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.