The methanol-to-olefins reaction is an important industrial process for the production of light olefins (C2-C4). Silicoaluminophosphates are the most common catalysts for this process with SAPO-34 (CHA), SAPO-18 (AEI) and their intergrowths being considered the most catalytically active and selective. Understanding the crystal growth of such materials is important for control of the structure and defect incorporation, which can have a large effect on the catalytic behaviour. In this thesis, the synthesis, characterisation, catalysis and crystal growth of such materials are investigated. A series of CHA/AEI intergrowth materials were synthesised by sequential increases in silicon content, where low silicon content led to formation of AEI and higher silicon content led to CHA and intergrowth formation. X-ray diffraction and MAS-NMR were used to quantify the amount of intergrowth and there was a strong correlation between both techniques. Atomic Force Microscopy (AFM) revealed the mechanism by which these intergrowth structures grow. There is competition at the surface between the spiral-growth and layer-growth mechanisms, which has a significant effect on the resulting intergrowth, as intergrowth formation is only permitted with a layer-growth mechanism. Intergrowth on screw dislocations is not allowed, and thus discrete blocks of pure-phase AEI or CHA form. These intergrowth materials were tested for their performance in the methanol-to-olefins reaction. With a higher level of silicon, the catalysts had a larger acid site density but equivalent acid strength. The conversion of methanol over the catalysts correlated with the acid site density, where a greater acid site density led to higher conversion and faster deactivation. The selectivity over time was similar for all catalysts, with a high selectivity to ethylene and propylene. However, at the same percentage conversion, the C2/C3 ratio showed a strong correlation to the cage shape. Catalysts with a higher ratio of AEI cages had a higher selectivity to C3 and C4 products than the other catalysts, owing to the larger size of the internal AEI cage compared to the CHA cage. The crystal growth mechanism on SAPO-18 was investigated in detail to interrogate the complex spiral pattern that forms on the surface. Spirals form in a triangular type pattern due to differences in growth rates in different crystallographic directions. Interlaced terraces were also present. The unit cell and the relative orientation of the AEI cages define the different growth rates. In-situ AFM was used to investigate the dissolution behaviour of SAPO-18 and SAPO-34. In both cases, dissolution occurred via classical step retreat. The similarity in the layer stacking in both materials led to equivalent structure dissolution in both cases. The 0.9 nm layers dissolved first to 0.7 nm (closed cages) then to 0.4 nm (unstable intermediates). Dissolution of SAPO-18 revealed unusual spiral dissolution pits near the core of the dislocations. CHA/AEI intergrowth materials were also prepared using a dual-template method, where two templates, morpholine for CHA and N,N-diisopropylethylamine for AEI, were combined during synthesis. The phase transition from CHA to AEI occurred at different molar ratios with different synthesis procedures. XRD modelling confirmed the synthesis of an intergrowth phase at a molar ratio of 70% morpholine and 30% DPEA. Changes in chemical shift in the 13C MAS-NMR were used to observe the different template interactions with the framework as the ratio of CHA and AEI cages changed.

Afin de mieux comprendre les évolutions structurales mises en évidence dans les oxydes lamellaires de formule générale Li1+x(Ni0.425Mn0.425Co0.15)O2 utilisés comme électrode positive pour batterie lithium-ion, la structure du composé Li2MnO3 a été étudiée en détail. Obtenu selon différentes voies de synthèses, réalisées à différentes températures, ce matériau qui peut être considéré comme un matériau model à fait l’objet d’une étude cristallographique où l’utilisation de la microscopie électronique a été privilégiée. Deux types de défauts ont été identifiés. D’une part, l’existence de fautes d’empilement au sein du matériau a été démontrée. Leurs conséquences sur les clichés de diffraction électronique et les diagrammes de diffraction des rayons-X ont étés expliquées permettant d’unifier les controverses présentent à ce sujet dans la littérature. D’autre part, l’étude de la stabilité thermique du composé Li2MnO3 a mis en évidence l’apparition de défauts de type « phase spinelle » en surface des grains lorsque la température de traitement thermique devient supérieure ou égale à 900°C. Le traitement du matériau par la voie acide a pu être étudié et le mécanisme de désintercalation chimique du lithium par la voie acide a finalement pu être précisé. Il est montré que ce mécanisme est le même quelle que soit la taille des particules. / In order to get a better understanding of the complex structural evolutions occurring in the layered oxides like Li1+x(Ni0.425Mn0.425Co0.15)O2 materials when they are used as positive electrodes in lithium batteries, the structure of Li2MnO3 has been studied in detail. Obtained from several synthesis ways, annealed at various temperatures, this compound that can be considered as a model one regarding these complex materials has been the object of a crystallographic study where the use of electron microscopy was privileged. Two kinds of defects could be identified. From one part, the existence of stacking faults in the Li2MnO3 material has been proved and they have been visualized for the first time. Their consequences on X ray and electron diffraction patterns are explained allowing the unification of discrepancies existing in the bibliography. For other part, the study of the thermal stability of Li2MnO3 evidenced the appearance of spinel type defects when the annealing treatment is performed above 900°C. Finally the delithiation by acid leaching is studied and the lithium extraction mechanism is clarified. It is shown that this mechanism is the same whatever the particle size is.

Solid oxide fuel cells (SOFCs) offer the advantages of (i) employing less expensive catalysts compared to the expensive Pt catalyst used in proton exchange membrane fuel cells and (ii) directly using hydrocarbon fuels without requiring external fuel reforming due to the high operating temperature. However, the conventional high operating temperatures of 800 - 1000 °C lead to interfacial reactions and thermal expansion mismatch among the components and limitations in the choice of electrode and interconnect materials. These problems have prompted a lowering of the operating temperature to an intermediate range of 500 - 800 °C, but the poor oxygen reduction reaction kinetics of the conventional La[subscript 1-x]Sr[subscript x]MnO₃ perovskite cathode remains a major obstacle for the intermediate temperature SOFC. In this regard, cobalt-containing oxides with perovskite or perovskite-related structures have been widely investigated, but they suffer from large thermal expansion coefficient (TEC) mismatch with the electrolytes. With an aim to lower the TEC and maximize the electrochemical performance, this dissertation focuses on perovskite-related and trigonal RBaCo₄O₇-based oxide cathode materials. First, the effect of M = Fe and Cu in the perovskite-related layered LnBaCo₂₋xMxO₊[delta] (Ln = Nd and Gd) oxides has been investigated. The Fe and Cu substitutions lower the polarization resistance and offer fuel cell performance comparable to that of La[subscript 1-x]Sr[subscript x]CoO₃₋[delta] perovskite due to improved chemical stability with the electrolyte and a better matching of the TEC with those of standard electrolytes. Second, the perovskite-related intergrowth oxides Ln(Sr,Ca)₃Fe₁.₅Co₁.₅O₀ and La₁.₈₅Sr₁.₁₅Cu[subscript 2-x]Co[subscript x]O[subscript 6 +delta] and their composites with gadolinia-doped ceria (GDC) have been investigated. The electrical conductivity, TEC, and catalytic activity increase with increasing Co content. The composite cathodes exhibit enhanced electrochemical performance due to lower TEC and increased triple-phase boundary. Third, RBa(Co,Zn)₄O₇ (R = Y, Ca, and In) oxides with a trigonal structure and tetrahedral-site Con+ ions have been investigated. The chemical instability normally encountered with this class of oxides has been overcome by appropriate cationic substitutions as in (Y₀.₅Ca₀.₅)Ba(Co₂.₅Zn₁.₅)O₇ and (Y₀.₅In₀.₅)BaCo₃ZnO₇. With an ideal matching of TEC with those of standard electrolytes, the RBa(Co,Zn)₄O₇ (R = Y, Ca, and In) + GDC composite cathodes exhibit low polarization resistance and electrochemical performance comparable to that of perovskite oxides. / text