Sulfur Poisoning of a NO<sub>x</sub> Storage Catalyst - A Comprehensive Modelling Approach

Hadl, Klaus; Ratzberger, Reinhard; Eichlseder, Helmut; Schuessler, M.; Linares, Waldemar G.; Pucher, Hannes

doi:10.4271/2016-01-0964

Cited by 4 publications

(2 citation statements)

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“…In particular, Choi et al [4] showed that the sulfation process of the LNT proceeded axially along the catalyst, producing a displacement of the NO X storage area, and an increase in NH 3 production towards the outlet of the catalyst. Spatially-resolved measurement techniques were also used by Easterling et al to study the effect of hydrothermal treatments on the production of NH 3 in coupled LNT-SCR systems [33][34][35]. The study showed that Pt/Ba segregation produced a stretch of the NO X storage zone during the lean phase, because a lower concentration of active storage sites was present.…”

Section: Introductionmentioning

confidence: 99%

Thermal ageing of a commercial LNT catalyst: Effects on the structure and functionalities

et al. 2022

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Section: Introductionmentioning

confidence: 99%

Thermal ageing of a commercial LNT catalyst: Effects on the structure and functionalities

et al. 2022

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“…Nevertheless, the LNT system is highly susceptible to sulfur, and its performance can be severely affected as NO x storage sites are blocked by sulfur [5][6][7]. Sulfates formed on the NO x storage sites have higher thermal stability than nitrates and nitrites and, therefore, their decomposition needs very high temperatures and alternating rich/lean exhaust mixtures [8,9]. This does not only lead to higher fuel consumption due to regular desulfation events, but may also cause structural deactivation of the catalyst, such as sintering of precious metals and the formation of mixed oxides (e.g., BaAl 2 O 4 for the reaction between Al 2 O 3 and BaO at high temperatures), affecting the overall NO x storage and reduction activity of the catalyst [10][11][12].Therefore, the sulfur tolerance of modern LNT catalysts should be improved by replacing the NO x trapping material with a component with lower affinity towards sulfation, and with enhanced desorption of sulfur species during regeneration.…”

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Sulfur Poisoning Effects on Modern Lean NOx Trap Catalysts Components

2019

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In the present work, a series of different materials was investigated in order to enhance the understanding of the role of modern lean NO x trap (LNT) components on the sulfur poisoning and regeneration characteristics. Nine different types of model catalysts were prepared, which mainly consisted of three compounds: (i) Al 2 O 3 , (ii) Mg/Al 2 O 3 , and (iii) Mg/Ce/Al 2 O 3 mixed with Pt, Pd, and Pt-Pd. A micro flow reactor and a diffuse reflectance infrared Fourier transform spectrometer (DRIFTS) were employed in order to investigate the evolution and stability of the species formed during SO 2 poisoning. The results showed that the addition of palladium and magnesium into the LNT formulation can be beneficial for the catalyst desulfation due mainly to the ability to release the sulfur trapped at relatively low temperatures. This was especially evident for Pd/Mg/Al 2 O 3 model catalyst, which demonstrated an efficient LNT desulfation with low H 2 consumption. In contrast, the addition of ceria was found to increase the formation of bulk sulfate species during SO 2 poisoning, which requires higher temperatures for the sulfur removal. The noble metal nature was also observed to play an important role on the SO x storage and release properties. Monometallic Pd-based catalysts exhibited the formation of surface palladium sulfate species during SO 2 exposure, whereas Pt-Pd bimetallic formulations presented higher stability of the sulfur species formed compared to the corresponding Pt-and Pd-monometallic samples.Catalysts 2019, 9, 492 2 of 18 urea [4]. Nevertheless, the LNT system is highly susceptible to sulfur, and its performance can be severely affected as NO x storage sites are blocked by sulfur [5][6][7]. Sulfates formed on the NO x storage sites have higher thermal stability than nitrates and nitrites and, therefore, their decomposition needs very high temperatures and alternating rich/lean exhaust mixtures [8,9]. This does not only lead to higher fuel consumption due to regular desulfation events, but may also cause structural deactivation of the catalyst, such as sintering of precious metals and the formation of mixed oxides (e.g., BaAl 2 O 4 for the reaction between Al 2 O 3 and BaO at high temperatures), affecting the overall NO x storage and reduction activity of the catalyst [10][11][12].Therefore, the sulfur tolerance of modern LNT catalysts should be improved by replacing the NO x trapping material with a component with lower affinity towards sulfation, and with enhanced desorption of sulfur species during regeneration. Barium is frequently employed as a storage material because of its high thermal stability, however, it is responsible for the major LNT catalyst deterioration due to its high affinity for sulfation [13]. Ji et al. [14] studied the incorporation of ceria to Ba-based LNT catalysts and determined to provide a positive impact on LNT performance in the presence of sulfur. Ceria was found to enhance sulfur tolerance of the LNT catalyst by storing sulfur species, which mitigates the sulfation o...

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Impact of cyclic lean–rich aging under DeSO x condition on the lean-gas light-off and hydrogen formation ability of a lean NO x trap (LNT)

Maurer¹,

Fortner²,

Holler³

et al. 2017

Automot. Engine Technol.

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In this paper, the aging impact of desulphation (DeSO x) procedures on lean NO x traps (LNT) was investigated. With accelerated aging procedures on an engine test bench and on a synthetic-gas test bench, LNTs were stressed with lean rich cycling under realistic desulphation conditions. Exhaust gas chassis dynamometer tests showed the impact on emissions of the lean rich treatment. High carbon monoxide (CO) slips were detected in NEDC tests during NO x regeneration (DeNO x). With light-off tests, the pattern of damage was further investigated. A pronounced deactivation in CO-rich gas conversion was found to be the main reason for the carbon monoxide emissions in the chassis dynamometer tests. A correlation between DeSO x duration (cumulated duration of rich pulses) and the inhibited CO conversion was observed. Determinations of oxygen storage capacities of aged catalysts indicated that the lean-rich cycling mainly damaged the ceria oxide of the LNT. Variations of the rich gas components indicated that hydrogen in the feed gas as well as in situ generated hydrogen out of feed gas components (steam reforming, water gas shift) is accountable for the degradation in carbon monoxide conversion in rich purges. Investigations for lower desulphation temperatures showed that the effect is negligible for temperature \350°C. Therefore, catalyst deactivation throughout NO x regeneration events with much lower temperatures than at DeSO x was not observed. As reference to other aging treatments used in the literature, samples aged hydrothermally at 750°C, a phosphorus poisoned and hydrothermally aged LNT as well as a LNT sample from a vehicle endurance run were compared to the DeSO x aged catalysts. All LNTs had the same conventional LNT coating.

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Sulfur Poisoning of a NO_x Storage Catalyst - A Comprehensive Modelling Approach

Cited by 4 publications

References 35 publications

Thermal ageing of a commercial LNT catalyst: Effects on the structure and functionalities

Thermal ageing of a commercial LNT catalyst: Effects on the structure and functionalities

Sulfur Poisoning Effects on Modern Lean NOx Trap Catalysts Components

Impact of cyclic lean–rich aging under DeSO x condition on the lean-gas light-off and hydrogen formation ability of a lean NO x trap (LNT)

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Sulfur Poisoning of a NOx Storage Catalyst - A Comprehensive Modelling Approach

Cited by 4 publications

References 35 publications

Thermal ageing of a commercial LNT catalyst: Effects on the structure and functionalities

Thermal ageing of a commercial LNT catalyst: Effects on the structure and functionalities

Sulfur Poisoning Effects on Modern Lean NOx Trap Catalysts Components

Impact of cyclic lean–rich aging under DeSO x condition on the lean-gas light-off and hydrogen formation ability of a lean NO x trap (LNT)

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Sulfur Poisoning of a NO_x Storage Catalyst - A Comprehensive Modelling Approach