Screening of doped MnOx–CeO2 catalysts for low-temperature NO-SCR

The effect of different dopants including niobium, iron, tungsten and zirconium oxide on the low-temperature activity of MnO_x–CeO₂ catalysts for the selective catalytic reduction (SCR) of NO_x with ammonia has been studied with coated cordierite monoliths in model gas experiments. A clearly higher activity and particularly superior nitrogen selectivity was obtained with the niobium-doped catalyst in comparison with the MnO_x–CeO₂ reference system. At 200 °C, the DeNO_x was 80% while the N₂ selectivity reached more than 96%. In contrast, a decrease of the SCR activity was observed when iron, zirconium or tungsten oxides were added to MnO_x–CeO₂. However, the addition of niobium oxide did not improve the resistance of the catalyst against SO₂ poisoning. A strong and irreversible deactivation occurred after exposure to SO₂.