| 1. |
- Birgersson, Henrik, et al.
(författare)
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An investigation of a new regeneration method of commercial aged three-way catalysts
- 2006
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Ingår i: Applied Catalysis B. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 65, s. 93-100
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Tidskriftsartikel (refereegranskat)abstract
- The ability to modify aged three-way catalysts (TWC) by regaining part of the fresh catalyst surface structure has been verified by both bulk and surface-sensitive characterisation techniques. X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM/EDX) techniques were applied to fully evaluate the efficiency of a regeneration procedure of commercial three-way catalysts targeting the washcoat surface. The regeneration comprised combined thermal and liquid chlorine treatments. Structural changes of the washcoat were further investigated with nitrogen adsorption-desorption (BET) and Laser Ablation methods. The investigation showed that the regeneration treatments resulted in an enrichment of the washcoat surface with palladium, thereby increasing the number of catalytically active surface sites. Furthermore, the observed removal of phosphorous and sulphur contaminants resulted in an increase of the relative amount of small pores between 1 and 10 nm and washcoat surface area. An increased catalytic activity regarding CO, NOx, and HC emissions was observed after regeneration. providing proof of the proposed concept.
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| 2. |
- Birgersson, Henrik, 1976-
(författare)
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Development and Assessment of Regeneration Methods for Commercial Automotive Three-Way Catalysts
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Car exhaust catalysts were introduced in the early 1980’s, to limit the release of pollutants such as hydrocarbons, carbon monoxide and nitrogen oxides. These catalysts contain noble metals such as palladium (Pd), platinum (Pt) and rhodium (Rh) and are able to simultaneously abate all three of the above-mentioned pollutants, hence the name three-way catalyst (TWC). The exposure to high temperatures (800-1000 °C) during operation and the presence of additives in gasoline and lubricants will, after a certain time, lower the activity of the TWC. High temperatures reduce the active area by causing the noble metals to agglomerate and sinter, whereas the additives alter the activity either by fouling the pores of the support material or by interacting with the metals. The main objective of this work was to develop a method which allows for the removal of contaminants (additives) from the washcoat and enables the redispersion of the active sites (noble metals), in an effort to recover lost catalyst activity. For this purpose, regeneration experiments were carried out on a wide spectrum of different commercial car exhaust catalysts. The influence of a thermal treatment in a controlled gas atmosphere, such as oxygen or hydrogen, and a redispersing agent, e.g. chlorine, on the activity of TWC was investigated by means of laboratory-scale activity measurements. Several complementary characterization methods such as SEM/TEM, XRD, BET, LA, XPS and TPR were employed to verify the effects of the regeneration treatments on the catalyst morphology (Papers I, II). The results show that partial regeneration of catalyst activity and noble metal dispersion was achieved after thermal treatment in an oxygen-chlorine rich atmosphere at temperatures below 500 °C. A wet-chemical regeneration treatment with dilute oxalic and citric acid solutions is evaluated in Paper III. These acidic solutions are able to dissolve and remove contaminants from the washcoat, thus partly restoring the catalyst activity. An investigation of the effects of an oxy-chlorine thermal treatment for regeneration of a ‘full-scale’ commercial automotive three-way catalyst was carried out (Paper IV). Improved catalyst activity for a high mileage catalyst could be observed, with emissions lowered by approximately 30 to 40 vol.% over the EC2000 driving cycle. The properties of fresh, aged and regenerated catalysts were then studied by means of labscale experiments, on a local as well as a global level using a mathematical model (Paper V). The model allows for comparison of the intrinsic properties of the active surface by deriving and tuning parameters of a fresh catalyst and verifying the activity of a regenerated or aged catalyst.
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| 3. |
- Boutonnet, Magali, et al.
(författare)
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Recent developments in the application of nanoparticles prepared from w/o microemulsions in heterogeneous catalysis
- 2008
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Ingår i: Current Opinion in Colloid & Interface Science. - : Elsevier BV. - 1359-0294 .- 1879-0399. ; 13:4, s. 270-286
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Tidskriftsartikel (refereegranskat)abstract
- This paper reviews the use of microemulsions, especially the water-in-oil (w/o) microemulsions, for preparation of nanoparticles that are employed as catalyst components in heterogeneous catalytic reactions. The objective is to show the growing interest of using microemulsions in the preparation of different types of materials such as metals, single metal oxides or mixed metal oxides with a broad range of application in heterogeneous catalysis and also in electrocatalysis. In most cases, the catalytic material showed improved catalytic properties as a result of the special synthesis environment created by the microemulsions. Still, research is needed for a better understanding of such beneficial effects. In addition, this method needs improvements in order to produce, in an environmentally friendly way, a suitable amount of material for use in industrial-scale catalytic processes.
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| 4. |
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| 5. |
- Elm Svensson, Erik, et al.
(författare)
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Microemulsion synthesis of MgO-supported LaMnO3 for catalytic combustion of methane
- 2006
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 117:4, s. 484-490
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Tidskriftsartikel (refereegranskat)abstract
- Catalysts with 20% LaMnO3 supported on MgO have been prepared via CTAB-1-butanol-iso-octane-nitrate salt microemulsion. The preparation method was successfully varied in order to obtain different degrees of interaction between LaMnO3 and MgO as shown by TPR and activity tests after calcination at 900 degrees C. Activity was tested on structured catalysts with 1.5% CH4 in air as test gas giving a GHSV of 100,000 h(-1). The activity was greatly enhanced by supporting LaMnO3 on MgO compared with the bulk LaMnO3. After calcination at 1100 degrees C both the surface area and TPR profiles were similar, indicating that the preparation method is of little importance at this high temperature due to interaction between the phases. Pure LaMmO(3) and MgO were prepared using the same microemulsion method for comparison purposes. Pure MgO showed an impressive thermal stability with a BET surface area exceeding 30 m(2)/g after calcination at 1300 degrees C. The method used to prepare pure LaMnO3 appeared not to be suitable since the surface area dropped to 1.1 m(2)/g already after calcination in 900 degrees C.
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| 6. |
- Elm Svensson, Erik, 1976-
(författare)
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Nanomaterials for high-temperature catalytic combustion
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Katalytisk förbränning är en lovande teknik för användning vid kraftgenerering, särskilt för gasturbiner. Genom att använda katalytisk förbränning kan man nå mycket låga emissioner av kväveoxider (NOX), kolmonoxid (CO) och oförbrända kolväten (UHC) samtidigt, vilket är svårt vid konventionell förbränning. Förutom att man erhåller låga emissioner, kan katalytisk förbränning stabilisera förbränningen och kan därmed användas för att uppnå stabil förbränning för gaser med låga värmevärden. Denna avhandling behandlar huvudsakligen högtemperaturdelen av den katalytiska förbränningskammaren. Kraven på denna del har visat sig svåra att nå. För att den katalytiska förbränningskammaren ska kunna göras till ett alternativ till den konventionella, måste katalysatorer med bättre stabilitet och aktivitet utvecklas. Målet med denna avhandling har varit att utveckla katalysatorer med högre aktivitet och stabilitet, lämpliga för högtemperaturdelen av en katalytisk förbränningskammare för förbränning av naturgas. En mikroemulsionsbaserad framställningsmetod utvecklades för att undersöka om den kunde ge katalysatorer med bättre stabilitet och aktivitet. Bärarmaterial som är kända för sin stabilitet, magnesia och hexaaluminat, framställdes med den nya metoden. Mikroemulsionsmetoden användes också för att impregnera de framställda materialen med de mer aktiva materialen perovskit (LaMnO3) och ceriumdioxid (CeO2). Det visade sig att mikroemulsionsmetoden kan användas för att framställa katalysatorer med bättre aktivitet jämfört med de konventionella framställningsmetoderna. Genom att använda mikroemulsionen för att lägga på aktiva material på bäraren erhölls också en högre aktivitet jämfört med konventionella beläggningsstekniker. Eftersom katalysatorerna ska användas under lång tid i förbräningskammaren utfördes också en åldringsstudie. Som jämförelse användes en av de mest stabila materialen som rapporterats i litteraturen: LMHA (mangan-substituerad lantan-hexaaluminat). Resultaten visade att LMHA deaktiverade mycket mer jämfört med flera av katalysatorerna innehållande ceriumdioxid på hexaaluminat som framställts med den utvecklade mikroemulsionstekniken.
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| 7. |
- 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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| 8. |
- Elm Svensson, Erik, et al.
(författare)
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Preparation of hexaaluminate
- 2008
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Patent (populärvet., debatt m.m.)abstract
- A method for preparing a hexaaluminate. The method comprises the steps of a) providing a porous template material, wherein pores having a pore size of about 5-200 nm form at least about 50% of the total pore volume; b) impregnating the material with a liquid comprising metal elements corresponding to the elements of said hexaaluminate to provide an impregnated material; c) drying the impregnated material to provide a dried material; d) optionally, repeating at least once step b), using the dried material, and step c); e) calcining the dried material in an inert atmosphere to provide a calcined material; and f) recovering the hexaaluminate by removing template material from the calcined material. A composition obtainable by such a method. A catalyst composition comprising a hexaaluminate, wherein the composition has an average surface area of at least about 9 m2/g after ageing of the composition in a moist high-temperature atmosphere. A supported catalyst comprising such a composition. Use of such a composition as a catalyst in a high-temperature application.
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| 9. |
- Elm Svensson, Erik, et al.
(författare)
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Stability of hexaaluminate-based catalysts for high-temperature catalytic combustion of methane
- 2008
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Ingår i: Applied Catalysis B. - : Elsevier BV. - 0926-3373 .- 1873-3883. ; 84:1-2, s. 241-250
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Tidskriftsartikel (refereegranskat)abstract
- Lanthanum hexaaluminate with a nominal composition of LaAl11O18 Was used to support 20 wt.% of LaMnO3 and CeO2. LaAl11O18 was prepared through co-precipitation of metal nitrates within the water phase of an isooctane/CFAB/1-butanol microemulsion. The stabilities of the prepared catalysts were assessed by measuring the activities for combustion of methane before and after aging at 1000 degrees C for 100h in air with 10 vol.% H2O. The activities were compared with LaMnAl11O19, due to its well-documented stability. It was shown that by using hydrothermal treatment of the microemulsion, a significantly higher surface area was obtained for the LaAl11O18. For LaMnO3, the reference support (Al2O3) was shown to be superior to LaAl11O18 as support, both in terms of activity and stability. Reactions between LaMnO3 and support were observed for all supports included in the study. For CeO2, LaAl11O18 was superior to Al2O3 as support. Deactivations of the CeO2 catalysts were linked to crystal growth of CeO2. LMHA deactivated strongly during aging; LaMnO3 on Al2O3 and several of the catalysts with CeO2 supported on LaAl11O18 showed a much more stable behavior.
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| 10. |
- Eriksson, Sara, et al.
(författare)
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Catalytic combustion of methane in steam and carbon dioxide-diluted reaction mixtures
- 2006
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Ingår i: Applied Catalysis. - : Elsevier BV. - 0166-9834 .- 1873-3867. ; 312, s. 95-101
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Tidskriftsartikel (refereegranskat)abstract
- Supported palladium catalysts have been tested for methane combustion under lean conditions in the temperature range of 200-800 degrees C. The effect of diluting the reaction mixture with high amounts of water and carbon dioxide was studied in order to simulate a combustion process with exhaust gas recirculation. The influence of support material, i.e. ZrO2 or doped CeO2, on the catalytic performance was also investigated. The catalyst support material was found to influence the light-off temperature significantly, which increased in the following order: Pd/ZrO2 < Pd/Zr-CeO2 < Pd/La-CeO2. The order of activity changed at higher temperatures resulting in Pd/La-CeO2 being the most active catalyst above 670 degrees C. This catalyst also shows a more stable performance with no distinct deactivation occurring at higher temperatures during cooling. Both water and CO2 were found to have a negative influence on the catalytic activity. The inhibitory effect was, however, more pronounced for water. This inhibitory effect was present in the entire temperature range investigated. Adding CO2 in the presence of water resulted in conversions similar to the ones observed when feeding water alone for Pd/ZrO2 and Pd/La-CeO2, On the contrary, the activity of Pd/Zr-CeO2 was further decreased when co-feeding water and CO2.
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