Promotional mechanisms of activity and SO2 tolerance of Co- or Ni-doped MnOx-CeO2 catalysts for SCR of NOx with NH3 at low temperature

Metals doped MnOx-CeO2 catalysts with a molar ratio of M:Mn:Ce = 1:4:5 (M = Cu, Co, Cr, Ni, Fe, Sn, Mg) were prepared by a co-precipitation method for low-temperature selective catalytic reduction of NOx with NH3 (NOx-NH3-SCR). The results showed Co/Ni doped catalysts had high SCR performance and good tolerance to SO2. Solid solutions with higher surface area and smaller pore size were obtained over Co/Ni doped catalysts. XPS analysis presented Co/Ni doped catalysts had more chemisorbed oxygen, more active sites (Mn3+ and Mn4+) and higher ratio of Ce4+/Ce3+, which were favorable for improving the SCR activity accompanied by the fast-SCR due to a high activity for NO oxidation to NO2. The in-situ DRIFTS revealed NOx-absorbed species over Co/Ni doped catalysts tended to bidentate nitrate without influences by SO2, which further transformed to monodentate nitrate producing new Bronsted acid sites for adsorbing NH4+. While that over MnOx-CeO2 catalyst was more in favor of monodentate nitrite species, significantly inhibiting by SO2. Thermogravimetric analysis (TGA) presented the formations of ammonium sulfate and metal sulfate species over Co/Ni doped catalysts were markedly inhibited. The possible SCR reaction pathways and mechanisms of SO2 tolerance were proposed over Co/Ni doped catalysts contrasted to MnOx-CeO2 catalyst. (c) 2017 Elsevier B.V. All rights reserved.