Conversion of natural gas into valuable chemicals can be a viable option to mitigate the flaring of stranded natural gas and to decarbonize upstream emissions. Applying microwave energy to heterogenous catalyst materials offers advantages in terms of higher rates and product selectivities in comparison to traditional thermal systems which can be designed for on-demand chemical production in modular reactor systems. Methane dehydroaromatization produces transportable, liquid aromatic products directly from natural gas, which is ideal for remote production but is hindered by low thermodynamic yields and conversions. Further, Mo deposited on H-ZSM-5 is the most widely studied catalyst but is a poor microwave absorber, and suffers rapid deactivation through carbon deposition and sintering.

Herein, we investigate co-feeding of H₂ and CO₂ in microwave-assisted CH₄ dehydroaromatization to reduce coking on the catalysts. For this, a 4 wt% Mo/ZSM-5 catalyst was synthesized and characterized using H₂-TPR, BET, and XRD. This catalyst was enhanced for microwave activity with a silicon carbide absorbing material and tested for CH₄ aromatization under microwaves following a pre-activation step. The coke deposited on the spent catalysts was characterized through Raman and TGA. It was observed that the addition of additives at low concentrations enhanced the activity of the catalyst and resulted in higher benzene yields. This improvement likely resulted from simultaneous occurrence of dry reforming, Boudouard, and reverse water gas shift reactions in the case of CO₂ limiting carbon formation, whereas the presence of H₂ suppressed excessive dehydrogenation of the surface carbon intermediates. CH₄ conversion on the other hand was highly stabilized with CO₂ indicating the role of different active sites, whereas with H₂ only a slight improvement was observed.

Xinwei Bai

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