Role of Pt-precursor on the performance of Pt/BaCO3Al2O3-NOx storage catalysts

The influence of the choice of platinum precursor on the catalytic performance of Pt/BaCO3/Al2O3 NO, storage catalysts was studied. The precursors used in the preparation of the catalysts were: (i) hexachloroplatinic acid [H2Pt(Cl)(6)], (ii) tetraammineplatinum hydroxide [Pt(NH3)(4)(OH)(2)], (iii) diammineplatinum nitrite [Pt(NH3)(2)(NO2)(2)] and (iv) platinum nitrate [Pt(NO3)(2)]. The catalytic activity of the prepared catalysts was tested for continuous lean NOx reduction with C3H6, NOx storage and reduction, and NO2 dissociation in a flow reactor. The reactor experiments show that the sample prepared using platinum nitrate is the most active catalyst followed by the catalyst prepared from tetraammineplatinum hydroxide. The catalyst prepared from hexachloroplatinic acid is more active for continuous NOx reduction, and NO2 storage and reduction than the catalyst prepared from diammineplatinum nitrite, but deactivates faster during NO2 dissociation than the catalyst prepared using diammineplatinum nitrite. In order to be able to predict mechanisms for the interaction between the platinum precursors and the BaCO3/Al2O3 surface during the platinum impregnation, powder samples of gamma-Al2O3, BaCO3 and BaCO3 precipitated on gamma-Al2O3 were studied using FTIR and zeta potential measurements. Additionally, XRD measurements were performed to verify the transformation of the barium precursor to BaCO3. The results from these studies show that up to 18% BaO content, the BaCO3/Al2O3 surfaces contain domains of both BaCO3 and Al2O3. (C) 2004 Elsevier B.V. All rights reserved.