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 degrees C, the DeNO(x) was 80% while the N-2 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. (C) 2008 Elsevier B.V. All rights reserved.