| 1. |
- Persson, Katarina, et al.
(författare)
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Characterisation and microstructure of Pd and bimetallic Pd-Pt catalysts duirng methane oxidation
- 2007
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 245:2, s. 401-414
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Tidskriftsartikel (refereegranskat)abstract
- The catalytic oxidation of methane was studied over Pd/Al2O3 and Pd-Pt/Al2O3. It was found that the activity of Pd/Al2O3 gradually decreases with time at temperatures well below that of PdO decomposition. The opposite was observed for Pd-Pt/Al2O3, of which the activity decreases slightly with time. Morphological studies of the two catalysts showed major changes during operation. The palladium particles in Pd/Al2O3 are initially composed of smaller, randomly oriented crystals of both PdO and Pd. In oxidising atmospheres, the crystals become more oxidised and form larger crystals. The activity increase of Pd-PuAl2O3 is probably related to more PdO being formed during operation. The particles in Pd-Pt/Al2O3 are split into two different domains: one with PdO and the other likely consisting of an alloy between Pd and Pt. The alloy is initially rich in palladium, but the composition changes to a more equalmolar Pd-Pt structure during operation. The ejected Pd is oxidised into PdO, which is more active than its metallic phase. The amount of PdO formed depends on the oxidation time and temperature.
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| 2. |
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| 3. |
- Persson, Katarina, et al.
(författare)
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Stability of palladium-based catalysts during catalytic combustion of methane: The influence of water
- 2007
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Ingår i: Applied Catalysis B. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 74:3-4, s. 242-250
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Tidskriftsartikel (refereegranskat)abstract
- The stability of methane conversion was studied over a Pd/Al2O3 catalyst and bimetallic Pd-Pt/Al2O3 catalysts. The activity of methane combustion over Pd/Al2O3 gradually decreased with time, whereas the methane conversion over bimetallic Pd-Pt catalysts was significantly more stable. The differences in combustion behavior were further investigated by activity tests where additional water vapor was periodically added to the feed stream. From these tests it was concluded that water speeds up the degradation process of the Pd/Al2O3 catalyst, whereas the catalyst containing Pt was not affected to the same extent. DRIFTS studies in a mixture of oxygen and methane revealed that both catalysts produce surface hydroxyls during combustion, although the steady state concentration on the pure Pd catalyst is higher for a fixed temperature and water partial pressure. The structure of the bimetallic catalyst grains with a PdO domain and a Pd-Pt alloy domain may be the reason for the higher stability, as the PdO domain appears to be more affected by the water generated in the combustion reaction than the alloy. Not all fuels that produce water during combustion will have stability issues. It appears that less strong binding in the fuel molecule will compensate for the degradation.
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| 4. |
- Ersson, Anders, et al.
(författare)
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A comparison between hexaaluminates and perovskites for catalytic combustion applications
- 2006
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 112:04-jan, s. 157-160
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Tidskriftsartikel (refereegranskat)abstract
- Hexaaluminates and perovskites are two promising candidates for use in catalytic combustion applications. In the present study two hexaaluminates, LaMnAl11O19 and LaCoAl11O19, were compared with two perovskites, LaMnO3 and LaCoO3, with respect to their thermal stability and catalytic activity for combustion of methane and gasified biomass. The results showed that the hexaaluminates retained a much higher surface area even after calcination at 1200 degrees C compared to the perovskites. LaMnAl11O19 showed the highest catalytic activity of all catalysts. LaCoAl11O19 generally showed low activity. Of the two perovskites, LaCoO3 was the most active, and the initial test run the activity for biomass combustion were close to that one of LaMnAl11O19 even though its surface area was only one tenth of the hexaaluminate's. However, it was severely deactivated in the second test run. Similar deactivation but less severe was also found for the other catalyst.
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| 5. |
- Persson, Katarina, 1977-
(författare)
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Bimetallic Palladium Catalysts for Methane Combustion in Gas Turbines
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Catalytic combustion is a promising combustion technology for gas turbines, which results in ultra low emission levels of nitrogen oxides (NOx), carbon monoxide (CO) and unburned hydrocarbons (UHC). Due to the low temperature achieved in catalytic combustion almost no thermal NOx is formed. This thesis is concentrated on the first stage in a catalytic combustion chamber, i.e. the ignition catalyst. The catalyst used for this application is often a supported palladium based catalyst due to its excellent activity for methane combustion. However, this type of catalyst has a serious drawback; the methane conversion decreases severely with time during operation. The unstable activity will result in increasing difficulties to ignite the fuel. The parameters that govern the poor stability and other features of the palladium catalysts are discussed in the thesis. The objective of the work is to improve the catalytic performance of supported palladium catalysts, with focus on stabilising the methane conversion. A large number of different bimetallic palladium catalysts have been evaluated, where the influence of co-metals, molar ratio and support material is addressed. Results from the activity tests of methane combustion showed that it is possible to stabilise the activity by adding certain co-metals into the palladium catalyst. An extensive characterisation study has been carried out on the various bimetallic catalysts in order to gain a better understanding of how their morphology and physicochemical properties determine the various patterns of combustion behaviour. The environment inside a gas turbine combustor is very harsh for a catalyst. Since the stability of the catalyst is of great importance for ignition catalysts, it is essential to evaluate the risk of deactivation. In this work special emphasis has been given to thermal deactivation, water inhibition and sulphur poisoning. It was found that a bimetallic Pd Pt catalyst is significantly more tolerant to the various deactivation processes investigated than the monometallic palladium catalyst. Finally, the influence of pressure on the catalytic performance has been investigated. The catalysts were assessed at more realistic conditions for gas turbines, in a high-pressure test facility with 100 kW fuel power.
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| 6. |
- Persson, Katarina, et al.
(författare)
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Catalytic combustion of methane over bimetallic Pd-Pt catalysts: The influence of support materials
- 2006
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Ingår i: Applied Catalysis B: Environmental. - : Elsevier BV. - 0926-3373. ; 66, s. 175-185
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Tidskriftsartikel (refereegranskat)abstract
- The effect of support material on the catalytic performance for methane combustion has been studied for bimetallic palladium-platinum catalysts and compared with a monometallic palladium catalyst on alumina. The catalytic activities of the various catalysts were measured in a tubular reactor, in which both the activity and stability of methane conversion were monitored. In addition, all catalysts were analysed by temperature-programmed oxidation and in situ XRD operating at high temperatures in order to study the oxidation/reduction properties.The activity of the monometallic palladium catalyst decreases under steady-state conditions, even at a temperature as low as 470 degrees C. In situ XRD results showed that no decomposition of bulk PdO into metallic palladium occurred at temperatures below 800 degrees C. Hence, the reason for the drop in activity is probably not connected to the bulk PdO decomposition.All Pd-Pt catalysts, independently of the support, have considerably more stable methane conversion than the monometallic palladium catalyst. However. dissimilanties in activity and ability to reoxidise PdO were observed for the various support materials. Pd-Pt supported on Al2O3 was the most active catalyst in the low-temperature region, Pd-Pt supported on ceria-stabilised ZrO2 was the most active between 620 and 800 degrees C, whereas Pd-Pt supported on LaMnAl11O19 was superior for temperatures above 800 degrees C. The ability to reoxidise metallic Pd into PdO was observed to vary between the supports. The alumina sample showed a very slow reoxidation, whereas ceria-stabilised ZrO2 was clearly faster
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| 7. |
- Persson, Katarina, et al.
(författare)
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Influence of molar ratio on Pd-Pt catalysts for methane combustion
- 2006
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517. ; 243:1, s. 14-24
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Tidskriftsartikel (refereegranskat)abstract
- The catalytic oxidation of methane was investigated over six catalysts with different palladium and platinum molar ratios. The catalysts were characterised by TEM, EDS, XPS, PXRD and temperature-programmed oxidation. The results suggest that in the bimetallic catalysts, an alloy between Pd and Pt was formed in close contact with the PdO phase, with an exception for the Pt-rich catalyst, where no PdO was observed. It was found that the molar ratio between palladium and platinum clearly influences both the activity and the stability of methane conversion. By adding small amounts of platinum into the palladium catalyst, improved activity was obtained in comparison with the monometallic palladium catalyst. However, higher amounts of platinum are required for stabilising the methane conversion. The most promising catalysts with respect to both activity and stability were Pd67Pt33 and Pd50Pt50. The platinum-rich catalyst showed very poor activity for methane conversion.
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| 8. |
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| 9. |
- Persson, Katarina, et al.
(författare)
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Influence of co-metals on bimetallic palladium catalysts for methane combustion
- 2005
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Ingår i: Journal of Catalysis. - : Elsevier BV. - 0021-9517 .- 1090-2694. ; 231, s. 139-150
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Tidskriftsartikel (refereegranskat)abstract
- The catalytic combustion of methane has been investigated over eight different bimetallic palladium catalysts, comprising the co-metals Co, Rh, Ir, Ni, Pt, Cu, Ag, or An. The catalysts were characterized by TEM, EDS, PXRD, and temperature-programmed oxidation (TPO). It was found that a catalyst containing both Pd and Pt was the most promising, as it had a high activity that did not decline with time. The catalyst containing Pd and Ag was also a promising candidate, but its activity was slightly lower. For PdCo and PdNi, the co-metals formed spinel structures with the alumina support, with the result that the co-metals did not affect the combustion performance of palladium. For PdRh, PdIr, PdCu, and PdAg, the co-metals formed separate particles consisting of the corresponding metal oxide. These catalysts, except PdRh, showed a stable activity. For PdPt and PdAu, the co-metals formed alloys with palladium, and both catalysts showed a stable activity.
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| 10. |
- Persson, Katarina, et al.
(författare)
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Supported palladium-platinum catalyst for methane combustion at high pressure
- 2005
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 100, s. 479-483
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Tidskriftsartikel (refereegranskat)abstract
- Catalytic combustion of methane over a supported bimetallic Pd-Pt catalyst and a monometallic Pd catalyst has been investigated experimentally. Two different reactor configurations were used in the study, i.e. a tubular lab-scale reactor working at atmospheric pressure and a high-pressure reactor working at up to 15 bar. The results showed that the bimetallic catalyst has a clearly more stable activity during steady-state operation compare to the palladium only catalyst. The activity of the bimetallic catalyst was slightly higher than for the palladium catalyst. These results were established in both test facilities. Further, the impact of pressure on the combustion activity has been studied experimentally. The tests showed that the methane conversion decreases with increasing pressure. However, the impact of pressure is more prominent at lower pressures and levels out for pressures above 10 bar
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