Phenomenological Studies on the Storage and Regeneration Process of NOx Storage Catalysts for Gasoline Lean Burn Applications

Theis, Joe; Göbel, U.; Kögel, M.; Kreuzer, Thomas; Lindner, D.; Lox, E.S.; Ruwisch, Lutz

doi:10.4271/2002-01-0057

Cited by 16 publications

(11 citation statements)

References 10 publications

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“…Hepburn et al , assume that there are mass-transport limitations in the barium particles and use a shrinking-core model to account for this. Theis et al . also explain their experimental results with a shrinking-core model.…”

Section: Kinetic Modelmentioning

confidence: 86%

“…Hepburn et al 8,9 assume that there are mass-transport limitations in the barium particles and use a shrinking-core model to account for this. Theis et al 26 also explain their experimental results with a shrinking-core model. The form of the kinetic rate expression when including mass transfer has the potential to describe the storage process, with an initial rapid storage followed by a slow breakthrough of NO x .…”

Section: Kinetic Modelmentioning

confidence: 90%

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Global Kinetic Model for Lean NO_x Traps

Olsson

Blint

Fridell

2005

Ind. Eng. Chem. Res.

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Modeling and flow reactor experiments are used to investigate the global kinetics for lean NO x traps (LNTs). Experiments were conducted with a Pt/Rh/BaO/Al 2 O 3 model catalyst, and the inlet feed gas was switched between lean and rich periods. It has previously been observed that NO oxidation to NO 2 is important for NO x storage, and therefore a global mechanism for NO oxidation on Pt/Al 2 O 3 is developed. This is then used in the NO x trap model, after the parameters had been adjusted to match the NO and NO 2 concentrations from experiments on the Pt/Rh/BaO/ Al 2 O 3 catalyst. The mass transport of NO and NO 2 inside the particles is described by a shrinkingcore model. Further, it is found that two global reaction steps are needed for storage in order to explain the experimental observations: one step for the formation of barium nitrates and the other step for the formation of loosely bound barium nitrites. Reaction steps were added to the model for regeneration of the trap with C 3 H 6 . The model is tuned based on six experiments at three different temperatures and two different NO concentration levels. The model is able to adequately describe NO x storage during the lean period, the NO reduction during the regeneration period, the NO x breakthrough peaks observed initially in the rich period, and the relation between the measured NO and NO 2 concentrations. Experimentally, we have observed that only a fraction of the barium is used for storage in our model catalysts. In the simulations, only 7% of the barium is used for NO x storage. In addition, TEM experiments have shown that our barium particles are large, and therefore a model is evaluated using an inert core in the center of the particle, which resulted in an equally good fit. However, when using catalysts with small particles, which probably is the case in commercial catalysts, a model without an inert core in barium particles seems to be the most realistic one. The model with an inert core is validated with three additional experiments not included in the fitting procedure. In these experiments the oxygen concentration was lowered to 4% during the lean period, compared to 8% O 2 in the experiments used when adjusting the kinetic parameters. The model can simulate the experimental features of these experiments well.

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Section: Kinetic Modelmentioning

confidence: 86%

Section: Kinetic Modelmentioning

confidence: 90%

Global Kinetic Model for Lean NO_x Traps

Olsson

Blint

Fridell

2005

Ind. Eng. Chem. Res.

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“…Tuttlies et al also included mass transfer in the particles in their model. Theis et al also explained their experimental results with a mechanism that was based on a shrinking-core model. Kojima et al assumed mass-transfer limitations in the wash coat instead, but used a mathematical expression that was similar to that used by Hepburn and co-workers 9,10 for mass-transport limitations in the particles.…”

Section: The Modelmentioning

confidence: 99%

Global Kinetic Modelling of a Supplier Barium- and Potassium-Containing Lean NO_x Trap

Olsson

Monroe

Blint

2006

Ind. Eng. Chem. Res.

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Kinetic modeling, in combination with flow reactor experiments, was used in this study to simulate a supplier lean NO x trap (LNT). The LNT catalyst used is a commercial catalyst that contains barium and potassium as storage components. The results presented in this paper are a continuation of a previous study, where a global kinetic model for NO x storage was developed for a model Pt/Rh/BaO/Al2O3 catalyst. In this work, a simplified model is used, where NO oxidation, nitrite, and nitrate formation are lumped together into one reaction, and the model predicts the total NO x . In this model, only one reaction step must be tuned for each storage component: that is, in our case, one reaction for the formation of barium nitrate and one reaction for potassium nitrate. A broad range of experimental conditions was used when developing this model; five temperatures (200, 300, 400, 500, and 600 °C) and three different inlet NO concentrations (100, 200, and 300 ppm) were used. Water and CO2 were present in all experiments, because these can affect the storage behavior. The reductant used in the regeneration period was CO. Long lean and rich cycles were used to capture the kinetics of the reactions accurately. The model was able to describe all 15 experiments well and could adequately capture the amount of stored NO x during the lean period and the NO x conversion during the rich period, including the NO x breakthrough peak that occurred at the beginning of the rich period. The model was validated with short lean−rich cycling experiments, where the lean period was 30 s and the rich period was 2 s. The model could predict the outlet NO x concentration well, and the error for the average conversion was only 1%−2% in the validation simulations.

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“…Unfortunately, the higher H 2 levels would be more beneficial for the diesel application where much lower exhaust and catalyst temperatures (<250ºC) are common for light-duty vehicles. [5,6] The higher exhaust temperatures for the lean gasoline engine case provide better LNT performance, but the higher NOx levels in the lean gasoline case present a significant challenge.…”

Section: Regeneration Chemistrymentioning

confidence: 99%

Lean Gasoline Engine Reductant Chemistry During Lean NOx Trap Regeneration

Parks

Prikhodko

Partridge

et al. 2010

SAE Int. J. Fuels Lubr.

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Lean NOx Trap (LNT) catalysts can effectively reduce NOx from lean engine exhaust. Significant research for LNTs in diesel engine applications has been performed and has led to commercialization of the technology. For lean gasoline engine applications, advanced direct injection engines have led to a renewed interest in the potential for lean gasoline vehicles and, thereby, a renewed demand for lean NOx control. To understand the gasoline-based reductant chemistry during regeneration, a BMW lean gasoline vehicle has been studied on a chassis dynamometer. Exhaust samples were collected and analyzed for key reductant species such as H 2 , CO, NH 3 , and hydrocarbons during transient drive cycles. The relation of the reductant species to LNT performance will be discussed. Furthermore, the challenges of NOx storage in the lean gasoline application are reviewed.

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Phenomenological Studies on the Storage and Regeneration Process of NOx Storage Catalysts for Gasoline Lean Burn Applications

Cited by 16 publications

References 10 publications

Global Kinetic Model for Lean NO_x Traps

Global Kinetic Model for Lean NO_x Traps

Global Kinetic Modelling of a Supplier Barium- and Potassium-Containing Lean NO_x Trap

Lean Gasoline Engine Reductant Chemistry During Lean NOx Trap Regeneration

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Phenomenological Studies on the Storage and Regeneration Process of NOx Storage Catalysts for Gasoline Lean Burn Applications

Cited by 16 publications

References 10 publications

Global Kinetic Model for Lean NOx Traps

Global Kinetic Model for Lean NOx Traps

Global Kinetic Modelling of a Supplier Barium- and Potassium-Containing Lean NOx Trap

Lean Gasoline Engine Reductant Chemistry During Lean NOx Trap Regeneration

Contact Info

Product

Resources

About

Global Kinetic Model for Lean NO_x Traps

Global Kinetic Model for Lean NO_x Traps

Global Kinetic Modelling of a Supplier Barium- and Potassium-Containing Lean NO_x Trap