The reduction of NOx from Diesel Engines or Lean-burn Gasoline Engines is a major issue in automotive catalysis. Over the last several years, many solutions to remove NOx under lean operating conditions have been considered. Attention is now focused on two main technologies: (i) Selective Catalytic Reduction using ammonia as reductant (urea SCR) and (ii) NOx-Storage Catalyst (NSC).
This paper deals with materials for NOx storage catalysts. NSC catalysts show high efficiency as fresh, but their durability is low due to a fast deactivation of the active sites [1,3]. This issue relates to a drastic sintering of the materials after ageing, especially during the regeneration and the desulfation [3, 4 and 5]. Moreover, the current materials are sensitive to SOx poisoning [1,3,4].
In this paper, ceria based oxides have been examined as NOx-storage materials and Pt carriers as well. These oxides contain high ceria loading and are thermally stable up to 900°C. The corresponding aged Pt model catalysts show high NOx-Storage capacity at low temperature from 200°C to 300°C, even after hydrothermal ageing at 700°C and sulfation treatments.
The homogeneously dispersion of these oxides on Ba or La stabilized alumina with a Rhodia proprietary process, leads to a new generation of functionalized alumina with very high NOx storage capacity on the whole temperature range - 200°C - 450°C