Elucidating the Promoting Roles of Ce in CeO2/Cu-SSZ-13 Composite NH3-SCR Catalysts
To elucidate how CeO2 additives enhance the activity and stability of Cu-SSZ-13 SCR catalysts, we investigated two CeO2/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, H2-TPR, NH3-TPD, DRIFTS, DFT and SCR reactions under both steady-state and transient kinetic analysis conditions. Our findings demonstrate that CeO2 promotes low-temperature SCR by forming exchanged, isolated Ce-ions, which enhance Cu-ion coupling efficiency. External surface CeO2 particles can convert NO + O2 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 CeO2 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 CeO2 particles, a benefit that applies irrespective of Cu loading.
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