Effect of Mn and Ce oxides on low-temperature NH₃-SCR performance over blast furnace slag-derived zeolite X supported catalysts

Several Mn and/or Ce oxides on blast furnace slag-derived (BFS-derived) zeolite X catalysts were prepared to investigate their low-temperature NH₃-SCR performance. It was found that Mn-Ce/X catalyst had the highest NO conversion of nearly 98% at 250 °C and excellent N₂ selectivity of nearly 100% during 75–175 °C. The co-addition of Ce and Mn could inhabit the growth of crystal grains, resulting in the increase of surface area and the generation of Mn-Ce double active sites. Besides, high concentration of Mn⁴⁺ and Mn³⁺ could promote oxidation of NO to NO₂ accelerating the “fast-SCR” reaction and high concentration of Ce⁴⁺ could form more oxygen vacancies on Mn-Ce/X catalyst. In addition, the Mn-Ce/X catalyst had large acid amount and high redox ability owing to the co-existed Mn-Ce double active sites on zeolite catalyst and the co-effect of Mn-Ce oxides and zeolite X. Furthermore, the decomposition of NH₄NO₃ species on Mn/X catalyst led to the low N₂ selectivity at higher temperature. While NH₂NO and NH₄NO₂ intermediates on Mn-Ce/X catalyst played a vital part in NH₃-SCR reaction and prevented the generation of N₂O, and Mn-Ce/X catalyst provided more Mn-Ce active sites for the reaction between NO₃^– species and gaseous NO, accelerating SCR catalytic reaction.