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- Abdulhamid, Hussam, 1974, et al.
(författare)
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Influence of the type of reducing agent (H2, CO, C3H6 and C3H8) on the reduction of stored NOX in a Pt/BaO/Al2O3 model catalyst
- 2004
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Ingår i: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 30-31:1-4, s. 161-168
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Tidskriftsartikel (refereegranskat)abstract
- In this investigation, a comparative study for a NOx storage catalytic system was performed focusing on the parameters that affect the reduction by using different reductants (H2, CO, C3H6 and C3H8) and different temperatures (350, 250 and 150 degrees C), for a Pt/BaO/Al2O3 catalyst. Transient experiments show that H2 and CO are highly efficient reductants compared to C3H6 which is somewhat less efficient. H2 shows a significant reduction effect at relatively low temperature (150 degrees C) but with a low storage capacity. We find that C3H8 does not show any NOx reduction ability for NOx stored in Pt/BaO/Al2O3 at any of the temperatures. The formation of ammonia and nitrous oxide is also discussed.
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| 4. |
- Amberntsson, Annika, 1974, et al.
(författare)
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Influence of platinum and rhodium composition on the NOx storage and sulphur tolerance of a barium based NOx storage catalyst
- 2003
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Ingår i: Applied Catalysis B: Environmental. - 0926-3373 .- 1873-3883. ; 46:3, s. 429-439
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Tidskriftsartikel (refereegranskat)abstract
- In the present work the influence of the type of noble metals present in barium oxide based NOx storage catalysts was investigated, regarding the NOx storage performance, NO oxidation, NO reduction, sulphur deactivation and sulphur regenerability. Monolith samples with combinations of platinum and rhodium, were prepared, tested in a flow-reactor, and characterised by XPS measurements. The flow-reactor experiments simulated NOx storage and reduction cycles at 400 degrees C in synthetic gas mixtures with oxygen, propene and nitric oxide. For the sulphur deactivation and regenerability investigations 25 ppm (v/v) SO2 was added to the feed gas stream. From the experiments, it was concluded that a combination of platinum and rhodium is required to achieve good NOx storage and reduction performance. The NOx storage capacity was, however, found higher for catalysts containing only platinum compared to catalysts including rhodium. When exposed to SO2 the NOx storage capacity also seemed to deactivate faster for the samples containing rhodium than for samples with platinum as the sole noble metal. Additionally, it was observed that platinum gives high NO oxidation activity during the lean periods both with and without SO2 present in the gas feed. During the rich periods, rhodium showed high activity for NO reduction in sulphur free gas feed as well as in the presence of SO2. Finally, the results implied that to provide good sulphur regeneration ability of the NOx storage catalyst, a combination of platinum and rhodium is necessary.
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| 6. |
- Amberntsson, Annika, 1974, et al.
(författare)
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Investigations of sulphur deactivation of NOx storage catalysts: influence of sulphur carrier and exposure conditions
- 2002
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Ingår i: Catalysis Today. - 0920-5861. ; 73:3-4, s. 279-286
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Tidskriftsartikel (refereegranskat)abstract
- The influence of SO2, H2S and COS in low concentrations on the deactivation of PURh/BaO/Al2O3 NOx storage catalysts was investigated. Different samples of the catalyst were exposed to synthetic gas mixtures mimicking lean/rich engine cycling in a mixed lean application at 400degreesC. The lean gas mixture contained 8 vol.% O2, 500 vol-ppm C3H6 and 400 vol-ppm NO balanced to 100 vol.% with Ar. The rich excursions were performed by switching off the oxygen supply. Sulphur, 25 vol-ppm of either SO2, H2S or COS, was added to the gas flow either during the lean, the rich or both periods. This procedure aimed at investigating the influence of the exposure conditions and therefore the lean and rich periods were kept equally long (5 min). In addition, thermodynamical calculations for the prevailing conditions were performed.
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| 9. |
- Amberntsson, Annika, 1974, et al.
(författare)
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Sulphur deactivation of NOx storage catalysts; Influence exposure conditions and noble metal
- 2003
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Ingår i: Journal of Catalysis. - 0021-9517 .- 1090-2694. ; 217:2, s. 253-263
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, barium-based NOx, storage catalysts containing platinum, rhodium, or both noble metals were investigated. The influence of SO2 exposure conditions on the performance of NOx storage catalysts was studied using flow reactor measurements, FTIR, and XPS where the samples were exposed to lean and/or rich SO2-containing gas mixtures, simulating the conditions in a mixed lean application. The main results show that all samples are sensitive to sulfur and that deactivation is faster when SO2 is present in the feed under rich conditions than under lean or continuous SO2 exposure. It was also found that SO2 affects the performance of noble metals strongly and that noble metal deactivation most likely occurs during the rich period of a NOx storage cycle. Additionally, the influence of the noble metals present in the catalysts was investigated with respect to sulfur sensitivity and it was found that a combination of platinum and rhodium seems to be preferable for retaining high performance (high NO oxidation and reduction activity) of the catalyst under SO2 exposure and subsequent regeneration.
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| 10. |
- Broqvist, Peter, 1975, et al.
(författare)
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Characterization of NOx species adsorbed on BaO: Experiment and theory
- 2004
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Ingår i: Journal of Physical Chemistry B. - 1520-5207 .- 1520-6106. ; 108:11, s. 3523-3530
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Tidskriftsartikel (refereegranskat)abstract
- Charged NO, species (x = 1,2,3) formed upon adsorption of NO2 on BaO are characterized by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and theoretical vibrational analysis using the density functional theory (DFT). Experiments at 30degreesC reveal nitrite formation. At T > 250degreesC, shifts associated with formation of nitrates are observed, indicating an interconversion of oxygen atoms among adsorbates. The theoretical study includes single and pairwise NO2 adsorption on (BaO)(9) clusters. As has been reported previously [Broqvist, P.; Panas, I.; Fridell, E.; Persson, H. J. Phys. Chem. B 2002, 106, 137], an additional energy gain is calculated for the second adsorbed NO2. A vibrational analysis of the investigated adsorption configurations supports the interpretation of nitrite to nitrate interconversion on the BaO surface. Moreover, the calculations demonstrate the sensitivity in the NO2 vibrational band splitting with respect to adsorption configuration.
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