NO Catalytic Reduction on Urea-Loaded Ferromanganese Catalysts: Performance, Characterization, and Mechanism

As one of the important atmospheric pollutants, the removal of NO in flue gas at low temperatures is still a severe challenge. Selective catalytic reduction (SCR) with urea is an effective method for NO removal at low temperatures. Herein, through directly loading urea, an Fe-modified Mn-based molecular sieve catalyst with good low-temperature urea-SCR activity was prepared by a stepwise impregnation method. The results show that with a mass ratio of Mn/Fe of 10:0.5 and a calcination temperature of 500 °C, the catalyst loaded with 15 wt % urea had the highest catalytic activity of 98.5% at 250 °C. Online mass spectrometry results show that NH3 formed from the decomposition of urea reacts with NO when the temperature is above 150 °C, while urea directly reacts with NO below 150 °C. The density functional theory calculation demonstrates that the doping of Fe weakens the strength of the Mn–O bond in MnO2, which makes NO easier to combine with lattice oxygen to oxidize into NO2, thereby promoting the whole urea-SCR reaction. This work provides an overall perspective and theoretical support for the design of urea-SCR catalysts over a wide temperature range.