High Coverage CO Adsorption on Fe6O6 Cluster Using GGA + U

The highest oxidation state observed in graphene-supported sub-nanometer iron oxide clusters

Size-selected iron oxide nanoclusters are outstanding candidates for technological-oriented applications due to their high efficiency-to-cost ratio. However, despite many theoretical studies, experimental works on their oxidation mechanism are still limited to gas-phase clusters. Herein we investigate the oxidation of graphene-supported size-selected Fe_n clusters by means of high-resolution X-ray Photoelectron Spectroscopy. We show a dependency of the core electron Fe 2p_3/2 binding energy of metallic and oxidized clusters on the cluster size. Binding energies are also linked to chemical reactivity through the asymmetry parameter which is related to electron density of states at the Fermi energy. Upon oxidation, iron atoms in clusters reach the oxidation state Fe(II) and the absence of other oxidation states indicates a Fe-to-O ratio close to 1:1, in agreement with previous theoretical calculations and gas-phase experiments. Such knowledge can provide a basis for a better understanding of the behavior of iron oxide nanoclusters as supported catalysts.

DFT study of the fouling deposition process in the steam generator by simulating the adsorption of Fe2+ on Fe3O4 (0 0 1)

In order to reveal the fouling problem on the outer surface of the steam generator (SG) tube in the secondary circuit condition of pressurized water reactor (PWR) nuclear power plant, based on the density functional theory (DFT) method, the Cambridge sequential total energy program package (CASTEP) is used to simulate seven kinds of highly symmetric adsorption structure models of termination with tetrahedral Fe (A termination) and termination with octahedral Fe (B termination) on Fe₃O₄ (0 0 1) surface. The adsorption energies and stable adsorption conformations are calculated. The results show that the most stable adsorption structures of the Fe²⁺/Fe₃O₄ (0 0 1) configurations are Fe²⁺ above Fe-O bond of B layer termination (Fe₃O₄(001) A-b). During the adsorption, the Fe-Fe, Fe-O bond length, and Fe-Fe-O bond angle of (0 0 1) surface change, and the atomic positions parallel and perpendicular to (0 0 1) surface change correspondingly. The change happened to the surface layer is the most drastic one. The calculation of charge population, the density of states (DOS), and electron local function of Fe²⁺/Fe₃O₄ (0 0 1) optimal adsorption configuration show that there is electron transfer between Fe²⁺ and Fe₃O₄ (0 0 1), and the adsorption type is chemisorption. Among them, Fe (Fe²⁺)-Fe (Fe₃O₄) forms a metal bond, and Fe (Fe²⁺)-O (Fe₃O₄) forms the ionic bond. The results illustrate the interaction between free Fe²⁺ and Fe₃O₄ is the reason of the nucleation and agglomeration of Fe₃O₄ scale and it provides the foundation for the further research on Fe₃O₄ scale deposition.