Abstract:The modified mechanism of iron-based OC doped by Co were studied. Three microscopic Co-doped models of iron-based OC were established based on density functional theory (DFT) to research the changes of electronic structure and reaction characteristics of doping model surfaces. Firstly, the periodic slab models of Fe₂O₃(104) were built using CASTEP, one of the module of Material Studio software; Secondly, the Co-doped models (Co-Fe₂O₃(104)) were built via replacing different coordinate Fe atoms (Fe_5f, Fe_6f and Fe_7f) with Co atoms; Finally, the surface energy, binding energy and density of state (DOS) of all models were calculated. Moreover, the bond length, angle and distance of doping sites atoms with other atoms were calculated. Besides the isothermal adsorption features of CO on Fe₂O₃(104) and Co-Fe₂O₃(104) were detected. CO molecules were selected as a probe to test the oxidation reaction properties of Co-doped and pure Fe₂O₃(104) models and get the information of the reaction path, transition state and reaction activation energy. The stability order of Co-doped models obtained after geometric optimization as follows: Co_5f-Fe₂O₃(104) > Co_6f-Fe₂O₃(104) > Co_7f-Fe₂O₃(104), corresponding to the binding energy is -0.399 eV, -0.215 eV and 0.487 eV (1 eV=96.485 3 kJ/mol), respectively. The doping of Co at Fe_5f and Fe_6f sites were exothermic process, and released much more energy at Fe_5f atom site. However, the doping of Fe_7f atoms was an endothermic reaction. Co doping changed the average bond length (L_O-M) of adjacent O atoms at doping site, where the M represents Fe or Co atoms. Especially, the L_{O3 f-M} increased 0.004 4 nm after Co atom replacing Fe_7f atom. The total state density (DOS) of the models all moved towards Fermi level (0 eV), and the delocalization was enhanced in the range of -8 eV～0 eV energy, and the filling state energy of the Co_5f-Fe₂O₃(104) model system near Fermi level was higher than that of other models. The isothermal adsorption of CO indicated that Co doping improved the adsorption amount of CO on the surface of the model. It shown two ways of adsorption: the peak near -2.0 eV was the adsorption peak of CO formed at the alkaline site on the surface of the model, and the peak near -0.75 eV was formed at the non-alkaline site. The adsorption energy of CO on the surface of Co_5f-Fe₂O₃(104) was largest (-0.851 eV), while the adsorption on the surface of Co_7f-Fe₂O₃(104) required additional energy (0.386 eV). The bond length (L_CO) of Co_6f and Co_7f doped sites were increased by 0.000 4 nm and 0.001 1 nm compared with the pure surface model, indicating that Co-doped surfaces had a greater activation effect on CO molecules. The transition state analysis illustrated that the reaction activation energy of CO oxidized to CO₂ at Co-doped surfaces decreased significantly. It also shown that the activation energy of CO on the surface of Co_5f-Fe₂O₃(104) was the lowest, decreased 0.518 eV (49.974 kJ/mol) less than that on the surface of Fe₂O₃(104), and the corresponding reaction energy increased by 0.445 eV. It is indicated that the different bonding structures in their oxides of Co and Fe lead to an increase in suspended bonds and surface energy on the doped model surface, and a shift in state density toward Fermi level, which improved the surface activity of Fe₂O₃(104). In addition, Co doping at the low coordination of Fe atom sites was more conducive to reducing the reaction activation energy of oxidized CO. Therefore, it was feasible to improve the reactivity of iron-base OC by doping metal Co, and its modification effect was closely related to the characteristics of the components and the doping mode.