NiFe and CoFe nanocatalysts supported on highly dispersed alumina-silica: Structure, surface properties, and...

The hydrogenation of CO₂ to CH₄ has gained considerable interest in terms of sustainable energy and environmental mitigation. In this regard, the present work aims to investigate the adsorptive concentration and CO₂ methanation performance over CoFe and NiFe bimetallic catalysts supported on fumed alumina-silica SA96 support at 170-450 °C and under atmospheric pressure. The catalysts were prepared by wet impregnation method, subjected to calcination and further reduced with hydrogen, and their performance in CO₂ methanation was investigated in a hydrogen-rich 2%CO₂-55%H₂-43%He gas mixture. In this study, we describe the crystal and mesoporous structures of the prepared catalysts by in-situ XRD and ex-situ nitrogen adsorption, evaluate the NiFe and CoFe metal surface states before and after catalysis by XPS, visualize the surface morphology by SEM, estimate the catalytic activity by gas chromatography, and investigate the adsorbed surface species, showing the presence of *HCOO/*HCO and *CO intermediates, determine two possible pathways of CH₄ formation on the studied catalysts by temperature-programmed desorption mass spectrometry, and correlate the structural and surface properties with high CO₂ conversions up to 100% and methanation selectivities up to 72%. The latter is related to changes in the elemental chemical states and surface composition of CoFe and NiFe nanocatalysts induced by treatment under reaction conditions, and the surface reconstruction during catalysis transfers the part of active 3d transition metals into the pores of the SA96 support. Our thorough characterization study with complementary techniques allowed us to conclude that this high activity is related to the formation of catalytically active Ni/Ni₃Fe and Co/CoFeO_x nanoscale crystallites under H₂ reduction and their maintenance under CO₂ methanation conditions. The successfully applied combination of CO₂ chemisorption and thermodesorption techniques demonstrates the ability to adsorb the CO₂ molecules by supported NiFe and CoFe nanocatalysts and the pure alumina-silica SA96 support.