Enhanced low-temperature selective catalytic reduction (SCR) activity and H2O and SO2 resistance of flower-like SmMnOx and SmMnOx-rGO catalysts

Reed flower-like SmMnO_x and cauliflower-like SmMnO_x-rGO catalysts were successfully synthesized by a coprecipitation-coupled solvothermal method for selective catalytic reduction (SCR) of NO_x. The NO_x conversion of the two catalysts is more than 90% in the temperature range of 75–200 °C, and the N₂ selectivity of SmMnO_x-rGO is above 90%. Moreover, both of them exhibit more than 62% of resistance to H₂O and SO₂ at a very low temperature of 100 °C, much superior than the fluffy spherical SmMnO_x prepared by coprecipitation method. The strong synergy between Mn and Sm endowed by the flower-like structure contributes to a low degree of crystallization, a high ratio of (Mn³⁺+Mn⁴⁺)/Mn, more chemisorbed oxygen species, strong redox ability, and more Lewis acid sites, hence effectively enhancing low-temperature SCR activity and resistance to H₂O and SO_2. In addition, the decreased ratio of Mn⁴⁺/Mn after rGO doping hinders the side reaction of NH₃ oxidation, thus enhancing the N₂ selectivity of rGO-doped SmMnO_x catalyst.