Mechanism of SO₂ effect on the simultaneous removal of NO_x and propane over bifunctional NiMn₂O₄-CeO₂ catalysts

Nitrogen oxides (NO_x) and volatile organic compounds (VOCs) are the main pollutants in flue gas, and the synergistic removal of NO_x and VOCs in the presence of SO₂ is still a challenge. In this work, the microstructure of NiMn₂O₄-CeO₂ catalysts and the distribution of sulfur-containing substances were studied to reveal the inactivation mechanism of sulfur poisoning. NO_x conversion could reach more than 80 % at 100-250 °C, and C₃H₈ conversion could achieve 90 % at 210 °C in the synergistic reaction on NiMn₂O₄-CeO₂ catalyst, which has dual active sites with propane oxidation and SCR reactions carried out at Mn and Ni sites, respectively. In addition, the intrinsic effect of SO₂ on propane oxidation and NO_x reduction were investigated by decoupling. For propane oxidation, mechanistic studies have shown that manganese sulfate generated by SO₂ hindered further reactions by inhibiting the breaking of the CC bond. For denitration reaction, the generation of sulfate not only resulted in electron transfer from Ni to Mn thereby reducing reaction activity, but also blocked the L-H pathway by inhibiting NO adsorption. This work provides guidelines and strategies to mitigate SO₂ poisoning in the simultaneous removal of NO_x and light alkane.