A series of ceria supported lean-burn NOx trap catalysts LaCoO3/K2CO3/CeO2 using perovskite as active component

• Non-platinic LNT catalysts LaCoO3/K2CO3/CeO2 are highly active for lean NOx trap.
• NOx reduction percentage of 97.7% and NOx-to-N2 selectivity of 98.5% are achieved.
• The catalysts also exhibit high stability in 10 NOx storage and reduction cycles.
• NOx trap performance is highly related to the oxidizability of LaCoO3 perovskite.

A series of ceria supported perovskite-based lean-burn NOx trap (LNT) catalysts 10 wt.% LaCoO3/xK2CO3/CeO2 (denoted as L/xK/C, x = 1, 3, 5, 8 wt.%) were prepared by successive impregnation. They display excellent performance for NOx storage and reduction, especially the one with 3% K2CO3. The formation of supported perovskite LaCoO3 on CeO2 is confirmed by XAFS characterization. The results of XPS and O2-TPD reveal that the supported perovskite LaCoO3 contains considerable amounts of surface adsorbed oxygen, which are responsible for NO to NO2 oxidation during NOx storage. The catalyst L/3K/C exhibits fast and complete NOx trapping in lean condition, showing little NOx leak for long time, over which a particularly high NOx reduction percentage (97.7%) and NOx to N2 selectivity (98.5%) are simultaneously achieved in cyclic lean/rich atmospheres. FT-IR and CO2-TPD results demonstrate the diversity of K species including –OK groups, dispersed surface K2CO3 species and bulk or bulk-like K2CO3 species. The dispersion and states of K species show big impact on NOx storage pathways. In situ DRIFTS results indicate that on L/xK/C NOx is stored as diverse nitrates without evident nitrite species detected during NOx adsorption and storage, which further verifies their excellent oxidation ability.