Towards rational design of Cu-SSZ-13 catalysts with less N2O formation in NH3-SCR reaction: The effect of Brønsted acid sites
Jianqi Liu, Jinpeng Du, Jingyi Wang, Shichao Han, Yulong Shan, Yan Zhang, Xuanhao Wu, Shan Gao, Yunbo Yu, Zhongbiao Wu, Wenpo Shan, Hong He
Abstract
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 N 2 O is produced as a byproduct when using Cu-SSZ-13 as the NH 3 -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 N 2 O was investigated. Mild thermal treatment was innovatively employed to prepare Cu-SSZ-13 catalysts with different amounts of Brønsted acid sites. EPR, H 2 -TPR, NH 3 -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 N 2 O formation could be achieved. Our results showed that Cu-SSZ-13 with more Brønsted acid sites produced less N 2 O during the NH 3 -SCR reaction. In the low-temperature region, the presence of framework acid sites facilitates the decomposition of the NH 4 NO 3 assisted by NO to form N 2 and H 2 O, reducing the formation of N 2 O. In the high-temperature region, the Brønsted acid sites promote the decomposition of NH 2 NO into N 2 and H 2 O. Meanwhile, the N 2 O-SCR reaction can also be promoted by Brønsted acid sites, thereby decreasing N 2 O 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 N 2 O emissions.