In this work, we present a detailed investigation into the formation of distinct active sites in bimetallic Mo-Fe/ZSM-5 catalysts compared to their monometallic counterparts, Mo/ZSM-5 and Fe/ZSM-5. Catalysts were synthesized via co-impregnation to achieve the co-location of Mo and Fe species within the zeolite framework. Advanced characterization techniques, including XPS, UV-Vis, and Raman spectroscopy revealed the formation of unique bimetallic active sites, possibly a bimetallic carbide (MoFeCx) phase, which significantly enhanced methane conversion and benzene selectivity. At equivalent methane conversion, the Mo-Fe/ZSM-5 catalyst exhibited up to 150% higher benzene formation rate compared to Mo/ZSM-5. Characterization of spent catalysts also indicates that polyaromatic coke, rather than graphitic coke on the zeolite surface, is the primary cause of catalyst deactivation. The bimetallic Mo-Fe/ZSM-5 catalyst effectively suppresses aromatic coke formation and promotes the growth of carbon nanotubes, resulting in a lower deactivation rate compared to Mo/ZSM-5. Consequently, the bimetallic catalyst exhibits superior activity and stability, demonstrating its potential for enhanced performance in methane aromatization.
This study bridges a key knowledge gap by elucidating the structural and functional effects of Mo-Fe interactions, offering a foundation for designing more efficient and stable catalysts to advance methane valorization technologies and other reactions (i.e., selective reduction of NOx, biomass conversion, methanol aromatization (MTA), etc.) where these are the catalysts of choice.