Impact of secondary phase on Cu-SSZ-13 catalyst SCR durability

Kenneth  Rappé, Pacific Northwest National Laboratory

Cu-SSZ-13 was reported for NH₃-SCR (selective catalytic reduction) of NO_x because of its superior low-temperature activity and high-temperature durability in comparison to its predecessors (e.g., MFI- and BEA-based SCR catalysts). ^[1] The low-temperature activity can be attributed to the redox property of the ion-exchanged Cu species, which is, however, partially transformed into CuO_x clusters (i.e., extra-framework Cu) under hydrothermal conditions. This transformation is the primary pathway of degradation of Cu-SSZ-13 due the activity of extra-framework Cu for non-selective NH₃ oxidation, ^[2] as well as the detrimental impact of the CuO_x clusters on the zeolite structure. ^[3]

The presentation will discuss the introduction of a secondary phase in small portion neighboring the primary zeolitic phase. The interaction between the two phases is characterized by various advanced techniques, e.g. XRD, H₂-TPR, FT-IR and SEM. As shown in Figure 1, the result of that interaction is the inhibition of NH₃ oxidation even after hydrothermal aging at 800 °C resulting in enhanced selectivity at 550 °C from < 50% to ca. 80%. The mechanism will be discussed.

[1] C. H. F. Peden et al., J. Catal. 275, 187, 2010

[2] F. Gao, C. H. F. Peden et al., J. Catal. 331, 25, 2015

[3] D. Mei, F. Gao et al., ACS Catal. 7, 8214, 2018