La ions-enhanced NH₃-SCR performance over Cu-SSZ-13 catalysts

Lanthanum (La) ions are generally recognized to cause a decline of the catalytic performance for Cu-SSZ-13 zeolite in the selective catalytic reduction of NO_x with NH₃ (NH₃-SCR). Herein, we demonstrate that the NH₃-SCR performance and hydrothermal stability of Cu-La-SSZ-13 zeolites can be enhanced with the incorporation of a small amount of La ions. The incorporation of La ions into SSZ-13 favors more Z₂Cu²⁺ ions at six-membered rings (6MRs), which results in higher hydrothermal stability of Cu-La-SSZ-13 than that of Cu-SSZ-13. The NO conversion of Cu-La-SSZ-13 achieves 5%–10% higher than that of Cu-SSZ-13 at the temperature range of 400–550 °C after hydrothermal ageing. While introducing excess amount of La ions in SSZ-13 may cause the formation of inactive CuO_x, leading to the decrease of catalytic activity and hydrothermal stability. Notably, the low-temperature activity of Cu-SSZ-13 with a low Cu content (≤ 2 wt.%) can be boosted by the introduction of La ions, which is largely due to the improved redox ability of Cu active sites modified by La ions. Density functional theory (DFT) calculations indicate that La ions prefer to locate at eight-membered rings (8MRs) and thus promoting the formation of more Z₂Cu²⁺ ions. Meanwhile, the existence of La ions in SSZ-13 inhibits the dealumination process and the transformation from Z₂Cu²⁺ to CuO_x, resulting in its enhanced hydrothermal stability. The present work sheds a new insight into the regulation of secondary metal cations for promoting high NH₃-SCR performance over Cu-SSZ-13 zeolite catalysts.