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The catalytic NO removal efficiencies of MnFeOx/SiO2 catalysts with different Fe/Si were compared and studied. The reaction pathway analysis of NH3-SCR on the surface of MnFeOx/SiO2 catalyst was performed based on DFT calculations. The experimental results of catalytic activity show that the addition of an appropriate amount of iron oxide has significant improvement for the NO conversion from 240 °C to 330 °C and the N2 selectivity from 150 °C to 330 °C. The XRD test also shows that the addition of iron oxide can greatly improve the dispersion of MnO2. In addition, DFT calculations indicate that the main process of N2 formation is the NH2NO decomposition and N-NO reaction. The N-NO reaction to form N2 is a unique reaction pathway possessed by MnFeOx/SiO2, which is the main reason for the high NO conversion and good N2 selectivity of MnFeOx/SiO2 catalyst and shows good synergy between manganese oxide and iron oxide.

Based on the density functional theory, the adsorption processes of NH3, and NO and O2 on the Mn active sites of MnOx/SiO2 β-cristobalite (101) surface were simulated. The results show that NH3, NO and O2 can be effectively adsorbed on the Mn active sites of both MnO2/SiO2 β-cristobalite (101) and Mn2O3/SiO2 β-cristobalite (101) surface. The adsorption characteristics of the two catalysts are different. The adsorption energy of NH3 molecule on the MnO2/SiO2 β-cristobalite (101) surface is much higher than that on the Mn active sites of Mn2O3/SiO2 β-cristobalite (101) surface. The NO molecule and the O2 molecule are a little easier to be adsorbed on the Mn active sites of Mn2O3/SiO2 β-cristobalite (101) surface. The large difference of NH3 adsorption energy between the two catalysts becomes one of the main reasons why MnO2/SiO2 has better catalytic activity than Mn2O3/SiO2. Furthermore, the high adsorption energy of NH3 on MnO2/SiO2 surface proves that SiO2 is an excellent carrier and MnO2/SiO2 catalyst is an outstanding NH3-SCR catalyst at low temperature.

The low-temperature catalytic NO removal efficiencies of catalysts with two different manganese precursors, manganese acetate (αMA catalyst) and manganese nitrate (αMN catalyst), were compared and studied. The NH3-SCR of NO tests using these catalysts were carried out in a self-made reaction device to measure the catalytic activity of the catalysts. Moreover, the reaction pathway analysis of NH3-SCR of NO on the surface of MnO2/SiO2 catalyst and Mn2O3/SiO2 catalyst were performed based on DFT calculations individually. The experimental results show that the NO conversion of αMN catalyst is higher than the αMA catalyst at low temperature (