Superior indicative and regulative function of Fe doping amount for MnO2 catalyst with an oxygen vacancy in NH3-SCR reaction: A DFT + U study

MnO2 was a promising catalyst in selective catalytic reduction (SCR) reaction at low temperature. In this research, density functional theory calculations were carried out to evaluate the NH3-SCR performance of MnO2 catalyst with an oxygen vacancy (MnO2-x). Results demonstrated that MnO2-x became the thermodynamically most preferred structure after Fe doping, and its structure was kept stable as the doping amount increased. The adsorption behaviors of gaseous molecules on the MnO2-x showed that NH3 and H2O preferred to be adsorbed on the Mn Lewis acid sites, while NO and SO2 preferred O sites. Good SO2-tolerance also exhibited in MnO2-x for its enhanced acidity after Fe doping. Moreover, outstanding linear relationships were emerged in doping ratio with oxygen vacancy formation energy and adsorption energy, suggesting its important role in the balance of redox and acidity properties. Thermodynamic calculation results confirmed the inhibitory effect of temperature on adsorption and found the implication of doping amount to H2O-tolerance. Overall, Fe2-MnO2-x catalyst performed best in our work. Strong indication of doping amount was found by further calculations of four physical quantities. In general, doping amount was an outstanding indicator to reflect the characteristics of catalysts, and can be employed in the future directional catalyst designs.