| 1. |
- Rojas, S., et al.
(författare)
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Preparation of carbon supported Pt and PtRu nanoparticles from microemulsion - Electrocatalysts for fuel cell applications
- 2005
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Ingår i: Applied Catalysis A. - : Elsevier BV. - 0926-860X .- 1873-3875. ; 285:02-jan, s. 24-35
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Tidskriftsartikel (refereegranskat)abstract
- A series of platinum and platinum ruthenium carbon supported electrocatalyst have been prepared by the microemulsion technique. The influence of parameters such as the preparation route, the metal loading and the PtRu stoichiometry on the morphology of the final nanoparticles has been studied. Irrespective the total metal loading, nanosized particles, displaying a narrow size distribution were obtained. In addition, particle size was found to be independent of the metal loading. Structural characteristics of these systems have been studied by XPS, X-ray diffraction, TEM, and TPR-TPO and their textural parameters by N-2 adsorption. The catalytic performance of the samples was evaluated in the electrochemical oxidation of methanol. The influence of the morphology on the catalytic performance of the catalysts is discussed in terms of their synthesis route. © 2005 Elsevier B.V. All rights reserved.
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| 2. |
- Elm Svensson, Erik, 1976-
(författare)
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Nanotemplated High-Temperature Materials for Catalytic Combustion
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Catalytic combustion is a promising technology for heat and power applications, especially gas turbines. By using catalytic combustion ultra low emissions of nitrogen oxides (NOX), carbon monoxide (CO) and unburned hydrocarbons (UHC) can be reached simultaneously, which is very difficult with conventional combustion technologies. Besides achieving low emission levels, catalytic combustion can stabilize the combustion and thereby be used to obtain stable combustion with low heating-value gases. This thesis is focused on the high-temperature part of the catalytic combustor. The level of performance demanded on this part has proven hard to achieve. In order to make the catalytic combustor an alternative to the conventional flame combustor, more stable catalysts with higher activity have to be developed. The objective of this work was to develop catalysts with higher activity and stability, suitable for the high-temperature part of a catalytic combustor fueled by natural gas. Two template-based preparation methods were developed for this purpose. One method was based on soft templates (microemulsion) and the other on hard templates (carbon). Supports known for their stability, magnesia and hexaaluminate, were prepared using the developed methods. Catalytically active materials, perovskite (LaMnO3) and ceria (CeO2), were added to the supports in order to obtain catalysts with high activities and stabilities. The supports were impregnated with active materials by using a conventional technique as well as by using the microemulsion technique. It was shown that the microemulsion method can be used to prepare catalysts with higher activity compared to the conventional methods. Furthermore, by using a microemulsion to apply active materials onto the support a significantly higher activity was obtained than when using the conventional impregnation technique. Since the catalysts will operate in the catalytic combustor for extended periods of time under harsh conditions, an aging study was performed on selected catalysts prepared by the microemulsion technique. The stability of the catalysts was assessed by measuring the activity before and after aging at 1000 C in humid air for 100 h. One of the most stable catalysts reported in the literature, LMHA (manganese-substituted lanthanum hexaaluminate), was included in the study for comparative purposes. The results showed that LMHA deactivated much more strongly compared to several of the catalysts consisting of ceria supported on lanthanum hexaaluminate prepared by the developed microemulsion method. Carbon templating was shown be a very good technique for the preparation of high-surface-area hexaaluminates with excellent sintering resistance. It was found that the pore size distribution of the carbon used as template was a crucial parameter in the preparation of hexaaluminates. When a carbon with small pores was used as template, the formation of the hexaaluminate crystals was strongly inhibited. This resulted in a material with poor sintering resistance. On the other hand, if a carbon with larger pores was used as template, it was possible to prepare materials with hexaaluminate as the major phase. These materials were, after accelerated aging at 1400 C in humid air, shown to retain surface areas twice as high as reported for conventionally prepared materials.
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| 3. |
- Eriksson, Sara, et al.
(författare)
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Experimental and numerical investigation of supported rhodium catalysts for partial oxidation of methane in exhaust gas diluted reaction mixtures
- 2007
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Ingår i: Chemical Engineering Science. - : Elsevier BV. - 0009-2509 .- 1873-4405. ; 62:15, s. 3991-4011
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Tidskriftsartikel (refereegranskat)abstract
- The partial oxidation of methane/oxygen mixtures with large exhaust gas dilution (46.3 vol% H2O and 23.1 vol% CO2) has been investigated experimentally and numerically over Rh/CeO2-ZrO2, Rh/ZrO2 and Rh/alpha-Al2O3 catalysts. Experiments were carried out in a short-contact-time (similar to 8 ms) reactor at 5 bar and included exhaust gas analysis, temperature measurements along the reactor, and catalyst characterization. Additional experiments were performed in an optically accessible channel-flow reactor and involved in situ Raman measurements of major gas-phase species concentrations over the catalyst boundary layer and laser-induced fluorescence (LIF) of formaldehyde. A full elliptic two-dimensional numerical code that included elementary hetero-/homogeneous chemical reaction schemes and relevant heat transfer mechanisms in the solid was used in the simulations. The employed heterogeneous reaction mechanism, including only active Rh sites, reproduced the experiments with good accuracy. The ratio of active to geometrical surface area, deduced from hydrogen chemisorption measurements, was the single model parameter needed to account for the effect of different supports. This indicated that water activation occurring on support sites, resulting in inverse OH spillover from the support to the noble metal sites, could be neglected under the present conditions with high water dilution. An evident relationship between noble metal dispersion and catalytic behavior, in terms of methane conversion and synthesis gas yields, could be established. Both measurements and predictions indicated that an increasing Rh dispersion (in the order Rh/alpha-Al2O3, Rh/ZrO2, and Rh/CeO2-ZrO2) resulted in higher methane conversions, lower surface temperatures, and higher synthesis gas yields.
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| 4. |
- Eriksson, Sara, et al.
(författare)
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Fuel-rich catalytic combustion of methane in zero emissions power generation processes
- 2006
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 117:4, s. 447-453
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Tidskriftsartikel (refereegranskat)abstract
- A novel catalytic combustion concept for zero emissions power generation has been investigated. Catalysts consisting of Rh supported on ZrO2, Ce-ZrO2 or alpha-Al2O3 were prepared and tested under fuel-rich conditions, i.e. for catalytic partial oxidation (CPO) of methane. The experiments were performed in a subscale gas-turbine reactor operating at 5 bar with exhaust gas-diluted feed mixtures.The catalyst support material was found to influence the light-off temperature significantly, which increased in the following order Rh/Ce-ZrO2 < Rh/ZrO2 < Rh/alpha-Al2O3. The Rh loading, however, only had a minor influence. The high activity of Rh/Ce-ZrO2 is probably related to the high dispersion of Rh on Ce-ZrO2 and the high oxygen mobility of this support compared to pure ZrO2. The formation of hydrogen was also found to increase over the catalyst containing ceria in the support material.
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| 5. |
- Kusar, H. M. J., et al.
(författare)
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Selective catalytic oxidation of NH3 to N-2 for catalytic combustion of low heating value gas under lean/rich conditions
- 2005
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Ingår i: Applied Catalysis B. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 58:02-jan, s. 25-32
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Tidskriftsartikel (refereegranskat)abstract
- The selective catalytic oxidation (SCO) of ammonia to nitrogen has been examined over 5% Fe/Al2O3, 5% Mn/Al2O3, 20% Cuo/Al2O3, 1% Pt/20% CuO/Al2O3, 2% Rh/Al2O3 and a Fe zeolite (Fe-SH-27) under fuel-lean and fuel-rich conditions in a monolith lab-scale reactor. For simulating fuel-bound nitrogen in a low heating value (LHV) gas 400 ppm NH3 was added to the test gas. The SCO performance of the catalysts was tested both with and without water added to the gas stream. For SCO under fuel-lean conditions the Fe-zeolite catalyst exhibited the lowest NO, yield. For SCO under fuel-rich conditions the 20% CuO/Al2O3 was superior with close to zero NO, formation.
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| 6. |
- 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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