Effects of cerium and vanadium on the activity and selectivity of MnOx-TiO2 catalyst for low-temperature NH3-SCR

MnO x -TiO 2 , CeO 2 -MnO x -TiO 2 and V 2 O 5 -MnO x -TiO 2 catalysts for low-temperature NH 3 -SCR were prepared by sol-gel method. The results showed that both cerium and vanadium prevented the transformation of anatase TiO 2 to the rutile phase. The addition of vanadium oxide induced the segregation of crystalline Mn 2 O 3 , which contributed little to low-temperature SCR and ammonia oxidation, from the MnO x -TiO 2 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 N 2 selectivity than MnO x -TiO 2 despite the slightly elevated light-off temperature for NO conversion.