Insights into samarium doping effects on catalytic activity and SO₂ tolerance of MnFeO_x catalyst for low-temperature NH₃-SCR reaction

The development of catalysts with high NH₃-SCR activity in the presence of SO₂ was urgent for non-electric industries to control NO_x emission at low temperature. Herein, a series of Sm-doping MnFeO_x catalysts were synthesized through a typical PEG-assisted co-precipitation method and applied for low-temperature NH₃-SCR process. SmMnFe-0.1 catalyst significantly broadened the activation temperature window and yielded almost 100% NO conversion from 75 to 200 °C, simultaneously, the NO removal efficiency still maintained at about 90% in the presence of SO₂ and H₂O. The characterization results confirmed that Sm could optimize the dispersity of active components and enlarge the surface area of catalyst. Furthermore, strong interaction among active ions facilitated more oxygen vacancies and accelerated NO oxidizing to NO₂, further cooperating with abundant adsorbed NH₃, leading to cause “Fast SCR” reaction. Both catalysts were dominated by the E-R mechanism despite MnFeO_x catalyst also obeyed the L-H pathway. Particularly, the intense redox circles between Sm and Mn inhibited the electron transferring from SO₂ to Mn ions, and induced Fe species serving as sacrificial sites along with Sm to preferentially react with SO₂, resulting in an excellent SO₂ tolerance, and the possible mechanism model was proposed.