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- Olsson, Louise, 1974, et al.
(author)
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Global kinetic model for lean NOx traps
- 2005
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In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 44:9, s. 3021-3032
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Journal article (peer-reviewed)abstract
- 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 shrinking-core 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. © 2005 American Chemical Society.
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- Olsson, Louise, 1974, et al.
(author)
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Global Kinetic Modelling of a Supplier Barium- and Potassium- Containing Lean NOx Trap
- 2006
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In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 45:26, s. 8883-8890
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Journal article (peer-reviewed)abstract
- Kinetic modeling, in combination with flow reactor experiments, was used in this study to simulate a supplier lean NOx 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 NOx 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 NOx. 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 degrees 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 NOx during the lean period and the NOx conversion during the rich period, including the NOx 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 NOx concentration well, and the error for the average conversion was only 1%-2% in the validation simulations.
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- Olsson, Louise, 1974, et al.
(author)
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Kinetic modeling of sulfur poisoning and regeneration of lean NOx traps
- 2010
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In: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 100:1-2, s. 31-41
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Journal article (peer-reviewed)abstract
- Sulfur poisoning and regeneration of lean NOx traps were investigated using experiments and kinetic modeling. A commercial Pt, Rh and barium containing NOx storage catalyst was used. The catalyst also contained oxygen storage material. First the oxygen storage capacity (OSC) was investigated using steps with oxygen and hydrogen. The OSC was substantial with a total use of all hydrogen (1%) for about 20 s. The results were similar at the three investigated temperatures (300, 400 and 500 degrees C), indicating that it is a low activation barrier connected with the process. Further, no effect was observed when adding 15 ppm SO2 to the feed. Since no SO2 was observed in the outlet it is possible that SO2 is adsorbed during the lean period and then reduced to form H2S in the rich period (not measured). Further, the NOx storage was found to decrease during SO2 exposure, and the decrease was linear and dose dependent. In addition, we investigated different regeneration strategies. When using 500 ppm H-2 for 60 min at 700 degrees C the regeneration was poor. However, when adding 5% CO2 to the 500 ppm H-2 the regeneration was increased drastically. Further, the regeneration was decreased when decreasing the temperature to 600 degrees C, and further decreased when using 500 degrees C. In addition, it was beneficial with increasing the hydrogen concentration. The kinetic model contains three sub-models; (i)NOx storage and regeneration, (ii) oxygen storage and reduction and (iii) sulfur poisoning and sulfur regeneration. It was crucial to add NOx storage on two sites; barium and alumina. The NOx adsorbed on alumina is more loosely bound. Further, in the model formation of sulfates were added on both components. This was important in order to describe the rate of the sulfur deactivation. If sulfur was adsorbed only on barium the deactivation would have been too rapid. The model could describe the experimental features well.
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- Sjövall, Hanna Maria, 1977, et al.
(author)
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A Kinetic Model for the Selective Catalytic Reduction of NOx with NH3 over an Fe-zeolite Catalyst
- 2010
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In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 49:1, s. 39-52
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Journal article (peer-reviewed)abstract
- The selective catalytic reduction of NOx with ammonia over all Fe-zeolite catalyst was investigated experimentally and a transient kinetic model was developed. The model includes reactions that describe ammonia storage and oxidation, NO oxidation, selective catalytic reduction (SCR) of NO and NO2, formation of N2O, ammonia inhibition and ammonium nitrate formation. The model call account for a broad range of experimental conditions in the presence of H2O, CO2 and O-2 at temperatures from 150 to 650 degrees C. The catalyst stores ammonia at temperatures up to 400 degrees C and shows ammonia oxidation activity from 350 degrees C. The catalyst is also active for the oxidation of NO to NO2 and the oxidation reaches equilibrium at 500 degrees C. The SCR of NO is already active at 150 degrees C and the introduction of equal amounts of NO and NO2 greatly enhances the conversion of NOx at temperatures up to 300 degrees C. The formation of N2O is negligible if small fractions of NO2 are fed to the reactor, but a significant amount of N2O is formed at high NO2 to NO ratios. An ammonia inhibition oil the SCR of NO is observed at 200 degrees C. This kinetic model contains 12 reactions and is able to describe the experimental results Well. The model was validated using short transient experiments and experimental conditions not used in the parameter estimation and predicted these new conditions adequately.
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