Study on the Mechanism of Selective Catalytic Reduction of NOx by NH3 over Mn-Doped CoCr2O4

Abstract

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.