Dans un contexte environnemental où les législations concernant la teneur ensoufre présent dans les coupes pétrolières sont de plus en plus drastiques, le développementde nouveaux catalyseurs toujours plus actifs est donc nécessaire. Cette augmentation del´activité catalytique est possible à plusieurs niveaux dont, par exemple, par l´utilisation denouveaux procédés de synthèse tel que l´emploi de la voie fluides supercritiques. Dans unpremier temps, l´objectif est d´étudier les éléments utilisés pour préparer ces catalyseurs afind´avoir une vision plus large des réserves, des utilisations, des possibilités de substitutions…La criticité de ces éléments a donc été évaluée par le biais de plusieurs indicateurs. Dans unsecond temps, la compréhension de la synthèse de catalyseurs d´hydrodésulfuration (HDS) aété étudiée. Pour cela des expériences utilisant différents solvants et précurseurs métalliquesont été suivies via des analyses in situ Raman. Après avoir défini les résultats les plusprobants, le procédé de préparation de catalyseurs HDS assisté par le CO2 supercritique(scCO2) a été optimisé à travers une étude paramétrique. Pour cela, la température, lapression, le solvant d´imprégnation, le ratio entre CO2 et solvant d´imprégnation, le temps deréaction et le chargement en métaux ont été variés. Les matériaux obtenus ont ensuite étéfinement caractérisés (microscopie, DRX, Raman, ICP, microsonde) avant d´être activés parsulfuration et testés dans différentes réactions catalytiques (hydrogénation du toluène,hydrodésulfuration du dibenzothiophène et du 4,6-diméthyldibenzothiophène). / In an environmental context where legislations concerning the sulfur content in oilare increasingly drastic, the research for new and ever more active catalysts is necessary. Thisincrease of the catalytic activity is possible at several levels, for example, with the use of novelsynthetic processes such as the use of the supercritical fluids route. In a first stage, theobjective is to study the elements used to prepare these catalysts in order to have a broaderview of the reserves, the uses, the possibility of substitutions ... The criticality of these elementshas therefore been evaluated by means of several indicators. In a second stage, theunderstanding of the synthesis of hydrodesulfurization catalysts (HDS) was studied. For thispurpose, experiments using different solvents and metallic precursors were followed by in situRaman analyses. After defining the most convincing results, the process for preparing HDScatalysts assisted by supercritical CO2 medium (scCO2) was optimized through a parametricstudy. For this, temperature, pressure, impregnation solvent, ratio of CO2 to impregnationsolvent, reaction time and metal loading were varied. The materials obtained were thencharacterized (microscopy, DRX, Raman, ICP, microprobe) before being activated bysulfidation and tested in various catalytic reactions (hydrogenation of toluene,hydrodesulfurization of dibenzothiophene and 4,6-dimethyldibenzothiophene).

京都大学 / 新制・論文博士 / 博士(工学) / 乙第13407号 / 論工博第4193号 / 新制||工||1762(附属図書館) / (主査)教授 安部 武志, 教授 作花 哲夫, 教授 阿部 竜 / 学位規則第4条第2項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Ce travail de thèse consiste en une étude des mécanismes de croissance des nanotubes de carbone monofeuillets par spectroscopie Raman in situ. La première partie de ce travail est consacrée à la mise en évidence des limites en température et en pression partielle de précurseur carboné du domaine de croissance des nanotubes de carbone monofeuillets. L’atout principal de la spectroscopie Raman in situ étant de pouvoir corréler informations structurales et cinétiques, cette approche a aussi permis d'étudier l'influence des principaux paramètres de synthèse (T, P, nature du précurseur carboné et du catalyseur) sur les cinétiques de croissance et de désactivation, ainsi que sur la nature et la quantité des espèces carbonées désordonnées produites. Enfin, l’influence de la température et de la pression partielle de précurseur sur le diamètre des nanotubes formés a également été étudiée. Ce travail a finalement conduit à la mise en évidence de plusieurs processus élémentaires impliqués dans : l’activation, la croissance, la désactivation, la qualité structurale, la pureté et la sélectivité en diamètre des nanotubes. / This work presents a study of the Single-Walled Carbon Nanotubes growth mechanisms by in situ Raman measurements. The first part of the manuscript is devoted to the determination of the temperature and precursor partial pressure limits of the Single-Walled Carbon Nanotubes growth domain. Furthermore, in situ Raman spectroscopy allows to correlate structural information and kinetics: this approach permits to study the influence of the main synthesis parameters (T, P, nature of the carbon precursor and of the catalyst) on the growth and deactivation kinetics, and on the nature and the quantity of disordered carbon species synthesized. Lastly, a study on the temperature and precursor partial pressure effects on the nanotubes diameters is reported. All the data collected have finally led to a discussion about the elementary processes involved in: activation, growth, deactivation, structural quality, purity and diameter selectivity of Single-Walled Carbon Nanotubes.

Carbon nanotubes (CNTs) have been assessed for their use in electrochemical energy storage applications, namely Hydrogen Storage and Vanadium Redox Flow Batteries. Furthermore;fundamental electrochemical studies have been conducted on aligned arrays of carbon nanotubes, and for the first time electrochemistry on pure, defect free, single layer graphene is reported. CNTs have been assessed for their potential as an electrochemical hydrogen storage material,finding a maximum recorded capacity for a single walled nanotube sample (SWNT) that was comparable to literature gas phase adsorption values. In-situ Raman spectroelectrochemistry was used to probe structural changes of the SWNTs with applied potential: no chemical functionalisation of the tubes or intercalation of protons was observed. It was concluded, therefore, that CNTs present no unique electrochemical hydrogen storage ability, other than their role as an adsorbent for gaseous hydrogen, which was evolved electrochemically. CNTs were also assessed as a possible electrode material for the VO(2+)/VO2(+) reaction, used in the positive half cell of commercial vanadium redox flow batteries and widely reported to exhibit quasi-reversible kinetics on carbon electrodes. Initial investigations revealed apparently reversible kinetics using a SWNT, the first time such a response has been observed on Carbon, and in contradiction to published work using CNTs for this application. Analysis via a range of electrochemical techniques highlighted the difficulty in using cyclic voltammetry to assess reversibility, particularly for CNT modified electrodes. The system was subsequently found to be quasi-reversible, with the deceptively small peak separation inferred to arise from the pores of the CNT electrode, therefore thin layer cell behaviour was observed. The porous contribution was confirmed using an electrode exhibiting poor kinetics (very small, indistinct Faradaic peaks), increasing the electrode porosity (using an aligned array of CNT) had a remarkable effect, with large Faradaic peaks (low separation ˜ 0.02-0.04 V) observed for a sample that was chemically identical. This work highlights the fundamental error in a portion of CNT literature, where kinetic enhancement is quantified by voltammetric peak separation, which can be erroneous unless the inherent porosity of the electrodes is considered. In contrast to the complexity of CNTs, graphene represents an ideal electrode material, allowing for direct determination of the electrochemical response of the graphene basal plane, eliminating the contribution of edge sites. An initial investigation towards this goal is presented.

Une SOFC peut être alimentée en biogaz sans reformage préliminaire du fait de sa température de fonctionnement élevée. Cependant, la présence de polluants comme le soufre peut empoisonner les électrodes. Cette thèse se concentre sur la compréhension des effets de H2S sur la structure de l'anode et les performances électriques. Spectroscopie Raman, imagerie optique et spectroscopie d'impédance ont été utilisées in situ pour évaluer la cinétique de sulfuration et les modifications morphologiques de Ni et Ni-CGO en présence de H2S à différentes températures. Les performances électriques de Ni-YSZ/YSZ/Pt ont été mesurées à 500°C à l'abandon et sous polarisation (500 mV). Un circuit électrique avec une impédance de concentration du second ordre est proposé. Les caractéristiques de l'anode avec combustibles propre et pollué sont discutées à partir des formes et des décompositions des spectres. Les corrélations entre propriétés électriques et accumulation de sulfure de nickel sont présentées. / A Solid Oxide Fuel Cell (SOFC) can be fed with biogas without a preliminary reforming due to its high operating temperature. However, the biogas contains numerous pollutants like sulfur which poison the electrodes. This thesis focuses on the understanding of the H2S impacts on the anode structure and electrical performances. Raman Spectroscopy, optical imagery and Impedance Spectroscopy have been used in situ to evaluate the sulfidation kinetics and the morphological changes of Ni and Ni-CGO pellets exposed to H2S at various temperatures. The electrical performances of Ni-YSZ/YSZ/Pt cells under open circuit and 500 mV-polarizing conditions at 500°C have been measured. An electrical circuit with a second-order concentration impedance is proposed. The anode behaviors in clean and polluted fuel are discussed based on the evolutions of impedance shapes and on the fitted parameters. Correlations between the electrical properties and the build-up of nickel sulfide are presented.

Les alliages légers (Al, Mg) sont aujourd’hui majoritairement utilisés dans les industries aéronautique, électronique, automobile. Toutefois, la faible résistance à la corrosion et à l’abrasion de ces alliages restreint leur développement à grande échelle. Les nouveaux concepts de protection contre la corrosion des alliages légers se basent non seulement sur un effet barrière par une couche épaisse d'oxyde (PEO) ou peindre, mais surtout sur une protection active à l’aide d’inhibiteurs de corrosion spécifiques. Ces inhibiteurs de corrosion pourraient être libérés "sur demande" et génèrent un phénomène ‘d’auto guérison’. L’utilisation des méthodes d’analyse in situ and ex situ modernes spectroscopiques pourraient permettre de mettre en lumière l’évolution de systèmes aussi complexe et aider à mieux définir les facteurs régulant ces processus. / Nowadays light alloys (Al, Mg) are widely used in a number of areas such as electronics, aeronautic, automotive and construction industries. However, the low corrosion and wear resistance of these alloys hinders application of Al and Mg alloys on a larger scale. The new concepts for corrosion protection of light alloys should include not only barrier protection by a thick oxide layer (PEO) or by paint but also an active protection by specific corrosion inhibitors which can be released “on request” and ensure so-called “self-healing”. Use of in situ and ex situ spectroscopic methods could bring a new view to the evolution of such a complicated system and help to define factors controlling these processes.

No description available.

To minimize global carbon emissions, having efficient jet engines and internal combustion engines necessitates utilizing lightweight alloys such as Al, Ti, and Mg-based alloys. Because of their remarkable strength/weight ratio, these alloys have received a lot of attention. Nonetheless, they have very poor tribological behavior, particularly at elevated temperatures beyond 200 °C, when most liquid lubricants begin to fail in lubrication. Over the last two decades, there has been a lot of interest in protecting Al, and Ti-based alloys by developing multiphase solid lubricants with a hard sublayer that provide mechanical strength and maintain the part's integrity while providing lubricity. The development of novel coatings with superior lubricity, high toughness, and high-temperature tolerance remains a challenging and hot topic to research and provide new engineered solutions for. To address and provide solutions to protect light-weight, i.e., Al, and Ti alloys at high-temperature and bestow superior tribological properties to such alloys, three types of adaptive lubricious coatings have been studied in this thesis: Nb-Ag-O self-healing lubricious ternary oxide, PEO-chameleon a self-adaptive multi-phase coating, and Sb2O3-MSH-C lubricious adaptive coatings to address this challenge. The development of the Nb-Ag-O ternary resulted in a coefficient of friction as low as 0.2 at 600 °C and crack healing at 900 °C. PEO-chameleon coatings demonstrated a remarkably low COF, as low as 0.07 at 300 °C and 1.4 GPa applied pressure. Finally, the Sb2O3-MSH-C multi-phase lubricious solid lubricant revealed superlubricity, with a CoF of 0.008 at 300 °C, providing a potentially promising contender for high-temperature, high-load applications.

No description available.

No description available.