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 MnOx–CeO2 catalysts for the selective catalytic reduction (SCR) of NOx 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 MnOx–CeO2 reference system. At 200°C, the DeNOx 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 MnOx–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.