The structural evolution of Mo 2 C and Mo 2 C/SiO 2 under dry reforming of methane conditions: morphology and support effects.

The thermal carburization of MoO 3 nanobelts (nb) and SiO 2 -supported MoO 3 nanosheets under a 1 : 4 mixture of CH 4  : H 2 yields Mo 2 C-nb and Mo 2 C/SiO 2 . Following this process by in situ Mo K-edge X-ray absorption spectroscopy (XAS) reveals different carburization pathways for unsupported and supported MoO 3 . In particular, the carburization of α-MoO 3 -nb proceeds via MoO 2 , and that of MoO 3 /SiO 2 via the formation of highly dispersed MoO x species. Both Mo 2 C-nb and Mo 2 C/SiO 2 catalyze the dry reforming of methane (DRM, 800 °C, 8 bar) but their catalytic stability differs. Mo 2 C-nb shows a stable performance when using a CH 4 -rich feed (CH 4  : CO 2 = 4 : 2), however deactivation due to the formation of MoO 2 occurs for higher CO 2 concentrations (CH 4  : CO 2 = 4 : 3). In contrast, Mo 2 C/SiO 2 is notably more stable than Mo 2 C-nb under the CH 4  : CO 2 = 4 : 3 feed. The influence of the morphology of Mo 2 C and its dispersion on silica on the structural evolution of the catalysts under DRM is further studied by in situ Mo K-edge XAS. It is found that Mo 2 C/SiO 2 features a higher resistance to oxidation under DRM than the highly crystalline unsupported Mo 2 C-nb and this correlates with an improved catalytic stability. Lastly, the oxidation of Mo in both Mo 2 C-nb and Mo 2 C/SiO 2 under DRM conditions in the in situ XAS experiments leads to an increased activity of the competing reverse water gas shift reaction.