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.