The influence of the choice of platinum precursor on the catalytic performance of Pt/BaCO 3 /Al 2 O 3 NO x storage catalysts was studied. The precursors used in the preparation of the catalysts were: (i) hexachloroplatinic acid [H 2 Pt(Cl) 6 ], (ii) tetraammineplatinum hydroxide [Pt(NH 3 ) 4 (OH) 2 ], (iii) diammineplatinum nitrite [Pt(NH 3 ) 2 (NO 2 ) 2 ] and (iv) platinum nitrate [Pt(NO 3 ) 2 ]. The catalytic activity of the prepared catalysts was tested for continuous lean NO x reduction with C 3 H 6 , NO x storage and reduction, and NO 2 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 NO x reduction, and NO x storage and reduction than the catalyst prepared from diammineplatinum nitrite, but deactivates faster during NO 2 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 BaCO 3 /Al 2 O 3 surface during the platinum impregnation, powder samples of ␥-Al 2 O 3 , BaCO 3 and BaCO 3 precipitated on ␥-Al 2 O 3 were studied using FTIR and zeta potential measurements. Additionally, XRD measurements were performed to verify the transformation of the barium precursor to BaCO 3 . The results from these studies show that up to 18% BaO content, the BaCO 3 /Al 2 O 3 surfaces contain domains of both BaCO 3 and Al 2 O 3 .