NO_x storage and reduction properties of model ceria-based lean NO_x trap catalysts

Three kinds of model ceria-containing LNT catalysts, corresponding to Pt/Ba/CeO₂, Pt/CeO₂/Al₂O₃ and Pt/BaO/CeO₂/Al₂O₃, were prepared for comparison with a standard LNT catalyst of the Pt/BaO/Al₂O₃ type. In these catalysts ceria functioned as a NO_x storage component and/or a support material. The influence of ceria on the microstructure of the catalysts was investigated, in addition to the effect on NO_x storage capacity, regeneration behavior and catalyst performance during lean/rich cycling. The Pt/Ba/CeO₂ and Pt/BaO/CeO₂/Al₂O₃ catalysts exhibited higher NO_x storage capacity at 200 and 300°C relative to the Pt/BaO/Al₂O₃ catalyst, although the latter displayed better storage capacity at 400°C. Catalyst regeneration behavior at low temperature was also improved by the presence of ceria, as reflected by TPR measurements. These factors contributed to the superior NO_x storage-reduction performance exhibited by the Pt/Ba/CeO₂ and Pt/BaO/CeO₂/Al₂O₃ catalysts under cycling conditions in the temperature range 200-300°C. Overall, Pt/BaO/CeO₂/Al₂O₃ (which displayed well balanced NO_x storage and regeneration behavior), showed the best performance, affording consistently high NO_x conversion levels in the temperature range 200-400°C under lean-rich cycling conditions.