Retardation of Carbon Deposition in CO2—CH4 Reaction on Metal Sulfide Catalysts

The CO2-oxidation (reforming) of methane on MoS2 and WS2 catalysts was compared to that on a Ni/SiO2 catalyst using a continuous flow technique. The sulfide catalysts had lower activity than the Ni/SiO2 catalyst, however in contrast to Ni catalyst, deactivation due to carbon deposition was not observed on the sulfide catalysts. The direct decomposition of CH4[g] to C[s] and 2H2[g] was much less significant on the sulfides than on Ni, however, the dissociation of CO2[g] to CO[g] and O[ads] occurred to a greater extent on the sulfide surface. The rate was expressed by the following equations: r = kPCH40.54∼0.76PCO2-0.09∼-0.10 on MoS2 and WS2 and r = kPCH4-0.30 PCO20.16 on Ni/SiO2, respectively. The rate equations suggest that during steady-state reaction, CO2 species are abundant on the surface of the sulfide catalysts, while CH4 species are abundant on Ni. This is probably the cause for the retardation of carbon deposition on the sulfide catalysts and for their low activity for this reaction.