Towards rational design of Cu-SSZ-13 catalysts with less N2O formation in NH3-SCR reaction: The effect of Brønsted acid sites

Ammonia Selective Catalytic Reduction (NHs-SCR) technology has been employed to eliminate NO_x from diesel engine exhaust, with Cu-SSZ-13 serving as the commercial catalyst. The greenhouse gas N₂O is produced as a byproduct when using Cu-SSZ-13 as the NH₃-SCR catalyst. To achieve synergistic control of pollutants and greenhouse gases in diesel engine exhaust, rational design of Cu-SSZ-13 catalysts is required. In this study, the effect of Brønsted acid sites in Cu-SSZ-13 catalysts on the formation of N₂O was investigated. Mild thermal treatment was innovatively employed to prepare Cu-SSZ-13 catalysts with different amounts of Brønsted acid sites. EPR, H₂-TPR, NH₃-TPD, NMR were utilized to determine that the Brønsted acid sites were modified while the Cu species remained unchanged. Thereby an accurate assessment of the influence of Brønsted acid sites on N₂O formation could be achieved. Our results showed that Cu-SSZ-13 with more Brønsted acid sites produced less N₂O during the NH₃-SCR reaction. In the low-temperature region, the presence of framework acid sites facilitates the decomposition of the NH₄NO₃ assisted by NO to form N₂ and H₂O, reducing the formation of N₂O. In the high-temperature region, the Brønsted acid sites promote the decomposition of NH₂NO into N₂ and H₂O. Meanwhile, the N₂O-SCR reaction can also be promoted by Brønsted acid sites, thereby decreasing N₂O emissions. This study suggests that in the future design and synthesis of Cu-SSZ-13 zeolites, attention should be paid to creating more Brønsted acid sites in Cu-SSZ-13 to reduce N₂O emissions.