The relationship between various unsupported molybdenum carbides and their activity toward methane reforming at 973 K and 1 atm was studied. Unsupported molybdenum carbides catalyzed the formation of hydrogen in high selectivity, forming ethylene and ethane rather than benzene as the carbon-containing products. η-Mo3C2, which was nitrided at 973 K and subsequently carbided at 1173 K, was more active than both α-MoC1 - x and β-Mo2C in methane decomposition, forming hydrogen in high selectivity. α-MoC1 - x and γ-Mo2N were transformed to η-Mo3C2 in the bulk structure during methane reforming at 973 K. This transformation caused a significant increase in the turnover frequency of methane reforming. η-molybdenum carbide was also formed during CH4-TPR of γ-Mo2N at 788 K. The linear relationship between the amount of η-carbide determined through H2-TPR of the catalysts and the methane disappearance rate revealed that η-Mo3C2 is the active species for methane reforming. From the XPS analysis, Mo0 was the dominant molybdenum species for the η-Mo3C2 catalysts.

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η-Mo3C2 was the most active molybdenum carbide species for methane reforming, surpassing β-Mo2C which has been reported previously. From the correlation of the TPR results, the amount of η-Mo3C2 was directly related to the methane decomposition rate, indicating the importance of this type of carbide for methane reforming.