The impacts of fluorine doping of ceria are studied by means of surface science experimental methods. Fluorine-doped and fluorine-free ceria layers are epitaxially grown on rhodium single crystals and their properties are compared in regular and inverse catalyst configurations. A procedure for epitaxial growth of CeO2(110) and CeOxFy(110) layers on Rh(110) single crystal is developed and described in detail. Shape alterations of Ce 3d spectrum brought about by fluorine doping are explained and a suitable deconvolution method is proposed. Special attention is focused towards stability of fluorine in ceria. Presented data show that fluorine incorporation in ceria lattice causes stable reduction of ceria, which withstands up to 200řC in near-ambient pressure conditions. Morphological changes are observed due to elongation of surface lattice constant of reduced ceria. Oxygen storage capacities and hydrogen oxidation reaction rates of four different studied systems are compared and discussed. The twofold nature of oxygen exposure of fluorinated ceria is discovered and explained. Oxygen repels fluorine from the surface, while the remaining part of fluorine is expelled to adsorbate positions, where its electronic state is altered. Moreover, such fluorine is prone to interact with atomic hydrogen. This reaction is...

Devido a crescente preocupação com relação ao efeito estufa e com o objetivo de obter produtos de maior valor agregado a partir dos gases CH4 e CO2, este trabalho estudou catalisadores de níquel suportados em diferentes óxidos (Al2O3, CeO2, MgO e ZrO2) promovidos com ZnO aplicados na reação de reforma seca de metano para obter gás de síntese (H2 + CO). Primeiramente foram estudados catalisadores de níquel suportados em ZrO2 dopados com diferentes teores de zinco: 0%, 5%, 12,5% e 25% a fim de selecionar o catalisador mais promissor para estudos posteriores. Também foram utilizados dois métodos de preparo: impregnação e co-precipitação. Os resultados de DRX mostraram que a adição de zinco estabilizou a fase tetragonal da zircônia em todos os teores de zinco e em ambos os métodos de preparo. As análises de RTP mostraram que os catalisadores impregnados sofreram maior redução do que os co-precipitados e para maiores teores de zinco foram necessárias maiores temperaturas de redução. Os testes catalíticos mostraram que o aditivo zinco não exerceu efeito sobre os catalisadores impregnados, porém para as amostras co-precipitadas notou-se um teor ótimo com relação à conversão de reagentes na reação e o catalisador 5Ni12ZZc apresentou os melhores resultados. A deposição de carbono também foi menor nos catalisadores co-precipitados. No estudo dos diferentes suportes, as análises de DRX sugerem a dopagem de todos os óxidos com zinco, pois houve mudanças no parâmetro de rede em todas as amostras. As análises de RTP mostraram que a adição de zinco diminui a temperatura de redução do catalisador suportado em alumina e, no suporte CeO2 o efeito é o contrário. Nos testes catalíticos observaram-se efeitos distintos: nos catalisadores Ni-ZnO-CeO2 e Ni-ZnO-MgO o efeito da adição de zinco causou diminuição na conversão dos reagentes, por outro lado, causou diminuição na deposição de carbono e inibição da formação do carbono grafite; nos catalisadores Ni-ZnO-Al2O3 a conversão de reagentes não se alterou com a adição de zinco porém houve uma diminuição na deposição de carbono. Os melhores resultados, portanto, foram apresentados pelo catalisador 5NiZnAl que converteu acima de 80% dos reagentes e não sofreu desativação pela deposição de carbono. / Due to the increasing concern related to the greenhouse effect and aiming to obtain products with higher added-value from CH4 and CO2 gases, nickel catalysts supported on different oxides (Al2O3, CeO2, MgO and ZrO2) promoted with ZnO were studied and applied to the dry reforming of methane reaction to obtain syngas (H2+CO). Firstly, ZrO2 supported Nickel catalysts doped with different zinc content: 0, 5, 12,5 and 25% molar ratio were used to identify and select the best amount of zinc to further studies. Two preparation methods were investigated: impregnation and co-precipitation. The XRD results showed that the zinc addition stabilized the zircon tetrahedral phase of all catalysts from both preparation methods. The TPR analyses showed that the impregnated catalysts reduced more than the co-precipitated ones and higher reduction temperature was needed for the catalysts with higher zinc content. The catalytic tests indicated that the zinc content did not have any effect over the impregnated catalysts, whilst for the co-precipitated samples, a great content was noted and the 5Ni12ZZc catalyst showed the best results. The co-precipitated catalysts also had lower carbon deposition. In the study of different supports, the XRD analyses showed that the zinc interacts with all the used oxides, because there were changes of the cell parameter of all samples. The TPR analyses indicated that the zinc addition lowers the reduction temperature of the alumina supported catalyst and the effect is opposite for the CeO2 support. Different effects were observed during the catalytic tests: for the CeO2 and MgO supported catalysts the effect of zinc addition caused a decrease in the conversion of reactants, but it lowered the deposition of carbon and inhibited the formation of graffiti carbon; for the Al2O3 supported catalysts, the reactant conversion was the same with the addition of zinc, however there was a reduction on the carbon deposition. Therefore, the best results were obtained for the 5NiZnAl catalyst, which converted over 80% of the reactants and wasn\'t deactivated by carbon deposition.

Orientador: Daniela Zanchet / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-26T07:36:24Z (GMT). No. of bitstreams: 1 Kokumai_TathianaMidori_M.pdf: 2185484 bytes, checksum: f809cfde78398806bc98554749cf01c8 (MD5) Previous issue date: 2014 / Resumo: Nanobastões de céria (CeO2) funcionalizados com grupos amino foram utilizados como suporte em catalisadores de cobre para a reação de deslocamento gás-água (WGS). A funcionalização da superfície do óxido foi realizada visando uma melhor dispersão da fase metálica no suporte, através da interação entre o grupo amino e o precursor Cu2+, com a posterior correlação entre esta modificação e a atividade do catalisador. Utilizou-se o método hidrotérmico para a síntese dos nanobastões, que foram posteriormente funcionalizados com 3-(aminopropil)trimetoxisilano. A adição do precursor Cu2+ ao suporte foi feita via impregnação, seguida de calcinação e redução (ativação do catalisador), etapa na qual se formaram as nanopartículas metálicas (Cu0) suportadas. Comparando os catalisadores com suporte de céria pura e de céria funcionalizada, observou-se que de fato a funcionalização resultou na maior dispersão do Cu2+ na superfície. No entanto, ela causou a menor dispersão do metal (Cu0) após a redução, a diminuição da redutibilidade da céria superficial, a fragmentação dos bastões e o menor desempenho catalítico frente à reação de WGS. Visando a compreensão destes sistemas, verificou-se que a calcinação após a adição de Cu2+ na amostra funcionalizada formou uma camada de SiO2 na superfície da céria, o que diminui a atividade por reduzir as interações Cu-CeO2 (formação de Cu-O-Si), corroborando a grande influência desta interface no desempenho destes catalisadores. Além disso, a menor dispersão de Cu0 na superfície funcionalizada após a redução demonstrou a importância da céria também na estabilização da fase metálica. Desta maneira, a funcionalização da superfície se mostrou uma abordagem interessante no que se refere à dispersão do precursor metálico no suporte / Abstract: Amino functionalized ceria nanorods were explored as support on copper catalysts for the water-gas shift (WGS) reaction. The purpose of the design of a functionalized oxide surface was to obtain a better metal phase dispersion on the support provided by amino-Cu2+ interaction, in addition to further correlation between this modification and the catalyst activity. The hydrothermal method was used to synthetize the nanorods, which were subsequently functionalized with 3-(aminopropyl)trimethoxysilane. The Cu2+ precursor was added to the support by impregnation, followed by calcination and reduction (catalyst activation), when the supported metallic (Cu0) nanoparticles were formed. By comparison of the catalysts obtained with pure ceria and functionalized ceria supports it was observed that the functionalization indeed caused a greater Cu2+ dispersion on the oxide surface. However, it gave rise to a lower metal dispersion (Cu0) after reduction step, along with the decrease of surface ceria reducibility, nanorods fragmentation and inferior catalytic performance towards WGS reaction. In order to understand these systems, it was confirmed that the calcination step (after Cu2+ addition) on functionalized sample created a SiO2 layer above ceria surface, therefore lowering the activity due to the decrease of Cu-CeO2 interactions (formation of Cu-O-Si), which corroborated the great influence of Cu-CeO2 interface on the activity. Also, the lower Cu0 dispersion on the functionalized surface after reduction showed the importance of ceria on the metallic phase stabilization. Hence, the surface functionalization demonstrated to be an interesting approach to the dispersion of metal precursor on the catalyst support / Mestrado / Quimica Inorganica / Mestra em Química

Ce travail porte sur le procédé NSR (NOx Storage-Réduction) de dépollution des gaz d'échappement automobile Diesel. Des catalyseurs contenant 2,12% Pt déposés sur alumine, cérine-zircone ou cérine modifiée, ont été caractérisés et évalués dans des conditions NSR, avec un regard particulier sur la sélectivité de la réduction des NOx. Les tests catalytiques sont effectués dans des conditions complexes : cycles 60s de stockage (mélange pauvre)/ 4s de réduction (mélange riche), avec des traces de réducteurs dans la voie pauvre et d’oxydant dans la voie riche. Des sélectivités importantes en N2O (gaz à effet de serre) ont pu être observées. Les émissions de N2O varient en fonction de la nature du support, de la température et des réducteurs mis en œuvre (C3H6, CO, H2 ou mélange C3H6+CO+H2). Dans certaines conditions, la présence de réducteur dans les phases pauvres contribue à la majorité du N2O émis lors des cycles NSR. Ces valeurs sont en bon accord avec les résultats obtenus en parallèle en régime stationnaire (SCR). A 200°C, H2 donne la plus grande sélectivité en N2O, essentiellement à cause de la réduction partielle des NOx en milieu pauvre. En revanche, à 300°C, C3H6 est le réducteur le plus sélectif en N2O, toujours avec une forte contribution des phases pauvres. Les résultats sont plus homogènes avec les catalyseurs supportés sur oxydes redox car ils favorisent la transformation des réducteurs dans la voie riche (réactions du gaz à l’eau et reformage de C3H6), conduisant à mélange réducteur moyenné. Les propriétés redox du support permettent aussi de limiter les émissions de NH3. / Lean reduction of NOx was studied on NSR (NOx storage-reduction) catalyst, with a special attention on N-compound selectivities. Platinum (2.12wt%) catalysts supported on various supports (alumina, ceria-zirconia and modified ceria) were characterized and evaluated in cycling conditions. Catalytic tests were performed and realistic and complex conditions: 60s for the storage phases (lean periods)/ 4s for the reduction (rich pulses). Gas mixture was composed of reducers and oxidants in both lean and rich atmosphere. In these conditions, high N2O emissions were measured (powerful greenhouse gas). The N2O selectivity depends on the redox properties of the support, the temperature and the chemical nature of the reducer (C3H6, CO, H2 or C3H6+CO+H2 mixture). In some conditions, more than half of the N2O production can occur during the storage phase, in lean condition. These results are in good agreement with those obtained in specific SCR tests. At 200°C, H2 lead to the higher N2O selectivity especially due to the partial NOx reduction in the lean period. At 300°C, N2O emission is mainly favoured with C3H6, with still a high contribution of the lean pulses. Results are less distinct with supported catalysts on redox material, due to the support involvement in the reducer transformation reactions (water gas shift and steam reforming), leading to a blend of reducers in the rich pulses. In addition, lower NH3 emissions were observed on platinum supported on redox oxides.

Cette étude concerne la préparation de nouveaux matériaux pour l'élimination catalytique d'un composé organique volatil (COV) : l'acide acétique. La décomposition de cette molécule gazeuse conduit à la formation de produits nocifs tels que le CO2, l'acétone et le formaldéhyde. En présence d'oxygène, des études antérieures ont mis en évidence le caractère réfractaire de l'acide acétique en milieux aqueux. En phase gaz, la dégradation de la molécule est améliorée en présence de catalyseurs basiques et réductibles tels que les oxydes mixtes MgAl. Ces matériaux ont été synthétisés via les méthodes co-précipitation (cp) et sol-gel (sg). Sur chaque catalyseur, du cérium est déposé en surface afin d'améliorer les propriétés réductrices initiales. Les échantillons MgAlCey_cp et MgAlCey_sg (y : 0,03% ; 0,07% ; 0,14% molaire) ont montré une augmentation de la capacité de stockage de l'oxygène (CSO) et du nombre de sites basiques forts dues à la multiplicité des espèces oxygènes (O22-, O2- et/ou O2-) de surface provenant de la cérine (CeO2). En effet, la basicité et la CSO des matériaux ont augmenté pour les catalyseurs MgAlCey_sg tandis que pour MgAlCey_cp un effet de synergie apparait. La réductibilité des solides semble être indépendante du mode de préparation initial. En revanche, le nombre de sites basiques est supérieur pour les catalyseurs MgAlCey_cp par rapport à MgAlCey_sg. Cette basicité accrue des catalyseurs co-précipités leur confère une activité supérieure mais limitée par la formation supposée de carbonates au cours de la réaction d'oxydation de l'acide acétique. Hormis la cérine, la meilleure activité est obtenue par les matériaux MgAlCe0,14_cp et MgAlCe0,14_sg. / This work is devoted to the preparation of the new materials for the catalytic removal of volatile organic compound (VOC) : acetic acid. Decomposition of this gaseous molecule generate dangerous products such as CO2, acetone and formaldehyde. Removing acetic acid in aqueous phase is more difficult than gas phase. In fact, the presence of basic and redox catalysts like mixed oxides MgAl improve the oxidation of acetic acid reaction. This catalysts were prepared by co-precipitation and sol-gel methods. On each catalyst, cerium is deposited on the surface in order to improve their reducibility. MgAlCey_cp and MgAlCey_sg catalysts (y : 0.03% ; 0.07% ; 0.14% molar) have shown the increase of oxygen storage capacity (OSC) and number of strong basic sites because of various oxygen species (O22-, O2- and/or O2-) located on the surface of the materials and provided by ceria (CeO2). In fact, oxygen storage capacity of these catalysts is increased for MgAlCey_sg whereas a synergy effect appears for MgAlCey_cp. The results have shown that the reducibility of the catalysts is not related to the initial preparation method. However, basicity of MgAlCey_cp catalysts is higher than MgAlCey_sg. This basicity gives a high activity to co-precipitated catalysts which is limited by possible formation of carbonates during the oxidation reaction of acetic acid. Except for ceria, the best activity is obtained by MgAlCe0.14_cp and MgAlCe0.14_sg catalysts.

Abstract The aim of the thesis was to find new information on the effect of BaO and oxygen storage capacity material on NOx reduction. A total of nine different kinds of Pd/Al2O3-based metallic monoliths were studied. Promoters such as oxygen storage capacity material (OSC material in our case Cex-1ZrxO2 mixed oxides) and stabilisers such as barium (BaO) were added into the catalyst alone or together to improve catalyst properties such as catalytic activity, selectivity, and thermal stability. The key aspects in this thesis can be divided into four parts. First, the behaviour of NO reduction and CO as well as C2H4 oxidation over Pd/Al2O3-based catalysts in rich, stoichiometric and lean conditions were studied. Secondly, the effect of BaO and the OSC material in NO reduction was considered. Thirdly, the preparation procedure, i.e. the addition order of BaO, OSC material, and Pd on the catalyst was considered. Finally, the effect of ageing on the behaviour of catalysts was investigated. Several characterization methods (in situ DRIFT, catalytic activity measurements, N2 physisorption, CO chemisorption, dynamic oxygen storage capacity measurements, and X-ray diffraction (XRD)) were utilised to find answers to the behaviour of these catalysts in the studied model reactions. The Rapid Ageing Hot in Laboratory (RAHLAB) method was used to age the catalyst. First, it was demonstrated that the CO and hydrocarbon oxidation and NO reduction reactions over the Pd/Al2O3-based catalyst behave differently. NO reduction and CO and hydrocarbon oxidation reactions were dependent on the reaction conditions and temperatures. Secondly, the effect of OSC and BaO on NO reduction was studied separately. In the case of OSC material, it was observed that the OSC material has an effect on NO reduction as well as on CO and C2H4 oxidation. In the case of BaO, it was observed that BaO has a positive effect on NO reduction as well as CO and C2H4 oxidation especially in rich conditions. Thirdly, the effects of the addition order of OSC and BaO on the catalyst was studied separately. It was shown that these have an effect on NO reduction, especially after ageing. First, on the fresh Pd/Al2O3 catalyst it was observed that the addition order of OSC on the catalyst has not an influence on catalyst performance. The effect of the BaO addition order on the Pd/OSC/Al2O3-based catalyst is found to be insignificant, especially, after the ageing process. Furthermore, it is observed that the effect of RAHLAB ageing was that the catalyst lost its catalytic activity, stability, and selectivity.

La cérine est connue pour être très performant en tant que support, dans le domaine de l'oxydation catalytique. L'ajout de métaux de transitions améliore en général cette activité. Dans ce travail, l'argent a été ajouté sur la cérine. Deux méthodes de préparation ont été utilisées : l'imprégnation (Imp), connue par la formation de particules de tailles différentes sur la surface du support, et le dépôt-précipitation (DP) qui conduit en général à la formation de nanoparticules dispersées sur la surface et dans la masse du support. Deux séries de catalyseurs x%Ag/CeO₂(Imp) et x%Ag/CeO₂(DP) où x est le pourcentage massique de l'argent par rapport à la cérine, ont été préparés dans le but de comparer leurs propriétés physico-chimiques. Ensuite leurs activités catalytiques dans les réactions d'oxydation. Les catalyseurs ont été caractérisés par différentes techniques telles que la BET, la DRX, la RPE, l'ATD-ATG, la SPX, l'UV et la RTP. Dans les deux séries de catalyseurs, la DRX a montré que des particules de Ag⁰ ont été obtenues pour les fortes teneurs en argent ; ces particules sont plus grosses dans les imprégnés que dans les (DP). La présence des nanoparticules dans les deux séries de solides a été aussi confirmée par l'UV (résonance plasmonique). Ces nanoparticules sont de formes sphériques dans les (DP) et mi-sphériques, ou déformées, dans les (Imp). Trois états d'oxydation : Ag⁰, Ag⁺ et Ag²⁺ ont été identifiés dans les imprégnés et seulement deux : Ag⁰ et Ag⁺ dans les DP. La formation des ions Ag²⁺ semble être due à la présence de AgNO₃ sur la cérine au cours de la calcination du solide, ce qui était le cas pour les imprégnés et non pour les DP. De plus, les deux isotopes ¹⁰⁷Ag²⁺ et ¹⁰⁹Ag²⁺ ont été mis en évidence par la technique de la RPE ; ce résultat est considéré comme original et primordial. Par la suite, les deux séries de catalyseurs ont été testés dans les réacctions d'oxydations catalytique du propène, du monoxyde de carbone et du noir de carbone. Le résultat inattendu dans ce travail c'est que, contrairement à la bibliographie, les catalyseurs imprégnés étaient plus actifs que les (DP) pour les trois réactions. La performance catalytique des imprégnés a été reliée à la présence des espèces Ag²⁺ qui sont absents dans les DP. Autrement exprimé à la présence de trois couples redox Ag²⁺/ Ag⁺, Ag²⁺/ Ag⁰ et Ag⁺/ Ag⁰ dans le cas des solides (Imp), pour seulement un couple redox Ag⁺/ Ag⁰ dans le cas des solides (DP). Une présence adéquate dans les rapports de concentrations de ces trois couples redox dans le catalyseur 10%Ag/CeO₂(Imp) a rendu ce dernier le plus performant comparé aux autres de la même série. / Ceria is a well known support in the world of catalytic oxidation reactions. Adding transition metals tend to enhance the catalytic activity. Silver was used in our work, and was added using two different preparation methods : the impregnation (Imp) and the deposition-precipitation (DP). The first known by the formation of different particles size on the surface of the support, whereas the second is known by the formation of nanoparticles with a good dispersion on the surface and in the bulk of the support. Two catalysts series x%Ag/CeO₂(Imp) and x%Ag/CeO₂(DP) (where x is the weight percentage of silver over ceria) were prepared in order to compare their physico-chemical properties and afterward their catalytic performances in three different oxydation reactions. The catalysts were characterized using BET, XRD, EPR, DSG-TG, XPS, UV and TPR techniques. XRD showed on both series the formation of Ag⁰ particles for the catalysts with high weight percentages. The sizes of these particles are larger in the (Imp) solids compared to the (DP) ones. Beside of these particles, the formation of Ag⁰ nanoparticles was confirmed by the plasmonic resonance in the UV technique. The nanoparticles are spherical in the (DP) solids and half spherical (misshaped) in the (Imp) solids. Three oxidation states were found in the (Imp) catalysts : Ag⁰, Ag⁺ et Ag²⁺ compared to only two in the (DP) : Ag⁰ et Ag⁺. The nitrate present in the AgNO₃ (silver precursor) during the calcination might be the reason of the formation of the Ag²⁺. That is not the case for the (DP) solids. The two isotopes for Ag²⁺ (¹⁰⁷Ag²⁺ and ¹⁰⁹Ag²⁺) were identified with the EPR technique. This result is considered as original and very important. Afterward, the catalysts were tested in the total oxidation of the propylene, carbon monoxide and carbon black. The catalytic results were unexpected and oppose the literature results. (Imp) catalysts showed a higher activity than the (DP) in all the reactions. The catalytic performance of the (Imp) was ascribed to the presence of Ag²⁺ species that are missing in the (DP) catalysts. In other words, this performance is related to the presence of the 3 redox couples Ag²⁺/ Ag⁺, Ag²⁺/ Ag⁰ et Ag⁺/ Ag⁰ for the (Imp), compared to only one : Ag⁺/ Ag⁰ for the (DP). The 10%Ag/CeO₂(Imp) solid showed an appropriate concentration ratio of the redox couples, that's why it showed the highest catalytic activity among the other solids from the same series.

Cette thèse a pour but la mise au point de méthode de synthèse de nanoparticules de métaux nobles pour la catalyse. Le projet s’est concentré sur la synthèse de nanoparticules composées de platine et de palladium. Trois voies de synthèses ont été explorées, i) par chimie organométallique de surface (COMS)), ii) par dépôt chimique en phase vapeur de composés organométalliques (MOCVD, Metal Organic Chemical Vapor Deposition et enfin iii) par voie colloïdale. La voie chimie organométallique de surface a permis la synthèse de nanoparticules supportées sur silice avec des tailles d’environ 2 nm. Le transfert de cette méthodologie vers l’oxyde de cérium a été effectué et permet d’obtenir des nanoparticules de moins de 1.5 nm de diamètre. Ces dernières recherches ont pour finalité l’obtention de catalyseurs d’oxydation supportés sur oxyde de cérium utilisé pour la dépollution automobile et ouvre la voie à la chimie organométallique de surface sur oxyde de cérium. Par MOCVD des nanoparticules de 4 à 6 nm ont été synthétisées sur couche de diffusion de gaz (GDL) pour des applications en pile à combustible. Des essais en électrocatalyse ont démontré la viabilité de la méthode de synthèse et l’activité catalytique des particules ainsi formées pour la réaction de réduction de l’oxygène (ORR), réaction clé des piles à combustible H2/O2.Enfin, pour cette même application, des nanoparticules de Pt, Pd et Pt/Pd dans différentes proportions ont été synthétisé par voie colloïdale. Ces nanoparticules, stabilisées par l’octylsilane ont une taille allant de 1.5 à 1.8 nm. Pour la platine, l’influence du précurseur organométallique et de la température ont été étudié, la synthèse sans apport de réducteur extérieur (H2) et à partir de précurseur PtII a permis l’obtention de nanoparticles stables de 1.2 nm. Leur utilisation pour l’ORR a démontré l’intérêt de former des alliages Pt/Pd, la composition 3:1 démontrant une amélioration d’un facteur 1.4 par rapport au Pt / The goal of this thesis is to develop synthesis methods for platinum and palladium based nanoparticles. We mainly focused on three synthesis pathways, i) Surface Organometallic Chemistry (SOMC), ii) metal organic chemical vapor deposition (MOCVD) and iii) a colloidal approach. Surface organometallic chemistry allowed the synthesis of silica supported nanoparticles with sizes of about 2 nm. The transfer of this methodology to cerium oxide has been carried out and allowed obtaining nanoparticles of less than 1.5 nm in diameter. Those researches had for purpose the synthesis of oxidation catalysts supported on ceria used for automotive pollution and paves the way for the surface organometallic chemistry on this oxide. By MOCVD, Pt nanoparticles from 4 to 6 nm were synthesized onto gas diffusion layers (GDL) for applications in fuel cell catalysis. Electrocatalysis results demonstrated the viability of this synthesis method and the efficiency of these catalysts for the Oxygen Reduction Reaction (ORR). For the same application, nanoparticles of Pt, Pd and Pt/Pd in various proportions were synthesized by the colloidal approach. These nanoparticles stabilized by octylsilane had a size ranging from 1.5 to 1.8 nm. For platinum, the influence of the organometallic precursor and temperature have been studied and synthesis without adding external reducing (H2) and from PtII precursor allowed obtaining stable nanoparticles of 1.2 nm. Their use for the ORR has shown interest to form alloys, the Pt/Pd 3:1 composition demonstrating an improvement by a factor of 1.4 compared to pure Pt

Concentration of Ce3+ is one of the most important parameters that influence the reactivity of ceria based catalyst. In this work we examine different experimental approaches for controlling Ce3+ concentration in cerium oxide model catalyst systems such as: i) influencing the stoichiometry of ceria, ii) introducing high valence doping agent, and iii) growing ultra thin ceria films with a strong metal substrate interaction. Structure, morphology and chemical state of prepared reduced ceria based systems were examined by means of surface science techniques: scanning tunneling microscopy, low-energy electron diffraction and X-ray photoelectron spectroscopy. In the present work an original method of ceria film reduction was introduced that allows stepwise control on stoichiometry and degree of film reduction (i). Further we introduce preparation procedures for well-ordered tungsten doped ceria model system (ii) and for the high quality 2D ultrathin ceria system on Cu (1 1 1) (iii). Preparation methods and model systems introduced in this work incorporate different physicochemical principles of Ce3+ induction and provide a variety of model systems useful for examining different effects that diversely prepared Ce3+ ions have on the activity of the catalyst.

Die Nutzung fossiler Energieträger hat die wirtschaftliche und gesellschaftliche Entwicklung der Menschheit bedeutend geprägt. Die Relevanz der verschiedenen Brennstoffe ist dabei stark vom technologischen Niveau abhängig gewesen. Mit der fortschreitenden Entwicklung und dem Aufstreben der Automobilindustrie in der ersten Hälfte des 20. Jahrhunderts gewann Erdöl als Quelle für verschiedene Kraftstoffe und Grundchemikalien immer größere Bedeutung. Der Energieverbrauch der Industriestaaten ist seit dem stetig gestiegen und zum Ende des 20. Jahrhunderts treten immer mehr Schwellenländer wie China, Indien oder Brasilien mit großem Energiehunger in Erscheinung. Dadurch wurden die Vorkommen fossiler Brennstoffe mit immer höherem Tempo ausgebeutet, sodass Schätzungen davon ausgehen, dass bereits 2030 nur noch 75% des Bedarfs durch bereits erschlossene Lagerstätten gedeckt werden können.[1] Im Gegensatz dazu sind die Reserven an Erdgas noch deutlich größer. Erdgas besteht vor allem aus Methan, welches auch über alternative Methoden z.B. Biofermentation hergestellt werden kann. Neben der Nutzung als primärer Energieträger ist Methan Ausgangsstoff für die Herstellung einer Vielzahl chemischer Produkte, z.B. Methanol oder kurzkettige Olefine[2, 3]. Eine wichtige Zwischenstufe dieser Prozesse stellt die Herstellung von Synthesegas dar, einem Gemisch aus Wasserstoff und Kohlenmonoxid. Die Herstellung erfolgt industriell über die Reaktion von Methan und Wasserdampf, dem Steamreforming. Alternative Verfahren stellen die partielle Oxidation von Methan und das Dry Reforming dar. In dieser Arbeit wurde die Aktivität verschiedener Katalysatorsysteme in der Totaloxidation, der partiellen Oxidation und dem Dry Reforming von Methan untersucht. Zur Synthese der Katalysatoren wurde die von E.Kockrick[4, 5] entwickelte Mikroemulsionsmethode angewandt. Dabei wurde die Abhängigkeit der katalytischen Aktivität von der Zusammensetzung der Komposite und den Synthesebedingungen untersucht. Das modulare Syntheseprinzip der Mikroemulsionsmethode wurde durch die Substitution der katalytisch aktiven Spezies durch verschiedene Übergangsmetalle und Gemische demonstiert. Weiterhin wurde eine neue Methode zur Herstellung makroporöser SiC-Keramiken (Abbildung 1) entwickelt. Dabei wird ein flüssiges Polycarbosilan in einer Emulsion mit besonders hohem Anteil der inneren Phase (high internal phase emulsion = HIPE) polymerisiert und zum SiC umgesetzt. Diese SiC-PolyHIPEs zeichnen sich durch ihre hohe Porosität und geringe Dichte aus. Ausgehend von der Synthesevorschrift nach Schwab et al.,[6] die die Synthese styrolbasierter PolyHIPEs beschreibt, wurde Styrol schrittweise durch SMP-10 ersetzt. Die erfolgreiche Inkorporation wurde durch thermogravimetrische Untersuchungen nachgewiesen. Zur Vernetzung des HIPE wurden verschiedene Initiatoren verwendet. Über den Anteil des SMP-10 am PolyHIPE konnte direkt Einfluss auf den Porenradius und die Dichte genommen werden, wobei die Porosität konstant bei 75% gehalten werden konnte.[7] Das Potential der SiC-PolyHIPEs für den Einsatz als poröser Katalysatorträger konnte durch die Funktionalisierung mit CeO2 und den Einsatz in der temperaturprogrammierten Oxidation von Methan nachgewiesen werden. Bereits durch eine Beladung des SiC-PolyHIPEs mit 30 Gew.% CeO2 konnte die gleiche Umsetzungstemperatur des Methans erreicht werden wie bei reinem CeO2. Eine weitere Strategie zur Erzeugung katalytisch aktiver SiC-Materialien wurde über die Funktionalisierung des Polycarbosilans mit hydrophoben CeO2-Nanopartikeln und Cerkomplexen entwickelt. Dabei zeigte sich, dass durch das Einbringen von 5 Gew.% über Dodecylamin stabilisierter CeO2-Nanopartikel eine ähnliche Aktivität in der Methanoxidation erreicht wurde, wie mit reinem Cerdioxid. Die Funktionalisierung des SMP-10 mit Cerkomplexen ergab für alle Cerkomplexe eine Phasenseparation nach dem Entfernen des Lösungsmittels. Nach der getrennten Pyrolyse der Phasen konnte nur im Pyrolysat der festen Phase Cer nachgewiesen werden, wodurch die Methanoxidation katalysiert wird. Als weitere Methode zur Erzeugung katalytisch aktiver und poröser SiC-Komposite wurde die von E.Kockrick entwickelte inverse Mikroemulsionsmethode[4, 5] verwendet. Die gewonnenen CeO2/Pt-SiCKomposite zeigten spezifische Oberflächen von bis zu 482m²/g bei einer Pyrolysetemperatur von 840 °C. Bei höheren Pyrolysetemperaturen von 1200 bzw. 1500 °C wurden Komposite mit maximal 428 bzw. 87m²/g erhalten. Die katalytischen Untersuchungen der CeO2/Pt-SiC-Komposite erfolgten an einem selbst entwickelten Katalyseteststand mit online-Analytik.[8] Dabei wurden die Totaloxidation, die partielle Oxidation und das Dry Reforming von Methan untersucht. Die Umsetzungstemperatur in der Totaloxidation von Methan konnte um bis zu 443K abgesenkt werden. In der partiellen Oxidation von Methan, wie auch beim Dry Reforming konnte bereits ab einer Reaktortemperatur von 805 °C Umsätze gemäß dem thermodynamischen Gleichgewicht erreicht werden. Die Aktivität in der partiellen Oxidation ist vor allem abhängig vom Platingehalt im Komposit. Die höchste Aktivität war bei den Kompositen mit niedriger Pyrolysetemperatur zu verzeichnen. Nach der Pyrolyse bei 1500 °C hingegen wurden aufgrund der geringeren spezifischen Oberfläche und der damit einhergehenden verminderten Zugänglichkeit der aktiven Zentren geringere Umsätze beobachtet. Einen guten Kompromiss zwischen Oxidationsbeständigkeit und katalytischer Aktivität stellten hier die Komposite dar, die bei 1200 °C pyrolysiert wurden. Mit diesen Kompositen wurden ab 805 °C bis zu 90% Umsatz und 80% Selektivität zu CO in der partiellen Oxidation von Methan und im Dry Reforming erreicht. Beim wiederholten Einsatz der CeO2/Pt-SiC-Komposite in der temperaturprogrammierten Oxidation von Methan konnte nach über 7 Zyklen keine Deaktivierung des Katalysators beobachtet werden. Die Übertragbarkeit der Mikroemulsionsmethode konnte durch den Einsatz verschiedener anderer Katalysatormaterialien gezeigt werden. Die katalytische Aktivität der erhaltenen porösen MI/MII-SiCKomposite wurde in der temperaturprogrammierten Oxidation von Methan mit einer Absenkung der Onsettemperatur um 177K bis 267K bestimmt. Damit stellt die Mikroemulsionsmethode eine flexible und robuste Möglichkeit zur Herstellung poröser SiC-Komposit-Katalysatoren dar. Literatur [1] International Energy Agency; World Energy Outlook, 2010. [2] M. Stöcker, Microporous Mesoporous Mater., 1999, 29(1-2), 3–48. [3] A.P.E. York, T. Xiao, M.L.H. Green, and J.B. Claridge, Catal. Rev. - Sci. Eng., 2007, 49(4), 511 – 560. [4] E. Kockrick, P. Krawiec, U. Petasch, H.-P. Martin, M. Herrmann, and S. Kaskel, Chem. Mater., 2008, 20(1), 77–83. [5] E. Kockrick, R. Frind, M. Rose, U. Petasch, W. Böhlmann, D. Geiger, M. Herrmann, and S. Kaskel, J. Mater. Chem., 2009, 19(11), 1543–1553. [6] M.G. Schwab, I. Senkovska, M. Rose, N. Klein, M. Koch, J. Pahnke, G. Jonschker, B. Schmitz, M. Hirscher, and S. Kaskel, Soft Matter, 2009, 5(5), 1055. [7] R. Frind, M. Oschatz, and S. Kaskel, J. Mater. Chem., 2011, (in Revision). [8] R. Frind, L. Borchardt, E. Kockrick, L. Mammitzsch, U. Petasch, M. Herrmann, and S. Kaskel, Appl. Catal., A, 2011, (in Revision).