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•The impact of Fe and K species in Ni catalysts for CO and CO2 methanation is analysed.•In-situ DRIFTS spectroscopy evidenced similar reaction intermediates for all systems.•CO2 methanation rates relate to the generation of lineal carbonyl intermediates.•The addition of K to Ni-Fe catalysts resulted in depleted CO methanation rates.
Promoting the performance of catalytic systems by incorporating small amount ofalkali has been proved effective for several reactions whilst controversial outcomes are reported for the synthetic natural gas production. This work studies a series of Ni catalystsfor CO2and CO methanation reactions.In-situDRIFTS spectroscopy evidenced similar reaction intermediates for all evaluated systems and it is proposed a reaction mechanism based on: i) formatedecompositionand ii) hydrogenation of lineal carbonyl species to methane. Compared to bare Ni, the enhanced CO2methanation rates attained by NiFe/Al and NiFeK/Al systems are associated to promotedformates decomposition into lineal carbonyl species. Also forCO methanation, the differences in the catalysts’ performances were associated to the relative concentration of lineal carbonyl species. Under CO methanation conditions and opposing the CO2methanation results where the incorporation of K delivered promoted catalytic behaviours, worsened CO methanation rates were discerned for the NiFeK/Al system.