Abstract
The effects of CO 2 and steam on the morphological and chemical properties of Ba/Ce-based NO x storage reduction (NSR) catalysts during the aging were investigated. At 800 °C, BaCeO 3 formation was prevented by a CO 2 concentration as low as 5%, which shows little effect on suppressing BaAl 2O 4 and BaZrO 3 formation. CO 2 protects hexagonal BaCO 3, BaO 2, and CeO 2, to form BaCeO 3, by increasing one time higher activation energy for decarbonation, and maintaining orthorhombic BaCO 3 as the most stable storage component. Steam accelerates the particle aggregations, but it does not determine the above chemical equilibrium. In NSR reactions, although BaCeO 3 formation can be excluded in an atmosphere containing CO 2, the nitrite/nitrate bonding stabilization and the complete NO x reduction are hindered by the highly crystallized materials (induced by higher CO 2 and/or steam concentrations during aging). Particle aggregation is a major factor responsible for the deactivation of the aged Ba/Ce-based NSR catalysts.
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