Influence of ceria loading on the NOx storage and reduction performance of model Pt-Ba/Al2O3 NSR catalyst

摘要

The influence of the addition of ceria on the NOx storage and reduction behaviour of model Ba-Pt/Al2O3 catalyst has been studied. Several 15%Ba-1.5%Pt-Ce/Al2O3 catalysts were prepared with increasing ceria loading, from 0 to 20.3 wt.%. The prepared catalysts were characterized in terms of specific surface area (N-2 adsorption-desorption at -196 degrees C), platinum dispersion (H-2-chemisorption), reducibility (H-2-TPR) and acidity (NH3 adsorption-desorption experiments). The storage of NOx was followed by FTIR showing that low Ce loaded catalyst, i.e. Ba-Pt-4.5%Ce/Al2O3, was able to promote nitrate formation readily at low temperature (200 degrees C), while nitrites were predominant for model Ba-Pt/Al2O3 and high loaded Ce catalyst, i.e. Ba-Pt-15.4%Ce/Al2O3. Ammonia oxidation experiments confirmed that Ce was able to oxidize NH3 into N-2, the reaction extent increasing with temperature and Ce loading. The 4.5% Ce loaded catalyst achieved the highest NOx storage and reduction efficiency. The NOx storage capacity was increased with respect to the model Ba-Pt/Al2O3 catalyst due to the enhancement of NO oxidation conversion and due to the ability of Ce to take part as NOx storage material. On the other hand, NH3 emissions were reduced due to the participation of Ce in the oxidation of NH3 to N-2. In contrast, high Ce loaded catalyst penalized NOx storage capacity and increased NH3 selectivity. The limited NOx storage capacity was in concordance with the low NO to NO2 conversion, which was attributed to a possible migration of CeO2 to form an atomic layer over Pt which ultimately covers and blocks its catalytic activity. The increased NH3 emission was attributed to a lower acidity of the doped catalyst which reduced the NH3 adsorption capacity. (C) 2014 Elsevier B.V. All rights reserved.