NOx storage and reduction properties of model ceria-based lean NOx 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 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 degrees C relative to the Pt/BaO/Al2O3 catalyst, although the latter displayed better storage capacity at 400 degrees 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 degrees 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 degrees C under lean-rich cycling conditions. (C) 2012 Elsevier BM. All rights reserved.