MnOx-TiO2, CeO2-MnOx-TiO2 and V2O5-MnOx-TiO2 catalysts for low-temperature NH3-SCR were prepared by sol-gel method. The results showed that both cerium and vanadium prevented the transformation ofanatase TiO2 to the mille phase. The addition of vanadium oxide induced the segregation of crystalline Mn2O3, which contributed little to low-temperature SCR and ammonia oxidation, from the MnOx-TiO2 solid solutions. However, the selectivity of the V-containing catalyst was almost 100% due to the decreased ammonia consumption and enhanced adsorption capacity of ammonia on Bronsted acid sites at relatively high temperatures. The electron-donating effect of cerium reduced the Mn^4＋/Mn^3- ratio to some extent, resulting in a decreased activity for ammonia oxidation. This, in combination with the enhanced ammonia adsorption capacity by Ce^n＋ as additional Lewis acid sites, endowed the Ce-doped catalyst a higher N2 selectivity than MnOx-TiO2 despite the slightly elevated light-offtemperamre for NO conversion.
