The formation and evolution of carbonate species in CO oxidation over mono-dispersed Fe on graphene

Abstract

Fe is not only the most abundant metal on the planet but is also the key component of many enzymes in organisms that are capable of catalyzing many chemical conversions. Mono-dispersed Fe atoms on carbonaceous materials are single atom catalysts (SACs) that function like enzymes. To take advantage of the outstanding catalytic performance of Fe-based SACs, we extended a CO oxidation reaction network over mono-dispersed Fe atoms on graphene (FeGR) by first-principles based calculations. FeGR-catalyzed CO oxidation is initiated with a revised Langmuir–Hinshelwood pathway through a CO-assisted scission of the O–O bond in peroxide species (OCOO). We showed that carbonate species (CO₃), which were previously generally considered as a persistent species blocking reaction sites, may form from CO₂ and negatively charged O species. This pathway competes with desorption of CO₂ and reduction of the Fe center with gaseous CO, and it is exothermic and inevitable, especially at low temperatures and with high CO₂ content. Although direct dissociation of CO₃ is demanding on FeGR, further adsorption of CO on Fe in CO₃ is plausible and takes place spontaneously. We then showed that adsorbed CO may react with CO₃, forming a cyclic-carbonate-like species that dissociates easily to CO₂. These findings highlight the reaction condition-dependent formation and evolution of CO₃ as well as its contribution to CO conversion, and it may extend the understanding of the performance of SACs in low temperature CO oxidation.