Abstract

The methanation of CO 2 was performed on Rh/γ-Al 2O 3 catalyst at temperatures between 50 and 150°C at 2bar of pressure in a pulse reactor. Experiments confirm the formation of methane at low temperature and pressure. The formation of formiate species during the adsorption of CO 2 can be excluded. After reaction with CO 2, the catalyst is oxidized. Oxidation is not observed in the presence of CO. The CO 2 is adsorbed dissociatively, forming CO (ads) and O (ads). Gem-dicarbonyl Rh(CO) 2 species are more reactive than the Rh-CO linear species. The type of adsorbed species depends on the Rh oxidation state. The formation of methane by hydrogenation of CO 2 and CO is carried out with 100% selectivity. The activation energy for the hydrogenation of CO 2 and CO is lower than values presented in the literature which have been obtained at higher temperature. In the presence of CO 2 and CO, the reaction of methanation of CO 2 seems to be inhibited by CO. When oxygen is added in low amount in the reactant gas feed, a positive effect on methanation is observed. When the amount of oxygen is too high, oxygen has a negative effect. These results are in agreement with thermodynamics equilibrium calculations, except when O 2 is present, confirming the importance of kinetic effects in the reaction. These results open new perspectives of application of catalysis, in order to recycle CO 2 in the presence of H 2. © 2011 Elsevier B.V.