Elucidating the Promoting Roles of Ce in CeO<sub>2</sub>/Cu-SSZ-13 Composite NH<sub>3</sub>-SCR Catalysts
Zhiying Liu, Meiqing Shen, Shuhuan Wang, Chunjuan Zhang, Jun Wang, Wei Li, Feng Gao
Abstract
To elucidate how CeO 2 additives enhance the activity and stability of Cu-SSZ-13 SCR catalysts, we investigated two CeO 2 /Cu-SSZ-13 composite catalysts with Cu loadings of 1.0 and 2.5 wt %. These catalysts were characterized using an array of techniques, including XRD, SEM, TEM, NMR, H 2 -TPR, NH 3 -TPD, DRIFTS, DFT and SCR reactions under both steady-state and transient kinetic analysis conditions. Our findings demonstrate that CeO 2 promotes low-temperature SCR by forming exchanged, isolated Ce-ions, which enhance Cu-ion coupling efficiency. External surface CeO 2 particles can convert NO + O 2 to surface nitrates, but these species primarily act as spectators below ∼250 °C, and do not contribute to the enhancement of low-temperature SCR activity. In contrast, these surface CeO 2 particles can synergizes with Brønsted acid sites (BAS) to elevate high-temperature SCR activity. Furthermore, hydrothermal stability and sulfur resistance are improved by the presence of external surface CeO 2 particles, a benefit that applies irrespective of Cu loading.