Abstract: A hierarchical spherical-like ZSM-5 zeolite was synthesized using multiwall carbon nanotubes as secondary template. First, the nanotubes were purified by reflux with concentrated hydrochloric acid for 24 h. This purification step was repeated until the hydrochloric acid was no longer colored by impurities from the nanotubes (typically 3–4 times). Then the disposed nanotubes were added into the synthesis solution of ZSM-5, which was obtained by mixing H₂O, tetraethylorthosilicate, Al(C₃H₈O)₃, and tetrapropylammonium hydroxide (TPAOH). Afterward, this mixture was subjected to crystallization at varying temperatures. The obtained products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, and nitrogen adsorption analysis. The results indicated that ZSM-5 zeolite with uniform size of 300–400 nm was synthesized, and it was spherical-like aggregates and has hierarchical structure constructed by many ZSM-5 nanotubes of 20–40 nm. The hierarchical ZSM-5 zeolite was modified to form a Mo/HZSM-5 catalyst, and its catalytic performance for methane dehydroaromatization was investigated. The modified Mo/HZSM-5 catalyst exhibited CH₄ conversion as high as 19% and better life time. The CH₄ conversion was kept at 10% even when the reaction time was 24 h. It is suggested that hierarchical structure was favorable for the enhancement of catalyst performance, which is due to the presence of both micropores and mesopores.

Key words: hierarchical structure, ZSM-5 zeolite, hydrothermal synthesis, carbon nanotube, molybdenum catalyst, methane, dehydroaromatization