Optimizing CO2 hydrogenation to methane over CoFe bimetallic catalyst: Experimental and density functional theory studies

Alumina supported cobalt (Co) and cobalt-iron (CoFe) catalysts are active for CO₂ hydrogenation. Different amounts of CO and CH₄ are produced depending on the Co and Fe content. The composition of alumina supported CoFe that maximizes the methane yield for the CO₂ methanation reaction was determined using statistically defined experiments and response surface methodology. The catalyst that maximized the methane yield contained 21.47 wt% Co and 2.53 wt% Fe on this alumina support. X-ray diffraction and temperature programme reduction studies showed that Fe enhances the reducibility of cobalt oxides to metallic cobalt. Furthermore, transmission electron microscopy with elemental analysis showed uniform distribution of Co and Fe as an evidence of CoFe bimetallic alloy formation. DFT calculations were used to study the adsorption of CO₂ and its dissociation into CO and O on Co and CoFe catalysts. A comparison of reaction energy profiles reveals that CO₂ dissociation becomes difficult on the CoFe catalyst containing the optimized composition. The experimentally observed increase in methane formation over CoFe catalyst is probably due to this inhibition of CO formation via CO₂ dissociation.