Characterization of molybdenum carbides for methane reforming by TPR, XRD,and XPS

The relationship between various unsupported molybdenum carbides and their activity toward methane reforming at 973 K and 1 atm was studied. Unsupport ed molybdenum carbides catalyzed the formation of hydrogen in high selectiv ity, forming ethylene and ethane rather than benzene as the carbon-containi ng products. eta -Mo3C2, which was nitrided at 973 K and subsequently carbi ded at 1173 K, was more active than both alpha -MoC1-x and beta -Mo2C in me thane decomposition, forming hydrogen in high selectivity. alpha -MoC1-x an d gamma -Mo2N were transformed to eta -Mo3C2 in the bulk structure during m ethane reforming at 973 K. This transformation caused a significant increas e in the turnover frequency of methane reforming. eta -molybdenum carbide w as also formed during CH4-TPR Of gamma -Mo2N at 788 K. The linear relations hip between the amount of il-carbide determined through H-2-TPR of the cata lysts and the methane disappearance rate revealed that eta -Mo3C2 is the ac tive species for methane reforming. From the XPS analysis, Mo-0 was the dom inant molybdenum species for the eta -Mo3C2 catalysts.