| 1. |
|
|
| 2. |
- Fridell, Erik, 1963, et al.
(författare)
-
Fundamental studies of NOx storage catalysis
- 2002
-
Ingår i: EUCHEM Conference on Environmental Catalysis, Hindås, Sweden, November 27-December 1, 2002.
-
Konferensbidrag (refereegranskat)
|
|
| 3. |
- Fridell, Erik, 1963, et al.
(författare)
-
Model studies of NOx storage
- 2001
-
Ingår i: ENVICAT2001, Amolfi, Italy, May 2-6, 2001.
-
Konferensbidrag (refereegranskat)
|
|
| 4. |
- Fridell, Erik, 1963, et al.
(författare)
-
Model studies of NOx storage and sulphur deactivation of NOx storage catalysts
- 2001
-
Ingår i: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 16-17:1-4, s. 133-137
-
Tidskriftsartikel (refereegranskat)abstract
- The storage of NOx under lean conditions in model NOx storage catalysts as well as the deactivation by sulphur have been studied. We find that NO2 plays an important role in the storage mechanism as an oxidising agent. Two different mechanisms for this are discussed: the formation of surface peroxides and the oxidation of nitrites to nitrates, FTIR studies show that NOx is stored as surface nitrates, The sulphur deactivation is found to be more severe when SO2 is added during the rich phase than when SO2 is added during the lean period. FTIR shows the formation of bulk sulphates both under lean and rich conditions.
|
|
| 5. |
|
|
| 6. |
- Fridell, Erik, 1963, et al.
(författare)
-
Platinum oxidation and sulphur deactivation in NOx storage catalysts
- 2004
-
Ingår i: Topics in Catalysis. - 1572-9028 .- 1022-5528. ; 30-31:1-4, s. 143-146
-
Tidskriftsartikel (refereegranskat)abstract
- Flow reactor experiments and X-ray photoelectron spectroscopy (XPS) measurements were used to investigate the importance of platinum oxide formation on Pt/BaO/Al2O3 NOx storage catalysts during reactions conditions. The reaction studied was NO(g) + 1/2 O-2(g) NO2 (g). During NO2 exposure of the catalyst the NO2 dissociation rate decreased during the reaction. This activity decrease with time was also studied with XPS and it was found to be due to platinum oxide formation. The influence of sulphur exposure conditions on the performance of the NOx storage catalysts was studied by exposing the samples to lean and/or rich gas mixtures, simulating the conditions in a mixed lean application, containing SO2 The main results show that all samples are sensitive to sulphur and that the deactivation proceeds faster when SO2 is present in the feed under rich conditions than under lean or continuous SO2 exposure. Additionally, the influence of the noble metals present in the catalysts was investigated regarding sulphur sensitivity and it was found that a combination of platinum and rhodium seems to be preferable to retain high performance of the catalyst under SO2 exposure and subsequent regeneration. Finally, the behaviour of micro-fabricated model NOx storage catalysts was studied as a function of temperature and gas composition with area-resolved XPS. These model catalysts consisted of a thin film of Pt deposited on one-half of a BaCO3 pellet. It was found that the combination of SO2 and O-2 resulted in migration of Pt on the BaCO3 support up to one mm away from the Pt/BaCO3 interface.
|
|
| 7. |
- Fridell, Erik, 1963, et al.
(författare)
-
Regeneration of NOx storage catalysts
- 2004
-
Ingår i: 13th International Congress on Catalysis, Paris, France, July 11-16, 2004.
-
Konferensbidrag (refereegranskat)
|
|
| 8. |
- Amberntsson, Annika, 1974
(författare)
-
Experimental Studies of NOx Catalysts; Storage, Reduction and Sulphur Deactivation
- 2002
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis work was to investigate how different gaseous compounds, present in an automotive exhaust from lean-tuned combustion, interact with so-called NOx storage catalysts containing Al2O3 as a support, BaO as the NOx storage compound and noble metals to provide oxidation and reduction functions. The investigations included model sample preparations, flow reactor studies with various gas mixtures and spectroscopic experiments (FTIR and XPS). The results show that several of the exhaust gas components (CO2, NOx, SO2, O2) interact strongly with the catalyst, and both the storage compound (BaO) and the noble metals are affected. Due to the affinity of barium oxide for sulphate formation, and since sulphur is present in significant amounts in gasoline, diesel and lubricants, special attention was paid to sulphur compounds in the exhaust gas. The sulphur studies indicated that deactivation (poisoning) occurs in both net oxidising and net reducing gas mixtures containing SO2. After exposure in oxygen excess significant amounts of sulphates were detected with XPS and FTIR. Sulphates were also detected during net reducing sulphur exposure, but in much smaller amounts. It is suggested that the mechanism for sulphur deactivation under net oxidising and net reducing conditions are different. During lean conditions sulphate formation on the NOx storage sites on BaO seems to be the dominant mechanism. The results obtained during rich conditions, with SO2 in the gas mixture, suggest a mechanism dominated by deactivation of the NO oxidation and NOx reduction functions of the catalyst, e.g. by formation of (reduced) sulphur species on the noble metal particles.
|
|
| 9. |
|
|
| 10. |
- Amberntsson, Annika, 1974, et al.
(författare)
-
Influence of platinum and rhodium composition on the NOx storage and sulphur tolerance of a barium based NOx storage catalyst
- 2003
-
Ingår i: Applied Catalysis B: Environmental. - 0926-3373 .- 1873-3883. ; 46:3, s. 429-439
-
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.
|
|
