Mechanistic insight into the influence of O2 on N2O formation in the selective catalytic reduction of NO with NH3 over Pd/CeO2 catalyst

Abstract

Noble metal nanoparticles supported on metal oxides have been extensively investigated as potential selective catalytic reduction (SCR) catalysts to control NO_X emissions, but suffer from the formation of N₂O. Herein, the N₂O formation mechanism during the NH₃-SCR process over the Pd/CeO₂ catalyst was investigated by both experimental methods and density functional theory calculations. Our results revealed that O₂ greatly affected the pathway for NO reduction, which resulted in a temperature-dependent SCR performance and N₂O formation. At a temperature below 175 °C, fast-SCR was the main reaction route for NO removal, which was attributed to the spontaneous oxidation of NO to NO₂. In the temperature range of 175–250 °C, the activation of NH₃ facilitated the reduction of NO through standard-SCR, which promoted the removal of NO but also induced the formation of N₂O. At a temperature above 250 °C, NH₃ was severely deep oxidized, which induced the formation of excess N₂O in the presence of even a low amount of O₂ of 1 vol%.