(113b) Investigation of Molybdenum and Iron Catalysts for Non-Oxidative Coupling of Methane.

Methane coupling offers an attractive route for the production of valuable C₂ hydrocarbon products, however a viable catalyst for this reaction remains a significant challenge. To enable a feasible methane conversion process while elucidating the reaction pathways, our aim is to develop catalysts capable of operating at lower temperatures with high stability and selectivity. In this study, we synthesize and evaluate molybdenum (Mo) and iron (Fe) catalysts supported on carbon in a fixed bed flow reactor for non-oxidative coupling of methane. We employ a series of characterization techniques to understand the catalyst structure. We conduct reactions at 700^oC and observe that an in situ carburization of the catalysts prior to reaction reduces molybdenum oxides to carbides; such carbides are proposed as the active sites. For Mo-Fe/AC, we observe slight shifts in the reduction temperatures compared to Mo/AC, attributed to the formation of a Mo-Fe alloy. Raman shifts, particularly reduction of molybdenum oxide to molybdenum carbide, and XRD analyses (presence of different crystal phases) corroborate the changes occurring on the catalyst structure after carburization pretreatment and reaction. The Mo-Fe/AC catalyst exhibits improved activity, averaging total C₂ production as 855 μmol/(g-cat*h), compared to Mo/AC catalyst’s average value of 774 μmol/(g-cat*h) after reaching a steady-state. Both catalysts show a similar trend in ethylene production (740 μmol/(g-cat*h) for Mo-Fe/AC and 632 μmol/(g-cat*h) for Mo/AC), while Mo/AC demonstrates higher ethane production as compared to Mo-Fe/AC. These results underscore variations in the proposed reaction pathways: methane conversion directly to ethylene and ethane, as well as ethane dehydrogenation to ethylene. The bimetallic catalyst demonstrates enhanced performance due to the promotional effect of Fe, which can be attributed to the redox properties and electronic synergism between Mo and Fe.