ELEMENTARY STEPS ACCOMPANYING THE CHEMISORPTION OF CARBON-DIOXIDE ON A NICKEL-CATALYST IN RELATION WITH THE METHANATION REACTION .1. EXPOSURE OF THE CATALYST TO CARBON-DIOXIDE AND THERMOREACTION WITH HYDROGEN OF THE CHEMISORBED SPECIES

The chemisorption of CO2 on a silica supported Ni catalyst was studied in a wide range of temperature (20-350-degrees-C) by TPSR with H-2. Several processes could be identified (dissociation of CO2 into CO(ads) and O(ads), disproportionation of CO(ads),, evolution of CO at T > 150-degrees-C, incorporation of oxygen into the sub-surface region at T > 100-degrees-C). Hydrogen can react very quickly with O(ads) and C(ads) and most probably assists the preliminary breaking of CO(ads). The latter process constitutes the slow step of the CO2 methanation.