Methane dehydroaromatization over Mo/HZSM-5 catalyst: Effect of dealumination of HZSM-5 zeolite

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) approximate to 27, the presence of superfluous strong Bronsted 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 Bronsted 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 C-2 intermediates. High-temperature N-2, treatment induced mild dealumination of HZSM-5, destroyed the origin strong Bronsted acid sites, but retained sufficient weak acid sites. This treatment effectively restrained coke deposition and satisfied the requirement of the aromatization of C-2 intermediates during the reaction. Therefore, a remarkable improvement in the catalyst durability and selectivity for aromatics was observed