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Depuis les années 70, les oxydes mixtes de type hexaaluminate suscitent un intérêt certain pour les réactions catalytiques du fait de leur stabilité thermique élevée qui leur confère un fort potentiel pour les réactions à haute température. Cependant, la majorité des procédés de synthèse adoptés pour la préparation de ces derniers nécessite au moins une étape de traitement thermique à haute température afin d'achever le processus de cristallisation. Ainsi, les hexaaluminates préparées par voie chimique classique présentent des tailles de particules larges et des aires spécifiques réduites (< 20 m2 g-1). Dans le cadre de ce travail, l'optimisation des paramètres et des conditions de synthèse pour la préparation d'hexaaluminate nanocristalline de grande aire spécifique a fait l'objet d'une étude détaillée. Le broyage réactif s'est révélé être une méthode de synthèse efficace, et des aires spécifiques très élevées ont été obtenues (> 70 m2 g-1). Il a été observé que la nature et la concentration du métal de transition inséré dans la structure influence fortement les propriétés redox et la mobilité d'oxygène de ces solides. Cependant, pour une même composition chimique, les propriétés redox et la mobilité de l'oxygène sont conditionnées par les propriétés structurales et texturales. L'étude des propriétés catalytique des hexaaluminates en oxydation de CH4 et de CO a montré que l'activité de ces derniers résulte d'un équilibre complexe entre les propriétés texturales et structurales, l'état de la surface (nature et concentration des sites redox), et les propriétés de réductibilité et de mobilité d'oxygène. / Since the beginning of the 1970's, hexaaluminate mixed oxides gained were studied as active materials for catalytic reaction at high temperature, e.g. catalytic combustion. Their abilities to maintain phase stability and high surface area are considered of a great interest. Unfortunately, most of the reported chemical synthesis methods for hexaaluminate preparation involve at least one calcination step at high temperature (> 1100 °C) to crystallize the desired pure phase, which leads to crystal growth and unavoidable surface reduction.The catalytic performance of hexaaluminate materials depends essentially to the structural and textural properties i.e. surface area, crystal size, and phase purity. Thus the first part of this study was dedicated to the development of an original synthesis route, the "Activated Reactive Synthesis" process that is evidenced as a promising top down approach to generate nanostructured hexaaluminate with high surface area. Values of surface areas obtained were largely higher (>77 m2 g-1) to those reported for hexaaluminates prepared by conventional routes (~ 20 m2 g-1). The nature of the transition metal Mn+ inserted in the hexaaluminate structure, as well as its concentration, plays a key role on the redox behaviours and the oxygen transfer properties. Nevertheless, for a same chemical composition, the redox properties and oxygen mobility was found to be dependent to the structural and textural properties. Activities of hexaaluminate materials in oxidation reaction of CO and CH4 is reported to depend on a complex balance between structural and textural properties, surface state, reducibility, and oxygen mobility in the bulk.

Catalytic combustion is an environmentally friendlytechnique to combust fuels in e.g. gas turbines. Introducing acatalyst into the combustion chamber of a gas turbine allowscombustion outside the normal flammability limits. Hence, theadiabatic flame temperature may be lowered below the thresholdtemperature for thermal NOXformation while maintaining a stable combustion.However, several challenges are connected to the application ofcatalytic combustion in gas turbines. The first part of thisthesis reviews the use of catalytic combustion in gas turbines.The influence of the fuel has been studied and compared overdifferent catalyst materials. The material section is divided into two parts. The firstconcerns bimetallic palladium catalysts. These catalysts showeda more stable activity compared to their pure palladiumcounterparts for methane combustion. This was verified both byusing an annular reactor at ambient pressure and a pilot-scalereactor at elevated pressures and flows closely resembling theones found in a gas turbine combustor. The second part concerns high-temperature materials, whichmay be used either as active or washcoat materials. A novelgroup of materials for catalysis, i.e. garnets, has beensynthesised and tested in combustion of methane, a low-heatingvalue gas and diesel fuel. The garnets showed some interestingabilities especially for combustion of low-heating value, LHV,gas. Two other materials were also studied, i.e. spinels andhexaaluminates, both showed very promising thermal stabilityand the substituted hexaaluminates also showed a good catalyticactivity. Finally, deactivation of the catalyst materials was studied.In this part the sulphur poisoning of palladium, platinum andthe above-mentioned complex metal oxides has been studied forcombustion of a LHV gas. Platinum and surprisingly the garnetwere least deactivated. Palladium was severely affected formethane combustion while the other washcoat materials were mostaffected for carbon monoxide and hydrogen. <b>Keywords:</b>catalytic combustion, catalyst materials,palladium, platinum, bimetallic, garnet, spinel, hexaaluminate,deactivation, sulphur, poisoning, diesel, methane,hydrocarbons

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. / QC 20100719

<p>Catalytic combustion is an environmentally friendlytechnique to combust fuels in e.g. gas turbines. Introducing acatalyst into the combustion chamber of a gas turbine allowscombustion outside the normal flammability limits. Hence, theadiabatic flame temperature may be lowered below the thresholdtemperature for thermal NO_Xformation while maintaining a stable combustion.However, several challenges are connected to the application ofcatalytic combustion in gas turbines. The first part of thisthesis reviews the use of catalytic combustion in gas turbines.The influence of the fuel has been studied and compared overdifferent catalyst materials.</p><p>The material section is divided into two parts. The firstconcerns bimetallic palladium catalysts. These catalysts showeda more stable activity compared to their pure palladiumcounterparts for methane combustion. This was verified both byusing an annular reactor at ambient pressure and a pilot-scalereactor at elevated pressures and flows closely resembling theones found in a gas turbine combustor.</p><p>The second part concerns high-temperature materials, whichmay be used either as active or washcoat materials. A novelgroup of materials for catalysis, i.e. garnets, has beensynthesised and tested in combustion of methane, a low-heatingvalue gas and diesel fuel. The garnets showed some interestingabilities especially for combustion of low-heating value, LHV,gas. Two other materials were also studied, i.e. spinels andhexaaluminates, both showed very promising thermal stabilityand the substituted hexaaluminates also showed a good catalyticactivity.</p><p>Finally, deactivation of the catalyst materials was studied.In this part the sulphur poisoning of palladium, platinum andthe above-mentioned complex metal oxides has been studied forcombustion of a LHV gas. Platinum and surprisingly the garnetwere least deactivated. Palladium was severely affected formethane combustion while the other washcoat materials were mostaffected for carbon monoxide and hydrogen.</p><p><b>Keywords:</b>catalytic combustion, catalyst materials,palladium, platinum, bimetallic, garnet, spinel, hexaaluminate,deactivation, sulphur, poisoning, diesel, methane,hydrocarbons</p>

The fossil hydrocarbons are not inexhaustible, and their use is not without impact in our need of energy, fuels and hydrocarbons as building blocks for organic materials. The quest for renewable, environmentally more friendly technologies are in need and woody biomass is a promising candidate, well provided in the boreal parts of the world. To convert the constituents of wood into valuable gaseous products, suitable for the end use required, we need a reliable gasification technology. But to become an industrial application on full scale there are still a few issues to take into account since the presence of contaminants in the process gas will pose several issues, both technical and operational, for instance by corrosion, fouling and catalyst deactivation. Furthermore the downstream applications may have very stringent needs for syngas cleanliness depending on its use. Therefore, the levels of contaminants must be decreased by gas cleanup to fulfil the requirements of the downstream applications. One of the most prominent problems in biomass gasification is the formation of tars – an organic byproduct in the degradation of larger hydrocarbons. So, tar degrading catalysts are needed in order to avoid tar related operational problems such as fouling but also reduced conversion efficiency. Deactivation of catalysts is generally inevitable, but the process may be slowed or even prevented. Catalysts are often very sensitive to poisonous compounds in the process gas, but also to the harsh conditions in the gasifier, risking problems as coke formation and attrition. Alongside with having to be resistant to any physical and chemical damage, the catalyst also needs to have high selectivity and conversion rate, which would result in a more or less tar-free gas. Commercial tar reforming catalysts of today often contain nickel as the active element, but also often display a moderate to rapid deactivation due to the causes mentioned.

This thesis concerns catalytic combustion for gas turbineapplication using a low heating-value (LHV) gas, derived fromgasified waste. The main research in catalytic combustionfocuses on methane as fuel, but an increasing interest isdirected towards catalytic combustion of LHV fuels. This thesisshows that it is possible to catalytically combust a LHV gasand to oxidize fuel-bound nitrogen (NH3) directly into N2without forming NOX. The first part of the thesis gives abackground to the system. It defines waste, shortly describesgasification and more thoroughly catalytic combustion. The second part of the present thesis, paper I, concerns thedevelopment and testing of potential catalysts for catalyticcombustion of LHV gases. The objective of this work was toinvestigate the possibility to use a stable metal oxide insteadof noble metals as ignition catalyst and at the same timereduce the formation of NOX. In paper II pilot-scale tests werecarried out to prove the potential of catalytic combustionusing real gasified waste and to compare with the resultsobtained in laboratory scale using a synthetic gas simulatinggasified waste. In paper III, selective catalytic oxidation fordecreasing the NOX formation from fuel-bound nitrogen wasexamined using two different approaches: fuel-lean andfuel-rich conditions. Finally, the last part of the thesis deals with deactivationof catalysts. The various deactivation processes which mayaffect high-temperature catalytic combustion are reviewed inpaper IV. In paper V the poisoning effect of low amounts ofsulfur was studied; various metal oxides as well as supportedpalladium and platinum catalysts were used as catalysts forcombustion of a synthetic gas. In conclusion, with the results obtained in this thesis itwould be possible to compose a working catalytic system for gasturbine application using a LHV gas. <b>Keywords:</b>Catalytic combustion; Gasified waste; LHVfuel; RDF; Biomass; Selective catalytic oxidation; NH3; NOX;Palladium; Platinum; Hexaaluminate; Garnet; Spinel;Deactivation; Sulfur; Poisoning

<p>This thesis concerns catalytic combustion for gas turbineapplication using a low heating-value (LHV) gas, derived fromgasified waste. The main research in catalytic combustionfocuses on methane as fuel, but an increasing interest isdirected towards catalytic combustion of LHV fuels. This thesisshows that it is possible to catalytically combust a LHV gasand to oxidize fuel-bound nitrogen (NH3) directly into N2without forming NOX. The first part of the thesis gives abackground to the system. It defines waste, shortly describesgasification and more thoroughly catalytic combustion.</p><p>The second part of the present thesis, paper I, concerns thedevelopment and testing of potential catalysts for catalyticcombustion of LHV gases. The objective of this work was toinvestigate the possibility to use a stable metal oxide insteadof noble metals as ignition catalyst and at the same timereduce the formation of NOX. In paper II pilot-scale tests werecarried out to prove the potential of catalytic combustionusing real gasified waste and to compare with the resultsobtained in laboratory scale using a synthetic gas simulatinggasified waste. In paper III, selective catalytic oxidation fordecreasing the NOX formation from fuel-bound nitrogen wasexamined using two different approaches: fuel-lean andfuel-rich conditions.</p><p>Finally, the last part of the thesis deals with deactivationof catalysts. The various deactivation processes which mayaffect high-temperature catalytic combustion are reviewed inpaper IV. In paper V the poisoning effect of low amounts ofsulfur was studied; various metal oxides as well as supportedpalladium and platinum catalysts were used as catalysts forcombustion of a synthetic gas.</p><p>In conclusion, with the results obtained in this thesis itwould be possible to compose a working catalytic system for gasturbine application using a LHV gas.</p><p><b>Keywords:</b>Catalytic combustion; Gasified waste; LHVfuel; RDF; Biomass; Selective catalytic oxidation; NH3; NOX;Palladium; Platinum; Hexaaluminate; Garnet; Spinel;Deactivation; Sulfur; Poisoning</p>

<p>Katalytisk förbränning är en lovande teknik för användning vid kraftgenerering, särskilt för</p><p>gasturbiner. Genom att använda katalytisk förbränning kan man nå mycket låga emissioner av kväveoxider</p><p>(NOX), kolmonoxid (CO) och oförbrända kolväten (UHC) samtidigt, vilket är svårt vid</p><p>konventionell förbränning. Förutom att man erhåller låga emissioner, kan katalytisk förbränning stabilisera</p><p>förbränningen och kan därmed användas för att uppnå stabil förbränning för gaser med låga</p><p>värmevärden. Denna avhandling behandlar huvudsakligen högtemperaturdelen av den katalytiska</p><p>förbränningskammaren. Kraven på denna del har visat sig svåra att nå. För att den katalytiska förbränningskammaren</p><p>ska kunna göras till ett alternativ till den konventionella, måste katalysatorer</p><p>med bättre stabilitet och aktivitet utvecklas.</p><p>Målet med denna avhandling har varit att utveckla katalysatorer med högre aktivitet och stabilitet,</p><p>lämpliga för högtemperaturdelen av en katalytisk förbränningskammare för förbränning av naturgas.</p><p>En mikroemulsionsbaserad framställningsmetod utvecklades för att undersöka om den kunde ge</p><p>katalysatorer med bättre stabilitet och aktivitet. Bärarmaterial som är kända för sin stabilitet, magnesia</p><p>och hexaaluminat, framställdes med den nya metoden. Mikroemulsionsmetoden användes också</p><p>för att impregnera de framställda materialen med de mer aktiva materialen perovskit (LaMnO3) och</p><p>ceriumdioxid (CeO2). Det visade sig att mikroemulsionsmetoden kan användas för att framställa katalysatorer</p><p>med bättre aktivitet jämfört med de konventionella framställningsmetoderna. Genom att</p><p>använda mikroemulsionen för att lägga på aktiva material på bäraren erhölls också en högre aktivitet</p><p>jämfört med konventionella beläggningsstekniker.</p><p>Eftersom katalysatorerna ska användas under lång tid i förbräningskammaren utfördes också en</p><p>åldringsstudie. Som jämförelse användes en av de mest stabila materialen som rapporterats i litteraturen:</p><p>LMHA (mangan-substituerad lantan-hexaaluminat). Resultaten visade att LMHA deaktiverade</p><p>mycket mer jämfört med flera av katalysatorerna innehållande ceriumdioxid på hexaaluminat som</p><p>framställts med den utvecklade mikroemulsionstekniken.</p> / <p>Catalytic combustion is a promising technology for power applications, especially gas turbines.</p><p>By using catalytic combustion ultra low emissions of nitrogen oxides (NO_X), carbon monoxide (CO)</p><p>and unburned hydrocarbons (UHC) can be reached simultaneously, which is very difficult with conventional</p><p>combustion technologies. Besides achieving low emission levels, catalytic combustion can</p><p>stabilize the combustion and thereby be used to obtain stable combustion with low heating-value</p><p>gases. This thesis is focused on the high temperature part of the catalytic combustor. The level of</p><p>performance demanded on this part has been proven hard to achieve. In order to make the catalytic</p><p>combustor an alternative to the conventional flame combustor, more stable catalysts with higher activity</p><p>have to be developed.</p><p>The objective of this work was to develop catalysts with higher activity and stability, suitable</p><p>for the high-temperature part of a catalytic combustor fueled by natural gas. A microemulsion-based</p><p>preparation method was developed for this purpose in an attempt to increase the stability and activity</p><p>of the catalysts. Supports known for their stability, magnesia and hexaaluminate, were prepared using</p><p>the new method. The microemulsion method was also used to impregnate the prepared material with</p><p>the more active materials perovskite (LaMnO₃) and ceria (CeO₂). It was shown that the microemulsion</p><p>method could be used to prepare catalysts with better activity compared to the conventional</p><p>methods. Furthermore, by using the microemulsion to apply active materials onto the support a</p><p>significantly higher activity was obtained than when using conventional impregnation techniques.</p><p>Since the catalysts will operate in the catalytic combustor for extended periods of time under</p><p>harsh conditions, an aging study was performed. One of the most stable catalysts reported in the</p><p>literature, LMHA (manganese-substituted lanthanum hexaaluminate), was included in the study for</p><p>comparison purposes. The results show that LMHA deactivated much more strongly compared to</p><p>several of the catalysts consisting of ceria supported on lanthanum hexaaluminate prepared by the</p><p>developed microemulsion method.</p>

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. / Catalytic combustion is a promising technology for 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 been 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. A microemulsion-based preparation method was developed for this purpose in an attempt to increase the stability and activity of the catalysts. Supports known for their stability, magnesia and hexaaluminate, were prepared using the new method. The microemulsion method was also used to impregnate the prepared material with the more active materials perovskite (LaMnO3) and ceria (CeO2). It was shown that the microemulsion method could be used to prepare catalysts with better activity compared to the conventional methods. Furthermore, by using the microemulsion to apply active materials onto the support a significantly higher activity was obtained than when using conventional impregnation techniques. Since the catalysts will operate in the catalytic combustor for extended periods of time under harsh conditions, an aging study was performed. One of the most stable catalysts reported in the literature, LMHA (manganese-substituted lanthanum hexaaluminate), was included in the study for comparison purposes. The results show 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. / QC 20101104