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.

L’objectif de ce travail concerne l’étude de deux classes de catalyseurs, les oxydes mixtes (CuO/Al2O3, CuAl2O4, CuO-CuCr2O4, CuO-ZnO-Al2O3 dopés ou non par Ag et Mn) et les métaux nobles supportés (Pd/Al2O3 et Pt/Al2O3, Pd-Pt/Al2O3 dopés ou non par B) utilisés dans deux réactions différentes: la réaction d’oxydation à basse température de l’ammoniac en azote et la combustion catalytique à haute température du méthane pour la production d’énergie. Le biogaz, énergie renouvelable, est constitué majoritairement de méthane et de dioxyde de carbone. Il contient, entre autres, des traces d’ammoniac (NH3 < 1000 ppm) qu’il convient d’éliminer avant d’envisager son utilisation comme vecteur d’énergie. Nous avons synthétisé des systèmes catalytiques à base d’oxydes de cuivre par différentes méthodes. Ces catalyseurs existent sous différentes formes dont l’obtention dépend du mode de synthèse utilisé, de la teneur en cuivre et de la température de calcination. Ils présentent des propriétés physico-chimiques différentes ce qui affecte à la fois leur activité en oxydation de l’ammoniac et leur sélectivité en azote.Des catalyseurs mono et bimétalliques à base de palladium et de platine ont été déposés sur -Al2O3 puis stabilisés par un traitement à haute température en présence de vapeur d’eau. Ils ont été ensuite utilisés en combustion de CH4 (200-800°C).L’activité des catalyseurs utilisés en oxydation de NH3 ou en combustion de CH4 est affectée par l’empoisonnement par H2S. Toutefois l’importance de la désactivation de ces catalyseurs est fonction de la méthode de synthèse utilisée. / The objective of this work concerns the study of two classes of catalysts, mixed oxides (CuO/Al2O3, CuO-CuAl2O4, CuO-CuCr2O4, CuO-ZnO-Al2O3 undoped or doped with Ag and Mn) and nobles supported metals (Pd/Al2O3 and Pt/ Al2O3, Pd-Pt /Al2O3 undoped or doped with B) used in two different reactions: low temperature gas phase ammonia oxidation into nitrogen and high temperature methane catalytic combustion for energy production. Biogas, a renewable energy, is mainly constituted of methane and carbon dioxide. It contains, among others, traces of ammonia (NH3 < 1000 ppm) which has to be eliminated before its use as vector of energy. We synthesized several catalytic systems based copper oxides by various methods. These catalysts exist under various forms the obtaining of which depends on preparative route used, copper content and calcination temperatures. They present different physico-chemical properties which affects both their activity in ammonia oxidation and their selectivity in nitrogen.Mono- and bi-metallic palladium and platinum catalysts were deposited on -Al2O3 then were aged at high temperature in the presence of steam before use in CH4 combustion (200- 800°C). The activity of catalysts used in NH3 oxidation or in CH4 combustion was affected by H2S poisoning. However the importance of the catalysts deactivation was function of the synthesis method used.

Les émissions de composés organiques volatiles (COV) dans l'atmosphère sont réglementées à caus de leur impact sur la santé. L'oxydation catalytique est une des techniques prometteuses pour limiter ces émissions. L'objectif de ce travail était de mettre au point des catalyseurs actifs, sélectifs en dioxyde de carbone et stables pour la destruction de COV. Afin de trouver une alternative à l'utilisation de catalyseurs à base de métaux nobles, ce travail de recherche a été orienté sur la synthèse de matériaux à base d'oxydes de métaux de transition. Les différents oxydes mixtes ont été caractérisés par différentes techniques physico-chimiques dont la Diffraction des Rayons X (DRX), les Analyses Thermiques (ATD/ATG), la Réduction en Température Programmée (H₂-RTP), la Microscopie Électronique à Transmission (MET), la Spectrométrie de Photoélectrons induits par rayons X (SPX),... Dans un premier temps, une étude sur la préparation d'oxydes mixtes issus de précurseurs de type hydrotalcite a été menée, concernant le remplacement du cation bivalent. Cette étude a montré que l'oxyde mixte contenant du cobalt et de l'aluminium présentait une activité catalytique intéressante pour l'oxydation du toluène ainsi que du monoxyde de carbone. Afin d'améliorer cet oxyde mixte, une étude sur l'influence des méthodes non conventionnelles de préparations du précurseur hydrotalcite a été effectuée. Les micro-ondes ainsi que les ultrasons ont été utilisés lors de cette synthèse et les différents oxydes mixtes ont été testés dans les réactions du toluène et du CO. Lors de cette application, un effet bénéfique de l'utilisation des micro-ondes lors de la synthèse a été observé. Dans un troisième temps, une étude de l'incorporation de cérium dans la structure hydrotalcite a été menée. Un oxyde mixte du type CoAlCe a montré une activité catalytique intéressante pour l'oxydation totale du toluène. De plus, une relation entre la réductabilité et l'activité catalytique a pu être mise en évidence. Une comparaison entre les meilleurs catalyseurs de cette étude et des catalyseurs à base de métaux nobles commerciaux a été abordée. L'étude cinétique de l'oxydation totale du toluène a montré, que dans le cas des oxydes mixtes CoAlCe et CoAl, un mécanisme du type Mars Van Krevelen décrirait le mieux la réaction. Enfin, les quatre meilleurs oxydes mixtes ont été testés dans la réaction d'oxydation du toluène en présence de monoxyde de carbone. Un effet bénéfique de celui-ci sur la réactivité vis-à-vis du toluène a été observé. / Catalytic oxidation is one of the promising technologies to reduce VOC emissions. The objective of this work was to develop active, selective and stable catalyst for the destruction of VOC. In order to find an alternative to the use of noble metals based catalysts, this research has been focused on the synthesis of materials based on transition metal oxides. The various mixed oxides were characterized by different physico-chemical techniques including XRD, Thermal Analysis, H2-TPR, TEM, XPS...Initially, a study on the preparation of mixed oxides derived from hydrotalcite-like precursors was conducted. Thus, it was shown that the mixed oxide containing cobalt and aluminum exhibited interesting for catalytic activity for the toluene aznd carbon monoxide total oxidation. To improve this mixed oxide, a study of the influence of non-conventional methods for the preparation of the precursor was performed. The microwave and ultrasound have been used in these syntheses. The various mixed oxides thus prepared were tested in the oxidation reactions of CO and toluene. In this application, a beneficial effectvof the use of microwaves in the synthesis was observed. Thirdly, a study of the incorporation of cerium in the hydrotalcite structure was conducted. Mixed oxides of CoAlCe show interest for the total oxidation of toluene catalytic activity. Moreover, a relationship between the reductibility and the catalytic activity has been demonstrated. A comparison of the best catalysts of this study and catalysts of noble metals business was discussed. The kinetic study of the complete oxidation of toluene showed that in the case of mixed oxides CoAlCe and CoAl, a mechanism of March Van Krevelen type described the reaction.

Ce travail de thèse porte sur l’étude et le développement de matériaux adaptés pour la conversion et le stockage thermochimique de l’énergie solaire concentrée à haute température (400-1200°C), en utilisant des réactions solide-gaz réversibles. Ce type de stockage peut être associé aux centrales solaires thermodynamiques pour la génération d’électricité. Une étude bibliographique a permis d’identifier et de sélectionner les matériaux les plus adaptés possédant une densité d’énergie élevée pour le stockage thermochimique, suivant les critères de domaine de température et de non-toxicité requis. Les matériaux sélectionnés sont des oxydes métalliques (de Fe, Mn, Co, Cu), ainsi que des carbonates et des hydroxydes (de Ca, Sr, Ba). Les travaux ont porté ensuite sur les équilibres thermodynamiques des systèmes afin de prévoir les températures de transition et capacités de stockage théoriques. Une étude expérimentale a également été effectuée avec pour objectifs de déterminer précisément les niveaux de température, capacités de stockage en oxygène et enthalpies pour chaque réaction, et de démontrer leur réversibilité complète sur plusieurs cycles successifs. Des oxydes métalliques mixtes (systèmes binaires de Co-Cu, Co-Fe, Mn-Fe, Mn-Co, Mn-Cu) et des pérovskites substituées sur sites A et B ont été développés afin d’optimiser les propriétés redox des matériaux pour le stockage thermochimique. Concernant les carbonates et les hydroxydes de Ca, Sr, Ba, l’addition d’un agent stabilisant (MgO) a permis d’améliorer la stabilité des matériaux et la réversibilité des réactions au cours des cycles. Enfin, un nouveau réacteur thermochimique solaire, permettant la conversion en continu de particules réactives solides, a été validé expérimentalement et optimisé dans le cas de la décomposition de CaCO3 pour le stockage de l’énergie solaire. / This PhD thesis deals with the study and development of suitable materials for thermochemical conversion and storage of concentrated solar energy at high temperature (400-1200°C), by using reversible solid-gas reactions. This type of storage can be associated with solar thermal power plants. A bibliographic survey was performed to identify and select the most promising materials with a high energy storage density for thermochemical storage, based on different required criteria. The selected materials are metal oxides (of Fe, Mn, Co, Cu), carbonates and hydroxides (of Ca, Sr, Ba). The work then focused on the thermodynamic equilibria to determine the theoretical transition temperatures and energy storage capacities of the selected materials. An experimental study was carried out in order to determine the reaction temperatures, oxygen storage capacities and enthalpies for each reaction, and to demonstrate their complete reversibility upon cycling. Mixed metal oxides (binary systems of Mn-Fe, Co-Fe, Co-Cu, Mn-Cu, Mn-Co) and A- and B-site substituted perovskites were developed to optimize their thermochemical energy storage properties. Regarding carbonates and hydroxides of Ca, Sr, Ba, the addition of a stabilizing agent (MgO) allowed improving the materials cycling stability and reactions reversibility during successive cycles. Finally, a novel lab-scale solar reactor was experimentally tested in order to investigate the continuous decomposition of CaCO3 particles for thermochemical solar energy storage application.

Στα πλαίσια της αναζήτησης νέων μεθόδων παραγωγής ενέργειας υψηλής απόδοσης και φιλικής προς το περιβάλλον, ένα μεγάλο μέρος των ερευνητικών δραστηριοτήτων σε διεθνή κλίμακα έχει στραφεί στην ανάπτυξη της τεχνολογίας των κελιών καυσίμου στερεού ηλεκτρολύτη, SOFCs (Solid Oxide Fuel Cells). Ένα από τα μειονεκτήματα που εμφανίζονται κατά την μακρόχρονη λειτουργία ενός ‘state of the art’ κελιού καυσίμου αποτελούμενο από Ni/8YSZ (8 mol% Y2O3 stabilized ZrO2) κεραμομεταλλικό (άνοδος) - 8YSZ (ηλεκτρολύτης) - (La,Sr)MnO3 περοβσκίτη (κάθοδος) - LaCrO3 περοβσκίτη (συνδέτης) είναι η υποβάθμιση της απόδοσής του, η οποία μεταξύ άλλων οφείλεται στην αστάθεια της μικροδομής του κεραμομεταλλικού ηλεκτροδίου της ανόδου στις υψηλές θερμοκρασίες λειτουργίας του, λόγω συσσωμάτωσης της μεταλλικής φάσης. Στόχος της παρούσας εργασίας είναι η ανάπτυξη νέων υλικών με σκοπό την εφαρμογή τους ως ανοδικά ηλεκτρόδια σε κελιά καυσίμου στερεού ηλεκτρολύτη τόσο υψηλών (High Temperature SOFCs, 800-1000oC) όσο και μέσων θερμοκρασιών (Intermediate Temperature SOFCs, 650-800oC). Για το σκοπό αυτό και όσον αφορά τα HT-SOFCs παρασκευάσθηκαν, χαρακτηρίσθηκαν και ελέγχθηκαν οι ιδιότητες μικτών κεραμικών οξειδίων επιλεγμένων συνθέσεων των τριμερών συστημάτων Y2O3-ZrO2-TiO2 (YZT), Y2O3-ZrO2-Nb2O5 (YZN) και Y2O3-ZrO2-CeO2 (YZC) σε σύγκριση με το κεραμικό 8YSZ, ενώ έπειτα από την εξαγωγή των αποτελεσμάτων η έρευνα εστιάσθηκε στα κεραμομεταλλικά υλικά του συστήματος Ni/YZT με προσθήκη 30, 40 και 45 vol% Ni. Tα αποτελέσματα έδειξαν ότι τα Ni/YZT κεραμομεταλλικά συστήματα παρουσιάζουν βελτιωμένη μηχανική συμβατότητα με το στερεό ηλεκτρολύτη. Ο μεταλλογραφικός έλεγχος σε συνδυασμό με ανάλυση εικόνας έδειξε ότι η μικροδομή τους παραμένει σταθερή διατηρώντας τις τιμές της ηλεκτρικής αγωγιμότητας πρακτικά αμετάβλητες μετά από μακροχρόνια έκθεση (1000 h) σε αναγωγική ατμόσφαιρα (Ar/4%H2). Η εν λόγω συμπεριφορά παρουσιάσθηκε πιο ενισχυμένη ιδιαίτερα για τα κεραμομεταλλικά με αυξημένα ποσοστά TiO2 στην κεραμική φάση. Πειράματα διαβροχής σε συστήματα κεραμικών (YZT) σε επαφή με ρευστό Ni έδειξαν ότι η προσθήκη TiO2 βελτιώνει την ισχύ του δεσμού στη διεπιφάνεια μετάλλου/κεραμικού. Ηλεκτροχημικές μετρήσεις σε κελιά καυσίμου με Ni/YZT κεραμομεταλλικές ανόδους έδωσαν ενθαρρυντικά αποτελέσματα, επιτυγχάνοντας για ένα από τα υπό μελέτη συστήματα βελτιωμένη απόδοση σε σύγκριση με τη συμβατική άνοδο, Ni/8YSZ. Όσον αφορά τη δυνατότητα μείωσης της θερμοκρασίας λειτουργίας ενός SOFC από τους 900-1000οC στους 650-800οC και την ανάπτυξη των IT-SOFCs, η έρευνα στράφηκε προς κεραμικές συνθέσεις βασισμένες στο CeO2 και πιο συγκεκριμένα προς τα συστήματα Y2O3-CeO2 (YC) και Y2O3-CeO2-TiO2 (YCT). Ο κρυσταλλογραφικός έλεγχος των κεραμικών κόνεων, μετά από θερμική ανόπτηση μέχρι τους 1400οC στον αέρα, έδειξε ότι η βασική κρυσταλλική τους δομή αντιστοιχεί στο κυβικό πλέγμα του φθορίτη. Στα συστήματα που περιέχουν TiO2 εμφανίζεται ο σχηματισμός μιας επιπλέον φάσης με πυροχλωριτική δομή (Y2Ti2O7). Οι μετρήσεις του συντελεστή θερμικής διαστολής (TEC) στον αέρα στη θερμοκρασιακή περιοχή 25-1000°C έδωσε παρεμφερείς τιμές μειούμενες με αυξανόμενο το ποσοστό σε Ti. Σε ατμόσφαιρα Ar/4%H2 οι τιμές του TEC αυξάνονται σημαντικά για θερμοκρασίες T ≥ 800°C. Οι απόλυτες τιμές της συνολικής ηλεκτρικής αγωγιμότητας των κεραμικών σε αναγωγικές συνθήκες (Ar/4%H2) στη θερμοκρασιακή περιοχή 450-900°C εμφανίζονται σημαντικά υψηλότερες συγκριτικά με τις αντίστοιχες τιμές στον αέρα λόγω του μικτού ιοντικού-ηλεκτρονικού της χαρακτήρα. Οι απόλυτες τιμές της ιοντικής αγωγιμότητας παρουσιάζονται σημαντικά ενισχυμένες, περίπου μισή τάξη μεγέθους σε σχέση με τις αντίστοιχες του 8YSZ, για τις κεραμικές συνθέσεις του συστήματος Y0.20Ce0.80-xTixO1.9 με τις χαμηλότερες περιεκτικότητες σε Ti. Τα αντίστοιχα Ni-cermets με υψηλά ποσοστά σε ύττρια και χαμηλά ποσοστά σε τιτάνια στην κεραμική φάση επέδειξαν εξαιρετική μακροχρόνια σταθερότητα της ηλεκτρικής αγωγιμότητας, ενώ υπό τις συνθήκες λειτουργίας ενός SOFC (~900οC) η διάχυση του Ce προς το στερεό ηλεκτρολύτη 8YSZ είναι αμελητέα. / In the frame of research for the development of alternative, friendly to the environment methods for the production of energy, significant effort is focusing on SOFC (Solid Oxide Fuel Cell) technology. This work aims to the development of new promising materials for their application as anode electrodes in solid oxide fuel cells operating at high temperatures (HT-SOFCs), as well as at the intermediate temperature range (IT-SOFCs). Concerning the HT-SOFCs, mixed ZrO2-based ceramic oxides of the ternary systems Y2O3-ZrO2-TiO2 (YZT), Y2O3-ZrO2-Nb2O5 (YZN) and Y2O3-ZrO2-CeO2 (YZC) were prepared, characterized and studied in terms of thermal expansion and electrical properties, as well as their potential application as the ceramic components in the anode cermet material of a SOFC, focusing on the Ni/YZT system containing 30, 40 and 45 vol% Ni. The results showed that Ni/YZT cermets exhibit improved mechanical adjustment with the solid electrolyte and enhanced structural stability compared to Ni/8YSZ while the values of the electrical conductivity remain practical constant after long-term annealing at 1000oC for up to 1000 h in reducing atmosphere (Ar/4%H2), especially for the cermets with high TiO2-content in the ceramic phase. Wetting experiments in the system of YZT ceramics in contact with Ni showed that TiO2 presence enhances the bond strength at the metal/ceramic interface, which results in the decrease of the agglomeration tendency of the metallic particles. Electrochemical tests performed on fuel cells with Ni/YZT anode cermets showed encouraging results, whereas it is remarkable that for a specific composition was achieved improved performance compared to Ni/8YSZ anode. With regard to the possible reduction of the operating temperature from 900-1000oC to 650-800°C and the development of IT-SOFCs, the study was focused on CeO2-based oxides and more specifically on the binary Y2O3-CeO2 (YC) and ternary Y2O3-CeO2-TiO2 (YCT) systems. The XRD analysis of the ceramic powders after heating at temperatures up to 1400°C in air showed the formation of the cubic fluorite structure for the YC ceramic, whereas for the YCT ceramics an additional phase (Y2Ti2O7) with pyrochlore structure was formed. The thermal expansion coefficient (TEC) of the ceramics measured in air between 25 and 1000°C gave comparable values, decreasing with increasing Ti content, while in Ar/4%H2 atmosphere the TEC values of the ceramics increase dramatically at T ≥ 800 °C. The absolute values of the total electrical conductivity of the ceramics measured between 450-900°C in Ar/4%H2 increase significantly compared to those measured in air, due to their mixed conducting ionic-electronic character. The ionic conductivity of the Y0.20Ce0.80-xTixO1.9 ceramics with low amounts of Ti, measured in air, is appeared strongly increased, by about half order of magnitude, compared to 8YSZ. The corresponding Ni-cermets with high amounts of yttria and low amounts of titania in the ceramic phase exhibit improved long-term stability of the electrical conductivity, while under the operating conditions of a SOFC (~ 900oC) no detectable diffusion of Ce4+ in the 8YSZ electrolyte was observed.

Ce travail porte sur la synthèse et la caractérisation d’oxydes de manganèse de formule généraleCaxMnyOz avec y/x > 1. Par une approche de chimie du solide, les propriétés redox de ces matériauxseront corrélées à leur composition chimique et leur structure cristalline ce qui constitue une étude enamont de l’application pour ces systèmes pouvant jouer le rôle de tampon à oxygène dans desprocessus catalytiques. Les composés ont été synthétisés par autocombustion en voie aqueuse etcaractérisés d’un point de vue structural. Les propriétés redox ont été évaluées par ATG et lespropriétés de réductibilité par H2-TPR pour certains composés. Quelles que soient la structure, ladimensionnalité ou la valence du manganèse dans les composés oxydés (Mn4+/Mn3+), le manganèsese réduit totalement en Mn2+ sous atmosphère réductrice (Ar/H2). Les composés réduits cristallisentdans une solution solide de type NaCl de formule Ca1-xMnxO. Les mécanismes de réduction dumanganèse au sein de ces structures ont été appréhendés sur la base des analysesthermogravimétriques. Afin de faire varier les températures de réduction, l’iono-covalence de la liaisonMn-O a été modifiée via des substitutions cationiques (i) sur les sites du calcium principalement ausein de réseaux 2D ou (ii) sur les sites du manganèse essentiellement dans les réseaux 3D avec laprésence d’Al3+ ou de Fe3+ de rayons ioniques comparables respectivement à Mn4+ et Mn3+. Lessolutions solides ont été caractérisées d’un point de vue structural mais aussi pour leurs propriétésredox. Il convient de souligner que les phases substituées au Fer présentent des propriétés redox toutà fait remarquables dans la mesure où les ions Fe3+ tout comme Mn4+/3+ se réduisent d’abord en Fe2+puis en Fe° qui est dès lors expulsé hors de la matrice oxyde. Lors de la réoxydation, le fer réintègrele réseau 3D et les matériaux sont cyclables dans des conditions réductrices puis oxydantes à l’air àdes températures inférieures à 1000°C. / This work deals with the synthesis and characterization of manganese oxides with CaxMnyOz formulaand y/x >1. According to a solid state chemistry scope, the redox properties of these materials will becorrelated to their chemical composition and crystallographic structure which constitutes a forehandexploratory study of compounds that are intended to be used for the automotive catalysis exhaustbased on the three-way catalysis principle. The materials were synthesized by aqueous selfcombustionroute and structurally characterized. Redox properties and reducibility properties wereevaluated by TGA and H2-TPR, respectively. Whatever the structure, the dimensionality of the networkor the manganese valence in the starting oxidized material, all of the manganese ions are completelyreduced (Mn2+) in a Ar/H2 atmosphere. The reduced compounds crystallize in a rock-salt type solidsolution with the formula Ca1-xMnxO. The mechanisms of manganese reduction within these structureswere explored on the basis of TGA analysis. In order to tune the reduction temperatures, the ionocovalenceof the Mn-O bond has been modified by either cationic substitution of calcium in the 2Dnetworks or either substitution of manganese in the 3D networks. In this last case, Substituting ionswere Al3+ and Fe3+ which ionic radii comparable to Mn4+ and Mn3+, respectively. Solid solutions havebeen characterized from a structural point of view but also for their redox properties. One shouldnotice that iron substituted compounds exhibit remarkable redox properties because Fe3+ ions firstreduce in Fe2+ iron before a final reduction in Fe° that is consequently expulsed from the matrix. Atreoxidation, iron returns into the 3D network and cycling can be observed when reducing and oxidizingat temperatures lower than 1000°C.

Made available in DSpace on 2014-12-17T14:07:06Z (GMT). No. of bitstreams: 1 RayssaRNMS_DISSERT.pdf: 4171010 bytes, checksum: 0d447597643468751a7d9a8d1824c61d (MD5) Previous issue date: 2012-08-31 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The field of "Materials Chemistry" has been developing in recent years and there has been a great increase of interest in the synthesis and chemical and physical properties of new inorganic solids. New routes of synthesis and synthesis modified has been developed with the aim not only to optimize the processes in laboratory scale, but also on an industrial scale, and make them acceptable by current environmental legislation. The phenomenology of current solid state chemistry properties coupled with the high temperature superconductivity, ferromagnetism, porosity molecular and colors are evidence affected by the synthesis method, which in turn can influence the technological application of these materials. From this understanding, mixed oxides of nickel and zinc nanoparticulate were synthesized by microwave-assisted combustion route using three specific types of organic fuels employing the weight ratios 1:1/2 and 1:1 of cation metallic/fuel, in order to investigate the influence of such proportions to obtain the solids. The new fuels were chosen to replace, for example, urea or glycine that are the fuels most commonly preferred in this kind of synthesis. The powders without heat treatment were studied by Thermogravimetric analysis (TGA), X-Ray Diffraction (XRD) and then calcined at 900?C. After heat treatment, the samples were characterized by analysis of X Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The modified synthesis route porposed was effective for obtaining powders. Both the alternative fuels chosen as the different weight ratios employed, influenced in the morphology and obtaining oxides / O campo da Qu?mica de Materiais vem se desenvolvendo nos ?ltimos anos, tendo havido um grande aumento do interesse na s?ntese e nas propriedades qu?micas e f?sicas de novos s?lidos inorg?nicos. Novas rotas de s?nteses e s?nteses modificadas tem sido desenvolvidas com o intuito n?o apenas de otimizar os processos em escala laboratorial, como tamb?m em escala industrial, al?m de torn?-los aceit?veis pela legisla??o ambiental vigente. A atual fenomelogia da qu?mica do estado s?lido aliada ?s propriedades de supercondutividade ? alta temperatura, ferromagnetismo, porosidade molecular e cores s?o evid?ncias afetadas pelo m?todo de s?ntese, que por sua vez, podem influenciar na aplica??o tecnol?gica desses materiais. Foi a partir desta compreens?o, que ?xidos mistos de n?quel e zinco nanoparticulados foram sintetizados atrav?s da rota combust?o por microondas utilizando tr?s tipos espec?ficos de combust?veis e empregando as raz?es m?ssicas 1:1 e 1:1/2 de c?tions met?licos/combust?vel, com o intuito de averiguar a influ?ncia de tais propor??es na obten??o dos s?lidos. Os novos combust?veis foram escolhidos em substitui??o a ur?ia ou glicina que s?o mais comumente preferidos nesse tipo de s?ntese. Os p?s sem tratamento t?rmico foram estudados atrav?s da An?lise Termogravim?trica (ATG) e da Difra??o de Raios-X (DRX), sendo, em seguida, submetidos ao tratamento t?rmico ? 900?C. Ap?s as calcina??es, foram caracterizados atrav?s das an?lises Difra??o de raiosx (DRX) e Microscopia Eletr?nica de Varredura (MEV). A rota de s?ntese modificada foi eficaz para obten??o dos p?s. Tanto os combust?veis alternativos escolhidos quanto as diferentes raz?es m?ssicas empregadas, influenciaram na morfologia e na obten??o dos ?xidos

Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro / Convencionalmente, metais nobres são empregados como metais ativos em catalisadores automotivos, mas o uso de cobre vem sendo estudado pelo fato de promover sítios ativos para adsorção química e redução de NOx. Diante deste contexto, esta dissertação visa testar novas formulações de catalisadores, com foco em seu desempenho na reação de redução do NO pelo CO e sua seletividade a N2. Foram avaliados o método de adição de cobre no preparo e os teores de cobre utilizados na preparação. Os métodos de adição utilizados foram impregnação a seco (IS), reação em estado sólido (RS) e coprecipitação (CO). Os teores de cobre estudados ficaram entre 0,36 e 6,9% (m/m). Além disso, foi estudado o impacto no desempenho do catalisador após envelhecimento térmico a 950C por 12h. Foram empregadas as seguintes técnicas de caracterização textural e físico-química como espectrometria de absorção atômica, fisissorção de N2, difração de raios X, espectroscopia Raman e redução a temperatura programada. Os catalisadores também foram avaliados na reação de redução do NO pelo CO. A análise textural indicou que o método de coprecipitação levou a características texturais diferentes dos outros catalisadores. Análises de DRX mostraram a formação de CuO cristalino para teores iguais ou superiores a 3,3% (m/m) de cobre. As análises de Redução a Temperatura Programada (RTP) indicaram que ocorreu uma forte interação na interface entre o suporte e as espécies de cobre dispersas, acompanhada da diminuição da temperatura de redução do CuO e da redução parcial da céria em temperaturas mais baixas. Os testes catalíticos mostraram um melhor desempenho dos catalisadores (IS) que apresentaram conversões mais elevadas em menores temperaturas. Com relação ao envelhecimento, observou-se uma diminuição significativa da eficiência dos catalisadores. Uma comparação com catalisadores à base de metal nobre mostrou um bom desempenho dos catalisadores à base de cobre, com a vantagem destes apresentarem emissão de N2O restrita a baixas temperaturas / Conventionally, noble metals are used as active metals in automotive catalytic converters, but the use of copper has been studied because copper promote active sites for chemical adsorption and reduction of NOx. Thus, this work aims to test new formulations of automotive catalysts, focusing on their performance in catalytic reduction of NO by CO and its selectivity to N2. The method of copper addition and the copper contents used in the preparation were evaluated. The addition methods used were dry impregnation (IS), solid state reaction (RS) and coprecipitation (CO). The copper contents studied were between 0,36 e 6,9 wt%. In addition, the impact on catalyst performance after thermal aging at 950 C for 12h was also studied. Textural and physico-chemical caracterization techniques were employed, such as atomic absorption spectrometry, N2 physisorption, X-ray diffraction, Raman spectroscopy and temperature programmed reduction. Catalysts were evaluated in the reduction reaction of NO by CO. The textural analysis indicated that addition of copper by the coprecipitation method led to textural characteristics different from the other catalysts. XRD analysis showed the formation of crystalline CuO for contents equal to or greater than 3,3 wt% of copper. TPR analysis indicated that there was a strong interaction at the interface between the substrate and the copper species dispersed together with the lowering of the temperature reduction of CuO and the partial reduction of ceria at lower temperatures. The catalytic activity results showed a better performance of the (IS) catalysts, which showed higher conversions at lower temperatures. Concerning the aging process, there was a significant decrease in the efficiency of the catalysts. A comparison with catalysts doped with noble metal showed good performance of the catalysts doped with copper, with the advantage of these presenting N2O emission restricted to low temperatures

Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro / Convencionalmente, metais nobres são empregados como metais ativos em catalisadores automotivos, mas o uso de cobre vem sendo estudado pelo fato de promover sítios ativos para adsorção química e redução de NOx. Diante deste contexto, esta dissertação visa testar novas formulações de catalisadores, com foco em seu desempenho na reação de redução do NO pelo CO e sua seletividade a N2. Foram avaliados o método de adição de cobre no preparo e os teores de cobre utilizados na preparação. Os métodos de adição utilizados foram impregnação a seco (IS), reação em estado sólido (RS) e coprecipitação (CO). Os teores de cobre estudados ficaram entre 0,36 e 6,9% (m/m). Além disso, foi estudado o impacto no desempenho do catalisador após envelhecimento térmico a 950C por 12h. Foram empregadas as seguintes técnicas de caracterização textural e físico-química como espectrometria de absorção atômica, fisissorção de N2, difração de raios X, espectroscopia Raman e redução a temperatura programada. Os catalisadores também foram avaliados na reação de redução do NO pelo CO. A análise textural indicou que o método de coprecipitação levou a características texturais diferentes dos outros catalisadores. Análises de DRX mostraram a formação de CuO cristalino para teores iguais ou superiores a 3,3% (m/m) de cobre. As análises de Redução a Temperatura Programada (RTP) indicaram que ocorreu uma forte interação na interface entre o suporte e as espécies de cobre dispersas, acompanhada da diminuição da temperatura de redução do CuO e da redução parcial da céria em temperaturas mais baixas. Os testes catalíticos mostraram um melhor desempenho dos catalisadores (IS) que apresentaram conversões mais elevadas em menores temperaturas. Com relação ao envelhecimento, observou-se uma diminuição significativa da eficiência dos catalisadores. Uma comparação com catalisadores à base de metal nobre mostrou um bom desempenho dos catalisadores à base de cobre, com a vantagem destes apresentarem emissão de N2O restrita a baixas temperaturas / Conventionally, noble metals are used as active metals in automotive catalytic converters, but the use of copper has been studied because copper promote active sites for chemical adsorption and reduction of NOx. Thus, this work aims to test new formulations of automotive catalysts, focusing on their performance in catalytic reduction of NO by CO and its selectivity to N2. The method of copper addition and the copper contents used in the preparation were evaluated. The addition methods used were dry impregnation (IS), solid state reaction (RS) and coprecipitation (CO). The copper contents studied were between 0,36 e 6,9 wt%. In addition, the impact on catalyst performance after thermal aging at 950 C for 12h was also studied. Textural and physico-chemical caracterization techniques were employed, such as atomic absorption spectrometry, N2 physisorption, X-ray diffraction, Raman spectroscopy and temperature programmed reduction. Catalysts were evaluated in the reduction reaction of NO by CO. The textural analysis indicated that addition of copper by the coprecipitation method led to textural characteristics different from the other catalysts. XRD analysis showed the formation of crystalline CuO for contents equal to or greater than 3,3 wt% of copper. TPR analysis indicated that there was a strong interaction at the interface between the substrate and the copper species dispersed together with the lowering of the temperature reduction of CuO and the partial reduction of ceria at lower temperatures. The catalytic activity results showed a better performance of the (IS) catalysts, which showed higher conversions at lower temperatures. Concerning the aging process, there was a significant decrease in the efficiency of the catalysts. A comparison with catalysts doped with noble metal showed good performance of the catalysts doped with copper, with the advantage of these presenting N2O emission restricted to low temperatures

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-07-21T11:52:53Z No. of bitstreams: 1 carlagrijofonseca.pdf: 2158196 bytes, checksum: 37ce85a4e86118ec5feb00909a92bb90 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-08-09T13:13:20Z (GMT) No. of bitstreams: 1 carlagrijofonseca.pdf: 2158196 bytes, checksum: 37ce85a4e86118ec5feb00909a92bb90 (MD5) / Made available in DSpace on 2017-08-09T13:13:20Z (GMT). No. of bitstreams: 1 carlagrijofonseca.pdf: 2158196 bytes, checksum: 37ce85a4e86118ec5feb00909a92bb90 (MD5) Previous issue date: 2013-07-26 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Compostos tipo hidrotalcita têm sido amplamente utilizados em catálise heterogênea, como catalisadores, suporte para catalisadores ou como precursor de catalisadores. A principal razão para isso é a capacidade desses materiais para gerar, por decomposição térmica, óxidos mistos de composição Mg1-x Alx □x/2 O(1+x/2) , com área superficial elevada (>200 m2 g-1). Embora se reconheça a importância desse óxido, a estrutura destes materiais não é bem conhecida. Eles são obtidos na forma de pó e em geral apresentam baixa cristalinidade, o que dificulta a análise via difração de raios X por policristais. Dados de RMN de 27Al e EXAFS mostraram que alguns cátions de Al migram de sítios octaédricos para sítios tetraédricos durante o processo de decomposição térmica. Com isso, algumas propostas de estrutura têm sido sugeridas por alguns autores: a princípio estruturas com cátions em sítios octaédricos somente, e a partir dos resultados de RMN, estruturas com átomos de Al localizados em sítios octaédricos e tetraédricos. Como não há informações conclusivas sobre a estrutura, a utilização de cálculos teóricos para propor modelos estruturais que podem descrever este composto, se torna uma abordagem promissora. Este trabalho tem por objetivo a utilização de um algoritmo genético (AG), de modo a obter modelos estruturais com diferentes composições que possam simular as características estruturais do Mg(Al)O. Nestes modelos, somente sítios octaédricos foram ocupados por cátions e vacâncias e a estabilidade relativa entre as diferentes propostas foi avaliada pela energia total, que foi inicialmente calculada com o GULP, por meio de potenciais interatômicos, e em uma segunda etapa por cálculos ab initio baseados na Teoria do Funcional da Densidade. AG's são robustos, genéricos e facilmente adaptáveis. Basicamente, o que um AG faz é criar uma população de possíveis respostas para o problema a ser tratado para depois submetê-la ao processo de evolução em busca das melhores soluções. O AG foi previamente testado e mostra resultados satisfatórios, pois converge em 100% dos casos para a estrutura teste previamente conhecida, sendo possível a sua utilização em problemas onde a estrutura não é completamente resolvida, como é o caso do Mg(Al)O. Este estudo também demonstrou a vantagem do uso de potenciais interatômicos, devido ao grande número de candidatos produzidos pelo AG. As características das estruturas mais estáveis do óxido misto Mg(Al)O foram confrontadas com propriedades disponíveis na literatura, tais como, DRX por policristais, parâmetros geométricos e dados termodinâmicos. Os resultados sugerem que os modelos investigados são a princípio representativos da estrutura do óxido misto obtido por algumas rotas da calcinação da hidrotalcita. / Hydrotalcite-type compounds have been widely used in heterogeneous catalysis, as catalysts as supports for catalysts or as catalyst precursor. The main reason for this is the ability of these materials to generate, by thermal decomposition, mixed oxides of composition Mg1-x Alx □x/2 O(1+x/2) , with a relatively high surface area (> 200 m2 g-1). In spite of the importance of the mixed oxides being recognized, the structure of these materials is not wellknown. They are obtained in powder form and usually have low crystallinity degree, making it difficult to analyze in detail the structure of the mixed oxide by X-ray diffraction . 27Al MAS-NMR and EXAFS data showed that some Al cations migrate from octahedral to tetrahedral sites during thermal decomposition. Thus, some models have been suggested by some authors: first, structures with cations in octahedral sites only, and due to the results of NMR, structures with Al atoms located in tetrahedral and octahedral sites. Since there is no conclusive information about the structure, the use of theoretical calculations to propose structural models which can describe the structure, can be a promising approach. This work aims to the use of a genetic algorithm (GA), in order to obtain structural models with different compositions that can simulate the structural characteristics of the Mg(Al)O. In these models only octahedral sites were occupied by cations and vacancies. The relative stability between the various proposals was evaluated by the total energy, that was first calculated with the GULP program, through interatomic potential, and in a second step by ab initio calculations based on Density Functional Theory. GA's are robust, generic and easily adaptable. Basically, what makes a GA is create a population of possible answers to the problem being treated and then submit it to the process of evolution in search of the best solutions. GA was previously tested and showed satisfactory results because converges in 100% of cases for the test structure previously described, being possible its use in problems where the structure is not completely solved, as is the case of the Mg(Al)O oxide. This study also demonstrated the advantage of using interatomic potential due to the large number of candidates produced by the GA. The characteristics of the more stable Mg(Al)O mixed oxide structures were compared with the properties available in the literature, such as XRD, geometrical parameters and thermodynamic data, The results suggest that the models investigated are representative of the mixeds oxides structure obtained by some routes of the thermal decomposition of the MgAl hydrotalcite.