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- Olsson, Louise, 1974, et al.
(författare)
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A Kinetic Study of NO Oxidation and NOx Storage on Pt/Al2O3 and Pt/BaO/Al2O3
- 2001
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Ingår i: Journal of Physical Chemistry B Materials. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 105:29, s. 6895-6906
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Tidskriftsartikel (refereegranskat)abstract
- Modeling and flow reactor experiments were used to study the kinetics of NO, storage/release on a Pt/BaO/Al2O3 model catalyst. The mechanism for this concept can be divided into four steps: (i) NO to NO2 oxidation on Pt, (ii) NO2 storage on BaO, (iii) NO, release, and (iv) NO, reduction to N2. In this paper, we have focused on the first three steps. From the NO oxidation study on Pt/Al2O3 compared to Pt/BaO/Al2O3, we observed that the presence of BaO decreases the formation of NO2. To test the importance of this step for effective storage, experiments were performed with a Pt/Al2O3 catalyst placed before the Pt/BaO/Al2O3 catalyst. This resulted in increased NO, storage for the combined system compared to the Pt/BaO/Al2O3 case. To resolve the second and third steps, an experimental investigation of NOx storage/release on BaO/Al2O3 was performed using only NO2 and N2 in the gas feed. We propose a kinetic model, which first includes adsorption of NO2, which oxidizes the surface, followed by nitrate formation. Finally, NO3-BaO-NO2, i.e., Ba(NO3)2, is formed. By using the kinetic parameters from the NO oxidation on Pt/BaO/Al2O3 and the NO, storage on BaO/Al2O3, a kinetic model was constructed to describe NO, storage/release experiments on Pt/BaO/Al2O3. However, the rate for NO, release was increased when Pt was present, and the kinetic model could not accurately describe this phenomenon. Therefore, the mechanism was modified by including a reversible surface spillover step of NO2 between Pt sites and BaO sites. Further, experiments with NO2 exposure followed by a temperature ramp with NO/N2 showed that the desorption behaviors from the BaO/Al2O3 and Pt/BaO/Al2O3 were significantly different, which further supports the spillover mechanism. Finally, the models describing NO, storage on BaO/Al2O3 and on Pt/BaO/Al2O3 were successfully validated with independent experiments.
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| 2. |
- Olsson, Louise, 1974, et al.
(författare)
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Mean Field Modelling of NOx Storage on Pt/BaO/Al2O3
- 2002
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Ingår i: Catalysis Today. - 0920-5861. ; 73:3-4, s. 263-270
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Tidskriftsartikel (refereegranskat)abstract
- A mean field model, for storage and desorption of NOx in a Pt/BaO/Al2O3 catalyst is developed using data from flow reactor experiments. This relatively complex system is divided into five smaller sub-systems and the model is divided into the following steps: (i) NO oxidation on Pt/Al2O3; (ii) NO oxidation on Pt/BaO/Al2O3; (iii) NOx storage on BaO/Al2O3; (iv) NOx storage on Pt/BaO/Al2O3 with thermal regeneration and (v) NOx storage on Pt/BaO/Al2O3 with regeneration using C3H6. In this paper, we focus on the last sub-system. The kinetic model for NO, storage on Pt/BaO/Al2O3 was constructed with kinetic parameters obtained from the NO oxidation model together with a NO, storage model on BaO/Al2O3. This model was not sufficient to describe the NO, storage experiments for the Pt/BaO/Al2O3, because the NO, desorption in TPD experiments was larger for Pt/BaO/Al2O3, compared to BaO/Al2O3. The model was therefore modified by adding a reversible spill-over step. Further, the model was validated with additional experiments, which showed that NO significantly promoted desorption of NOx from Pt/BaO/Al2O3. To this NOx storage model, additional steps were added to describe the reduction by hydrocarbon in experiments with NO2 and C3H6. The main reactions for continuous reduction of NOx occurs on Pt by reactions between hydrocarbon species and NO in the model. The model is also able to describe the reduction phase, the storage and NO breakthrough peaks, observed in experiments.
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