Deactivation mechanism of potassium on the V₂O ₅/CeO₂ catalysts for SCR reaction: Acidity, reducibility and adsorbed-NO_x

A series of V₂O₅/CeO₂ catalysts with different potassium loadings were prepared to investigate alkali deactivations for selective catalytic reduction of NO_x with NH₃. An alkali poisoning mechanism could be attributed to surface acidity, reducibility, and NO_x adsorption/desorption behaviors. The detailed factors are as follows: (1) decrease of surface acidity suppresses NH₃ adsorption by strong bonding of alkali to vanadia (major factor); (2) low reducibility prohibits NH₃ activation and NO oxidation by formation bonding of alkali to vanadia and ceria (important factor); (3) active NO_x ^- species at low temperature diminish because of coverage of alkali on the surfaces (minor factor); and (4) stable, inactive nitrate species at high temperature increase by generating new basic sites (important factor).