Effect of CO₂ on the DeNO_x activity of a small pore zeolite copper catalyst for NH₃/SCR

Exposure of CuSSZ13 to CO₂ at temperatures below 300 °C can deactivate its low-temperature deNOx activity during NH₃/SCR, with the severity of deactivation being dependent on reaction temperature. The adsorption of NO on Cu²⁺ ion is inhibited by CO₂ due to its competitive adsorption, while NH₃ adsorption on acidic sites of CuSSZ13 is largely unaffected by CO₂, as evidenced by NO- and NH ₃-TPD in the presence of CO₂. Under O₂-rich conditions, CO₂ forms unidentate carbonates on Cu²⁺ sites suppressing the formation of nitrates, a key reaction intermediate essential for NOx reduction during the NH₃/SCR reaction, as revealed in an in situ FTIR study. Fort NOX: The activity of CuSSZ13 for the selective catalytic reduction of nitrogen oxides by NH₃ at low temperatures below 300 °C gradually decreases in the presence of CO₂. The formation of nitrate species is substantially inhibited by unidentate carbonate species that are formed on the catalyst surface. This is believed to be the primary cause for the CO₂-induced deactivation of CuSSZ13. X_NO=conversion of NO.