Diesel Lean NOx-Trap Thermal Aging and Performance Evolution Characterization

The work described in this paper focuses on the impact of thermal aging on NOxtrap structure and functions. They were evaluated on a Synthetic Gas Bench (SGB) and correlated with the analysis of the structural and chemical evolution of the catalyst. A FTIR Operando study allowed to further analyse the mechanisms occurring on the catalyst surface and highlight the most critical points. NOxtrap samples were hydrothermally aged in a furnace up to 900°C under an oxidising flow. The main following impacts on the material were highlighted: reduction of the surface area, sintering of Pt yielding a decrease of the NO oxidation efficiency and hence of the NOxstorage capacity, and a loss of CO and HC conversion, barium structural evolution into BaAl2O4also being partly responsible for the loss of NOxstorage capacity. Other possibilities for loss of NSC are: the transition of -Al2O3to -Al2O3and the evolution of Ba crystalline structure which needs further analysis. Both XRD and surface IR Operando studies show that hydrothermal aging has a rather homogeneous impact on all materials: alumina phase transition and BaAl2O4production, which all lead to a partial decrease of all storage sites.