Diesel Lean NOx-Trap Thermal Aging and Performance Evolution Characterization

Oil & Gas Science and Technology, Jul 2018

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 BaAl2O4 also being partly responsible for the loss of NOx storage capacity. Other possibilities for loss of NSC are: the transition of -Al2O3 to -Al2O3 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 BaAl2O4 production, which all lead to a partial decrease of all storage sites.L’étude suivante porte sur l’impact du vieillissement thermique sur la structure et les fonctions d’un piège à NOx. Les essais ont été réalisés sur un banc gaz synthétiques (BGS) et les résultats ont été corrélés à des analyses structurale et chimique du catalyseur. Une étude FTIR Operando a permis de mieux analyser les mécanismes se produisant sur la surface du catalyseur et de mettre en évidence les points les plus critiques. Des échantillons ont été vieillis hydrothermiquement à 900 °C sous un flux oxydant. Les principaux impacts ont été les suivants : la réduction de la surface spécifique, le frittage du Pt qui mène à une diminution de l’efficacité d’oxydation de NO, CO, HC et de la capacité de stockage, la formation de BaAl2O4 est en partie responsable de la perte de capacité de stockage de NOx. D’autres possibilités pour la perte de NSC sont : la transition de la -Al2O3 à la -Al2O3 et l’évolution de la structure cristalline du baryum qui demande des analyses approfondies. Les études DRX et Operando IR montrent que le vieillissement hydrothermique a un impact assez homogène sur tous les matériaux : la transition de phase de l’alumine et la formation de BaAl2O4, qui toutes mènent à une diminution partielle de tous les sites de stockage.

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Diesel Lean NOx-Trap Thermal Aging and Performance Evolution Characterization

Oil & Gas Science and Technology - Rev. IFP Energies nouvelles, Vol. Diesel Lean NO -Trap Thermal Aging and x Performance Evolution Characterization S. Benramdhane 1 C.-N. Millet 1 E. Jeudy 1 J. Lavy 1 V. Blasin-Aubé 0 M. Daturi 0 0 Laboratoire Catalyse et Spectrochimie, ENSICAEN, Université de Caen , CNRS, 6 Bd Maréchal Juin, 14050 Caen - France 1 IFP Energies nouvelles, Rond-point de l'échangeur de Solaize , BP 3, 69360 Solaize - France - 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. 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 BaAl2O4 also being partly responsible for the loss of NOx storage capacity. Other possibilities for loss of NSC are: the transition of γ-Al2O3 to δ-Al2O3 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 BaAl2O4 production, which all lead to a partial decrease of all storage sites. - Page 846 846 INTRODUCTION Environmental, ecological and health concerns result in increasingly stringent regulations of pollutant emissions from vehicle engines. Diesel and lean-burn gasoline engines are attractive alternatives to conventional gasoline engines to improve fuel economy and reduce CO2 emissions for light duty vehicles. A major challenge is the abatement of NOx (NO + NO2) emissions. Two main approaches are being developed to answer to this challenge. The first technology deals with the continuous Selective Catalytic Reduction (SCR) of NOx. It takes advantage of the ability of some catalysts to allow the selective reaction of a limited amount of reductant (NH ) with NOx rather than O2. The second tech3 nology is based on a cycle of NOx storage and reduction in a Lean NOx Trap (LNT) [ 1 ], which operates on a principle of alternating phases. The concept is based on the adsorption of NOx during long periods of oxygen excess followed by shorter periods of oxygen deficiency in the presence of reducing agents during which the stored NOx are released and reduced to N2, N2O or NH3. Reductants are mainly hydrocarbons issued from a specific fuel injection strategy into the cylinder or the exhaust pipe. Lean/rich transitions are managed by the engine control unit. Main components of the catalytic washcoat are usually alumina for the support, Pt, Pd and Rh as noble metals to provide oxidative and reductive functions, and a basic additive (often a barium salt) known for its high affinity for NOx [ 2 ] to provide their storage. NOx traps also show some undesired reactivity in regards to sulphur compounds which are present in exhaust gases from both Diesel and gasoline engines. It is commonly agreed [ 3, 4 ] that sulphur dioxide is first oxidized to sulphur trioxide over platinum. Then, the SO3 reacts with barium and alumina to form barium and aluminium sulphates which are more stable than the corresponding nitrates. This causes gradual saturation of the storage material with sulphur and leading to significant NOx storage activity loss. Periodic desulfation (DeSOx) hence requires higher temperatures which are detrimental to the life of the catalyst. For this reason, sulphur deactivation and the corresponding thermal aging are key obstacles to a widespread implementation of the LNT [ 5, 6 ]. Thermal deterioration is due both to the growth of precious metal particles and to the formation of mixed oxides such as aluminates, cerates, and zirconates by the reaction of NOx storage material with the support or other compounds in the washcoat [ 7, 8 ]. 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 hence 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. 1 EXPERIMENTAL 1.1 Catalyst The commercial NOx trap that was investigated in this study was supplied by Renault. It has a square monolithic honeycomb structure of 400 cells per square inch (cpsi). The thin ceramic walls are coated with a NOx storage / reduction catalyst. The catalytic coating was characterized by X-Ray Fluorescence analysis (XRF), X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). TEM observations were performed on a JEOL 2100F 200 kV microscope equipped with a X-ray dispersive Spectrometer. X-ray Diffraction (XRD) patterns were obtained with a PANalytical X’Pert Pro MPD Diffractometer with Bragg-Brentano X-ray tube anticathode Cu (wavenumber kA1 = 1.5406 Å). Samples were loosely packed in a shallow cavity (0.2 cm deep and 1 cm in diameter). The washcoat was separated from the cordierite support before being analyzed. 1.2 IR Operando Apparatus The purpose of FTIR Operando study was to analyze NOx and carbonates storage sites of the LNT samples under representative running conditions so as to determine the impact of thermal aging on the storage sites. The description of the Operando setup, with gas line and analysis tools (IR, MS and chemiluminescence) and the IR reactor cell, is described in [ 11 ]. The material was pressed into self-supporting wafers of 10 mg.cm-2 and placed into the quartz reactor-cell equipped with KBr windows. For the analysis of the surface, Operando measurements were carried out with a Nicolet FT-IR Nexus spectrometer equipped with a MCT detector. FT-IR spectra were collected with a resolution of 4 cm-1. The analysis of the outlet gases was performed by means of a Pfeiffer Omnistar mass spectrometer. Likewise, FT-IR spectra of the gas phase were collected using a gas microcell. The sample was activated in the same way as SGB (described in Sect. 2.3). The lean reacting gas composition is 900 ppmC HC (C3H6), 800 ppm CO, 270 ppm H2, 300 ppm NOx, 5% CO2, 15% O2 and 2% H O in Ar as a carrier gas. The total flow is adjusted 2 to 25 cm3.min-1. This composition is equivalent to the one used in the Synthetic Gas Bench and is very similar to the real Page 847 The purpose of the Synthetic Gas Bench study was to quantify the NOx storage and reduction capacities of the LNT samples under representative running conditions so as to determine the impact of thermal aging. The following types of experiments were performed: – sample pre-treatment, – catalyst light-off during a temperature ramp, – isothermal NOx storage experiments with different gas compositions, – lean and rich pulses to mimic storage / reduction cycles occurring in real driving conditions. LNT samples cut from the monolith for our study were 25 mm in diameter and 50 mm in length for the Synthetic Gas Bench analysis. Experiments were carried out in a flow reactor under atmospheric pressure and realistic flow conditions representative of Diesel exhaust gas by synthetic gas mixture. The catalyst sample was placed in a quartz tube. A thermocouple in front of the catalyst was used to control the temperature and another one was inserted downstream from the catalyst. The quartz tube was placed in an electrically heated oven. Valves allowed to rapidly switch from one gas composition to another, and to generate alternating rich and lean phases. Gas compositions were chosen close to a lean Diesel environment (equivalence ratios ER = 0.3) and to a rich pulse environment (ER = 1.1) as detailed in Table 1. Other compositions were also tested when considered useful to better understand the catalyst behaviour. Propylene was used to represent unburned hydrocarbons emitted by engine combustion. Samples were pre-treated to stabilize their active surface and thus their catalytic activity so as to ensure good test reproducibility and a constant concentration of surface residual impurities before starting any analysis. The gas flow was switched between 290 s lean feed periods (ER = 0.3) and 15 s rich pulses (ER = 1.1, see Tab. 1). Temperature was increased at 5°C/min rate from 50°C up to 620°C and then stabilized at 620°C for 2 hours. The catalyst was cooled back to room temperature in a synthetic air flow. To ensure that samples were being evaluated under similar initial states, all experiments were terminated by a step at 620°C in an air flow until stabilisation was reached. 1.3.2 Catalyst Light-off During a Temperature Ramp For this experiment, the temperature was increased from 50 to 620°C at a 10°C/min rate. The CO and HC conversion efficiencies of the LNT were determined as a function of the temperature measured upstream of the catalyst. The temperature at which 50% conversion was achieved was defined as the “light-off” temperature for the particular pollutant. 1.3.3 Isothermal NOx Storage The gas temperature was increased up to the desired value under a N2 flow. The experiment was then switched to a lean feed and NOx were monitored downstream from the catalyst. The gas mixture was switched back to N2 after the NOx trap became saturated and the temperature was increased so as to thermally release the complete amount of stored NOx (N2-TPD: temperature programmed desorption). The NOx Storage Capacity (NSC), the NO to NO2 oxidation efficiency and the DeNOx efficiency of the LNT were determined at different temperatures and storage times. 1.3.4 Lean-Rich Cycling Conditions The method to evaluate NOx storage, reduction and global conversion efficiency of the NOx trap is by cycling between lean and rich conditions to mimic engine operation. In this test, the gas temperature was increased up to the desired value (300°C) under an N2 flow. The gas flow was then switched between 290 s lean feed periods (ER = 0.3) and 15 s rich pulses (ER = 1.1). Once the lean/rich cycling exhibited a repeatable behaviour (storage efficiency variation below 1%), the gas mixture was switched back to N2 and a temperature programmed desorption was performed. The NOx storage efficiency during the lean phase, the NOx reduction efficiency during the rich phase and the overall NOx conversion efficiency were thus determined. The NOx storage efficiency represents the proportion of NOx stored in the trap during the lean phase: ⎛ t1 ⎞ ⎜ ∫ NOxout ⎟ ηstorage NOx (%) =⎜ ⎜⎜ 1 − tt01 ⎟⎟ × 100 ⎜⎜ ∫ NOxsat ⎟⎟ ⎝ t0 ⎠ 848 where the lean phase starts at time t0 and ends at time t1, NOxout are NOx mesured downstream from the NOx trap, and NOxsat is the level of NOx that would be reached if the lean phase is long enough to saturate the trap. NOxsat can also be determined from the amount of N2O emitted because the DeNOx is completely non-selective in our lean conditions. The NOx reduction efficiency is determined during the rich phase: ⎛ ⎜ t2 ∫ NOxout t1 ηred NOx (%) = ⎜⎜ 1 − t2 ⎜⎜ ∫ NOxin + NOxstored ⎟⎟ ⎝ t1 ⎠ ⎞ ⎟ ⎟⎟ × 100 where the rich phase starts at time t1 and ends at time t2, NOxin are NOx mesured upstream of the NOx trap, and NOxstored is the quantity of NOx that were stored during the lean phase: t1 NOxstored = ∫ (NOxsat − NOxout ) t0 The NOx conversion efficiency is determined during the two phases. ⎛ t2 ⎞ ⎞ ⎜ ∫ NOxout ⎟ ηconv NOx (%) = ⎜⎜ 1 − tt02 ⎟⎟ × 100 ⎜⎜ ∫ NOxin ⎟⎟ ⎝ t0 ⎠ 1.4 Hydrothermal Aging NOx trap samples were hydrothermally aged in a furnace at 750, 800, 850 or 900°C for 5 h under a flow of 10% O2, 10% H2O and N2. A new sample was used for each temperature. 2 RESULTS AND DISCUSSION 2.1 Catalyst Composition and Characterisation Main components of the washcoat are Al2O3, ZrO2 and CeO2. Trapping materials are mainly Ba and Sr. Active metals are Pt and Rh. A combination of these two noble metals is required to achieve good NOx storage and reduction performances, together with good sulfur regeneration ability from sulphur deposit [ 12 ]. SEM reveals that the washcoat hence intimately bound to the cordierite support. Figure 1 displays XRD spectra of the fresh and thermal aged catalysts. The Pt peak at 2θ = 40° sharpens with aging temperature, indicating that Pt particle sintering increases [ 13 ]. Ceria particles only sinter from the 800°C aging, according to the peak at 2θ = 47°. TEM results on Pt and ceria coarsening are in agreement with those obtained by XRD. In the fresh catalyst, BaCO3 and BaC2O4 are the dominant Ba-phases observed in the XRD patterns, but can not be distinguished from each other. Hydrothermal aging at all temperatures makes the Ba-phase react in solid phase with Pt BaAl2O4 CeO2 Al2O3 C2BaO4, BaCO3 900°C 850°C 800°C 750°C Fresh 1 500 1 400 1 300 1 200 1100 1 000 ) 900 s tun 800 o (C 700 n iL 600 500 400 300 200 100 0 30 40 2-Theta - Scale 3 10 20 50 60 70 Page 849 IR surface difference spectra of the fresh and hydrothermally aged (800°C) NOx-trap after exposure to a flow of NO + O2 at 200°C. The negative peak in the aged sample is due to bulk carbonate removal upon NOx adsorption. γ-Al2O3 leading to BaAl2O4 as can be seen at 2θ = 20°. Another interesting feature of the XRD patterns is the change in the shape of the alumina peak at 2θ = 68° in the samples aged at 850 and 900°C: the split of the alumina peak at 2θ = 67.5° indicates the transition of a fraction of γ-Al2O3 (cubic structure) to δ-Al2O3 (tetragonal structure), as was already found by Toops et al. [ 9 ] above 860°C. This transition induces a decrease of the surface area. This is in agreement with surface area measurements (Tab. 2): hydrothermal aging makes the surface area of the washcoat decreasing from 20% at 750°C up to 42% at 900°C compared to the fresh catalyst. 2.2 Surface Characterisation by IR Operando The NOx storage properties of the samples were evaluated by IR Operando during isothermal NOx storage experiments under a 300 ppm NO and 15% O2 flow to saturation. Figure 2 shows the IR spectrum of NOx species on the surface of saturated fresh and hydrothermally aged (800°C) catalysts. The various wavenumber of surface species are based on literature and experiments carried out in in situ conditions and are listed in the table below. 0,02 IR surface difference spectra of the fresh and hydrothermal (800°C) aged NOx-trap after exposure to the lean flow (ER = 0.3; Tab. 1) at 200°C. In Figure 2, we can distinguish the formation of bidentate nitrates coordinated with alumina cations (bands at 1 6061 260 cm-1) [ 14, 15 ], nitrates coordinated at the interface between alumina and barium oxide (bands at 1 585 and 1 297 cm-1) [16], bidentate nitrates coordinated with Ba2+ cations (1 555 and 1 303 cm-1) [ 17 ], monodentate nitrates coordinated with Al2O3 (1 526 and 1 311 cm-1) [ 14 ], monodentate nitrates coordinated with Ba2+ cations (1 452 and 1325 cm-1) [ 18, 19 ] and polydentate nitrates coordinated with Ba2+ cations (1 424 and 1 350 cm-1) [20]. The feature centred at 1 026 cm-1 contains the ν1 mode of the nitrate species. We can also distinguish the formation of nitrites species: bridge and/or bidentates alumina and/or barium nitrites (1 230 cm-1). A band at 1 214 cm-1 was assigned to ionic nitrites [ 21, 22 ]. The presence of these ionic nitrites may indicate that NO2 oxidation into NO3 on the storage sites becomes a limiting step in NOx storage at 200°C (cf. Tab. 3). The significantly reduced IR spectra show that hydrothermal aging leads to a partial decrease of all storage sites. It also appears to be some information as to which phases are being impacted: the nitrate peak at 1 026 cm-1 is nearly gone altogether and the dominant peak is now at 1 226 cm-1 (ionic nitrites), replacing almost totally the nitrates. That means that the nitrite to nitrate oxidation function of the material has been mainly impacted by the hydrothermal treatment. Both XRD and surface IR Operando studies show that hydrothermal aging has a rather homogeneous impact on all materials: particle sintering, alumina phase transition and BaAl2O4 production, which all lead to a partial decrease of all storage sites. An isothermal storage experiment was also performed with a flow composition close to automotive exhaust catalysis (ER = 0.3; Tab. 1). Figure 3 shows the spectra of the nitrate and carbonate species on the surface of saturated fresh and hydrothermally aged (800°C) catalysts. The profiles shows the same storage sites as those observed with the binary mixture (NO/O2), partially concealed by competition between nitrates and carbonates as well as hydrocarbon species: acrylates coordinated with Al2O3 (1 637 and 1 424 cm-1), acetates (1 574 and 1 452 cm-1) [ 23, 24 ]. These compounds are formed by the partial oxidation of propylene. Barium carbonates (1 380 cm-1) [ 25 ] were also presents (cf. Tab. 3). 2.3 Isothermal NOx Storage on the Synthetic Gas Bench Figure 4 shows the NO oxidation efficiency of fresh and aged catalysts as a function of the inlet gas temperature (200 and 300°C). As also shown by IR studies, hydrothermal aging induces a loss of NO oxidation efficiency which is more significant at 200°C than at 300°C. The impact increases with the aging temperature. It is due to Pt sintering that progressively reduces the number of sites available to oxidize NO to NO . 2 NO2 formation is kinetically controlled at 200°C and is hence strongly sensitive to Pt sintering, as was demonstrated by Takahashi et al. [ 1 ] in engine close conditions: NO oxidation efficiency is divided by a factor of 2 between the fresh and the 700°C aged samples, and is close to zero on the catalyst hydrothermally aged at 900°C. In this figure, the impact of aging weakens at 300°C and above when thermodynamical equilibrium becomes dominant and favours NO formation: the NO oxidation efficiency only decreases by 16% between the fresh and the 900°C aged samples. Figure 5 shows the NOx storage capacity of fresh and aged catalysts as a function of the inlet gas temperature (200 and 300°C). Hydrothermal aging makes the NOx storage capacity decrease and shows again a stronger impact at 200°C. This was expected since it partly depends on the catalyst NO oxidation efficiency, as the most effective pathway for NOx storage from NO/O2 mixtures is the “nitrite” route, which implies the stepwise oxidation of NO leading to the formation of nitrite ad-species [ 26 ]. This explains why the catalyst hydrothermally aged at 900°C sample had no more storage capacity at 200°C (no more NO oxidation). At 300°C, NO2 was formed and NOx was stored. The NOx storage capacity also depends on the storage material performance [ 2, 27 ]. A specific isothermal NOx storage test was performed to better distinguish the impact of the storage material and the oxidation Pt sites on aged samples. 300 ppm NO2 in nitrogen was used in order to bypass the NO oxidation step. This experiment was performed on the fresh NOx trap and on the 800 and 900°C hydrothermally aged samples. Results are displayed in Figure 6 and show that the NOx storage capacity decreases by up to 45% due to hydrothermal aging. This storage site reduction is partly attributed to BaAl2O4 formation, as was suggested by XRD patterns at an aging temperature of 750°C and above [9]. The transition of γ-Al2O3 to δ-Al2O3 above 850°C also reduces the alumina NOx storage capacity, as was observed in other surface IR tests (results not displayed). Page 852 852 Fresh HA 750 HA 800 HA 850 HA 900 180 170 )C160 ° ( reu150 t a r pe140 m e t ff130 o t igh120 L 110 100 Pt sintering changes the Pt/Ba interface and may hence be partly responsible for the NSC decrease, as was demonstrated by Rodriguez [ 28 ]. 2.4 Catalyst Light-off Figure 7 shows the light-off temperatures (T50) of CO and HC for fresh and aged catalysts. The impact of hydrothermal aging on catalyst light-off is not significant below 800°C, probably because the reductant amount is small. Light-off temperatures of CO and C H 3 6 undergo 10 and 20°C increase after the 850 and 900°C aging respectively. The loss of CO and HC conversion can be attributed to thermal sintering of Pt particles, resulting in a loss of adjacent active Pt sites, and to the loss of surface area due to thermal sintering of the γ-Al2O3 washcoat. 2.5 Lean-Rich Cycling Conditions The impact of thermal aging was also investigated in conditions close to real use, i.e. by periodically switching the gas composition between 290 s lean feed periods and 15 s rich pulses to regenerate the NOx trap. Results are summarized in Figure 8. The NOx storage efficiency during NOx storage/reduction cycles at 300°C decreased with the hydrothermal aging temperature: from 90% for the fresh sample down to 42% for the HA 900 sample. On the other hand, the NOx reduction efficiency during rich pulses remained constant and close to 100%. The decrease of the global NOx conversion efficiency was then mainly due to the NOx storage efficiency reduction. Similar observations were made at 200°C. It also appeared that the rich pulse duration was not sufficient anymore to 100 90 80 70 ensure complete NOx-trap regeneration: an amount of NOx (8% of the NSC) remained stored in the aged trap in the same condition. This might be due to a greater proportion of bulk Ba storage sites leading to more stable nitrates, whose diffusion is kinetically limited. Another possible reason is Pt sintering and its effect on the Pt/Ba interface: as demonstrated by Rodrigues [ 28 ], the proximity of platinum and barium is important because Pt helps to remove and reduce NOx from the trap when it is present in its surrounding. CONCLUSIONS This paper presents the effect of hydrothermal aging on NOx trap structure and functions. The main following impacts on the tested material were highlighted: – NO oxidation decreases because of Pt sintering; – NSC decreases because of the formation of BaAl2O4 which diminishes storage sites, and of Pt sintering which changes Pt/Ba interface. Other parameters impacting the NSC loss are: the transition of γ-Al2O3 to δ-Al2O3 and the evolution of Ba crystalline structure which needs further analysis. In Operando FTIR, nitrates adsorbed on Ba, Sr, Al2O3, CeO2 and Ba/Al2O3 interface. Hydrothermal aging leads to a partial decrease of all storage sites; – Regenerations appeared to be less efficient, which was attributed to a slower NOx release during rich pulses. The change of Pt/Ba interface after Pt sintering could also partly explain this failure. These phenomena are of paramount importance to understand the catalyst failure on duty, even if in real S Benramdhane et al. / Diesel Lean NOx-Trap Thermal Aging and Performance Evolution Characterization 853 application conditions more parameters intervene. The effects of temperature and sulphur + temperature will be investigated on the Synthetic Gas Bench in aging conditions closer to real driving conditions and will be described in a next paper. 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S. Benramdhane, C.-N. Millet, E. Jeudy, J. Lavy, V. Blasin-Aubé, M. Daturi. Diesel Lean NOx-Trap Thermal Aging and Performance Evolution Characterization, Oil & Gas Science and Technology, 845-853, DOI: 10.2516/ogst/2011151