Efficient NOx Reduction against Alkali Poisoning over a Self-Protection Armor by Fabricating Surface Ce2(SO4)3 Species: Comparison to Commercial Vanadia Catalysts.

Abstract

Resolving severe deactivation by alkali metals for selective catalytic reduction of NOx with NH3 (NH3-SCR) is challenging. Herein, surface Ce2(SO4)3 species as a self-protection armor originally exhibited antipoisoning of potassium over ceria-based catalysts. The self-protection armor was also effective for other alkali (Na), alkali-earth (Ca), and heavy (Pb) metals, considerably resolving the deactivation of ceria-based SCR catalysts in practical applications. The catalytic activity tests indicated that the presence of ∼0.8 wt % potassium did not deactivate sulfated CeO2 catalysts, yet commercial V2O5-WO3/TiO2 catalysts almost lost the NOx conversions. Potassium preferably bonded with surface sulfates to form K2SO4 accompanied with the majority of surface Ce2(SO4)3 over sulfated CeO2 catalysts, but preferably coupled with active vanadia to generate inactive KVO3 species over V2O5-WO3/TiO2 catalysts. Such an active Ce2(SO4)3 species facilitated the adsorption and reactivity of NH3 and NOx, enabling ceria catalysts to maintain high catalytic efficiency in the presence of potassium. Conversely, the introduction of potassium into V2O5-WO3/TiO2 catalysts caused a considerable loss of surface acidity, hindering catalyst reactivity during the SCR reaction. The self-protection armor of Ce2(SO4)3 species may open a promising pathway to develop efficient ceria-based SCR catalysts with strong antipoisoning ability.