NOx storage properties of Pt/Ba/Al model catalysts prepared by different methods: Beneficial effects of a N2 pre-treatment before hydrothermal aging

The influence of a pre-treatment at 700 °C, either under a O₂/N₂ mixture or only under N₂, and followed by a hydrothermal aging at 700 °C under wet air, was studied for Pt/Ba/Al NSR model catalysts prepared by different methods: (i) successive impregnation of Ba and Pt, (ii) co-addition of Pt and Ba and (iii) barium precipitation followed by Pt impregnation. The catalysts were evaluated by NOx storage capacity measurements and were characterized by N₂ adsorption, XRD, CO₂-TPD, H₂ chemisorption and H₂-TPR. The pre-treatment under N₂ largely improves the NOx storage performance in the whole studied temperature range (200–400 °C), with or without H₂O and CO₂ in the inlet gas. The better NOx storage properties of the catalysts treated under N₂ before aging are due to: (i) a higher NO oxidation activity (mainly linked to a higher platinum dispersion), (ii) a higher number of NOx storage sites resulting from a higher barium dispersion, and consequently to (iii) a higher Pt-Ba proximity.