Theoretical Investigation On CO And Benzene Oxidation Over Fe Atoms Mono-dispersed On Graphene

Fe is not only the most abundant metals on the planet,but also the key component of many enzymes in organism which are capable to catalyze many chemical conversions.Mono-dispersed iron atoms on carbonaceous materials are a kind of mono-atomic catalyst with enzymatic catalytic performance,which can efficiently catalyze various chemical reactions.For the same catalyst,the catalytic performance may be different under different reaction conditions.Similar type of catalyst under different gradient structures may also result in different catalytic performance.In view of the above two situations,the following work has been carried out in this paper.The CO oxidation reaction network catalyzed by mono-dispersed Fe atoms on graphene（Fe GR）was studied by first-principles based calculations.CO oxidation was catalyzed by Fe GR initially through revised Langmuir–Hinshelwood pathway,which may assist the scission of O-O bond in peroxide species（OCOO）through CO.We showed that carbonate species（CO₃）,which was conventionally considered as persistence species blocking reaction sites before,may come from CO₂ and the remnant O.This pathway is exothermic and inevitable in thermodynamics,and it competes with desorption of CO₂ and reduction of Fe center with gaseous CO,especially at low temperatures and with high CO₂ content.Though direct dissociation of CO₃ is demanding,further CO would be adsorbed on Fe in the CO₃ is plausibly and spontaneously.The adsorbed CO may react with CO₃,forming a cyclic-carbonate-like species that dissociates easily to CO₂.The finding highlights the influence of reaction conditions to the formation and evolution of CO₃,as well as its contribution to CO conversion,which may extend the understanding in the performance of SACs in low temperature CO oxidation.The mechanism of benzene oxidation catalyzed by stabilized Fe atom in N-doped graphene（Fe N₄）has also been studied through the first principles method.The influence of possible coordination structure on Fe monatomic catalyst was also considered.The reaction energy barrier of each step of Fe N₄ indicates that the rate-controlling step is that benzene molecules are gradually approaching to O=Fe=O species.The energy barriers of Fe N₄,Fe N₃and Fe N₂ are 0.75 e V,0.83 e V and 0.84 e V,respectively,which indicates that the benzene oxidation activity of monatomic Fe catalyst gradually decreased after the coordination N atom was replaced by one or two C atoms.The increase of N coordination number is beneficial to the generation and reaction of intermediate O=Fe=O species,thus improving the oxidation activity of benzene.These findings will help to understand the mechanism of benzene oxidation catalyzed by mono-dispersed Fe atoms on graphene and demonstrate that the same catalytic properties change with the change of coordination environment.