Synthesis and characterization of ZSM-5/MCM-41 composite molecular sieves

ZSM-5/MCM-41 composite molecular sieves with multiple micro-mesoporous structure were hydrothermally synthesized via self-assembly by using the alkali-treated ZSM-5 seriflux as the source of silica and aluminum. The as-synthesized molecular sieves were characterized by XRD, N₂ adsorption, HRTEM, Py-IR, and hydrothermal treatment methods. The results showed that the crystallinity of the as-synthesized molecular sieves is dependent on the intensity of the alkali-treatment; the suitable alkali treatment conditions for ZSM-5 are 80℃ for 1 h with a NaOH concentration of 1 mol/L. The composite molecular sieves obtained exhibit a typical MCM-41 structure, with a hierarchical micro-mesoporous structure and large specific surface area. Compared with MCM-41, the ZSM-5/MCM-41 composite molecular sieves show higher quantity of Bronsted acid sites (especially strong ones) and higher hydrothermal stability.