Methane reforming reaction with carbon dioxide over a Ni/SiO2 catalyst: The nature of the active phase

The nature of the active phase of a Ni/SiO2 catalyst for the CO2 reforming of methane has been studied. It is shown that nickel carbide-like layers, established in the very initial period of the run, constitute the active phase for this reaction. The related carbon adspecies are in equilibrium with gaseous methane and can be also irreversibly converted into CO with oxygen adspecies arising from the carbon dioxide activation. The amount of carbon equivalent to a carbide sublayer dissolves rapidly. This carbon, diffusing through the particles, is related to the formation of external carbon deposits. The fast and rate-limiting steps of the reforming mechanism are described on the basis of the above active carbon surface.