Thèses sur le sujet « Performances catalytiques »
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Cojocariu, Ana Mihaela. « Matériaux mésostructurés pour des applications dans les oxydations catalytiques : optimisation de la synthèse et des performances catalytiques ». Electronic Thesis or Diss., Montpellier 2, 2010. http://www.theses.fr/2010MON20030.
Texte intégralThe objective of this thesis was the optimization of the synthesis and catalytic performances of Ti-containing materials in the oxidation with H2O2 of a wide range of model organic compounds. The original part is represented by the synthesis of SiO2-TiO2 mixed oxides by a non hydrolytic sol-gel procedure and their use in different catalytic reactions like: sulfoxidation, epoxidation of olefins, oxidation of aromatic hydrocarbons and phenols. These materials were compared with ordered mesoporous materials (Ti-MCM-41 and Ti-MCM-48) and microporous titanosilicalite TS-1. The non-hydrolytic sol-gel process based on the etherolysis and condensation of chloride precursors offers a simple one-step route to mesoporous SiO2-TiO2 xerogels with a good dispersion of Ti species and outstanding textural properties, without resorting to supercritical drying procedures as in the case of the mixed oxides obtained by a hydrolytic way. Moreover, these materials exhibited a remarkable catalytic activity in the oxidation with H2O2 of all the organic compounds investigated (significant conversions, good selectivities and H2O2 efficiencies). The catalysts were stable under operating conditions
Cojocariu, Ana Mihaela. « Matériaux mésostructurés pour des applications dans les oxydations catalytiques : optimisation de la synthèse et des performances catalytiques ». Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20030.
Texte intégralThe objective of this thesis was the optimization of the synthesis and catalytic performances of Ti-containing materials in the oxidation with H2O2 of a wide range of model organic compounds. The original part is represented by the synthesis of SiO2-TiO2 mixed oxides by a non hydrolytic sol-gel procedure and their use in different catalytic reactions like: sulfoxidation, epoxidation of olefins, oxidation of aromatic hydrocarbons and phenols. These materials were compared with ordered mesoporous materials (Ti-MCM-41 and Ti-MCM-48) and microporous titanosilicalite TS-1. The non-hydrolytic sol-gel process based on the etherolysis and condensation of chloride precursors offers a simple one-step route to mesoporous SiO2-TiO2 xerogels with a good dispersion of Ti species and outstanding textural properties, without resorting to supercritical drying procedures as in the case of the mixed oxides obtained by a hydrolytic way. Moreover, these materials exhibited a remarkable catalytic activity in the oxidation with H2O2 of all the organic compounds investigated (significant conversions, good selectivities and H2O2 efficiencies). The catalysts were stable under operating conditions
Astafan, Amir. « Synthèses, caractérisations et performances catalytiques des zéolithes nanoéponge de type structurale *BEA ». Thesis, Poitiers, 2016. http://www.theses.fr/2016POIT2269/document.
Texte intégralThe method to ameliorate the diffusion of reactants, reaction intermediates, and products inside the zeolite is by shortening the diffusion path length, i.e., crystals size. The growth of the crystals is a function of gel composition synthesis, crystallization time, temperature, etc. The mastering of this growth allows to obtain a wide range of the size which ranges from several micrometers to a few tens of nanometers. It is possible now to limit the diffusion path to only three unit cells by inhibiting the crystals' growth in one direction during the hydrothermal synthesis. For that, the use of a peculiar organic surfactant geminate is indispensable, it gives a hierarchical material with zeolitic crystals of 4 nm thickness separated by structured and regular mesopores in the case of *BEA type zeolite. The morphology of this material resembles a sea sponge.Two reaction models, n-hexadecane hydroisomerization and ethanol transformation to hydrocarbons, demonstrate that the reactants and the products diffusion was optimized in the beta nanosponges. Surprisingly the catalyst stability and selectivity were improved instead of activity. In fact this is due to the extreme reducing of the zeolite crystals’ thickness that leads to increase the aluminum number in the pore mouth, which although very accessible, but incapable to catalyze the isomerization and cracking reactions. The aluminums near the external surface, in contrary to those in the crystal heart, do not benefit from the long distance effects, which makes them weaker
Julian, Aurélie. « Elaboration par coulage en bande et cofrittage de réacteurs catalytiques membranaires multicouches-performances ». Phd thesis, Université de Limoges, 2008. http://tel.archives-ouvertes.fr/tel-00347929.
Texte intégralL'architecture des réacteurs intègre un catalyseur, une membrane conductrice mixte de type La1-xSrxFe1-yGayO3-d et un support poreux actif. Le choix du matériau du support s'est porté sur La0,8Sr0,2FeO3-d, en vue du co-frittage des couches denses et poreuses, ce qui permet d'assurer une continuité chimique et de diminuer les coûts. Des membranes supportées planes LSFG8273/LSF821 et LSFN8273/LSFG8273/LSF821 ont été élaborées par coulage en bande, thermocompression et co-frittage. Les performances du réacteur ont pu être largement améliorées par la présence du support poreux et de la couche catalytique. Enfin, les matériaux ont fait l'objet d'une étude thermomécanique.
Pinabiau, Maryse. « Préparation, caractérisation et performances catalytiques de réservoirs d'hydrogène "intermétalliques terres rares - nickel oxydes" ». Lille 1, 1987. http://www.theses.fr/1987LIL10116.
Texte intégralPinabiau, Maryse. « Préparation, caractérisation et performances catalytiques de réservoirs d'hydrogène "intermétalliques terres rares-nickel oxydes" ». Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb37608932d.
Texte intégralBoisdron, Nathalie. « Oxydation sélective du propane : performances catalytiques de systèmes oxydes et étude mécanistique de l'oxydéshydrogénation en propène ». Lille 1, 1991. http://www.theses.fr/1991LIL10096.
Texte intégralPoulet, Olivier. « Influence de différents ajouts (alcalins, phosphore, fluor) sur les performances catalytiques d'un catalyseur d'hydrotraitement de type MoS2-Al2O3 ». Lille 1, 1991. http://www.theses.fr/1991LIL10057.
Texte intégralNahama, Florence. « Influence des proprietes acido-basiques de l'oxyde de rhenium supporte sur les performances catalytiques en metathese des olefines ». Paris 6, 1996. http://www.theses.fr/1996PA066644.
Texte intégralMarchal, Catherine. « Deshydrogenation oxydante de l'acide isobutyrique : contribution a l'etude des facteurs determinant la stabilite des performances catalytiques des heteropolyanions ». Paris 6, 1991. http://www.theses.fr/1991PA066568.
Texte intégralSaab, Elias. « Comparaison des performances catalytiques des systèmes oxydes de Ce, Al et Mn dans l'oxydation totale des particules carbonées et le vaporeformage du méthanol ». Littoral, 2007. http://www.theses.fr/2007DUNK0180.
Texte intégralThe carbonaceous particles are one of the sources of the air pollution. Their collection is done by particulate filters followed by their elimination by catalytic or thermal ways. Another possibility for the reduction of the air pollution will be to change towards sources of clean energy to replace fossil energies. To this end, catalysts containing cerium, aluminum and manganese were studied in the combustion of the carbon black like in the reaction of steam reforming of methanol in order to produce hydrogen for fuel cells. Concerning the combustion of the carbon black, two types of contacts between the carbon particles and the catalyst were studied. The weak contact and the strong contact. The carbon black is characterized by the presence of intrinsic paramagnetic centres which are sensitive to oxygen in air. The formation of new species ascribable to localised paramagnetic spins with the interface of catalyst-NC, is highlighted following the strong contact between the two solids. Under these conditions, the ceria and contrary to alumina, is powerful in the reaction of combustion of the carbon black. Catalysts xMn/Ce and xMn/Al (x can change from 10-4 to 1) were prepared and activated at 600°C. The manganese addition improves the catalytic reactivity of these solids in the combustion of carbon black. The increase in the manganese content returns the oxidation of the possible carbon black at temperatures close to those obtained in a muffler. The catalysts present primarily the Mn2O3 phase at their surface with more marked presence of Mn(II) species in the case of alumina compared to the ceria. The setting in contact of the carbon black with the manganese deposited on the ceria causes the reduction of the manganese species and contributes to the reactivity of these solids. The low reactivity of the Mn/Al catalysts was explained by the strong stability of the manganese species being on alumina. All these catalysts are completely selective for the formation of CO2. The catalytic performances of these solids used in the reaction of steam reforming of methanol for the production of the hydrogen gas, remain below those obtained for transition metal oxide bases catalysts (Cr, Co, Ni, Mo,. . . ) considered as the current state of art in this field. Nevertheless, catalysts containing copper impregnated on a binary system ceria-alumina, show themselves very powerful and promising for the production of H2 supplying the fuel cells
Cherrak, Ahmed. « Dimérisation oxydante du méthane : Contribution au mécanisme par étude comparative des performances catalytiques et du potential de surface de différents oxydes ». Lille 1, 1993. http://www.theses.fr/1993LIL10025.
Texte intégralZair, Leïla Fournier Michel. « Oxydation sélective de l'isobutane en acide méthacrylique sur des composés molybdo-vanado-phosphoriques influence de la texture sur les performances catalytiques / ». [S.l.] : [s.n.], 2003. http://www.univ-lille1.fr/bustl-grisemine/pdf/extheses/50376-2003-157-158.pdf.
Texte intégralAit, Lachgar Khadija. « Oxydation ménagée du n-butane : modification des performances catalytiques du pyrophosphate de vanadyle par ajout de α-Sb2O4 ou par traitement oxydant ». Lyon 1, 1997. http://www.theses.fr/1997LYO10364.
Texte intégralJiménez-Calvo, Pablo Isaí. « Synthèses, caractérisations et performances de matériaux à base de g-C3N4 décorés avec des nanoparticules d´Au pour des applications (photo) catalytiques ». Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAF012/document.
Texte intégralTo date, mankind is facing an energy and environmental crisis simultaneously due to mainly two factors: growth population and the dependency on fossil fuels. For this reason, the urgency of using renewables sources, e.g., solar energy, is a potential solution. For example, non-carbon based H2 production from solar light driven water photodissociation is a promising approach. Nevertheless, to target the mentioned objective, an ideal photocatalytic system (semiconductors, SCs) has to meet four main features: (1) capacity of absorption of visible-light (2) suitable VB and CB positions of SCs to undergo the two half reactions of water splitting (3) efficient use of absorbed photons and generated charges and (4) good stability over time. For this purpose, this thesis contributes to the design and optimization of three innovative materials: Au/g-C3N4, Au/TiO2 (P25)-gC3N4, and Au/TiO2 (NTs)-gC3N4 composites. Their photocatalytic activities were correlated with their physico-chemical properties. In addition some of these composites also exhibited interesting CO conversion yields. To highlight the efficiency on the as-prepared composites, comparative studies were tested using commercial, pertinent references, and physical mixtures homologs
Gola, Annabelle. « Influence des techniques de desalumination de la zeolithe y sur ses proprietes physicochimiques et sur ses performances catalytiques en hydrocraquage du n-decane ». Paris 6, 1996. http://www.theses.fr/1996PA066824.
Texte intégralAzgui, Samira. « Comparaison des performances catalytiques entre un réacteur à lit fixe et un réacteur à lit fluidisé : application à la réduction des oxydes d'azote ». Compiègne, 1997. http://www.theses.fr/1997COMP1036.
Texte intégralBAYER, RENAUD. « Caracterisation des contre-ions vanadyle et cuivre de polyoxometallates. Influence de ces contre-ions sur les performances catalytiques en oxydeshydrogenation de l'acide isobutyrique ». Paris 6, 1995. http://www.theses.fr/1995PA066252.
Texte intégralBlanchard, Pascal. « Synthèse de catalyseurs CoMo/Al2O3 par ajout d'un agent complexant. Amélioration de leurs performances catalytiques en hydrodésulfuration de gazoles lourds par ajout de dopants ». Lille 1, 1995. http://www.theses.fr/1995LIL10041.
Texte intégralRua, Gonzalez Diego. « Synthèse de matériaux catalytiques de type oxydes mixtes pour la production de méthanol par la précipitation en flux continu en système microfluidique ». Electronic Thesis or Diss., Strasbourg, 2024. http://www.theses.fr/2024STRAF001.
Texte intégralGlobal warming is a concern for the current and future generations due to the increasing greenhouse gases (GHG) emissions to the atmosphere, mainly due to the dependence on fossil fuels. The use of alternative fuels such as sustainable methanol produced from renewable H2 and from CO2 would contribute to reduce the GHG emissions and the effects of climate change. The synthesis of methanol using CO2 rich feedstock is preferentially done by using a solid catalyst composed of CuO, ZnO and ZrO2. This type of catalyst can be produced by coprecipitation of the metal species using a microfluidic device, with advantages that have been demonstrated over catalysts synthesized by batch coprecipitation. In this work, different catalysts for the hydrogenation of CO2 to methanol were synthesized using the microfluidic technique under different conditions, in order to explore different synthesis parameters that could lead to the development of more active catalysts. The differences in the properties and activity between a catalyst synthesized by the microfluidic method and another synthesized by the batch method were investigated, followed by an exploration of the effects of the aging time and the coprecipitation temperature on the catalysts. Lastly, the effect of different compositions of catalysts on the properties and activity were determined, by investigating different CuO contents, the use of CeO2 as a catalyst promoter, and the use of In2O3 as a catalyst promoter and as active metal
Gouerec, Pascal. « Electrocatalyse de la reduction de l'oxygene par des chelates de cobalt con4 : effet du traitement thermique sur l'evolution de la structure macrocyclique et des performances catalytiques ». Paris 6, 1996. http://www.theses.fr/1996PA066574.
Texte intégralM'Nasri, Najib. « Elaboration de nanomatériaux composites métal@nanoparticules de silice mésoporeuses (MSN) : étude des performances catalytiques en phase aqueuse et des propriétés d'adsorption sélective du diiode en phase gaz ». Thesis, Montpellier 2, 2014. http://www.theses.fr/2014MON20199.
Texte intégralThe objective of this thesis was to develop efficient synthesis routes to prepare mesoporous silica-based nano-sized particles, designated as MSN, with controllable morphology and derivatised with selected transition metals. One-pot preparation and surface functionalisation procedures based on the insertion of the metal-phase precursor into the porogen aggregates were thoroughly optimised leading to silica particles containing such single metals as copper, palladium, platinum, silver or gold, as well as a two-metal phase of copper and palladium or that of palladium and platinum. It was demonstrated that the highly dispersed metal phase was localised on the pore surface and therefore it was readily accessible to the target chemicals on which to base the catalytic performance of the resulting materials. Among others, the remarkable catalytic performance of the Cu@MSN material in Huisgen and Sonogashira reactions and its propensity to undergo efficient recycling were proven through laboratory-scale testing. Experimental study of the selective adsorption of iodine vapour onto MSN supports functionalised with silver nanoparticles indicated an excellent retention capacity of such materials
Crusson-Blouet, Emilie. « Optimisation des performances catalytiques des sels de l'acide H4PVMo11O40 dans l'oxydéshydrogénation de l'acide isobutyrique. Caractérisation du rôle du cuivre et du vanadium par RPE et RMN solide 51V ». Lille 1, 1994. http://www.theses.fr/1994LIL10005.
Texte intégralLe, Bras Solène. « Etude de catalyseurs Pt-Pd supportés sur spinelle MgAl2O4 pour la dépollution automobile : synthèse, stabilité hydrothermale et perfomances catalytiques ». Thesis, Limoges, 2015. http://www.theses.fr/2015LIMO0053/document.
Texte intégralThe improvement of air quality is a major issue for the health and the environment. The challenge for the manufacturers of catalytic converters for automotive depollution is to optimize their formulation to meet the standards regulating the polluting emissions hardening, while making a profitable use of the precious metals whose resources are becoming exhausted. In this thesis, a new, mesoporous, MgAl2O4, catalytic support was synthesized by atomization of an aqueous sol containing a tri-block copolymer. The MgAl2O4 nanocristallites in point contact enable to reach higher dispersion rates of the Pt-Pd active phase than those of a commercialized DOC taken as reference by Renault. The active phase of the 2,5%m.PtPd(3:2)[450°C]/MgAl2O4[900°C] catalyst presents similar hydrothermal stability to that of the reference DOC thanks to chemical anchoring (epitaxial growth, solid solutions) and mechanical anchoring (atomic steps, pores). Although the totality of the precious metal content is not accessible (insertion, encapsulation) for CO, HC and NO oxidation, the catalytic performances reached by this catalyst during hydrothermal aging are comparable with that of the reference DOC. The conversion of the HC is similar to that of the reference DOC and depends on the local concentration of the active sites. The CO conversion rate is slightly penalized since the particles are too smalls and in an oxidized state. Lastly, this catalyst does not reduce NOx but ensures a more important oxidation of NO in NO2 after a hydrothermal aging than the reference DOC and also the storage of NO2 which have a positive impact on the proper functioning of the downstream diesel particulate filter
Mercier, Anne-Gaelle. « Etude et réalisation de couches actives de PEFMC architecturées ». Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENI050.
Texte intégralPEM fuel cells stand for an essential link in the cycle using hydrogen as an energy carrier.However, their development is still limited by initial performance, costs and durability.This study focuses on the electrode catalyst layer which contains most of the time platinum, anexpensive catalyst that can represent 25% of the overall cost of a system. Thus, one of the issues hasbeen to provide a better understanding of electrode operating, which can be heterogeneous. The aim ofthis study is particularly to enhance platinum distribution in the catalyst layer to optimize itsutilization.Architectured electrodes, that is to say with variable platinum loading inside the catalyst layerhave been developed thanks to the flexibility of two printing processes : inkjet printing and screenprinting. The adjustment of catalyst ink formulation and printing parameters enabled to fabricatecatalyst layers with a wide range of platinum loading, from 0,05mgPt/cm² to 0,5mgPt/cm². Severalplatinum distributions were compared to uniform catalyst layers at different scales: the scale of ribsand channels and of gas inlet and oultet of bipolar plate, as well as through the catalyst layer thickness.Electrodes architecture enabled to point out different contribution of catalyst layers according to itslocalizing under the bipolar plate and to suggest modifications of its structure that provide an increaseof performance.Otherwise, the estimation of lifetime of several architectures thanks to ageing tests in loadcycling mode showed that these structures enabled to reduce their performance decay rate
Tête, Johann. « Oxydation catalytique du propane en acide acrylique, optimisation des performances en mode pulsé et cinétique de réoxydation ». Compiègne, 2003. http://www.theses.fr/2003COMP1485.
Texte intégralThe propane oxidation into acrylic acid is studied on MoVTeNbO catalyst. The application target is a circulating fluid bed reactor (CFB). In this aim, a innovating set up is developed order to simulate the kinetic part of the spatial decoupling. Thus a fixed bed is altemately scanned by oxidant mixture and then by a reducing mix. Ln spite of a qantified effect of relaxation, this temporal decoupling is exaggerated order to authorize different operating conditions between reoxidation and reduction. Moreover several oxidant (or reducing) pulses are successively injected. By this means, it is possible to follow the performances versus the oxidation state of catalyst. The performances are optimised thanks to several studies on the parameters such as the relative pressure of oxygen, the temperature of reoxydation,. . . But a precise oxidation state winch enables optimal catalytic performances is defined. Before this irreversible degradation of the activity of the catalyst is observed. Beyond this, the formation of MoO3 is supposed and conducts to irreversible transformation of the catalyst and its properties. In this optimal state, another irreversible degradation could be observed : a decrease of the selectivity when reduction during one cycle is to high. The omnipresence of tins potential degradation explains the poor performances aunced a lot of papers on the same MoVTeNbO catalyst. Moreover and spite of few publications on the subject, an activation under oxidant atmosphere is proved and is in fact the most important recommended outlook. Finally a kinetic model is proposed for the reoxydation. It shows two different catalytic sites, the first is selective and the second favours combustion
Ayadi, Hana. « Catalyseurs performants pour le traitement de la pollution organique azotée par Oxydation en Voie Humide Catalytique ». Thesis, Lyon, 2017. http://www.theses.fr/2017LYSE1273/document.
Texte intégralManganese oxide-based catalysts have been synthesized through different routes and evaluated in the Catalytic Wet Air Oxidation of ammonia. Such catalysts are active, selective towards molecular nitrogen and stable under the applied reaction conditions. Molecular nitrogen and nitrite are primary products. A detailed study of the impact of the operating conditions (manganese content, oxygen partial pressure, ammonia concentration, initial pH, and charge at the catalyst surface) on the catalytic performances was carried out. The selectivity in molecular nitrogen is optimum when i) the amount of catalyst is low, ii) the ratio nO2:nNH4+ is close to stoichiometry (˜ 0.75) and ii) the pH at the point of zero charge of the catalyst is neutral. Although strongly basic conditions (pH 13) improve the catalytic activity, the conversion nitrite to nitrate is inhibited and the selectivity in molecular nitrogen is degraded. From a kinetic point of view, the reaction order with respect to oxygen and ammonia are 0 and 1, respectively. The influence of the oxidation state of manganese (+II, +III and +IV) in the presence of bulk manganese oxides or ceria-supported manganese oxides indicated that the active site would consist of a pair of Mn(+III) and Mn(+IV). The reaction makes the active site and the oxides where manganese is initially present at a low oxidation state are markedly modified upon reaction. A synergy between manganese and cerium is also confirmed, involving the two Mn(+III)/Mn(+IV) and Ce(+III)/Ce(+IV) redox couples in a concerted way
Zamboni-Corredor, Ingrid-Rocio. « Préparation et étude de systèmes catalytiques Fe/CaO performants pour la pyrolyse/gazéification de la biomasse "Miscanthus" et la capture de CO2 ». Thesis, Strasbourg, 2013. http://www.theses.fr/2013STRAF037.
Texte intégralImprove the hydrogen production from the conversion of renewable resources such as biomass is a real challenge in the context of the production of clean and efficient energy. In fact, during the biomass steam gasification, hydrogen is produced with significant amounts of CO2, CH4 and heavy, toxic and complex aromatic molecules called tars. This work focuses on the production of hydrogen by steam reforming of tar with in-situ CO2 capture. We propose a catalytic bi-functional material Fe/CaO-Ca12Al14O33 where iron favors the H2 production and simultaneously the CaO-Ca12Al14O33 capture CO2 in a fixed bed reactor. This work led also to the development of a CaOCa12Al14O33/ olivine system adapted for biomass gasification "Miscanthus" in a fluidized bed reactor
Majoli, Laetitia. « Elaboration, caractérisation et étude des performances de nouveaux adsorbants hydrophobes : application aux atmosphères odorantes et / ou chargées en composés organiques volatils (COV) ». Phd thesis, Ecole Nationale Supérieure des Mines de Saint-Etienne, 2005. http://tel.archives-ouvertes.fr/tel-00790773.
Texte intégralMrad, Nadia. « Valorisation des déchets graisseux de poisson en biocombustible pour moteur diesel ». Nantes, 2011. http://www.theses.fr/2011NANT2101.
Texte intégralAs the continuously increasing world's population, has resulted in a huge demand for processed foods which result in a large amount waste from food industries. Although one of the most heavily polluting, the food industry does contribute to the increase in volume of waste fat. The waste fat from food industries is composed of triglycerides and fatty acids. This organic waste can be converted as biofuel by various methods such as biochemical and thermo-chemical process. In the present work, waste fish fat is considered as an energy source for diesel engines. In this regard, catalytic cracking (thermo-chemical) process is considered in the present study. Initially, tests were conducted to optimize the experimental parameters to get high biofuel yield and also to reduce the corrosiveness of the biofuel by reducing its high content of carboxylic acids. The physical and chemical properties of derived biofuel are compared with the European Norms (EN) and American Society for Testing and Materials for diesel (ASTMD) and it is on par with these standards. Finally, experiments were conducted in a stationary ingle cylinder diesel engine to study the performance, emission and combustion characteristics of biofuel. The results show that despite of high NOx and CO2 the engine has lesser UHC, CO and PM and better brake thermal efficiency than standard diesel fuel. The higher emissions of NOx and CO2 can be reduced by blending biofuel with diesel fuel. It is concluded that the biofuel derived from waste fish fat by catalytic cracking process can be considered as an alternative fuel for diesel engines
Vergel, Hernandez César A. « Les Réacteurs catalytiques à lit fixe avec écoulement de gaz et de liquide : comparaison sur le plan théorique et expérimental de la performance du réacteur dans différents sens d'écoulement ». Vandoeuvre-les-Nancy, INPL, 1993. http://docnum.univ-lorraine.fr/public/INPL_T_1993_VERGEL_HERNANDEZ_C_A.pdf.
Texte intégralWang, Fagen. « Hydrogen production from steam reforming of ethanol over an Ir/ceria-based catalyst : catalyst ageing analysis and performance improvement upon ceria doping ». Phd thesis, Université Claude Bernard - Lyon I, 2012. http://tel.archives-ouvertes.fr/tel-00967128.
Texte intégralBarreiros, Salvado Miguel. « Optimisation des transports dans la couche active de PEMFC par une approche couplée modélisation/caractérisation : augmentation des performances des couches actives aux hautes densités de courant ». Thesis, Université Grenoble Alpes, 2021. http://www.theses.fr/2021GRALI016.
Texte intégralPEMFCs are among the most promising technologies for the future of the automotive industry. However, major barriers must be overcome in order to achieve a solid position in the electric vehicle market. These include the cost, where a significant fraction can be attributed to the employment of Pt in the catalyst layers.In the region of high current densities, a steep drop is commonly observed and it is usually associated with ionic and mass transport limitations in the cathode catalyst layer (CCL). Therefore, simultaneously reducing the Pt loading and improving the performance at high current density requires at first an identification of the main source(s) of performance limitations. Since the CCL is a highly heterogeneous material with features of disparate length scales, a multiscale imaging characterization setup is required in order to analyze its structure.In this work, a framework including multiscale electron microscopy (EM) characterization and multiscale modeling has been developed. Such framework allows reproducing real 3D CCL geometries using an innovative reconstruction algorithm that was designed for the purpose. Moreover, a physical model is implemented in these 3D geometries, and subsequently, numerical simulations at the local and CCL scales are performed. The multiscale EM setup includes FIB-SEM from which the carbon phase distribution is determined, HAADF-STEM to determine the representative Pt particle size distribution, and finally, HRTEM from which an average thickness for the Nafion thin film is measured. These images go through a post-treatment procedure which includes segmentation and alignment for the tomographic images. From these, geometries are then reproduced. Moreover, a physical model including multispecies transport on the Nafion and pore phases, ionic transport on the Nafion phase and a Butler-Volmer law at the Pt interface to describe the ORR kinetics, is implemented. The CCL 3D model is then coupled with a 2D MEA-scale model, from which local conditions are extracted and subsequently used as input in the local model. An analysis on the 3D geometries is then performed at both local and CCL scales. Regarding the former, it is found that structures with smaller Pt particles always present a better performance due to an increase in the amount of surface available for the electrochemical reaction to proceed. Though, the presence of Pt particles in large Nafion agglomerations as well as Pt interparticle competition effects can play a major detrimental role on performance (differences in local performance up to 26%). In the CCL scale analysis, the effects of the Pt particle size, the Nafion layer thickness and carbon aggreggate size are analyzed. In accordance to what is observed at the local scale, structures with smaller particles also display a better performance. Regarding the Nafion layer thickness, a balance between an enhancement in ionic transport and an increased resistance to oxygen transport upon thickening of the Nafion film has been highlighted. Results show that increasing the Nafion layer thickness from 8 to 10 nm is only benefitial for performance when the porosity is above 30%. Furthermore, these support the fact that understanding the swelling behavior of the Nafion thin film is crucial for a more accurate determination of the CCL's response. In its turn, enlarging the carbon aggregates can be detrimental for performance since some pores may vanish and regions with Pt particles located on large Nafion agglomerations may become starved from oxygen. Finally, the impact of the structure arrangement has been analyzed and gains in performance upon minimizing the tortuosities of both Nafion and pore phases to unity have been quantified. An improvement in performance of 25% was found, mainly as a result of the favoured ionic transport
Srour, Toni. « Optimisation de l'interface entre la couche catalytique anodique et la couche de transport dans un électrolyseur PEM : effet d'un dépôt de métal noble et de la contrainte de serrage sur les performances et la durabilité ». Electronic Thesis or Diss., Université de Lorraine, 2023. https://docnum.univ-lorraine.fr/ulprive/DDOC_T_2023_0283_SROUR.pdf.
Texte intégralFrom an economic perspective, the widespread adoption of PEMWE electrolyzers in mass markets depends on reducing cell manufacturing costs (currently over €1000/kW) and improving their lifespan. Additionally, due to the variable nature of renewable energy sources, efficient and rapid power fluctuations are vital for large-scale development. Industry aims to cut PEM electrolyzer CAPEX by increasing active surface area and current density. However, this creates operational inconsistencies, leading to hotspots and limiting durability. In our Super Stack project, we studied the sensitivity of PEM electrolysis cells to non-uniform clamping forces, common in large-scale systems. Results show a sensitivity of approximately 3 mΩ.cm².MPa⁻¹ for materials used. Noble metal depositions like iridium and platinum reduce electrical contact resistance by over 30%, boosting efficiency by 6%. They also lower thermal resistance, reducing membrane temperature at high current densities. For example, at 70°C and 5A/cm², membrane temperature drops from around 105°C to 75°C with a 10nm iridium deposition on the anodic catalytic layer-facing PTL. This deposition proves crucial in mitigating membrane degradation, especially in low clamping force areas. Accelerated Stress Tests confirm the durability benefits of depositions, particularly iridium, making them economically viable
Whyte, Henrietta Essie. « Evaluation of the performance of photocatalytic systems for the treatment of indoor air in medical environments ». Thesis, Ecole nationale supérieure Mines-Télécom Atlantique Bretagne Pays de la Loire, 2018. http://www.theses.fr/2018IMTA0112/document.
Texte intégralPhotocatalytic oxidation (PCO) is an advanced air cleaning technology that is used asa means to improve air quality in indoor environments and could potentially be used inthe operating rooms (OR). In hospitals, operating rooms (ORs) are very demanding interms of the indoor air quality (IAQ) and require systems that minimize the concentrations of pollutants. In this work, the fate of two OR pollutants acrylonitrile (chemical found insurgical smoke) and isoflurane (anesthetic gas) when they go through a PCO device was investigated. Firstly, a parametric evaluation on the degradation of isoflurane and acrylonitrile by studying the influence of air velocity, light intensity, the change in media geometry, initial pollutant concentration, presence of chemical co-pollutants, presence of particles (bioaerosols) and relative humidity on their degradation efficiencies is performed. Secondly the safety of the use of PCO for the degradation of isoflurane and acrylonitrile through the identification of possible intermediates formed during their degradation is evaluated. The experiments were conducted in a closed loop reactor which has been designed to study low concentration air pollutants and has also been recently modeled. Finally, to better understand how the change in media geometry influenced the degradation efficiency, simulations with ANSYS 14.5 were performed and discussed