The performance of NOx storage-reduction catalyst containing Fe-compound after thermal aging

The three-way catalytic performance (TWC performance) and the NOx purification activity through storage-reduction (NSR activity) over a Pt/Ba/(Al2O3-CeO2-Fe2O3) catalyst were investigated in comparison with a Pt/Ba/(Al2O3-CeO2) catalyst. Two kinds of reducing agents, C3H6 and COx were used for the measurement of the NSR activity. There was no difference in the TWC performance and the NSR activity between these two fresh catalysts. After thermal aging at 1123 K, however, the aged Pt/Ba/(Al2O3-CeO2-Fe2O3) catalyst was found to show a higher TWC performance and a higher NSR activity in the case of using CO as a reducing agent than did the aged Pt/Ba/(Al2O3-CeO2) catalyst, although there was no difference in the NSR activity in the case of using C3H6 as a reducing agent between these two aged catalysts. Oxygen storage-release capacity measurement showed that an Fe-compound on the aged Pt/Ba/(Al2O3-CeO2-Fe2O3) catalyst acted to store oxygen more effectively than did CeO2. Reaction analysis of a simple binary gas system showed that the Fe-compound weakened the CO self-poisoning for the CO-O-2 reaction and the CO-NOx reaction under reducing conditions, probably by provision of oxygen to the CO from Fe2O3 or/and Fe in a Pt-Fe alloy. The more effective storing of oxygen and the weaker CO self-poisoning for the CO-O-2 reaction and the CO-NOx reaction lead to a higher TWC performance after thermal aging. The weaker CO self-poisoning for the CO-NOx reaction also leads to a greater ability to reduce stored NOx on the catalysts by CO under reducing conditions, causing a higher NSR activity in the case of using CO as a reducing agent after thermal aging. (C) 2004 Elsevier B.V. All rights reserved.