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

Abstract

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 NOx 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 NOx storage capacity, regeneration behavior and catalyst performance during lean/rich cycling. The Pt/Ba/CeO2 and Pt/BaO/CeO2/Al2O3 catalysts exhibited higher NOx 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 NOx 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 NOx storage and regeneration behavior), showed the best performance, affording consistently high NOx conversion levels in the temperature range 200–400°C under lean-rich cycling conditions.