Catalytic production of methane from CO2 and H2 at low temperature: Insight on the reaction mechanism

Experimental evidences show that it is possible to produce methane from an exclusively inorganic way using CO2 and H2 on a Rh/γ-Al2O3 catalyst at low temperature and atmospheric pressure. New insights on the mechanism of methanation are given. The first step of the mechanism in the methanation reaction could be the chemisorption of CO2 on the catalyst. The second step is the dissociation of CO2 into CO and O adsorbed on the surface. The third step is the reaction of dissociated species with H2. Adsorption, dissociation of CO2 and the reaction of dissociated species with H2 are evidenced by in situ DRIFT experiments. The reaction could occur between the adsorbed species. However a reaction between adsorbed species and gaseous hydrogen cannot be excluded. XPS shows that the CO2 oxidizes the catalyst and this oxidation deactivates the catalyst. The conversion of CO2 also increases with temperature. Methane is the unique hydrocarbon molecule formed and obtained with almost 100% selectivity. No other hydrocarbonated products have been observed.