Study on the Mechanism of Selective Catalytic Reduction of NOₓ by NH₃ over Mn-Doped CoCr₂O₄
2021
Liu, Jianqi | Ren, Xiang | Zhang, Zhengdong | Sun, Nan | Tan, Honglin | Cai, Jinming
In this paper, the first-principles calculation method based on density functional theory is used to calculate the structure of CoCr₂O₄ and Mn-doped Mn₀.₁Co₀.₉Cr₂O₄ low-refractive-index surface (100) and the adsorption model of NH₃ and other molecules. Moreover, the process of the NOₓ removal reaction with NH₃ was studied in detail. The results showed that the adsorption energy of NH₃ and the amount of Mulliken charge transfer increased after Mn doping. The projected density of states indicates that the interactions between the adsorbed molecule and the substrate are stronger. It is worth noting that the doped Mn sites are also favorable sites for catalytic reactions. Based on the calculation results, we know that NH₃ molecules are easily adsorbed on the surface of the catalyst and then dehydrogenated to produce NH₂, NH, and other products. The next major step is the reaction of NH₂ with gaseous NO to form an intermediate product of NH₂NO, which is then decomposed into N₂ and H₂O. However, the route of N₂O as an intermediate is energetically infeasible. Among them, NH₃ dehydrogenation is a rate-determining step, and the activation energy barrier is 1.01 eV. However, under aerobic conditions, the activation energy barrier (0.71 eV) from NH₃ to NH₂ is significantly reduced. In addition, the adsorbed NO reacts with the active O atoms to generate NO₂ on the surface, and NO₂ can undergo a “fast selective catalytic reduction” process. To sum up, doping manganese on the surface of the CoCr₂O₄ catalyst can improve the catalytic activity of denitration, and the Mn₀.₁Co₀.₉Cr₂O₄ catalyst has a good selectivity.
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