Ceria promotion on the potassium resistance of MnOx/TiO2 SCR catalysts: an experimental and DFT study.

The deactivation of catalysts by potassium and the promotion of cerium on MnO_x/TiO₂ for selective catalytic reduction (SCR) of NO with NH₃ are investigated by both experiments and DFT calculations. Catalyst poisoning by K is due to the decrease of surface acidity, the loss of reducibility and the improvement of stable nitrite/nitrate species. When the catalyst is modified by CeO₂, SCR activities of both fresh and poisoned catalysts are improved. Cerium provides new Lewis acid sites for NH₃ adsorption, which does not seem to be influenced by K. The Ce 4f orbitals of poisoned surfaces are nearly unaffected, which preserve reducibility of catalyst for NH₃ activation. Stable, inactive nitrite species do not build up and the reactive nitrate species are still present on the surface. These advantages can be attributed to the unique active sites, the [–O–Ce–O–Mn–O–]_units. These active sites induce the movement of alkali metals to assemble together, leaving more surface active sites for SCR reaction.