Metal- and Nonmetal-Atom-Modified Graphene as Efficient Catalysts for CO Oxidation Reactions

This study explores the metal Co- and nonmetal-atom-codoped graphene (CoNMx-graphene, x = 1-3 and NM = N, Si, P) as substrates for CO oxidation reactions. By density functional theory calculations, we show the formation mechanism of CoNM3-graphene configurations and their corresponding electronic structures and magnetic properties. On the CoNM3-graphene sheets, the adsorbed O-2 is more stable than that of the CO molecule and serves as the reactive species. Besides, the coadsorption of CO/O-2 (or 2CO) has larger adsorption energies than those of the isolated O-2 and CO molecules, which would be used as an initial state for the CO oxidation reactions. Furthermore, the possible reaction mechanisms for CO oxidation on CoNM3-graphene are investigated in detail. It is found that the Eley-Rideal (ER) mechanism (CO + O-2 -> CO2 + O-ads) on CoN3-graphene sheets has a smaller energy barrier than that of another initial state (CO + O-2 -> CO3), which is energetically more favorable than the Langmuir-Hinshelwood and new termolecular Eley-Rideal mechanisms. Among the CoNM3-graphene sheets, the CO oxidation reactions through the completely ER reactions are more likely to proceed rapidly on CoN3-graphene (<0.3 eV), which would be regarded as a potential graphene-based catalyst with high activity.