CO Activation and Methanation Mechanism on Hexagonal Close-packed Co Catalysts: Effect of Functionals, Carbon Deposition and Surface Structure

CO methanation is an industrially important reaction to remove trace amounts of CO from the hydrogen feed for ammonia production and proton exchange membrane fuel cells. Although the H-assisted CO dissociation mechanism has been extensively elucidated, discrepancies exist in via which C1-oxygenate intermediates the C-O bonds are broken. Using density functional theory calculations and microkinetic study, we show that the theoretical studies can reach an agreement in C-O bond scission via CHO intermediate on Co(0001) at low coverage regime, which mainly controls CO methanation rate. This mechanism is independent of the functionals considered and the presence of graphitic carbon, and likely also pertains to other Co surface structures, including some open facets and step sites. The work provides fundamental insights into the mechanistic discrepancies in CO activation and methanation on hexagonal close-packed Co catalysts, which can potentially be used to design improved CO hydrogenation catalysts.