Abstract
The work described in this paper focuses on the impact of thermal aging on NOx trap 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. NOx trap 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 NOx storage capacity, and a loss of CO and HC conversion, barium structural evolution into BaAl2 O4 also being partly responsible for the loss of NOx storage capacity. Other possibilities for loss of NSC are: the transition of -Al2 O3 to -Al2 O3 and 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 BaAl2 O4 production, which all lead to a partial decrease of all storage sites.
Highlights
Environmental, ecological and health concerns result in increasingly stringent regulations of pollutant emissions from vehicle engines
Diesel Lean NOx-Trap Thermal Aging and Performance Evolution Characterization — The work described in this paper focuses on the impact of thermal aging on NOx trap structure and functions
TEM results on Pt and ceria coarsening are in agreement with those obtained by X-Ray Diffraction (XRD)
Summary
Environmental, ecological and health concerns result in increasingly stringent regulations of pollutant emissions from vehicle engines. Some authors studied thermally aged NOx trap during lean/rich cycling at 600, 700 and 800°C in a flow reactor They demonstrated that the three following deactivation mechanisms dominate above 800°C: loss of dispersion of the precious metals, phase transitions of the adsorber material and loss of total surface area [9, 10]. The impact of thermal aging on the catalytic activity is more significant at low temperatures where reaction kinetics are the limiting step It is more problematic on Diesel vehicles where typical catalyst temperatures are in the range 150-300°C, compared to 300-600°C for gasoline. The work described in this paper focuses on the impact of thermal aging on the functionalities of a commercial Diesel Lean NOx-Trap 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 further analyzing the mechanisms occurring on the catalyst surface and highlighting the most critical points
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