Study of the effect of Ba loading for catalytic activity of Pt-Ba/Al2O3 model catalysts

A series of Pt-Ba/Al2O3 NOx storage-reduction (NSR) catalysts having different Ba loadings (in the range 0-30%, w/w) have been prepared, characterized and tested in the NOx adsorption-reduction under realistic operating conditions. Accordingly, the role of the Ba loading on the storage of NOx and on their subsequent reduction has been addressed. The results indicated that the presence of Ba negatively affects both the catalyst morphological properties and the Pt dispersion in the samples with Ba loading higher than 10%, while a strong increase of the NOx adsorption capacity is observed. This effect has been associated to the involvement in the NOx storage process of Pt-Ba neighboring species. The analysis of the storage phase also showed that the highest the Ba content, the lowest the NO2 concentration at catalyst saturation: this effect has been related to the decrease in the Pt content of the catalyst following Ba addition to the samples and/or to a possible masking of Pt sites when the Ba coverage approaches and exceeds the monolayer capacity of the support. Concerning the reduction phase, the data pointed out that for all the investigated catalysts the stored NOx species are readily reduced upon H-2 admission: nevertheless, the reduction process resulted very complex and it can lead to nitrogen and/or ammonia depending on the formulation and properties of the catalysts. (C) 2004 Elsevier B.V. All rights reserved.