Effects of parameters in the preparation of Mo/MWW-type catalysts on the dehydroaromatization of shale gas

Abstract

The direct non-oxidative aromatization of shale gas offers an unconventional production route for BTX (benzene, toluene, and xylene), potentially alleviating the heavy dependence of BTX supply on petroleum-based processes. Zeolite-supported transition metal catalysts have been successfully applied in the aromatization of light alkanes, where the zeolites provide the appropriate shape selectivity and acidity that are beneficial for the production of aromatics. In addition to HZSM-5, MCM-22 has also been recognized to be an effective support, owing to the characteristic topology of MWW structure. Here, we present a systematic investigation into the preparation and optimization of Mo/MWW-type catalysts, aiming to maximize their performance in shale gas aromatization. Mo/MCM-22 exhibited a superior initial BTX yield compared to Mo/ZSM-5 with a comparable Si/Al ratio, but was rapidly deactivated. A moderate value of Si/Al (∼ 11) was required for optimal catalytic performance, as an excessive amount of Al during the synthesis of MCM-22 led to insufficient amount of strong acid sites that are favorable for the reaction. The inclusion of Ga in MCM-22 greatly deteriorated the aromatization activity, owing to a significant degree of degalliation under reaction conditions. Contrary to ZSM-5, pelletization of MCM-22 also had a noticeable impact on catalytic performance, which was attributed to the nature of MWW topology. These results provide a comprehensive understanding of designing MWW-type zeolites for their application in shale gas aromatization.