Investingation Of Ageing Strategies For NSR Materials Under Lean-burn Condition

NOx storage reduction (NSR) catalysts with advanced performances have greatly been demanded, in order to meet the needs of strict regulations concerning automotive exhaust emission control and the application of lean-burn engine. As a promising material system, BaO/CeO₂ based NSR catalysts has attracted much attention, while driving forces for the high activity brought about from the Ba/Ce interaction await further investigation.Ba/Ce mixed oxides with molar ratio of 1:1 were prepared by co-precipitation method in order to amplify the interaction among barium and ceria based components in model NSR catalysts under typical lean-burn condition. Series of aged Ba/Ce mixed oxides have been obtained by the ageing stradegies varied in steam and CO₂ concentrations, as well as the ageing time at 800°C. Combinations of XRD, BET, in-situ DRIFTS and TG/DTA characterizations revealed that the formation of BaCeO₃, detrimental for NOx trapping, would be thermodynamically depressed under lean-burn emission containg 10v.t.% steam and 10v.t.% CO₂. Further analysis confirmed that the injection of CO₂ concentration as low as 5v.t.% would be adequate for BaCeO₃ decomposition, whilst existence of steam in ageing atmosphere would non-selectively promote the crystal growth of all particles. However, effect of coexisted 10v.t.% steam and 10v.t.% CO₂ differed from the additivity of the two respectively and performed a synergistic behavior.Series of 2w.t.%Pt/Al2O₃ + 30w.t.%BaO/CeO₂ samples for NSR evaluation have been prepared through different ageing treatments for BaO/CeO₂ components, which are corresponded to the previous aeing strategies. It has been observed that the reponse curves of different gas components varied due to the different state storage materials. BaCeO₃ formation deactivated the NOx adsorption and nitrate formation on barium storage sites. Morphology of barium species also played a significant role in modifying the reponse curves, thus demonstrating the importance of considering the influences of steam and CO₂ in NSR ageing treatment.