Towards rational design of Cu-SSZ-13 catalysts with less NO formation in NH-SCR reaction: The effect of Brønsted acid sites.

Ammonia Selective Catalytic Reduction (NHs-SCR) technology has been employed to eliminate NO from diesel engine exhaust, with Cu-SSZ-13 serving as the commercial catalyst. The greenhouse gas NO is produced as a byproduct when using Cu-SSZ-13 as the NH-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 NO was investigated. Mild thermal treatment was innovatively employed to prepare Cu-SSZ-13 catalysts with different amounts of Brønsted acid sites. EPR, H-TPR, NH-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 NO formation could be achieved. Our results showed that Cu-SSZ-13 with more Brønsted acid sites produced less NO during the NH-SCR reaction. In the low-temperature region, the presence of framework acid sites facilitates the decomposition of the NHNO assisted by NO to form N and HO, reducing the formation of NO. In the high-temperature region, the Brønsted acid sites promote the decomposition of NHNO into N and HO. Meanwhile, the NO-SCR reaction can also be promoted by Brønsted acid sites, thereby decreasing NO 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 NO emissions.