Ru/NiO-CeO2-catalyzed CO and CO2 CO-methanation

A highly active Ru/NiO-CeO 2 (NP) catalyst, synthesized by ruthenium impregnation on NiO-CeO 2 mixed oxide 7–8 nm nanoparticles, has been studied for the individual and simultaneous methanation of CO and CO 2 , showing onset CH 4 production in co-methanation at 200 °C, and maximum CH 4 production at 350 °C. Isotopic gas pulse experiments indicated that the catalyst is continuously reduced by H 2 , yielding catalyst oxygen ( 16 O)-containing water, and it is re-oxidised with 18 O once 12 C 18 O or 13 C 18 O 2 are pulsed. The catalyst exchanges 16 O atoms with the 12 C 18 O and 13 C 18 O 2 pulsed gases simultaneously to the hydrogenation to methane. Ru improves the hydrogenation steps and methane production, which is mainly relevant during the CO + CO 2 co-methanation, and the formation of NiO-CeO 2 solid solution improves the CO x chemisorption and favors the hydrogenation of the surface carbon reaction intermediates. DRIFTS experiments indicated that chemisorption of CO and CO 2 yields the same surface species (bicarbonates and carbonyls), which means that the catalyst dissociates the CO 2 molecule to yield carbonyls and it is also able to oxidize CO with catalyst oxygen to yield bicarbonates. NAP-XPS experiments evidenced that the main redox process during the solo CO 2 methanation occurs at the Ni 2+ -CeO 2 interface, and that ruthenium is highly and homogeneously reduced, keeping Ru 0 stable under reaction conditions. The effect of CO in the oxidation state of the catalyst surface is negligible using pure CO, a CO methanation mixture (CO + H 2 ), and a co-methanation mixture (CO + CO 2 + H 2 ), and the reducing effect of H 2 always prevails. • Onset CH 4 production in co-methanation at 200 °C and maximum CH 4 production at 350 °C • CO has a little negative effect in the methanation of CO 2 during co-methanation • CO 2 affects positively the methanation of CO in comparison to solo CO methanation • The catalyst exchanges 16 O atoms with the 12 C 18 O and 13 C 18 O 2 gases simultaneously to the hydrogenation to methane. • Chemisorption of CO and CO 2 yields the same surface species (bicarbonates and carbonyls)