Abstract: Two dealumination methods were used to modify the framework composition of the HZSM-5 zeolite. The structure and acidity of dealuminated zeolite samples were investigated by MAS NMR and FT-IR. It was found that the catalytic performance of the Mo/HZSM-5 catalyst for methane dehydroaromatization was closely related to the acidity of the HZSM-5 zeolite. On the parent zeolite with n(Si)/n(Al)≈27, the presence of superfluous strong Brnsted acid sites caused severe coke deposition during the reaction. Hydrothermal treatment of the parent zeolite extracted tetrahedral Al from the framework and thus led to a significant reduction in the number of Brnsted acid sites. The formation of aromatics over this hydrothermally treated zeolite was suppressed owing to the deficiency of acid sites available for the aromatization of C2 intermediates. High-temperature N2 treatment induced mild dealumination of HZSM-5, destroyed the origin strong Brnsted acid sites, but retained sufficient weak acid sites. This treatment effectively restrained coke deposition and satisfied the requirement of the aromatization of C2 intermediates during the reaction. Therefore, a remarkable improvement in the catalyst durability and selectivity for aromatics was observed.

Key words: methane, aromatization, molybdenum, HZSM-5 zeolite, supported catalyst, dealumination, hydrothermal treatment, high temperature nitrogen treatment