyridine/2,6-di-tert-butylpyridine adsorption FT-IR spectroscopy were used to characterize the acidity of the modified zeolites. Results indicate that the internal surface of the HZSM-5 zeolite is not an ideal place for the alkylation of benzene with methanol since the formation of the byproduct (ethylbenzene) is favored. In contrast, the external Bronsted acid sites on the internal surface passivated HZSM-5 zeolites exhibit not only significantly better xylene selectivity but also good alkylation activity, anticoking deactivation ability, and regeneration ability through coke burning.