The fate of platinum in Pt/Ba/CeO2 and Pt/Ba/Al2O3 catalysts during thermal aging

The behavior of Pt during aging of Pt/Ba/CeO 2 and Pt/Ba/Al 2 O 3 NO x storage-reduction catalysts (NSR) was studied using model catalysts with high and low Pt loadings. Pt composite formation, due to the possible reaction between BaO and platinum oxides, was observed in several cases and was elucidated by a series of analytical techniques, including X-ray diffraction (XRD), thermal analysis (TA), X-ray absorption spectroscopy (XANES, EXAFS), and electron microscopy. During calcination of mechanical mixtures of BaCO 3 and PtO 2 , BaPtO 3 was formed at ca. 600 °C, transforming to BaPtO 2.38 above 800 °C. Investigation of Pt/Ba/CeO 2 and Pt/Ba/Al 2 O 3 model catalysts with high and low Pt loadings revealed that in the case of Pt/Ba/CeO 2 , the mixed oxide BaPtO 3 was formed at relatively low temperature (600–700 °C) in oxidizing atmosphere. Above 800 °C, BaPtO 3 reacted further with BaCeO 3 to form a double perovskite, Ba 2 PtCeO 6 . In contrast, for Pt/Ba/Al 2 O 3 , only the sintering of Pt, with no mixed Pt–Ba oxides, was found. The recovery of the catalytically active metallic Pt species could be achieved in the aged Pt/Ba/CeO 2 catalyst by reduction with hydrogen at relatively low temperature. Finally, investigation of the NO x storage and reduction activity of the fresh, aged, and reduced catalyst confirmed that this treatment is beneficial for catalyst reactivation.