Improved benzene selectivity for methane dehydroaromatization via modifying the zeolitic pores by dual-templating approach

Abstract

Catalytic upgradation of methane into benzene and valuable chemicals over Mo/HZSM-5 has a great economic potential, yet it has serious drawback due to the obstacles in the micropores because of extensive coking at an elevated temperature during methane dehydroaromatization (MDA). Under such circumstances, it requires the design of micro/mesoporous ZSM-5, which has the advantages viz. enhanced product formation due to uniform Mo distribution inside the pores and lower carbon deposition because of improved mass transfer rate within the hierarchical pores. We infer herein a unique strategy to control the porous structures of ZSM-5 through a dual templating approach, employing both C6 and C12 -surfactants as porogen. The structural and morphological parameters of the synthesized ZSM-5 catalysts were investigated in detailed to ascertain the crystallinity, porosity, particle shape, size, Si/Al ratio, and acid strength which were further correlated with the physicochemical and catalytic properties of Mo modified HZSM-5 catalysts. After Mo impregnation, all the catalysts were evaluated for methane dehydroaromatization reaction. Compared with the conventional Mo/HZSM-5(C), C6 surfactant-treated hierarchically porous Mo/HZSM-5(H) showed the highest benzene formation rate (1.5 μmol/gcat. s) and longer stability of 270 min in TOS analysis. In contrary, C12 surfactant modified Mo/HZSM-5(D) is inferior towards MDA reaction (benzene formation rate: 0.5 μmol/gcat. s). We attribute to the difference in MDA reaction could be due to the hierarchically mesoporous feature of Mo/HZSM-5(H) with interconnected topology that precludes secondary reaction of coking from benzene and hence, contributing significant stability towards MDA reaction.