Rozprawy doktorskie na temat „Co2P Nanoparticles”

A high-pressure CO2 foam was generated with silica nanoparticle dispersion and CO2 for fracturing applications. The effects of different ions and temperature on nanoparticle aggregation were studied. Nanoparticle dispersions were mixed with individual monovalent, divalent ions with varying concentrations, and two synthesized Permian connate water solutions. Samples of nanoparticle dispersions with the presence of NaCl were put into chambers with constant temperature for 14 hours. The peak size of aggregated nanoparticles in each sample was measured. It was found this silica nanoparticle dispersion had a high thermal stability up to 85?. The silica nanoparticle dispersion used in this study maintained a desired stability under an 18% reservoir salinity condition, yet it could be sensitive to high concentrations of Na2SO4 solutions. To investigate foam rheology and stability, high-pressure CO2 foams were generated in a beadpack with different CO2/NP ratios in NaCl solutions. The resulting foam was observed in a sapphire tube. The differential pressure across a capillary tube was recorded to calculate the apparent viscosity of foams. Nanoparticle-stabilized foams could remain stable for days and foam stability decreased with the increasing foam quality. Foam apparent viscosity was found to increase with foam quality and could be 3 times as high as that of the ambient phase. The high stability and fine texture of high-pressure CO2-in-water foams stabilized by silica nanoparticles have broadened the development of foam fracturing, offering a new opportunity for the effective development and stimulation of unconventional reservoirs.

Cette thèse représente un projet multidisciplinaire qui explore des aspects allant de l'ingénierie des solvants à la catalyse à l'aide de nanoparticules métalliques. Dans le cadre de ce projet, l’ingénierie des solvants a été appliquée à des solvants eutectiques profonds (SEP) biosourcés synthétisés à partir de tosylalaninate de choline et de glycérol afin diminuer leur viscosité en utilisant différentes quantités de dioxyde de carbone. Les rotors moléculaires ont été utilisés comme méthode innovante pour mesurer la viscosité, évitant ainsi l’utilisation d’une instrumentation coûteuse et donnant accès à la microviscosité du système. De plus, ce système a été appliqué à la synthèse de nanoparticules de palladium, jouant également un rôle de stabilisants, qui ont été entièrement caractérisées. Les nanoparticules de palladium bien dispersées ont été ensuite utilisées pour l'hydrogénation catalytique de liaisons C-C insaturées, de groupes nitro et carbonyle. Le CO2 dans ses états sub- ou supercritique a été utilisé pour améliorer l'efficacité des nanoparticules de palladium dans les réactions d'hydrogénation catalytique et subséquemment pour l'extraction du produit après la réaction de catalyse. Ce travail représente an effort pour intensifier un procédé dehydrogénation dans un milieu très visqueux, non volatile, biodégradable, biosourcé et non-toxique en utilisant du CO2 1) pour améliorer le transfert de matière et 2) pour extraire les produits de la réaction du milieu réactionnel
This Thesis represents a multi-disciplinary project where aspects going from solvent engineering to catalysis using metal-based nanoparticles, are explored. In this project, solvent engineering has been applied to bio-based deep eutectic solvents (DES) synthesized from choline tosylalaninate and glycerol in an effort to decrease the solvent viscosity by using different amounts of carbon dioxide. In this context, molecular rotors were used as an innovative method to measure the viscosity, avoiding the use of expensive instrumentation and giving the possibility to access to the microviscosity of the system. Furthermore, DES have been applied for the synthesis of palladium nanoparticles, also acting as stabilizers, which were fully characterized. The as-prepared palladium nanoparticles were then used for catalytic hydrogenations of unsaturated C-C bonds, and nitro and carbonyl groups. Sub and supercritical CO2 conditions have been applied to improve the efficiency of the palladium nanocatalysts in hydrogenation reactions and afterwards for the extraction of organic products. This work represents an effort to intensify a hydrogenation process in a highly viscous, non-volatile, biodegradable, and non-toxic DES by using CO2 in order to decrease mass transfer limitations and to extract products from the reaction media

La séparation CO2/N2 et H2/CO2 permet de limiter le rejet de CO2 dans l’atmosphère issu des gaz industriels et les membranes présentent de nombreux avantages tant sur le plan économique que pratique. Les membranes polymère sont faciles à mettre en forme mais un compromis entre perméabilité et sélectivité doit généralement être trouvé : pour améliorer les performances, des membranes à matrice mixte (MMM) incorporant des MOFs (matériaux hybrides poreux cristallisés) dispersés dans la phase polymère ont été proposées. A la différence des matériaux poreux inorganiques, les MOFs ont une meilleure compatibilité avec la matrice polymère du fait de leur caractère hybride organiqueinorganique. Dans le cadre de cette thèse, des polycarboxylates de Fe3+ et Al3+ poreux, stables à l’eau, et possédant de bonnes propriétés d’adsorption sélective du CO2 ont été synthétisés en milieu aqueux et mis à l’échelle de quelques grammes. Deux nouveaux polycarboxylates de Fe3+ poreux fonctionnalisés par des fonctions -COOH libres ont été obtenus à température ambiante. Pour l’un d’entre eux, la structure a été déterminée par diffraction des rayons X. Une deuxième partie de la thèse a été consacrée à la synthèse de nanoparticules de MOFs avec un bon rendement. Une partie importante de ce travail a porté sur le contrôle de la taille et la morphologie des nanoparticules de MIL-96(Al). Ce travail a conduit à la préparation de MMMs à base de MIL-96(Al) dont les performances sont supérieures à la membrane pure polymère pour la séparation CO2/N2. La dernière partie de ce travail de thèse a porté sur l’étude physico-chimique de la compatibilité entre le ZIF-8 et deux polymères (PVA et PIM-1). Ce travail a consisté à effectuer une caractérisation complète de solutions colloïdales MOFs/polymère en couplant plusieurs techniques (DLS, TEM, SAXS). Cette étude a montré que la compatibilité MOF/polymère est très dépendante de la chimie de surface des MOFs et des propriétés physico-chimiques du polymère (rigidité, caractère hydrophile/hydrophobe…)
CO2 capture and storage (CCS) is of high economical and societal interest. CO2/N2 andH2/CO2 separations are able to limit atmospheric CO2 emissions produced by industrial exhausts andmembranes present numerous economical and practical advantages. Polymer membranes are easy toprocess and possess interesting mechanical properties. However, there is a trade-off to make betweenpermeability and selectivity. Mixed-matrix membranes (MMM) based on MOFs (porous crystallinehybrid materials) have been proposed to boost the performances of polymer membranes for CO2capture. In comparison to other inorganic porous materials, one may expect that the compatibilitybetween MOFs and polymers is enhanced due to the hybrid character of MOFs.In this work, porous water stable polycarboxylate MOFs based on Fe3+ and Al3+ with promisingproperties for CO2 adsorption were synthesized for large-scale production using water as the mainsolvent. Two new porous polycarboxylate Fe3+ MOF bearing free -COOH groups in the frameworkwere obtained at room temperature as nanoparticles. The crystallographic structure of one of thesematerials was determined by single crystal X-ray diffraction. A second part of the thesis was devotedto the synthesis of MOFs nanoparticles with good yield. We focused our attention on the control of thediameter and morphology of MIL-96(Al) nanoparticles. This study led to the preparation of MMMsbased on MIL-96(Al) with promising properties for CO2/N2 separation. Finally, the compatibilitybetween MOF particles and polymers was studied for two systems (ZIF-8/PIM-1 and ZIF-8/PVOH),showing the influence of the surface chemistry of MOFs and the physico-chemical properties ofpolymer on the matching between MOFs and polymers

L’hydrogénation du CO2 par voie catalytique hétérogène représente une stratégie pertinente pour atténuer les émissions. Cette thèse a pour but de contribuer à la compréhension des facteurs physico-chimiques qui déterminent l’activité de catalyseurs Ru/TiO2 en conditions douces (= 200 °C, 1 atm). Des nanoparticules de RuO2 de 2 nm sont utilisées comme précurseurs de la phase active de Ru métallique. Ces nanoparticules calibrées sont combinées avec plusieurs supports de TiO2 présentant diverses cristallinités, textures, stabilité et compositions, dans le but de comprendre les paramètres qui dictent l’activité des catalyseurs Ru/TiO2. Les interactions spécifiques entre le support de TiO2 et les nanoparticules de RuO2 sont mises en évidence via différentes techniques avancées incluant la tomographie et la microscopie électronique en transmission environnementale à pression atmosphérique. Il apparait que le paramètre clé conférant une activité catalytique élevée est la stabilisation épitaxiale de RuO2 sur le TiO2 rutile lors de l’étape d’activation qui précède la réduction vers la forme Ru métallique
The hydrogenation of CO2 performed through heterogeneous catalysis is a pertinent strategy for mitigating CO2 emissions. This thesis aims to contribute to the understanding of the physico-chemical factors related to the catalytic performance of Ru/TiO2 catalysts at mild conditions (= 200 °C, 1 atm). Pre-synthesized 2 nm-RuO2 nanoparticles (NPs) are used to serve as precursors for active metallic Ru. These calibrated NPs are coupled with various tailor made TiO2 supports with different crystallinity, textural properties, stability and composition to understand parameters that dictate the activity of Ru/TiO2 catalysts. The specific RuO2-TiO2 interactions and RuO2 NPs migration phenomenon are demonstrated using various techniques including the state-of-the-art tomography and environmental transmission electron microscopy at atmospheric pressure. The important parameter for the better catalytic performance is found to be the epitaxial stabilization of RuO2 on rutile TiO2 prior to the formation of active Ru phase

Dans une logique d’éco-conception et de développement durable, de nombreux travaux ont pour objectif l’étude de polymères biosourcés. Parmi les recherches menées à ce jour, une piste d’étude consiste à les structurer aux échelles micro et nanoscopiques tout en valorisant certaines de leurs propriétés spécifiques, l’objectif étant la création de matériaux à propriétés fonctionnelles originales et performantes. Dans ce contexte, une attention particulière a été portée sur l’utilisation du dioxyde de carbone supercritique (CO2-sc). En effet, sa capacité à se solubiliser en grande quantité dans de nombreux polymères et donc d’en modifier les propriétés (viscosité, tension interfaciale, …) peut permettre une amélioration des matériaux composites fabriqués. Ce projet s’intéresse plus particulièrement à l’élaboration d’assemblages de biopolymères nanostructurés et revêt deux enjeux principaux : (1) la synthèse de nanoparticules de biopolymères (dans notre cas, du chitosane), (2) l’élaboration d’assemblages de biopolymères nanostructurés. La première étape a consisté à concevoir et développer de nouveaux procédés de génération de nanoparticules de chitosane par des procédés utilisant le CO2-sc soit comme antisolvant soit comme agent de dissolution et d'atomisation. Pour la deuxième étape, des films composites à base de poly (acide lactique) PLA et de poly (hydroxybutyrate-co-valérate) PHBV ont été préparés par la voie hot-melt par extrusion bi-vis. Des analyses thermiques, moléculaires et structurales, morphologiques et de granulométrie ont permis de caractériser les films biocomposites ainsi produits
In a logic of eco-design and sustainable development, many works aim to study the bio-sourced polymers. Among these studies, a promising concept consists in structuring materials at micro and nanoscales while enhancing some of their properties, the objective being the creation of original materials with improved functional properties and performance. In this context, particular attention has been paid to the use of supercritical carbon dioxide (sc-CO2). Its ability to dissolve into many polymers in large quantities and thus to change their properties (viscosity, interfacial tension, ...), can improve both the composite material and its manufacturing process. This project focuses on the development of nanostructured biopolymers and addresses two main issues: (1) the synthesis of biopolymer nanoparticles (in this case, chitosan), and (2) the development of nanostructured biopolymers. The first step consisted in designing and developing new processing methods to generate biopolymer nanoparticles, using sc-CO2 as antisolvent agent or as dissolving and atomizing agent. For the second step, poly (lactic acid) PLA and poly (hydroxybutyric-co-hydroxyvaleric acid) PHBV based composite films were prepared by a hot-melt process by twin-screw extrusion of the nanoparticles and the matrix. Thermal, molecular and structural analysis, as well as morphological and particle size distribution studies allowed a good characterization of the biocomposite films

Malgré ses avantages économiques et environnementaux, le procédé de reformage à sec du méthane sur des catalyseurs au nickel supporté se heurte encore à des problèmes de frittage de la phase active (un métal de transition) et de dépôt de carbone, ce qui entraîne une diminution de l'activité catalytique. Cette thèse porte sur l'étude de l'effet de confinement du nickel dans des catalyseurs à base de silice mésoporeuse pour la production de gaz de synthèse par reformage du méthane par le CO2. Dans cette étude, les échantillons ont été caractérisés par physisorption de N2, DRX, MET/MEB, RTP, et, en plus, par Raman, SPX, HTP/SM, ATG/SM pour les catalyseurs après test catalytique. Les résultats montrent qu'un support mésoporeux bien structuré ayant une grande surface spécifique et un grand volume poreux est important pour une meilleure dispersion et stabilisation de la phase active à l'intérieur de la porosité. La silice mésoporeuse de SBA-15 (préparée en grande quantité), composée de grains allongés, semble être appropriée pour atteindre cet objectif. Il est de plus démontré que la formation de petites particules bien confinées à l'intérieur des pores favorise la résistance au dépôt de carbone. Ceci peut être obtenu en imposant un traitement hydrothermal au support, en utilisant la méthode deux solvants pour le dépôt de Ni, en passant à une réduction directe des échantillons non calcinés, en ajoutant du Rh en faibles quantités ou en utilisant du Ce comme promoteur, à condition que le Ni et Ce soient en interaction
Although economically and environmentally advantageous, the methane dry reforming process using supported nickel based catalysts still faces problems of active phase (a transition metal) sintering and of carbon deposition, which result in catalytic activity loss. This thesis is focused on the study of the confinement effect of nickel in mesoporous silica-based catalysts for syngas production by reforming of methane with CO2. In this study, the samples were characterized by N2 sorption, XRD, TEM/SEM, TPR, in addition to Raman, XPS, TPH/MS, TGA/MS for the spent catalysts. The results indicate that a well-structured mesoporous support with high surface area and large pore volume is important for better dispersion and stabilization of the active phase inside the porosity. The mesoporous SBA-15 silica support (prepared in large quantity), composed of elongated grains, appear to be suitable for the purpose. Moreover, it is demonstrated that the formation of small nickel particles well-confined inside the pores favors carbon resistance. This can be achieved by applying hydrothermal treatment to the support, using two solvents method for Ni deposition, using direct reduction of uncalcined samples, adding Rh in small quantities or promoting with Ce, provided that Ni and Ce are in interaction

Les réactions réalisées en catalyse hétérogène nécessitent des températures et pressions élevées. Une façon originale pour améliorer ces conditions de réaction est de générer des températures élevées directement à la surface des catalyseurs par des stimuli physiques (magnétiques ou plasmoniques). L’objectif de cette thèse a été la mise en place de la synthèse de nanoparticules complexes combinant des propriétés physiques et des propriétés catalytiques. Ainsi, deux types de nanoparticules ont été synthétisées, des nanoparticules de fer-nickel pour le chauffage magnétique et des nanoparticules bimétalliques or-ruthénium pour le chauffage plasmonique. Dans le contexte actuel de développement durable et de stockage des énergies renouvelables, nous avons étudié deux réactions catalytiques : la réaction de Sabatier et l’hydrodésoxygénation de molécules plateformes issues de la biomasse lignocellulosique. Sous champ magnétique, la génération au voisinage des nanoparticules de fer-nickel de très hautes températures a permis de créer un environnement hétérogène à la surface des nanoparticules. Ainsi, la conversion totale du furfural et de l’hydroxyméthylfurfural en biocarburants (le méthylfurane et le diméthylfurane) a pu être réalisée en solution dans des conditions très douces. Les propriétés de chauffe et les propriétés catalytiques des nanoparticules de fer-nickel ont permis d’activer la réaction de Sabatier, et d’atteindre pour la première fois des rendements en méthane de 100 %. Dans la même optique, les propriétés plasmoniques et catalytiques des nanoparticules d’or-ruthénium ont été étudiées pour la réaction de Sabatier. Un couplage entre chauffage classique et irradiation lumineuse a permis de mettre en évidence un effet synergique entre le ruthénium et l’or pour l’activation de la réaction
Heterogeneous catalytic reactions require often very harsh conditions, i.e. high temperature and high pressure in the overall system. An original way to lower these reaction conditions consists in generating a local heating directly at the surface of the catalysts by the means of physical stimuli (magnetic or plasmonics). However, up to now, the catalytic sites and the heating agents were spatially separated, reducing the efficiency of the heat transfer. The aim of this thesis is thus to elaborate complex bimetallic nanoparticles combining physical properties and catalytic properties in the very same object. Two types of nanoparticles have been synthesized, iron-nickel nanoparticles for magnetic heating and gold-ruthenium nanoparticles for plasmonic heating. In the current context of sustainable development and storage of renewable energies, we studied two catalytic reactions: the Sabatier reaction, to valorize CO2 gas and the hydrodeoxygenation of platforms molecules from lignocellulosic biomass to yield biofuel. Under alternating magnetic field, iron-nickel nanoparticles generate high temperatures creating a heterogeneous environment at their surface. Thanks to these peculiar conditions, the furfural and the hydroxymethylfurfural could be totally converted, in liquid phase, into biofuels (methylfurane and dimethylfurane) under mild conditions. Moreover, heat properties of iron-nickel nanoparticles combining with their catalytic properties have made possible the total conversion of carbon dioxide into methane. Similarly, plasmonic and catalytic properties of gold-ruthenium nanoparticles were studied for the Sabatier reaction. By coupling classical heating and light irradiation a synergetic effect between ruthenium and gold was observed leading to the efficient activation of the reaction

In this study, we have investigated the effect of various organic acids (hexanoic, lauric, stearic, and lignoceric acid) and nanoparticles (silica and alumina) on various geo-storage formations (sandstone, carbonate, and cap-rock) by conducting contact angle measurements at various physio-thermal conditions. The result showed that geo-storage minerals became super-hydrophobic in the presence of organic acids, thus, less CO2 trapping capacity and nano-fluids have significantly turned organic-aged geo-storage minerals to intermediate-wet, thus, increased CO2 trapping capacity.

Des membranes supports en polymère ont été photo-greffées par des poly(liquide ionique)s (polyLIs) à base d'imidazolium. Les polyLIs permettent de séparer le CO2 d'autres gaz et de stabiliser des nanoparticules. Dans le cas du captage de CO2, les expériences montrent qu'une couche fine homogène de gel réticulé en polyLI gonflé par du liquid ionique (LI) est obtenue sur la surface de fibres creuses. Les fibres ainsi obtenues ont montré des perméances au CO2 plus élevées (600-700 GPU) que des membranes commerciales et des sélectivités de CO2/N2 comparables (13 et 17). Dans le cas de membranes catalytiques, des nanoparticules de palladium (NPPd) servant de catalyseur ont été immobilisées en forte concentration locale au sein d'une couche de polyLI greffée à la surface de membranes. La réactivité des membranes catalytiques a été testée en configuration de contacteur traversé sur différentes réactions (couplage croisé C-C, hydrogénation, etc). Une conversion totale est obtenue pour des temps de séjours de quelques secondes, sans aucun sous-produit formé. Comparée aux NPPd colloïdaux dans un réacteur en batch, la membrane catalytique accélère les réactions d'environ 2000 fois en terme de temps de réaction sans perte de NPPd; la sélectivité est aussi accrue. Le réacteur membranaire catalytique a été modélisé afin d'obtenir les profils de concentration et de température et une meilleure compréhension des performances obtenues. Les membranes catalytiques se révèlent isothermes et les constantes cinétiques sont calculées. Enfin, les capacités de production de ces membranes catalytiques à une échelle industrielle sont estimées à environ 3 t/(hm3) pour le couplage de Suzuki
Polymeric support membranes were modified via photo-grafting by poly(ionic liquid)s (polyILs), featuring in the capability to separate CO2 from other gases and to stabilize metallic nanoparticles (MNPs). For CO2 capture, a thin polyIL-IL gel layer was homogenously coated on support hollow fibers. The composite fibers show high CO2 permeance and reasonable CO2/N2 selectivity. For the catalytic membrane, palladium NPs were generated inside a grafted polyLI layer. Compared to colloidal palladium system in a batch reactor, the catalytic membrane, as a contactor membrane reactor, is more efficient in terms of reaction time (ca. 2000 times faster), selectivity and MNP retainability. Theoretical study on reactor modeling, concentration & temperature profiles, and production capacity was done for an overall understanding of the catalytic membrane

Ce mémoire vise à montrer l’intérêt de nanoparticules (NPs) de TiO2 comme plateforme pour immobiliser dans un environnement proche des complexes de coordination pouvant interagir par transfert d’électron photoinduit. Nous nous sommes intéressés à l’étude de nanomatériaux hybrides associant le complexe [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) comme photosensibilisateur aux complexes [Cr(ttpy)2]3+ ou [Mn(ttpy)(CO)3Br] (ttpy = 4'-(p-tolyl)-2,2':6',2''-terpyridine) comme accepteurs d'électrons. Pour immobiliser les différents complexes à la surface du TiO2, une fonction acide phosphonique a été introduite sur une des bipyridines du centre [Ru(bpy)3]2+ et sur la terpyridine des complexes [Cr(ttpy)2]3+. L’étude des processus de transferts de charges photo-induits sous irradiation en lumière visible sur le colloïde TiO2/RuII montre que l'état à charges séparées (e-)TiO2/ RuIII possède une longue durée de vie, ce qui rend possible l'utilisation des charges dans des réactions successives d’oxydation ou de réduction. Notamment l’irradiation du colloïde TiO2/RuII en présence de [Cr(ttpy)2]3+ et de triéthanolamine (TEOA) comme donneur d'électron sacrificiel permet la réduction à deux électrons du [Cr(ttpy)2]3+. Par la suite, le complexe [Cr(ttpy)2]3+ est immobilisé sur les NPs de TiO2/RuII pour former un assemblage RuII/TiO2/CrIII au sein duquel les processus de transfert d'électrons photo-induits sont étudiés. De manière à proposer un système pour la réduction photocatalytique du CO2, le complexe [Mn(ttpy)(CO)3Br] a été co-immobilisé avec le [Ru(bpy)3]2+ suivant une approche de chimie sur surface pour former le colloïde RuII/TiO2/MnI. Ce système présente une excellente sélectivité vis-à-vis du HCOOH comme seul produit de la photoréduction du CO2 en présence de 1-benzyl-1,4-dihydronicotinamide (BNAH) comme donneur d'électron sacrificiel. Un système hybride associant le [Ru(bpy)3]2+ portant des fonctions pyrroles et immobilisé sur TiO2 a également été synthétisé et étudié. Sous irradiation lumineuse, le transfert de charges (e-)TiO2/[Ru-pyr]3+ permet d’induire la polymérisation du pyrrole. Le nanocomposite TiO2/poly(Ru-pyr) obtenu et déposé sur une électrode génère, en présence de TEOA, un photocourant anodique stable de plus de 10 μA.cm-2. L’ensemble des résultats montre que les NPs de TiO2 peuvent être un moyen d’assembler des complexes dans un environnement proche en limitant les interactions à l’état fondamental, mais permettant des transferts d’électrons photoinduits entre eux. Suivant les potentiels redox des différents composants, les transferts d’électron ont lieu soit via la nanoparticule soit en surface de celle-ci
This thesis aims to investigate the possibility of using TiO2 nanoparticles (NPs) as a platform to immobilize proximal coordination complexes that can interact with each other by photoinduced electron transfer. We have studied hybrid nanomaterials combining [Ru(bpy)3]2+ (bpy = 2,2'-bipyridine) as a photosensitizer and [Cr(ttpy)2]3+ or [Mn(ttpy)(CO)3Br (ttpy = 4'-(p-tolyl)-2,2':6',2''-terpyridine) as electron acceptors. To immobilize the various complexes on the surface of TiO2, a phosphonic acid functional group was introduced on one of the bipyridines of the [Ru(bpy)3]2+ center and on the terpyridines of the [Cr(ttpy)2]3+ complex. Under visible light, the TiO2/RuII colloid undergoes a photo-induced charge transfer process leading to a long-lived charge separation state (e )TiO2/RuIII, which makes it possible to be engaged in successive oxidation or reduction reactions. In particular, the visible irradiation of the TiO2/RuII colloid in the presence of [Cr(ttpy)2]3+ and triethanolamine (TEOA) as a sacrificial electron donor allows the two-electron reduction of [Cr(ttpy)2]3+. Subsequently, the [Cr(ttpy)2]3+ complex has been immobilized on the TiO2/RuII NPs to form a RuII/TiO2/CrIII assembly in which the photoinduced electron transfer processes were investigated. In order to propose a system for the photocatalytic reduction of CO2, the [Mn(ttpy)(CO)3Br] and [Ru(bpy)3]2+ complexes were co-immobilized on TiO2 NPs following a chemistry on surface approach to form a RuII/TiO2/MnI triad. Under irradiation at 470 nm, this system exhibits excellent selectivity towards HCOOH as the only product of CO2 photoreduction in DMF/TEOA solvent mixture, in the presence of 1-benzyl-1,4-dihydronicotinamide (BNAH) as a sacrificial electron donor. Another hybrid system linking a [Ru(bpy)3]2+ unit to two pyrrole functions and being immobilized on TiO2 has also been synthesized and studied. Under visible light, the transient (e-)TiO2/[Ru-pyr]3+ species induce the polymerization of pyrrole to form a TiO2/poly(Ru-pyr) nanocomposite. The nanocomposite deposited on an electrode generates, in the presence of TEOA, a stable anodic photocurrent of more than 10 μA.cm-2. All the results show that TiO2 NPs can be used to associate different complexes in a close environment by limiting the interactions in the ground state but allow photoinduced electron transfer processes between them. Depending on the redox potentials of the different components, the electron transfer takes place either through the semiconducting NPs or on the surface

In this doctoral dissertation, novel colloidal routes were used to synthesize nanomaterials with unique features. We have studied the impact of nanoparticle size of catalyst, role of high surface area of a photocatalyst, and the effect of varying elemental composition of co-catalytic nanoparticles in combination with core-shell plasmonic nanoparticles. We have demonstrated how physical and chemical characteristics of nanomaterials with these unique features play a role in catalytic reactions, specifically the oxidation of CO and the photoreduction of CO2. The first objective of this doctoral dissertation involved the preparation of CoO nanoparticles with discrete nanoparticles sizes (1-14 nm) using a colloidal thermal decomposition technique. The impact of size of CoO for CO oxidation reaction was studied using an in-situ FTIR reactor. By analyzing the reaction intermediates observed using in-situ IR, a two-step reaction mechanism was proposed. The average values of activation energies of step-1 and step-2 were ∼15 kJ/mol and ∼90 kJ/mol that showed step-2 was the rate determining step. From activation energy calculations for the catalysts of different CoO sizes, it was found that activation energy increased as nanoparticle size increased. The second objective of this doctoral research involved the development of high surface area TiO2 nanoshells using polymeric templates. The deposition of TiO2 was achieved by surface functionalization procedures. TiO2 was then deposited on colloidal SiO2 after the SiO2 surface was modified by grafting poly(NIPAAM) oligomers. TiO2 nanoshell composites possessed high surface of ∼35 m2/gm. The photocatalytic performances of TiO2 nanoshells and Pt deposited TiO2 nanoshells were evaluated for CO2 photoreduction reaction. Primary products from CO2 photoreduction reactions were carbon monoxide and methane. The product yield and product selectivity of hydrocarbons produced during CO2 photoreduction was measured using a home-built FTIR reactor. When Pt was deposited on TiO2 nanoshells, the overall yield was nearly doubled and the CH4 selectivity nearly quadrupled. The third objective pursued in this research project was to synthesize Ag, Pt and bimetallic Ag-Pt nanoparticles to demonstrate the role of elemental composition of metal co-catalysts for CO2 photoreduction reaction. The novel bimetallic nanoparticles played an important role in improving product selectivity in the photocatalytic reduction of CO2. Bimetallic Ag-Pt nanoparticles synthesized with low Pt content had 4-5 times higher CH4 selectivity compared to native TiO2. The final objective was to prepare Ag(core)/SiO2(shell) nanoparticles with specific core-shell structure to enhance photoactivity of TiO2 during catalytic reactions. Ag@SiO2 core-shell nanoparticles have plasmonic character that helped to improve product yield by increasing the number of electron-hole pair generations. When bimetallic Ag-Pt nanoparticles were used in combination with core-shell Ag@SiO2 plasmonic nanoparticles, the overall yield increased ∼8-fold compared to native TiO2.

This work aims to develop fundamental insights about the underlying surface and bulk chemical processes instrumental to the efficiency of chemical looping combustion (CLC). CLC, which uses a solid-state oxygen carrier (e.g., metal oxides) to drive hydrocarbon combustion, is a promising combustion alternative that minimizes byproduct formation and facilities capture of CO2. In this work, we compare the performance of different transition metal oxides, namely iron, copper, cobalt, manganese, and nickel oxides, as oxygen carriers in CLC using CH4 as the reducing agent. Experiments used a continuous flow reactor across temperatures ranging from 500 to 800 oC and feed flowrates from 12.5 to 250 h-1. In addition to monitoring size-, temperature- and flow rate-dependent performance trends for CH4 conversion to CO2, microscopic and spectroscopic techniques were used to investigate the solid-state mechanism of oxygen carrier reduction and the coupled surface chemical and bulk material processes influencing performance. Bulk (XRD) and surface (XPS) analysis reveal that oxygen carrier reduction can be generally represented by two models, the unreacted shrinking core model (USCM) and the nuclei growth model (NNGM). The reduction of some metal oxides can also proceed via a two-stage solid-state mechanism; for example, hematite reduction to magnetite follows USCM, while the subsequent reductions of magnetite to wustite and wustite to iron metal follow NNGM. Furthermore, our results reveal that minimizing the particle size promotes oxygen carrier performance, but only for metal oxides reduced according to the USCM, where metal oxide reduction initiates on the particle surface. In contrast, no benefit of decreasing particle size was observed for materials reduced according to the NNGM because the reaction initiates in the particle bulk, such that a more critical determinant of reactivity may be the available oxygen carrier volume rather than surface area. Beyond these fundamental insights, cycling experiments were also performed to provide more practical information about the effect of oxygen carrier particle size on their long-term performance in CLC applications.

This thesis provides a comprehensive concept on how catalysis can tackle climate change and global warming by reducing greenhouse gases using three different approaches. In a first approach, gold nanoparticles were synthesized by means of a colloidal synthesis method and subsequently transformed to 3D gold structures, which allowed for the selective oxidative coupling of methanol to methyl formate and by this, reducing the emission of carbon dioxide (CO2) as a side-product. In a second approach, the wetness incipient impregnation method was utilized to obtain a palladium catalyst supported on aluminum oxide, which was investigated for its activity in the lean methane oxidation at elevated pressures and temperatures. Elevated pressures allowed overall higher combustion rates of methane to CO2, which is, in perspective, less harmful as a greenhouse gas than methane. The last approach tackled the reduction of CO2, using this greenhouse gas as a feedstock to reduce it electrochemically over nanoparticulate copper and gold catalyst, which were synthesized using the chemical solution deposition method followed by an in-situ electrochemical reduction. The final products of this reaction can be hydrocarbons, which can be utilized as fuels or chemicals. All in all, the idea was to find catalysts and methods to contribute to the reduction of potential greenhouse gases and finally closing the carbon cycle for a more sustainable and greener future of planet Earth.

L'intérêt pour la synthèse de Fischer-Tropsch (FTS) est d'actualité. Elle permet la conversion de matière première (biomasse) en combustible liquide. Comparés aux catalyseurs à base de cobalt, ceux à base de fer présentent une désactivation rapide, une activité et une sélectivité faibles en produisant une quantité non désirable de CO2. Après plusieurs décennies d'études, l'origine de ces défauts reste méconnue. Les catalyseurs classiques sont généralement fortement chargés en fer (>70 wt.%) et composés de nombreuses phases empêchant l'établissement d'une relation structure-activité. Il est nécessaire de développer des catalyseurs contenant du fer plus actifs, plus sélectifs et plus stables par une approche rationnelle. La synthèse de nanoparticules de taille contrôlée (3.5 nm) encapsulées dans les murs d'une silicalite-1 creuse (Fe@hollow-silicalite-1) est présentée. L'encapsulation empêche le frittage pendant la synthèse de Fischer-Tropsch, permettant de garder une bonne dispersion du fer. Contrairement aux autres catalyseurs, le catalyseur Fe@hollow-silicalite-1actif ne produit pas de CO2. L'hydrophobicité de la silicalite-1 est très certainement à l'origine de la non-production de CO2 par inhibition de la réaction directe du gaz à l'eau. On démontre que le catalyseur Fe@hollow-silicalite-1convertit le CO2 en CO par réaction du gaz à l'eau inversée (R-WGS). Afin d'établir une relation structure-activité, des catalyseurs à base de fer de taille bien contrôlée sont synthétisés et caractérisés (MET, in-situ XANES, in-situ Mössbauer). Deux catégories de TOF suivant la taille des particules, ~10-2 s-1 pour les plus larges (>20 nm) et ~10-3 s-1 pour les plus petites, sont observées
Fischer-Tropsch synthesis (FTS) is gaining renewed interests as it allows converting alternative feedstocks (biomass) into liquid fuels. Compared to Co-based catalysts, state of the art Fe catalysts show lower activity, faster deactivation and lower selectivity as it produces an undesirable amount of CO2. Despite decades of studies, the origins of low activity and selectivity and fast deactivation are still unclear. Typical Fe based catalysts are highly metal loaded (>70 wt.%) and composed of many different phases, which strongly impedes the establishment of structure-activity relationships. There is a need to develop more active, more selective and more stable iron FTS catalysts by rational approaches.The synthesis of well-controlled 3.5 nm iron nanoparticles encapsulated in the walls of a hollow-silicalite-1 zeolite (Fe@hollow-silicalite-1) is presented. The encapsulation prevents particle sintering under FTS conditions leading to a high and stable Fe dispersion. The catalyst Fe@hollow-silicalite-1 is active and highly selective in FTS. Most importantly, Fe@hollow-silicalite-1 does not produce CO2 in contrast to all other Fe-based catalysts. The strong hydrophobicity of the silicalite-1 is likely the origin of the lack of CO2 production by inhibition of the forward WGS reaction. We demonstrated that Fe@hollow-silicalite-1converts CO2 into CO by the reverse WGS reaction. In order to establish a structure-activity relationship, a series of Fe-based catalysts with well-controlled particle sizes were synthesized and characterized (TEM, in-situ XANES, in-situ Mössbauer, XRD). We observed two distinct categories of TOFs depending on the particle size, ~10-2 s-1 for larger (>20 nm) and ~10-3 s-1 for smaller ones

[ES] Teniendo en cuenta el agotamiento de los combustibles fósiles y la creciente concentración de CO2 en la atmósfera, la hidrogenación de CO2 es una forma prometedora de convertir el CO2 en productos químicos y combustibles de carbono de alto valor añadido. Considerando la gran influencia del tamaño de partícula, la composición química, la naturaleza del soporte y las condiciones de operación sobre el comportamiento catalítico de los catalizadores, se han desarrollado una serie de catalizadores para la hidrogenación de CO2 basados en metales abundantes no nobles y polisacáridos naturales como precursores del grafeno. En la presente tesis doctoral, las especies metálicas soportadas sobre una matriz de carbono grafítico defectuosa, con diferentes tamaños de partículas, muestran diferente actividad catalítica y selectividad para la hidrogenación de CO2. Se prepararon, de forma controlada, nanopartículas de aleaciones de Co y Co-Fe soportadas en grafenos dopados con N defectuosos, con una amplia distribución de tamaño de nanopartículas, para la reacción de Sabatier, presentando una selectividad a metano superior al 90% con valores de conversión de CO2 superiores al 85%. En el caso de un solo metal, Co o Fe, y sus aleaciones en forma de "clusters" y pequeñas nanopartículas soportadas en el mismo material, la selectividad de la hidrogenación de CO2 cambia a CO, en lugar de metano, obteniéndose un valor del 98 % y alcanzando una conversión de CO2 del 56%. Conviene resaltar que, los catalizadores basados en "clusters" de aleaciones de metal con una carga de metal incluso por debajo del 0.2 % en peso, exhiben una mayor selectividad y rendimiento que los que tienen nanopartículas de aleaciones de Co-Fe más grandes que varían de 1 a 4 nm y una carga de metal más alta en una composición similar. Siguiendo la línea de investigación de hidrogenación de CO2, se desarrollaron una serie de nanopartículas de aleaciones de Co-Fe soportadas sobre grafenos dopados con N defectuosos con distribución de tamaño de nanopartículas controlada en el rango de 7-17 nm, obteniendo una selectividad hacia hidrocarburos C2+ alrededor del 45% y una conversión del CO2 cercana al 60%. Además, se realizó un estudio comparativo de la actividad catalítica de catalizadores similares basados en Co-Fe con promotores e inhibidores para la hidrogenación de CO2, observando su influencia en la conversión y selectividad de CO2. Finalmente, además de los catalizadores basados en Co-Fe, también se han preparado catalizadores basados en Cu-ZnO mediante un método de dos pasos. Estas nanopartículas de Cu-ZnO soportadas sobre grafeno defectuoso dopado con N exhiben una alta selectividad hacia la conversión de CO2 a metanol.
[CA] Tenint en compte l'esgotament dels combustibles fòssils i la creixent concentració de CO2 en l'atmosfera, la hidrogenació de CO2 és una forma prometedora de convertir el CO2 en productes químics i combustibles de carboni d'alt valor afegit. Considerant la gran influència de la grandària de partícula, la composició química, la naturalesa del suport i les condicions d'operació sobre el comportament catalític dels catalitzadors, s'han desenvolupat una sèrie de catalitzadors per a la hidrogenació de CO2 basats en metalls abundants no nobles i polisacàrids naturals com a precursors del grafé. En la present tesi doctoral, les espècies metàl·liques suportades sobre una matriu de carboni grafític defectuosa, amb diferents grandàries de partícules, mostren diferent activitat catalítica i selectivitat per a la hidrogenació de CO2. Es van preparar, de manera controlada, nanopartícules d'aliatges de Co i Co-Fe suportades en grafens dopats amb N defectuosos, amb una àmplia distribució de grandària de nanopartícules, per a la reacció de Sabatier, presentant una selectivitat a metà superior al 90% amb valors de conversió de CO2 superiors al 85%. En el cas d'un sol metall, Co o Fe, i els seus aliatges en forma de "clústers" i xicotetes nanopartícules suportades en el mateix material, la selectivitat de la hidrogenació de CO2 canvia a CO, en lloc de metà, obtenint-se un valor del 98% i aconseguint una conversió de CO2 del 56%. Convé ressaltar que, els catalitzadors basats en "clústers" d'aliatges de metall amb una càrrega de metall fins i tot per davall del 0.2% en pes, exhibeixen una major selectivitat i rendiment que els que tenen nanopartícules d'aliatges de Co-Fe més grans que varien d'1 a 4 nm i una càrrega de metall més alta en una composició similar. Seguint la línia d'investigació d'hidrogenació de CO2, es van desenvolupar una sèrie de nanopartícules d'aliatges de Co-Fe suportades sobre grafens dopats amb N defectuosos amb distribució de grandària de nanopartícules controlada en el rang de 7-17 nm, obtenint una selectivitat cap a hidrocarburs C2+ al voltant del 45% i una conversió del CO2 pròxima al 60%. A més, es va realitzar un estudi comparatiu de l'activitat catalítica de catalitzadors similars basats en Co-Fe amb promotors i inhibidors per a la hidrogenació de CO2, observant la seua influència en la conversió i selectivitat de CO2. Finalment, a més dels catalitzadors basats en Co-Fe, també s'han preparat catalitzadors basats en Cu-ZnO mitjançant un mètode de dos passos. Aquestes nanopartícules de Cu-ZnO suportades sobre grafé defectuós dopat amb N exhibeixen una alta selectivitat cap a la conversió de CO2 a metanol.
[EN] Considering the depletion of fossil fuels and the increasing atmospheric CO2 concentration, CO2 hydrogenation is a promising way to convert CO2 into value-added carbon-containing chemicals and fuels. Taking into account the significant influences of the particle size, chemical composition, nature of the support, and operation conditions on the catalytic performance of catalysts, a series of catalysts for CO2 hydrogenation have been developed based on the use of abundant non-noble metals and natural polysaccharides as graphene precursors. In the present PhD Thesis, metal species supported on defective graphitic carbon matrix with different particle sizes show different catalytic activity and selectivity for CO2 hydrogenation. Under effective control, Co and Co-Fe alloy nanoparticles wrapped on defective N-doped graphenes with a broad nanoparticle size distribution were prepared and performed for the Sabatier reaction, exhibiting a selectivity to methane over 90 % at CO2 conversion values over 85 %. In the case of single Co or Fe metal and their alloys in the form of clusters and small nanoparticles wrapped on the same support, the selectivity for CO2 hydrogenation shifts to CO, rather than methane, reaching a conversion of 56 % with 98 % CO selectivity. It is worth noting that the metal alloy clusters-based catalysts with the metal loading even below 0.2 wt.% exhibit a higher selectivity and better performance than the ones with larger Co-Fe alloy nanoparticles ranging from 1-4 nm and higher metal loading in a similar composition. Following the research line for CO2 hydrogenation, a series of Co-Fe alloy nanoparticles supported on defective N-doped graphenes with controlled nanoparticle size distribution in the range of 7-17 nm are developed, obtaining a selectivity towards C2+ hydrocarbons about 45% with a CO2 conversion close to 60%. In addition, a comparative catalytic activity of similar Co-Fe-based catalysts with promoters and poison has been studied for CO2 hydrogenation to observe their influence on CO2 conversion and selectivity. Finally, besides Co-Fe-based catalysts, Cu-ZnO-based catalysts have also been prepared by a two-step method. These Cu-ZnO nanoparticles supported on N-doped defective graphene exhibit a high selectivity for CO2 conversion to methanol.
Peng, L. (2021). Metal Nanoparticles Wrapped on Defective Nitrogen-doped Graphitic Carbons as Highly Selective Catalysts for C02 Hydrogenation [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/172329
TESIS

In this project, composite membranes containing nanoparticles of polydopamine PDA (dopamine polymer) will be manufactured and characterized in view of their use for the separation of CO2. Polysulfone will be used as a polymer matrix support while poly(vinyilalcohol) has been chosen as selective layer material. The work will first focus on the optimization of the manufacturing parameters of nano composite membranes and then on the influence of the integration of PDA nanoparticles in the polymeric support at different concentrations. The final objective is to test the material properties, with particular reference to the separation performances of the membranes produced, and critically comment on the results obtained.

Compte tenu du récent taux alarmant d'épuisement des réserves de combustibles fossiles et de l'augmentation drastique des niveaux de CO2 dans l'atmosphère qui a conduit au réchauffement de la planète et à des changements climatiques sévères, l'exploitation de toutes sortes d'énergies renouvelables a été la Parmi les principales priorités de la recherche Champs à travers le monde. L'une des nombreuses voies de ce genre est la réduction du CO2 aux combustibles utilisant des énergies renouvelables, plus communément appelées cellules photoélectro-catalytiques (PEC). Des essais expérimentaux sur la réduction du CO2 ont été réalisés sur différents types de catalyseurs dans les deux cellules (Conçu par un laboratoire) afin de comprendre la sélectivité, la productivité et les produits de réaction obtenus. Des essais expérimentaux ont été réalisés sur différents types de catalyseurs à la fois dans les cellules en phase gazeuse et en phase liquide pour comprendre la sélectivité, la productivité et les produits de réaction obtenus. Pour les études sur la réduction EC du CO2 en phase gazeuse, une série d'électrodes (à base de nanoparticules (NPs) de Cu, Fe, Pt et CuFe déposées sur des nanotubes de carbone ou de noir de carbone puis placées à l'interface entre une membrane Nafion et Une électrode à couche de diffusion de gaz). Les résultats démontrent le type divers de produits formés et leurs productivités. Dans des conditions sans électrolyte, la formation de produits ≥C1 tels que l'éthanol, l'acétone et l'isopropanol a été observée la plus élevée étant pour Fe et suivie de près par Pt. Pour améliorer Combustibles nets, un ensemble différent d'électrodes a été préparé sur la base de revêtements MOF de type imidazolate de type zéolitique substitué (SIM-1) (Fe-CNT, Pt-CNT et CuFe-CNT basés sur MOF) Et Pt-MOF a montré des carburants améliorés. En se reportant aux études sur la réduction EC du CO2 dans une cellule en phase liquide, un ensemble similaire d'électrodes a été prepare (NP - Cu, Fe, Pt, Ru, Co déposées sur des nanotubes de carbone ou du noir de carbone ont). Pour les conditions de phase liquide, en termes de produits C nets, les électrodes catalytiques à base de Pt sont en tête de la catégorie, suivies de près par Ru et Cu, tandis que Fe a obtenu la position la plus basse. Le mécanisme réactionnel sous-jacent probable a également été fourni. Afin d'améliorer encore les performances, on a synthétisé des NP de metal (Ru, Fe, Pt et Cu) de différentes tailles en utilisant différentes techniques de synthèse: (i) l'itinéraire d'imprégnation (ImR) pour obtenir des NP dans la plage de tailles de 10 à 50 nm; (Ii) Approche organométallique (OM) pour synthétiser des NPs uniformes et ultrafines dans la plage de tailles de 1-5 nm. Fe ont été synthétisés par une nouvelle voie de synthèse et des conditions pour atteindre des NP de 1 à 3 nm. (Iii) Approche de haut en bas de Nanowire pour obtenir des NP de cuivre ultrafin dans la plage de taille de 2-3,8 nm. Les améliorations apportées à la productivité du carburant se sont révélées être de 5 à 30 fois plus élevées pour les petites NP sur les NP plus importantes et, en outre, une charge réduite de 10 à 1-2% en poids. Un autre ensemble d'électrodes à base de nano-mousses (Cu NF et Fe NF sur Feuille de Cu, Feuille de Foie, Al Foil, Inconel foil et Al grid / mesh) préparés par électrodéposition ont également été étudiés afin d'améliorer encore la conversion de CO2 / carburant. Après, l'optimisation du dépôt et de la tension à l'aide de la voltamétrie cyclique, les carburants se sont améliorés de 2 à 10 fois par rapport aux combustibles nets les plus élevés obtenus à l'aide d'électrodes CNT dopées à base de NP
In view of the recent alarming rate of depletion of fossil fuel reserves and the drastic rise in the CO2 levels in the atmosphere leading to global warming and severe climate changes, tapping into all kinds of renewable energy sources has been among the top priorities in the research fields across the globe. One of the many such pathways is CO2 reduction to fuels using renewable energies, more commonly referred as photo-electro-catalytic (PEC) cells. Experimental tests were carried out on various types of catalysts in both the gas and liquid phase cells (lab-designed) to understand the different selectivity, productivity and the reaction products obtained. For the studies on the EC reduction of CO2 in gas phase cell, a series of electrodes (based on Cu, Fe, Pt and Cu/Fe metal nanoparticles – NPs - deposited on carbon nanotubes – CNTs - or carbon black and then placed at the interface between a Nafion membrane and a gas-diffusion-layer) were prepared. Under gas phase, the formation of ≥C1 products (such as ethanol, acetone and isopropanol) were observed, the highest being for Fe and closely followed by Pt, evidencing that also non-noble metals can be used as efficient catalysts under these conditions. To enhance the net fuels, a different set of electrodes were also prepared based on substituted Zeolitic Imidazolate (SIM-1) type MOF coatings (MOF-based Fe-CNTs, Pt-CNTs and Cu/Fe-CNTs) and Pt-MOF showed improved fuels. Moving to the studies on the EC reduction of CO2 in liquid phase cell, a similar set of electrodes were prepared (metal NPs of Cu, Fe, Pt, Ru and Co deposited on CNTs or carbon black). For liquid phase conditions, in terms of net C-products, catalytic electrodes based on Pt topped the class, closely followed by Ru and Cu, while Fe got the lowest position. The probable underlying reaction mechanism was also provided. In order to improve further the performances, varied sized metal NPs (Ru, Fe, Pt and Cu) have been synthesized using different techniques: (i) impregnation (ImR) route to achieve NPs in the size range of 10-50 nm; (ii) organometallic (OM) approach to synthesize uniform and ultrafine NPs in the size range of 1-5 nm (i.e., Fe NPs were synthesized through a novel synthesis route to attain 1-3 nm NPs); (iii) Nanowire (NW) top-down approach to obtain ultrafine copper metal NPs in the size range of 2-3.8 nm. The enhancements in the fuel productivity were found to be 5-30 times higher for the smaller metal NPs over the larger metal NPs and moreover, with reduced metal loading from 10 to 1-2 wt %. A different set of electrodes based on nano-foams (Cu NF and Fe NF on Cu foil, Fe foil, Al foil, Inconel foil and Al grid/mesh) prepared via electro-deposition were also investigated, to further improve CO2 to fuels conversion. After, optimization of deposition and voltage using cyclic voltammetry, the fuels improved by 2-10 times over the highest net fuels achieved using metal NPs doped CNT electrodes

Ce mémoire rapporte l'étude par spectroscopique infrarouge des nanoparticules de CO2 et de molécules organiques volatiles refroidies à très basse température (2̃5 K) par différents procédés de détente supersonique. La première partie rapporte une caractérisation expérimentale des différents écoulements rencontrés et la mise en place d'un nouveau type d'injection supersonique. Une injection centrale par capillaire a été utilisée pour former des nanoparticules de CO2 composés de quelques milliers de molécules. Une étude spectroscopique menée sur ces agrégats dans les régions autour de 660 cm-1 (mode de pliage) et de 2360 cm-1 (mode d'élongation antisymétrique), a permis de mettre en évidence l'influence du paramètre taille sur les signatures infrarouges. Enfin, des spectres infrarouges obtenus à très basse température ont été enregistrés sur des molécules organiques volatiles comme le benzène, le méthanol, le propanol-2, l'acide formique ou bien encore l'acide acétique.

Le reformage à sec du méthane (DRM) est un processus qui convertit simultanément CH4 et CO2 en un mélange gazeux de H2 et de CO appelé syngas. Les catalyseurs à base de Ni sont particulièrement prometteurs mais ils ne sont pas stables en raison du frittage du Ni et du dépôt de coke. Dans cette thèse, nous avons développé deux voies de synthèse de catalyseurs mésoporeux à base de Ni-Al2O3 dans lesquels Ni est stabilisé dans l'oxyde, ce qui donne une activité et une stabilité élevées en DRM. Des techniques physicochimiques complémentaires ont été appliquées pour identifier les propriétés des matériaux à toutes les étapes de préparation et d'activation. La première approche comprend la synthèse « EISA one-pot » de matériaux mésoporeux Ni-Mg-Al2O3. L’échantillon à base de 15% en poids de Mg (charge optimale) contribue à une dispersion élevée et homogène de Ni et de Mg tout en préservant la qualité structurale de la matrice Al2O3 mésoporeuse. La basicité accrue renforce l'activité et la stabilité. La seconde méthode consiste à synthétiser des matériaux mésoporeux Ni-Al2O3 innovants en utilisant une structure organométallique (MOF) comme matrice sacrificielle. Cette procédure permet la formation de petites nanoparticules de Ni stabilisées de manière homogène dans le support de grande surface spécifique, insensibles au frittage et à la formation de nanotubes de carbone lors de la réaction de DRM. Les tests catalytiques complétés par des calculs thermodynamiques montrent l’efficacité des matériaux synthétisés non seulement pour le reformage à sec du méthane, mais également pour la méthanation du CO2 et le reformage à sec de biogaz issu de pyrolyse
Dry reforming of methane (DRM) is a process that converts CH4 and CO2 gases into syngas, a gaseous mixture of H2 and CO. Ni based catalysts proved to be suitable for the reaction due to their good activity, wider availability and lower cost than noble-based materials. However, these catalysts are not stable due to Ni sintering and coke deposition. In this thesis we developed two different synthesis routes of mesoporous Ni-Al2O3 based catalysts that can occlude Ni inside the pores achieving high activity and stability in DRM. A set of complimentary physicochemical techniques was systematically applied to thoroughly investigate the materials properties at all steps of preparation and activation. The first approach embraces synthesis of mesoporous Ni-Mg-Al2O3 materials by one-pot EISA strategy. Results demonstrate that 15 wt% Mg (optimum loading) based sample contribute to high and homogenous dispersion of both Ni and Mg, preserving ordered mesoporous Al2O3 walls. The good structural and textural characteristics in addition to the enhanced basicity reinforce activity and stability. The second method involves synthesizing new mesoporous Ni-Al2O3 materials using metal-organic framework as sacrificial template. This procedure results in small Ni nanoparticles homogeneously dispersed and stabilized within the high surface area support resisting sintering and inhibiting carbon nanotubes formation during reforming reaction. Based on catalytic tests completed by thermodynamics calculations, the synthesized materials proved to be eficient not only for dry reforming of methane, but also for CO2 methanation reaction and dry reforming of waste pyrolysis products

2009/2010
Nanosized inorganic particles constitute a field of rapidly growing interest and their tailored synthesis is currently subject of intense study. These particles may show unique properties that are not shared by bulk materials and therefore find a palette of innovative applications, e.g., as diagnostic means, or in drug and even gene delivery, offering the advantage over polymer nanoparticles because they are stable, biologically inert, biocompatible and it is easy to introduce functional groups by modification of the surface hydroxyls. Among various synthetic routes the most explored are the ones carried out in bulk, especially the Stöber synthesis, however the final product are mostly polydisperse particles whose size is difficult to control. On the other hand, w/o microemulsion is providing suitable environment for the control of the particle nucleation and growth kinetics, as the nanodroplets of water are nanoreactors for the synthesis. The main advantage is that the procedure does not require extreme conditions of temperature and pressure and the particle size and shape can be controlled simply by controlling the microemulsion parameters where the most important are the water-to-surfactant molar ratio, R, and water-to-TEOS molar ratio, h. The previous studies focused on the latter synthetic route, in base-catalyzed systems, concerned mainly the evolution of silica nanoparticles and the best results were achieved by SAXS. The volume fraction versus time data gave an insight into nucleation and growth and is in agreement with first order kinetics with respect to TEOS concentration. However, we wanted to understand better the environment in which the synthesis takes place and shed light on the evolution of the soluble species, both of the constituents of the microemulsion and of those taking part to reaction. The soluble species present in the reaction mixture that leads to silica nanoparticle production through the base catalyzed hydrolysis of tetraethyl orthosilicate (TEOS) and the successive condensation were investigated in situ, under the actual synthesis conditions, by means of 1H, 13C, and 29Si NMR spectroscopy. The two former nuclei, owing to higher sensitivity and their presence both in the reacting species and in the constituents of the w/o microemulsion (cyclohexane-Igepal CA520 (5 polyoxyethylene iso-octylphenyl ether)-concentrated ammonia solution) afforded insight into the inverse microemulsion and allowed us to assess the kinetic rate of the hydrolysis step. It was verified that the microemulsion microstructure is maintained during the reaction. Special attention was paid to the reaction medium, and an extended assignment of the 1H and 13C resonances of the surfactant head group was performed. These head group signals undergo some changes due to the environmental modifications induced by transition from cyclohexane solution to w/o microemulsion and further to NH3 containing w/o microemulsion. We followed the quantitative evolution of TEOS and EtOH and assessed their preferential distribution in the various environments provided by this, on the mesoscale heterogeneous, reaction medium. Most authors agree that TEOS is localized mainly in the oil however they argue whether EtOH is preferentially in the water-pools or in oil. The clarification was achieved by means of PGSTE NMR since the diffusion coefficients are commonly exploited to characterize microemulsions, to determine the connectivity of the phase and they can be used to obtain the size of water droplets. It was revealed that NH3 exchanges among the inverse micelles diffusing through cyclohexane and confirmed that the preferred localization for ethanol, a byproduct of the reaction, is the bulk oil. Moreover, it was confirmed that TEOS is localized mainly in the oil. The characterization of the final nanoparticles was carried out by means of transmission electron microscopy (TEM) and it was revealed that the final product were monodispersed particles with radius of 20 nm. The synthesis of SiO2 nanoparticles in an acid-catalyzed system is especially interesting from nanotechnological point of view, owing to the different physical nature of silica synthesized under acidic rather than basic conditions, and from an applicative point of view since intended guest species are not always base resistant. Unfortunately, the application of an acid-catalyzed sol-gel process seems less than straightforward. An inverse microemulsion looks like an optimal reaction medium able to limit the growth of silica particles within the nanometer range. However, relatively few studies have been reported to date, and to the best of our knowledge, only one involves the entire process conducted in an inverse microemulsion with a water core that remains stable throughout the course of the reaction. The cyclohexane-Igepal inverse microemulsion, comprehensively established for the synthesis of silica nanoparticles in NH3-catalyzed sol-gel process, was alternatively studied with an acid-catalyzed sol-gel process. TEOS was used as the silica precursor, while two different aqueous phases containing either HNO3 or HCl at two different concentrations, 0.1 and 0.05 M, were examined in the presence and in the absence of NaF, a catalyst of the condensation step. The evolution of the overall reacting system, specifically hydrolysis and polycondensation of reaction intermediates, was monitored in situ by SAXS. No size variation of the inverse micelles was detected throughout the sol-gel process. Conversely, the density of the micellar core increased after a certain time interval, indicating the presence of the polycondensation product. The IR spectra of the reacting mixture were in agreement with such a hypothesis. 1H and 13C NMR measurements provided information on the soluble species, the surfactant, and TEOS. The TEOS consumption was well fitted by means of an exponential decay, suggesting that a first-order kinetics for TEOS transpires in the various systems examined, with rate constants dependent not only on the acid concentration but also on its nature (anion specific effect), on the presence of NaF, and on the amount of water in the core of the inverse micelle. The self-diffusion coefficients, determined by means of PGSTE NMR, proved that a sizable amount of the byproduct ethanol was partitioned inside the inverse micelles. Moreover, the DOSY spectrum contributed to the assignment of the signals of various oligomeric species present in the commercial mixture of Igepal CA520, since the head group, which is a short polyoxyehtylene chain, is somewhat polydisperse. The embedment of Igepal CA520 in an acid-catalyzed inverse microemulsion led to the separation of 1H signals of the various oligomeric components. This ensued from the differential partitioning between the oil and the surface of the inverse micelles, which depends on the ethyleneoxide number (EON) of the head group and the partition degree, between the two environments, for each individual oligomeric species, and afforded further insight into nonionic inverse microemulsions. It was possible to ascertain that the length distribution of the polyethyleneoxide chains is in good agreement with the Poisson distribution theoretically predicted for the polymerization of ethylene oxide. Characterization of the final product was carried out by means of thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and TEM, which concurrently confirmed that the silica isolated from the inverse nonionic microemulsion is not significantly different from the product of a bulk acid-catalyzed sol-gel synthesis. TEM micrographs illustrated particles with diameters smaller than the diameter of the inverse micelles as determined by SAXS, due to a shrinkage effect, in addition to nanostructured aggregates in the range 20-100 nm. The metal doped silica systems are important for optical applications and if the metal ions are finely dispersed on silica matrix very efficient catalysators can be obtained. The synthesis of silica nanoparticles in HCl-catalyzed inverse microemulsion was carried out in the presence of both Cu2+ and Co2+ ions with the aim to get correspondingly doped nanoparticles. The systems were characterized by means of 1H and 13C NMR and the quantitative evolution of TEOS and EtOH was followed. The introduction of metals in the glass matrix strongly influences their optical visible absorption spectrum so the UV-Vis spectroscopy was applied in the study. The isolated nanoparticles were characterized by means of IR and Raman spectroscopy and their size was determined by TEM. It was demonstrated that inverse micelles can be used to produce Co2+ and Cu2+ doped SiO2 nanoparticles with diameter of about 3 and 4 nm, respectively. Spherical particles smaller than the micellar size and, in the case of Cu2+ doped system, larger, irregularly shaped aggregates with diameter up to 1 μm were observed. Lots of darker zones were observed in the TEM images of some larger particles and aggregates containing Cu and may be assigned to Cu metal particles encapsulated in silica matrix. Therefore, cobalt was successfully doped in silica nanoparticles while copper doping seemed less satisfactory.
Particelle inorganiche di grandezza nanometrica costituiscono un settore di interesse in rapida crescita e la loro sintesi è attualmente oggetto di intenso studio. Queste particelle possono presentare proprietà uniche non condivise da materiali bulk e quindi trovare una vasta gamma di applicazioni innovative, ad esempio, come mezzo diagnostico, o per drug delivery e anche gene delivery, offrendo il vantaggio rispetto nanoparticelle polimeriche di essere stabili, biologicamente inerti, biocompatibili e facilmente funzionalizzabili con gruppi funzionali modificando dei ossidrili superficiali. Tra le varie vie sintetiche più esplorate sono quelle effettuate in bulk, in particolare la sintesi di Stöber, ma il prodotto finale sono particelle per lo più polidisperse la cui dimensione è difficile da controllare. D'altra parte, la microemulsione a/o sta fornendo l'ambiente adatto per il controllo della cinetica di nucleazione e crescita delle particelle, siccome le nanogoccioline d'acqua sono i nanoreattori per la sintesi. Il vantaggio principale è che la procedura non richiede condizioni estreme di temperatura e pressione e la dimensione delle particelle e la forma possono essere controllati semplicemente attraverso il controllo dei parametri di microemulsione tra cui i più importanti sono il rapporto molare acqua-tensioattivo, R, e acqua-TEOS, h. Gli studi precedenti focalizzati su quest'ultima linea sintetica, nei sistemi base-catalizzati, riguardavano principalmente l'evoluzione delle nanoparticelle di silice ed i migliori risultati sono stati raggiunti con SAXS. I dati di frazione di volume in funzione del tempo hanno fornito informazioni sui processi di nucleazione e di crescita e sono in accordo con una cinetica di primo ordine rispetto alla concentrazione di TEOS. Tuttavia, era importante capire meglio l'ambiente in cui la sintesi accade e mettere in luce l'evoluzione della specie solubile, sia dei componenti della microemulsione che di coloro che prendono parte alla reazione. Le specie solubili presenti nella miscela di reazione che porta alla produzione di nanoparticelle di silice attraverso l’idrolisi base-catalizzata di tetraetile ortosilicato (TEOS) e la successiva condensazione sono state studiate in situ, alle condizioni effettive di sintesi, mediante spettroscopia NMR di 1H, 13C, e 29Si. I primi due nuclei, a causa di una maggiore sensibilità e la loro presenza sia nel reagente che nei componenti della microemulsione a/o (cicloesano-Igepal CA520 (5 poliossietilene iso-octilfenil etere)-soluzione di ammoniaca concentrata) hanno offerto una visione della microemulsione inversa e ci hanno permesso di valutare la velocità di idrolisi. È stato verificato che la microstruttura della microemulsione è mantenuta durante la reazione. L’attenzione è stata rivolta particolarmente verso il mezzo di reazione, ed è stata effettuata un’assegnazione estesa delle 1H e 13C risonanze della testa del tensioattivo. Questi segnali della testa subiscono variazioni a causa delle modificazioni ambientali indotte dal passaggio dalla soluzione di cicloesano a microemulsione a/o e in seguito alla microemulsione a/o contenente NH3. Abbiamo seguito l'evoluzione quantitativa del TEOS e EtOH e valutato la loro distribuzione preferenziale nei vari ambienti forniti da questo mezzo di reazione, eterogeneo sulla mesoscala. Molti autori concordano sul fatto che il TEOS è localizzato principalmente in olio. Tuttavia, si dibatte se EtOH si trova preferenzialmente nelle goccioline d'acqua o nell’olio. Il chiarimento è stato realizzato per mezzo di PGSTE NMR in quanto i coefficienti di diffusione sono comunemente sfruttati per caratterizzare le microemulsioni, per determinare la connettività delle fasi e possono essere utilizzati per ottenere le dimensioni delle goccioline d’acqua. È stato rivelato che NH3 scambia tra le micelle inverse diffondendo attraverso il cicloesano ed è stato confermato che la localizzazione preferita per l'etanolo, il sottoprodotto della reazione, è l'olio. Inoltre, è stato confermato che il TEOS è localizzato principalmente nell’olio. La caratterizzazione delle nanoparticelle finali è stata effettuata per mezzo di microscopia elettronica a trasmissione (TEM) ed è stato rivelato che il prodotto finale sono le particelle monodisperse con raggio di 20 nm. La sintesi di nanoparticelle di SiO2 in un sistema con catalisi acida è particolarmente interessante dal punto di vista nanotecnologico, a causa della diversa natura fisica di silice sintetizzata in condizioni acide, piuttosto che in quelle basiche, e da un punto di vista applicativo in quanto le specie ospite previste non sempre sono resistenti alle basi. Purtroppo, l'applicazione di un processo sol-gel catalizzato da acido è meno chiara. Una microemulsione inversa sembra un mezzo di reazione ottimale in grado di limitare la crescita delle particelle di silice alle grandezze nanometriche. Tuttavia, relativamente pochi studi sono stati riportati fino ad oggi, e al meglio delle nostre conoscenze, solo uno riguarda l'intero processo condotto in una microemulsione inversa con un nucleo d’acqua che rimane stabile durante tutto il corso della reazione. La microemulsione inversa cicloesano-Igepal, stabilita per la sintesi di nanoparticelle di silice in processo sol-gel NH3-catalizzato, in alternativa è stata studiata con il processo sol-gel catalizzato da acido. Il TEOS è stato utilizzato come precursore di silice, mentre diverse fasi acquose contenenti HNO3 o HCl a due differenti concentrazioni, 0.1 o 0.05 M, sono state esaminate in presenza ed in assenza di NaF, un catalizzatore della fase di condensazione. L'evoluzione del sistema reagente complessivo, in particolare l’idrolisi e la policondensazione dei intermedi di reazione, è stata monitorata in situ mediante SAXS. Nessuna variazione delle dimensioni delle micelle inverse è stata rilevata durante tutto il processo sol-gel. Al contrario, è aumentata la densità dell’interno micellare dopo un certo intervallo di tempo, indicando la presenza del prodotto di policondensazione. Gli spettri IR della miscela di reazione erano d'accordo con tale ipotesi. Misure NMR 1H e 13C hanno fornito le informazioni sulle specie solubili.. Il consumo di TEOS era in accordo con un decadimento esponenziale, suggerendo una cinetica di primo ordine in TEOS, con costante di velocità dipendente non solo dalla concentrazione di acido, ma anche dalla natura (effetto anione specifico), dalla presenza di NaF, e dalla quantità di acqua nel nucleo della micella inversa. I coefficienti di auto-diffusione, determinati mediante PGSTE NMR, hanno dimostrato che una quantità considerevole del sottoprodotto etanolo è presente all'interno delle micelle inverse. Inoltre, lo spettro DOSY ha contribuito alla assegnazione dei segnali delle varie specie oligomeriche presenti nella miscela commerciale di Igepal CA520, poiché la testa, che è una breve catena di poliossietilene, è un po’ polidispersa. L’inserimento di Igepal CA520 in una microemulsione inversa contenente acido ha portato alla separazione di segnali 1H dei vari componenti oligomerici. Questo risulterebbe dal partizione differenziale tra l'olio e la superficie delle micelle inverse, che dipende dal numero di ossido di etilene (EON) della testa e il grado di partizione, tra i due ambienti, per ogni singola specie oligomerica, offrendo una visione più completa sulle microemulsioni inverse non ioniche. È stato possibile accertare che la distribuzione della lunghezza delle catene poliossietileniche è in buon accordo con la distribuzione di Poisson teoricamente prevista per la polimerizzazione di ossido di etilene. La caratterizzazione del prodotto finale è stata effettuata mediante analisi termogravimetrica (TGA), calorimetria differenziale a scansione (DSC), e TEM, che contemporaneamente hanno confermato che la silice isolata dalla microemulsione inversa non ionica non è significativamente diversa dal prodotto di sintesi sol-gel da catalisi acida in bulk. Le micrografie TEM hanno illustrato, oltre ad aggregati nanostrutturati nel range 20-100 nm, le particelle con diametro inferiore al diametro delle micelle inverse ,determinato da SAXS, a causa di un effetto di contrazione. I sistemi di silice dopati con metalli sono importanti per le applicazioni ottiche, e se gli ioni metallici sono finemente dispersi in matrice di silice possono essere ottenuti catalizzatori molto efficienti. La sintesi di nanoparticelle di silice in microemulsione inversa catalizzata da HCl è stata effettuata in presenza di entrambi ioni, Cu2+ e Co2+, con l'obiettivo di ottenere le nanoparticelle conseguentemente dopate. I sistemi sono stati caratterizzati mediante 1H e 13C NMR ed è stata seguita l'evoluzione quantitativa di TEOS e EtOH. L'introduzione dei metalli nella matrice vetrosa influenza fortemente il loro spettro di assorbimento ottico visibile per cui nello studio è stata applicata la spettroscopia UV-Vis. Le nanoparticelle isolate sono state caratterizzati mediante spettroscopia IR e Raman e la loro dimensione è stata determinata mediante TEM. È stato dimostrato che le micelle inverse possono essere utilizzate per produrre le nanoparticelle di SiO2 dopate di Co2+ e Cu2+ con diametro di circa 3 e 4 nm, rispettivamente. Sono state osservate le particelle sferiche più piccole rispetto alle dimensioni micellari e, nel caso del sistema dopato di Cu2+, aggregati più grandi di forma irregolare con diametro fino a 1 micron. Nei immagini TEM di alcune particelle più grandi e aggregati contenenti Cu sono state osservate molte zone più scure che possono essere assegnate alle particelle di metallo Cu incapsulato in matrice di silice. Pertanto, il cobalto è stato dopato con successo nelle nanoparticelle di silice, mentre il doping con il rame sembrava meno soddisfacente.
XXIII Ciclo
1983

Nous avons étudié la chimie de surface de carbones poreux fonctionnalisés avec des oximes et amidoximes d’une part, et avec de la guanidine d’autre part. Nous avons axé ces travaux sur la compréhension et la quantification de ces fonctionnalisations par analyse thermique et plus particulièrement par thermo-désorption programmée en température couplée à la spectroscopie de masse (TPD-MS). Par la suite, nous avons évalué l’intérêt de la fonctionnalisation par la guanidine des carbones mésoporeux pour deux applications : le piégeage du CO2 et la capacité à synthétiser et stabiliser des nanoparticules métallique. Pour la première application, des tests d’adsorption du CO2 à 0°C et 20°C à 1 bar ont été réalisés sur un carbone mésoporeux oxydé sous air en présence ou non de guanidine. L’intensité des interactions (physisorption versus chimisorption) a été sondée par des calculs de chaleurs isostériques d’adsorption. Pour la seconde applications, nous avons utilisé des carbones mésoporeux oxydés en présence ou non de guanidine pour synthétiser des nanoparticules d’argent de taille inférieure à 2 nm et relativement monodisperses en taille. Des particules bimétalliques d’AgCu ont également été obtenues au sein de ces matrices carbonées mésoporeuses imprégnées par la guanidine. On a pu mettre ici en évidence un rôle bénéfique de la guanidine sur le taux de cuivre réduit. Des suivis thermiques par MET in situ ont également été réalisés afin d’évaluer la stabilité thermique de ces nanoparticules et de mieux appréhender l’intérêt de la fonctionnalisation sur les phénomènes de frittage de ces nanoparticules. Finalement, des tests catalytiques pour l’époxydation sélective du styrène ont aussi été effectués sur le matériau Ag/C. Les résultats préliminaires sont très prometteurs pour un procédé de préparation de catalyseur très simple à mettre en œuvre
In this work, we studied the surface chemistry of porous carbons functionalized firstly with oximes and amidoximes and then with guanidine. We focused this work on the understanding and quantification of these functionalization with thermal analysis and more particularly by Temperature Programmed Desorption/Mass Spectrometry (TPD-MS). Subsequently, we evaluated the interest of guanidine functionalization of mesoporous carbons for two applications : the capture of CO2 and the ability to synthesize and stabilize metal nanoparticles. For the first application, CO2 adsorption tests at 0 ° C. and 20 ° C. at 1 bar were carried out on a mesoporous carbon oxidized under air in the presence or absence of guanidine. The intensity of interactions (physisorption versus chemisorption) was probed by isosteric adsorption heat calculations. For the second applications, we used oxidized mesoporous carbons with or without guanidine to synthesize silver nanoparticles less than 2 nm in size and relatively monodisperse in size. Bimetallic AgCu particles were also obtained from these mesoporous carbon matrices impregnated with guanidine. A beneficial role of guanidine on the reduced copper content has been shown here. In situ TEM has also been carried out in order to evaluate the thermal stability of these nanoparticles and to understand the interest of the functionalization on the sintering of these nanoparticles. Finally, catalytic tests for the selective epoxidation of styrene were also performed on these materials. The preliminary results are very promising for a catalyst preparation process and very simple to implement

Le travail qui est présenté dans ce manuscrit est le résultat d'une série d'expériences qui ont été effectuées à la fois à l'Université du Maine (IMMM Le Mans) et aux lignes de lumière lD10 et lD02 de l'ESRF (Grenoble) où j'ai passé la moitié de mon temps. Le projet que j'ai travaillé pendant trois ans a été principalement orienté sur l'étude des nanomatériaux qui ont été exposés au CO2 supercritique en utilisant de diffusion des rayons X. Par conséquent une partie de ce travail a été consacrée à la description des propriétés de ce fluide supercritique et comment il interagit avec des matériaux tels que les polymères par exemple. Les matériaux analysés ont été le polystyrène sous forme de film et des ilots, ensuite des matériaux meso-structures avec des tensioactifs fluorés et finalement le carbonate de calcium. Due à la taille nanométrique de tous ces matériaux, les techniques de rayons X qui ont été largement utilisés dans ce travail étaient Small angle X-ray scattering (SAXS), Grazing Small angle X-ray scattering ( (GISAXS) et X-ray reflectivity (XRR)
The work that is presented in this manuscript is the result of a series of experiments that were performed both at the Université du Maine (IMMM Le Mans) and at the ID10 and ID02 beam lines of the ESRF (Grenoble) where I have equally spent half of my time. The project I have been working on for three years was mostly oriented on the study by means of X-ray scattering probes of nanomaterials that were exposed to supercritical CO2. As a result another part of this work will be also dedicated to describing the properties of this supercritical fluid and how it interacts with materials such as polymers for instance. The analyzed materials were thin film and small island of polystyrene, then materials mesostructures using fluoro-surfactants and finally calcium carbonate. Due to the nanoscale of these materials, the X-ray probes that were extensively used in this work were Small Angle X-ray scattering (SAXS), Grazing Incidence Small Angle X-ray Scattering (GISAXS) and X-ray Reflectivity (XRR)

Hydrothermally treated biomass could not only be used as a fuel or a fertilizer but it can also be refined into high-value products. Activated carbons are one of those. In the studies of this thesis, four different hydrothermally carbonized (HTC) biomasses, including horse manure, grass cuttings, beer waste and biosludge, have been successfully made into activated carbons. The activated carbon materials were in the forms of powdered activated carbons, powdered composites of activated carbon and iron oxide nano-crystals, and activated carbon discs. The HTC biomasses and the activated carbons were characterized and analyzed using several methods. The biomasses were carbonized to different extent during the hydrothermal treatment, which depended on the different natures of the biomasses. The HTC biomasses were activated into powdered activated carbons by both physical activation, using CO2, and by chemical activation, using H3PO4. Full factorial design matrices were applied to design experiments and study the influence of different parameters used during both physical and chemical activation. Activated carbons with embedded iron oxide nanoparticles were synthesized through hydrothermal carbonization followed by CO2 activation. These composites had high surface areas and showed a strong magnetism, and the powders could be separated from liquid phase by applying a magnetic field. Strong and dense activated carbon discs were also prepared from powdered HTC beer waste by pulsed current processing (PCP) and a subsequent CO2 activation procedure. The potential for carbon dioxide separation from nitrogen, and methylene blue adsorption in aqueous solution, were assessed for the powdered activated carbons produced from HTC biomasses. They showed good performance in both applications.

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 1: In press.

Neste trabalho foi estudado o efeito da adição de íons haletos (Cl-, Br- e I-) sobre a morfologia das nanopartículas de Pt na produção de catalisadores de Pt/C e PtSnO2/C. Foi desenvolvida uma metodologia de síntese simples capaz de produzir nanopartículas de Pt predominantemente cúbicas com orientação preferencial Pt(100), diretamente suportadas em carbono sem o uso de agentes estabilizantes. Brometo de potássio foi utilizado como agente direcionador de superfície para obtenção do material preferencialmente orientado. O controle de adição do precursor de Pt e de KBr foi crucial para obter nanocubos de Pt de 8 nm bem dispersos sobre o suporte. Na preparação dos catalisadores de PtSnO2/C, o processo de adição do SnCl2 também foi decisivo na obtenção das nanopartículas de Pt com tamanho e morfologia de interesse. Nanocubos de Pt coexistindo com SnO2 disperso foram exclusivamente obtidos ao adicionar o SnCl2 na etapa final da síntese, quando as nanopartículas cúbicas de Pt já estavam formadas. Enriquecidos de domínios Pt(100), os materiais em forma cúbica de Pt/C e PtSnO2/C se mostraram menos afetados pelo acúmulo dos intermediários indesejados provenientes da reação de eletro-oxidação de etanol e foram mais tolerantes ao envenenamento por monóxido de carbono. Resultados similares foram observados para a oxidação de CO e metanol, utilizados como apoio para compreensão da eletro-oxidação de etanol. O efeito morfológico destes materiais no desempenho elétrico em célula a combustível de etanol direto foi avaliado. Pt/C e PtSnO2/C contendo nanopartículas de Pt com orientação preferencial Pt(100) forneceram maiores valores de densidade de potência e de seletividade para CO2 comparados aos catalisadores de Pt/C e PtSnO2/C com nanopartículas de Pt sem orientação preferencial.
The effect of the addition of halide ions (Cl-, Br- and I-) on the shape of Pt nanoparticles of Pt/C and PtSnO2/C catalysts was studied in this work. It was developed a simple methodology synthesis capable of producing Pt nanoparticles predominantly cubic with Pt(100) preferential orientation, directly supported on carbon without the use of stabilizing agents. Potassium bromide was used as a surface directing agent to obtain the preferentially oriented material. The control in addition of the Pt precursor and KBr was crucial to obtain well dispersed 8 nm Pt nanocubes on the support. For the preparation of PtSnO2/C catalysts, the addition process of SnCl2 was also decisive to obtain the Pt nanoparticles with desirable size and morphology. Pt nanocubes coexisting with disperse SnO2 were exclusively obtained by adding SnCl2 in the final step of the synthesis, when the cubic Pt nanoparticles were already formed. Enriched with Pt (100) domains, the Pt/C and PtSnO2/C cubic materials were less affected by the undesirable intermediates accumulation from the ethanol electro-oxidation reaction and were more tolerant to the poisoning of monoxide carbon. Similar results were observed for methanol and CO electro-oxidation reactions, which were employed to understand ethanol electro-oxidation. The morphological effect of these materials on electrical performance in direct ethanol fuel cell was evaluated. Pt/C and PtSnO2/C containing Pt(100) nanoparticles provided higher power density and CO2 selectivity values compared to Pt/C and PtSnO2/C catalysts with Pt nanoparticles without ant preferential orientation.

Le déclin de la production de pétrole, lié avec la diminution des matières premières carbonées pour la synthèse chimique ont mené les scientifiques à chercher de nouvelles sources de carbone pour l'industrie chimique. L'utilisation du dioxyde de carbone aiderait à réduire les émissions de gaz à effet de serre tout en fournissant une matière première renouvelable à base de bloc moléculaire en C1. En renversant les équilibres biologiques de trois déshydrogénases, nous avons effectué la biosynthèse multienzymatique en cascade du méthanol à partir de CO2 en utilisant la formiate déshydrogénase de Candida boidinii, la formaldéhyde déshydrogénase de Pseudomonas putida et l'alcool déshydrogénase de Saccacharomyces cerevisiae. Nous avons optimisé le système en ajustant les conditions catalytiques et la quantité relative de chaque déshydrogénase. La phosphite déshydrogénase de Pseudomonas stutzeri a été également choisi comme système de régénération du cofacteur nicotinamide adénine dinucléotide réduit (NADH) parmi 4 systèmes de régénération étudiés. L'ensemble du système a été encapsulé dans des nanocapsules poreuses de silice qui a permis d'augmenter 15 fois les productivités en méthanol. Nous avons montré que les dernières limitations rencontrées, comme la disponibilité du CO2 et l'accumulation du méthanol, peuvent être dépassées en mettant en place un système catalytique en flux continu en phase gaz
The decline of oil production, linked with the decrease of carbon feedstock for chemical synthesis leads scientist to find new sources of carbon for the chemical industry. Use of carbon dioxide would help to reduce the greenhouse gas emissions while providing a renewable feedstock of C1 molecular building blocks. By reversing the biological metabolic reaction pathway of three dehydrogenase, we carried out multistep multienzyme biosynthesis of methanol from CO2 using formate dehydrogenase from Candida Boidinii, formaldehyde dehydrogenase from Pseudomonas Putida and alcohol dehydrogenase from Saccacharomyces cerevisiae. We improved the system active by adjusting the catalytic conditions and the relative quantity of each dehydrogenase. Phosphite dehydrogenase from Pseudomonas stutzeri was also chosen among 4 different studied systems to be introduced into the catalysis as a cofactor regenerating system for reduced nicotinamide adenine dinucleotide. The enzymatic system was then immobilized by encapsulation into novel phospholipid templated silica nanocapsules, allowing an increase of the methanol productivity by a factor 15. We show that the last limitation of the process as substrate availability and product accumulation can be overcome by running continuous enzymatic flow conversion in a gas phase

La synthèse d'acide polyamique (APA) comportant des blocs élastomères de type oligo-oxyéthylène et -oxypropylène et des polyimides correspondants (PEI) a été étudiée et leurs propriétés de perméation gazeuse déterminées pour He, N2, O2, H2, CH4 et CO2. Il a été montré que la présence de la phase élastomère augmentait de façon très importante les coefficients de perméabilité au gaz comparativement aux polyimides aromatiques conventionnels. La perméabilité du CO2, augmentée de façon préférentielle par rapport celles de tous les autres gaz, conduit à des sélectivités idéales tout à fait remarquables, en particulier vis-à-vis de N2 (≈40). L’incorporation de nanoparticules de silice dans les PEI (de 1 à 15% en masse) a été effectuée lors de l’étape de cyclo-déshydratation de l'APA, soit par ajout de silice hydrophobes (16 nm) ou hydrophiles (12 nm), soit par méthode Sol-Gel à partir de précurseurs alcoxysilanes (TMOS et TEOS). L'influence des charges SiO2 sur les propriétés de perméation gazeuse a été étudiée par la méthode du temps de retard (time-lag) essentiellement sur la série préparée avec des particules préformées. On a observé que les nano-charges de silice ne semblent pas interférer dans le processus de cyclisation et que les propriétés mécaniques sont renforcées ; la perméabilité aux gaz varie surtout selon la quantité de charges incorporées mais aucune augmentation spectaculaire de perméabilité n’a pu être observée. On peut en déduire que, vraisemblablement, c’est la phase élastomère qui est le lieu d’incorporation des particules de SiO2. Ces résultats montrent l’intérêt des membranes PEI et PEI/SiO2 dans des applications industrielles de séparation de gaz, notamment pour la séparation de mélanges CO2/N2
The synthesis of polyamic acids (PAA) with oligo-oxyethylene and -oxypropylene rubbery blocks and the related polyimides (PEI) has been studied and their gas permeation properties determined for He, N2, O2, H2, CH4 and CO2. It was shown that the rubbery phase dramatically increased the gas permeability coefficients compared to conventional aromatic polyimides. The permeability of CO2 is preferentially increased in comparison to all other gases, leading to remarkable ideal selectivities, especially for the N2 mixture (≈40). The incorporation of silica nanoparticles in PEI (from 1 to 15 wt%) was carried out during the cyclo-dehydration of the PAA by adding fumed hydrophobic (16 nm) or hydrophilic (12 nm) silica, or by Sol-Gel approach using alkoxysilane precursors (TMOS and TEOS). The effect of SiO2-fillers on the properties of gas permeation has been studied by the time-lag method mainly on the series prepared with fumed silica. It was observed that nano-particles of silica do not seem to disturb the PAA cyclization process and that the mechanical properties are improved; the gas permeability varies essentially depending on the amount of fillers incorporated but no spectacular increase in permeability could be shown due to the nano-particles amounts. Apparently, it can be deduced that it is the rubbery phase which accommodates the SiO2 particles. These results showed the value of PEI and PEI/SiO2 membranes in industrial applications of gas separation, especially for the separation of CO2/N2 mixtures

Les Membranes à Matrices Mixtes (MMM’s) sont des matériaux prometteurs pour la capture de CO2 en comparaison aux technologies actuelles telles que l’absorption par solvants aminés (monoéthanolamine). Les ‘Metal-Organic Frameworks’ (MOFs) sont des matériaux poreux cristallins envisagés pour être intégrés sous forme de nanoparticules aux polymères des MMM’s. Ils résultent de la combinaison de nœuds métalliques et de ligands organiques pour former des structures tridimensionnelle (3D) organisées. Ils possèdent divers avantages : des aires spécifiques et des volumes poreux élevés, des tailles de pores contrôlables, et pour certains une stabilité à l’eau. Les MOFs ont une chimie adaptable aux applications souhaitées contrairement aux adsorbants classiques tels que les charbons actifs, les zéolithes.D’une part, ce travail a eu pour objectif l’évaluation des performances de séparation du CO2 par des MOFs microporeux en vue des séparations CO2/N2 et CO2/CH4. Les interactions ‘gaz-adsorbant’ sont favorisées au sein des MOFs par : (1) une réduction de la taille de pores et du volume poreux pouvant engendrer des effets de confinements, de tamis moléculaire ou (2) par la présence de groupements de surface. En conséquence, ces paramètres peuvent contribuer à l’amélioration de la sélectivité du CO2 et ont été étudiés pour divers systèmes de MOFs microporeux. D’autre part, les paramètres texturaux (aire spécifique, volume poreux) et thermodynamiques (enthalpies d’adsorption) ont été corrélés aux quantités maximales de CO2 adsorbées au travers d’une approche quantitative de relation de structure-propriété pour établir des tendances linéaires
Mixte Matrix Membranes (MMM’s) are promising materials for CO2 capture compared to current technologies as absorption using amines solvents (monoéthanolamine). Metal-Organic Frameworks (MOFs) are crystalline porous materials which can be integrate under nanoparticles shape to polymer phase of MMM’s. They are built from metal nods and organic ligand to yield well-defined tridimensional structure (3D). They possess various advantages: high specific surface area and pore volume, tunable pore size and some of them are stable in presence of water. MOFs have a sustainable chemistry to targeted applications unlike traditional adsorbents as activated carbons, zeolites.On the one hand, this work aimed the assessment of CO2 separation performances of microporous MOFs for CO2/N2 and CO2/CH4 gas separations. The ‘gas-adsorbent’ interactions are favored in MOFs by: (1) a decrease of pore size, pore volume which can involve confinement effects, molecular sieve effects or (2) the presence of surface groups. Therefore, these factors can contribute to the CO2 selectivity improvement and have been studied for various microporous MOFs. On the other hand, textural (specific surface area, pore volume) and thermodynamic (adsorption enthalpy) parameters have been correlated to CO2 maximum excess uptakes through a quantitative structure-property approach to establish some linear trends

"Resumo/Abstract", "palavras-chave/keywords" nos cap?tulos trabalho.
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Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES)
Funda??o de Amparo ? Pesquisa do Estado de Minas Gerais (FAPEMIG)
O comp?sito nFZV-CAG foi empregado para a ozoniza??o catal?tica heterog?nea da NMS em meio aquoso. O oz?nio foi gerado por uma central geradora de oz?nio IPABRAS, alimentada com ar. Foram avaliados diferentes processos catal?ticos como O3, CAG, O3-CAG, O3-nFZV- CAG, e a varia??o da concentra??o das nFZV para remo??o da NMS. Os resultados mostraram que a combina??o do O3-nFZV-CAG foi muito eficiente levando ? mineraliza??o de aproximadamente 70% da NMS em 120 min de rea??o. Tal efici?ncia pode estar atribu?da ao processo de eletr?lise, em que o Fe0 origina Fe2+ levando ? produ??o do radical hidroxila que ? altamente oxidante, levando a destrui??o do contaminante. As rea??es seguiram a cin?tica pseudo-primeira ordem para remo??o do f?rmaco. Ap?s realizada a coleta as amostras foram submetidas a an?lise qu?mica, empregando-se as t?cnicas de espectrofotometria de UV-Vis, cromatografia l?quida de alta efici?ncia (CLAE) e a determina??o da demanda qu?mica de oxig?nio (DQO) tamb?m foi realizada.
As nanopart?culas de FZV imobilizadas sobre a superf?cie do carv?o ativado (nFZV-CAG) foram sintetizadas e caracterizadas para remo??o do f?rmaco Nimesulida (NMS) em sistemas aquosos. Os estudos foram realizados em bateladas com agita??o de 250 rpm durante 120 minutos, onde foram avaliadas a efici?ncia, concentra??o (20, 25 e 30% do comp?sito) e diferentes dosagens (0,1 a 10g) de nFZV-CAG. Os resultados mostraram que a dosagem de 10 g de 20%nFZV-CAG removeu cerca de 80% da NMS 50 mg L-1 em apenas 30 minutos de rea??o, e atingindo 100% em 120 minutos. Foi observada ainda uma remo??o de 80% da DQO ao final da rea??o. As velocidades de rea??o aumentaram na medida em que foram aumentadas as dosagens do comp?sito, o que seria esperado. Por?m, com o aumento da concentra??o (%) de nFZV n?o houve aumento na velocidade das rea??es. As rea??es seguiram uma cin?tica de pseudo-primeira ordem em rela??o ? remo??o da NMS. Ap?s realizada a coleta, as amostras foram submetidas a an?lise qu?mica, empregando-se as t?cnicas de espectrofotometria de UV- VIS, cromatografia l?quida de alta efici?ncia (CLAE) e a determina??o da demanda qu?mica de oxig?nio (DQO) tamb?m foi realizada. Para caracteriza??o do comp?sito foram empregadas as t?cnicas Microscopia Eletr?nica de Varredura acoplada ? Espectrometria de Energia Dispersiva de Raios-X (MEV-EDS), que mostraram claramente a presen?a da nanopart?culas sobre a superf?cie do carv?o, e analise de superf?cie do nFZV-CAG e do CAG tamb?m foram realizadas.
Disserta??o (Mestrado) ? Programa de P?s-Gradua??o em Qu?mica, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2016.
The FZV nanoparticles immobilized onto the surface of the activated charcoal (nFZV-CAG) were synthesized and characterized for the removal of the pharmaceutical Nimesulide (NMS) in aqueous systems. The studies were performed in batch mode with stirring speeds of 250 rpm during 120 minutes, so that it was possible to evaluate efficiency, concentration (20, 25 and 30% of the composite) and different dosages (0,1 to 10g) of nFZV-CAG. The results showed that the dosage of 10g of 20%nFZV-CAG removed approximately 80% of NMS 50 mg L-1 in just 30 minutes of reaction, and reaching 100% in 120 minutes. It was still observed a removal of 80% of the COD (Chemical Oxygen Demand) at the end of the reaction. The reaction rates increased with the dosage of the composite, which was expected. Though, increasing the concentration (%) of nFZV did not result in higher reaction rates. The reactions followed a pseudo-first order kinetics for the removal of NMS. After the samples were collected, they were submitted to chemical analysis, employing the techniques of UV-VIS spectroscopy, high performance liquid chromatography (HPLC) and chemical oxygen demand (COD). In order to characterize the composite, the following techniques were used: Scanning Electron Microscopy (SEM) coupled with Energy Dispersive x-Ray spectroscopy (EDS), which showed clearly the presence of nanoparticles onto the charcoal surface. Analysis of the surface of nFZV-CAG were also performed.
The composite nFZV-CAG was used for the catalytic ozonation of NMS in aqueous media. The ozone was generated by an ozone generator IPABRAS, fuelled with air. Different catalytic processes were evaluated such as O3, CAG, O3-CAG, O3-nFZV-CAG, and the variation of the nFZV concentration for the removal of NMS. The results showed that the combination of O3- nFZV-CAG was very efficient, leading to the mineralization of approximately 70% of NMS in 120 minutes of reaction. Such efficiency can be attributed to the electrolysis process, in which the Fe0 generates Fe2+ which generates hydroxyl radicals that are highly oxidant, leading to the destruction of the contaminant. The reactions followed the pseudo-first order kinetics for the removal of the pharmaceutical. After the samples were collected, they were submitted to chemical analysis such as, UV-VIS spectroscopy, high performance liquid chromatography (HPLC) and chemical oxygen demand (COD).

Le réchauffement climatique est dû principalement à l'émission anthropique du dioxyde de carbone (CO2) dans l'atmosphère. Une réduction électrocatalytique et sélective de cette molécule a été proposée au cours de ce projet comme une solution prometteuse pour synthétiser des produits à valeur ajoutée. Une telle réaction requiert l'utilisation de matériaux efficaces et bas coût. Pour ce faire, les travaux de cette thèse ont porté sur la préparation de catalyseurs à base de cuivre dispersés sur différents substrats carbonés tels que le Vulcan XC-72R, les carbones mésoporeux CMK-3 et FDU-15, et des tanins à base d'IS2M pour réduire le CO2 en milieu aqueux. Les matériaux d'électrode ont été préparés à l'aide de la méthode polyol assistée par micro-ondes. Leurs caractérisations physiques et l'analyse élémentaire confirment des compositions atomiques et des taux de charge métallique proches de celles théoriquement envisagées. L'acide formique et le monoxyde de carbone sont les deux produits carbonés issus de la réduction du CO2 (2 bar) réalisée par chronoampérométrie en milieu NaHCO3. La détection et l'identification des produits de réaction ont été effectuées par des méthodes chromatographiques (µ-GC et HPLC), spectrométrique (DEMS) et spectroscopique (RMN). Une sélectivité de la réaction vis-à-vis de HCOOH (62 %) a été obtenue sur une cathode de Cu50Pd50/C. Cette conversion sélective du CO2 en HCOOH s'explique par une conjugaison d'effets électroniques et géométriques dans la structure de surface du catalyseur bimétallique et aussi celui de la texture du substrat carboné
The anthropogenic emissions of carbon dioxide (CO2) are the major cause of global warming. The selective CO2 reduction reaction (CO2RR) of has been proposed as a promising, convenient and efficient method for sustainable energy conversion systems. The reduction of CO2 to energetically valuable products requires the use of an appropriate electrode material. This study focuses on the preparation of Cu-based electrocatalysts supported on different types of carbon materials such as Vulcan XC-72R, mesoporous carbon CMK-3, mesoporous carbon FDU-15 and tannin based mesoporous carbon IS2M for the CO2RR under mild conditions. Besides, Vulcan XC-72R carbon supported bimetallic copper/palladium alloy materials were prepared for increasing the Faradaic yield. These copper-based catalysts were electrochemically characterized and preparative electrolyses set at constant potential were carried out in order to investigate the reduction products distribution and Faradaic yields as a function of the applied potential and catalyst loading. Chemicals such as HCOOH, CO and H2 issued from the CO2RR, were determined with in-situ and ex-situ complementary (electro)analytical and spectroscopic techniques. The significant difference in the product distribution is probably due to the ensemble (geometry and ligand) effects in the bimetallic CuPd materials, and textural structure of the supporting substrates. Selective CO2 to-HCOOH conversion has been successfully undertaken on Cu50Pd50/C with 62 % Faradaic efficiency

Depuis près d'un siècle, les chercheurs déploient des efforts importants pour apporter de nouvelles propriétés aux matériaux et aujourd'hui la modification de surface des matériaux est plus que jamais un sujet de recherche très attractif lié à une variété d'applications industrielles prometteuses. Le développement d'une méthodologie simple pour caractériser les interactions biomoléculaires a été, au fil des ans, une technologie indispensable pour soutenir les recherches dans les domaines de la biologie et de la microbiologie en raison de son haut degré de sensibilité. La fonctionnalisation de surface par revêtement chimique est une solution prometteuse pour obtenir de nombreuses propriétés bien définies. Cette étude présente la faisabilité de la fonctionnalisation de la surface de l'or en utilisant une chimie basée sur les sels d'aryldiazonium pour le développement de biocapteurs appliqués à la technologie de résonance plasmonique de surface (SPR). Une technique de haute qualité utilisée pour mesurer les interactions biomoléculaires en temps réel dans un environnement label-free. Depuis de nombreuses années, les activités industrielles sont responsables de la pollution de l'atmosphère. Bien que différents gaz à effet de serre soient impliqués dans la pollution atmosphérique, le CO2 reste l'un des plus importants en raison de ses concentrations élevées dans l'atmosphère et de sa capacité à provoquer des maladies graves. Plusieurs études dans la littérature ont démontré que certains adsorbants tels que les charbons actifs, les tamis basiques de silice fonctionnalisés, les zéolithes, etc. bien que disponibles dans le commerce sont encore sophistiqués et coûteux limitant leur application. Cependant, il est toujours nécessaire de capter le CO2 pour des activités à coûts d'exploitation limités. L'objectif de cette étude est de valoriser l’écorce du cacao, une ressource d'agro-déchets prête à l'emploi et facile à modifier, en tant que matériaux peu coûteux pour l'adsorption du CO2 et l'élimination des toxines des déchets industriels en solution appliquant un traitement chimique à partir des sels de diazonium et des composés de silane pour modifier ses propriétés physico-chimiques
For almost a century, the researchers have been making important efforts in order to bring new properties to materials and nowadays surface modification of materials is more than ever a very attractive research subject related to a variety of promising industrial applications. The development of simple methodology to characterize biomolecular interactions has been, over the years, an indispensable technology to support researches in the areas of biology and microbiology due its high degree of sensitivity. Surface functionalization by chemical coating is a promising solution to obtain numerous well-defined properties. This study presents the feasibility of gold surface functionalization using a chemistry based on aryldiazonium salts to the biosensors development applied to Surface Plasmon Resonance (SPR) technology. A high-quality technique used to measure biomolecular interactions in real time in a label free environment. Since many years, industrial activities are responsible to the pollution of the atmosphere. Although different greenhouse gases being involved in atmospheric pollution, CO2 is still one of the most important due its high concentrations in the atmosphere and due to its ability to induce serious health disease. Several studies in the literature have demonstrated that some adsorbents such as activated carbons, basic functionalized silica sieves, zeolites, etc.. although commercially available are still sophisticated and expensive limiting their application. However, there is still a need to capture CO2 for activities with limited operating cost. The objective of this study is to promote the cocoa shell, an agro-waste resource ready to use and easy to modify, as low-cost materials for CO2 adsorption and toxins removal from industrial waste in solution applying a chemical treatment from diazonium salts and silane compounds to modify its physic-chemical properties

Solar energy is by far the most abundant renewable resource available to mankind. However, it is diffused and intermittent, and often geographically separated from that of the production results in underwhelming utilization of this resource. Inspired by photosynthesis, various efforts were made to store solar energy in form of chemical bonds than can be used when the sun is not shining. A promising approach is to produce hydrogen, a carbon-neutral energy carrier is via water splitting which requires electrocatalysts to accelerate the two half-cell reactions, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The state-of-art catalysts used for HER is Pt and for OER is IrO2/RuO2 that are prohibitively expensive. We have developed new synthesis methodologies for various earth-abundant electrocatalysts supported heteroatom-doped carbon nanostructures and exploited for water splitting. An in-situ solid state route was developed to integrate ruthenium nanoparticles with N-doped graphene sheets which exhibited an HER activity rivalling state-of-art Pt/C over a wide pH range. In order to find further cost-effective materials, we sought inspiration from NiFe-hydrogenase (the most efficient catalyst for HER) to develop a general solid state method for bimetallic MFe@ N-doped carbon core-shell nanostructures (M = Ni, Cu, Co, Zn, Mn) as efficient total water splitting catalyst. Thereafter, a new, phosphine-free, solid state method to hybridize Co2P with N, P co-doped CNTs was developed which could also be extended to synthesize Fe2P, Ni2P and Cu3P. Moreover, glucose oxidation was attempted as a possible replacement for the kinetically sluggish OER half-cell reaction, wherein Co2P/N, P-CNTs were demonstrated to be an efficient non-enzymatic glucose sensor for the first time. Thereafter, Co-imidazolate frameworks (ZIF-67) were transformed into hierarchal Co-N-Se nanosheets via a simple selenization method. Investigations were carried out to establish a structure-property correlation between the nanostructures evolved over various interval of time along with their OER activity. Finally, an in-situ strategy was developed to hybridize N-doped graphitic carbon seets with Ni and MoxC (Mo2C and MoC) nanoparticles which exhibited resilient HER activity besides effectively accelerating OER, thereby resulting in overall water splitting that can be attributed to favorable electronic modulation between various strongly coupled components.

碩士
國立成功大學
化學工程學系碩博士班
97
The carbonation/calcination loop of CaO/CaCO3 is an efficient process for CO2 capture. This study investigated the CO2 capture capability of CaO powders derived from oyster shells and reagent-grade CaCO3. The CaO powder from oyster shells calcination consisted of nanoparticles of 53 nm and showed a CO2 absorption conversion as high as 84% at 650°C for 5 hours in 20% CO2/N2.The oyster shell-derived CaO powder had an oxide impurity content as high as 9 wt%, and a larger CaO crystal grain size and smaller specific surface area than the CaO derived from the reagent CaCO3. In cyclic CO2 capture tests, the cyclability and CO2 capacity of the oyster shell-derived CaO was significantly improved by inserting an intermediate cooling step between carbonation and calcination. At a carbonation temperature of 750°C, the overall performance of the oyster shell-derived CaO in cyclic carbonation was superior to that of the CaO from the reagent CaCO3. On the basis of X-ray diffraction analysis, it was suggested that the impurities contained in the oyster shell-derived CaO may have constituted transition zone on the CaO crystal grain boundary to suppress crystal growth in calcination as well as to ease up lattice expansion in CO2 fixation. The intermediate cooling enlarged the transition zone to mitigate lattice dislocations resulting from CO2 fixation and thus the decay in CO2 capacity. In addition, this study also investigated the CO2 capture capability of CaO powders derived from oyster shells and reagent-grade CaCO3 under deionized water hydration. The CO2 capacity and carbonation rate was significantly improved by the hydration of CaO powder. The correlation between the crystalline structure of the sorbents and the absorption performance will be explored.

碩士
國立臺灣大學
化學研究所
105
In the recent decades, electrochemical CO2 reduction has been of great interest for renewable energy source and for strategies to mitigate global warming. Prof. Hori had reported that copper is the only one of metal electrodes which has ability of reducing CO2 to hydrocarbons and oxygenates, such as methane, ethylene and ethanol. However, lots of research done on copper metal do not be consistent with others. We attribute our observation to the different morphologies of every metal copper catalyst. Moreover, Prof. Hori had also demonstrated that product distribution would be in different tendency with the change of crystal facets. In this study, we have combined properties of nanoparticles, such as high surface area and well-controlled shape, and facet effect toward product selectivity on electrochemical CO2 reduction. Here we synthesize three different morphologies of Cu nanoparticles, which in the order of cube, hexarhombic dodecahedron and octahedron in the figure, from left to right. With the characterization of TEM, SEM, SAED and XRD, copper nanocube and nanoctahedron have predominant facet with respect to (100) and (111). Hexarhomic dodecahedron has both specific crystal facets. Qualitatively and quantitatively analysis of gas and liquid products are achieved by gas chromatography, gas chromatography-mass spectrometry and nuclear magnetic resonance. Our results indicate that ethylene is the major product of Cu nanocube which has highest C2H4/CH4 ratio and is consistent with previous Cu (100) single crystal work. Ethylene is the major product of Cu nanoctahedron, which coincides with Cu (111) single crystal work. Cu hexarhombic dodecahedron which ethylene, methane and ethanol are major products reaches maximum current efficiency around 15 to 25% in the voltage of -1.2 V to -1.3 V (vs. RHE). On the other hand, Cu nanocube and nanoctahedron only reach the highest current efficiency of ethanol around 5 to 10%. Apparently, this product selectivity toward ethanol do not be the contribution of (100) or (111), either. We attribute this product selectivity to the structure difference of hexarhombic dodecahedron which has more numbers of edges than cube and octahedron and the atom arrangement on edge line is (110). Furthermore, we have applied in-situ x-ray absorption spectroscopy to monitoring copper nanoparticle catalyst how to participate in the carbon dioxide reduction reaction. Our results indicate that coordination numbers of Cu–C and Cu–O bond vary with potentials and the tendency is in line with the mechanism proposed in this study.

碩士
國立交通大學
材料科學與工程學系奈米科技碩博士班
107
In this study, we prepared magnesium oxide (MgO) in the MOF (metal-organic framework) material ZIF-8 for carbon dioxide adsorption and transesterification purpose. Due to the microporosity of ZIF-8, nanoconfinement effect has been adopted to control well-dispersed MgO at ZIF-8 (denoted as MgO@ZIF-8) with different metal oxide loadings. MgO was prepared via wet precipitation of Mg(OH)2, which was further calcinated into MgO. From powder X-ray diffraction (PXRD), MgO crystals in ZIF-8 have small and regulated size, regardless of magnesium loadings. After material properties analysis, we apply our MgO@ZIF-8 for CO¬2 adsorption. 50% MgO@ZIF-8 showed an improved CO2 adsorption capacity (1.23mmol) than those of neat MgO and ZIF-8. On the other hand, CO¬2 desorption was tested with CO2-TPD. It was discovered that the lowest CO2 desorption temperature of 40% MgO@ZIF-8, 345°C, which is lowered by 55 degrees compared to the commercial magnesium carbonate. Finally, we tested the activity of MgO@ZIF-8 for transesterification catalytic reactions. It showed higher catalytic activities than their physically-mixed counterparts, indicative of a synergistic effect between MgO and ZIF-8, explained by a proposed mechanism based on acid-base bifunctional sites on the surface.

碩士
國立中央大學
材料科學與工程研究所
107
In order to reduce global warming and develop the renewable energy, electrochemical CO2 reduction and water splitting for hydrogen production have been developed to solve these issues. However, there are still a lot of problems to overcome, such as low selectivity for CO2 reduction reaction (CO2RR) and lack of Pt-free highly efficient catalyst for hydrogen evolution reaction (HER) activity. In this study, carbon-supported PdxCu100-x with different compositions including Pd, Pd70Cu30, Pd50Cu50, and Pd25Cu75 with or without heat treatments have been prepared for CO2RR and HER. The phases and structures, surface compositions, chemical compositions, morphologies, electrochemical properties and the gas product of prepared catalyst are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma-optical emission spectrometer (ICP-OES), high resolution transmission electron microscope (HRTEM), rotating disk electrode (RDE) and gas chromatography (GC), respectively. This study is divided into two parts. In the first part, carbon-supported PdxCu100-x nanoparticles (NPs) have been prepared. The alloying of Cu into Pd demonstrates great promotion in the selectivity of CO towards CO2 reduction. Due to the synergistic effect of Pd and Cu, the d-band center of Pd is lowered and the chemisorption energy of intermediate is weakened, thereby enhancing the CO2RR performance with a CO Faradaic efficiency of 79% at -1 V. However, for HER, in comparison with other PdxCu100-x NPs, Pd shows the lowest overpotential and tafel slope, indicating that alloying Cu into Pd did not have positive effect on the HER performance. For the second part, carbon-supported PdxCu100-x NPs have been heat treated under air atmosphere. After the air heat treatment, except Pd the HER results of PdxCu100-x NPs have been significant improved. Based on XPS characterization, surface Cu segregation is observed on the catalyst after the air heat treatment, which may promote the HER performance, especially Pd70Cu30-HT, which shows better overpotentials (-52 mV) than Pd (-61 mV) and close to Pt commercial (-38 mV).

碩士
國立中興大學
化學工程學系所
100
Cellulose acetate (CA)-based mixed matrix membranes (MMMs) with the incorporation of inorganic fillers (spherical Titanium dioxide, TiO2 nanoparticles) were prepared in this study. The resulting MMMs were characterized by TGA, DSC, SEM, and TEM. It was found that inorganic filler agglomeration became more serious at higher-filler-content ( ≥ 3wt.%) MMMs. CO2 and CH4 permeabilities were measured for these prepared CA/TiO2 MMMs. The CO2/CH4 selectivity increased from 15.87 (pure CA membrane) to a maximum value of 34.30 at 1 wt.% TiO2 MMM, and then decreased for the TiO2 weight percentages > 1. The membrane morphology may be divided into two cases : ideal morphology ( ≤ 2 wt.%) and interface voids ( > 2 wt.%). The formation of interface voids and membrane defects in MMMs contributed to higher gas permeabilities but lower gas selectivity.

碩士
國立清華大學
材料科學工程學系
105
In response to challenges of energy crisis, global warming and climate change, electrochemical carbon dioxide reduction to produce chemicals or low-carbon fuels can serve as a means for carbon neutral and therefore has attracted much attention recently. The notorious greenhouse gas carbon dioxide can then become feedstock to synthesize numerous low-carbon fuels such as formate/formic acid, methanol, ethanol and others to provide renewable energy storage with high energy density forms. However, most of electrochemical reduction processes utilize precious metals (platinum or palladium) as electrode, or apply harsh temperature/pressure conditions which may limit the development of electrochemical reduction of carbon dioxide toward industrial applications. In this thesis work, we use copper nanoparticle decorated reduced graphene oxide (rGO), which is derived from one of the most abundant elements (i.e. carbon), as the electrochemical reduction electrode. The process can achieve carbon dioxide reduction with lower working potential. Electrode materials of platinum, palladium, rGO and copper decorated rGO as working potential were compared. The influences of reduction potential, electrode material and electrolyte acidity on production yield were discussed and characterized by scanning electron microscopy and gas chromatography. In addition, this process was conducted under ambient temperature/pressure without harsh condition or complicated equipments. The rGO/Cu electrode can achieve a cost reduction of 95% in average compared to precious metal electrodes (Pt and Pd). The work shall pave a new path toward developing carbon dioxide reduction electrodes and further promote development of electrochemical reduction process toward carbon dioxide derived low-carbon fuels.

碩士
國立清華大學
化學工程學系
104
The rapid decline of conventional energy sources coupled with a rapid increase in greenhouse gas production and thereby increasing ozone layer depletion and incessant rise in sea levels has ushered in a mad rush for renewable and CO2-neutral energy sources. There has thus been a growing interest for utilizing biomass as an energy source. Biomass derived from agricultural residues and energy crops such as corn are food-competing, and their use is therefore controversial and much debated about. As a result the focus of the industry has now shifted to utilize energy derived from non-food competing biomass feedstocks, such as forest residues and urban wastes. The biomass can be converted to bio-oils through a pyrolysis treatment in absence of oxygen. Biofuels derived from these sources are called second generation biofuels. Pyrolysis bio-oils have, in comparison to petroleum-based fuels, poor chemical properties, due to high water and oxygen content. Further upgrading to remove water and oxygen is needed to improve the bio-oil properties. A hydrotreating reaction to remove oxygen from bio-oils, hydrodeoxygenation (HDO), is carried out in this thesis. Previous research has shown that iron nanoparticles supported on mesoporous silica nanoparticles (MSN) denoted as (Fe-MSN) catalyzes the hydrotreatment of fatty acids with high selectivity for HDO over decarbonylation and hydrocracking. The catalysis is likely to involve a reverse Mars–Van Krevelen mechanism, in which the surface of iron is partially oxidized by the carboxylic groups of the substrate during the reaction. The strength of the metal–oxygen bonds that are formed affects the residence time of the reactants facilitating the successive conversion of carboxyl first into carbonyl and then into alcohol intermediates, thus dictating the selectivity of the process. The selectivity is also affected by the pretreatment of Fe-MSN, the more reduced the catalyst the higher the yield of HDO product. For this study the reaction system for the hydrotreatment of oleic acid using supported iron nanoparticles was adopted. Commercial SBA-15 was used as the support for impregnating iron nanoparticles for this study. SBA-15 has a hexagonal symmetry with pore diameters in the range of 5-8 nm and can be a perfect support for immobilization of metal nanoparticles. Also SBA-15 is thermally stable and can retain its structure at high temperatures used for the HDO reactions. Although HDO reactions are now being studied in detail all over the world, till now there has been no report of the effect of using CO2 alongside H2 while carrying out HDO reactions. The hydrotreatment of oleic acid in a green reaction media to produce the major HDO product octadecane was demonstrated in this thesis. The data show that hexane containing pressurized CO2 could dictate the selectivity of the hydrotreatment of oleic acid with high selectivity for HDO over decarboxylation/decarbonylation. Since the decarboxylation/decarbonylation pathway involves the removal of CO2 and CO, respectively, according to Le Chatelier’s principle, it was hypothesized that hexane containing CO2 could increase the yield of HDO product by preventing the forward reaction for decarboxylation/decarbonylation. It was also speculated that hexane containing pressurized CO2 could offer further beneficial effects on the yield of HDO products. One is that the presence of pressurized CO2 in hexane could reduce the viscosity of the reactant solution. As a result more uniform dispersion of the catalyst occurred in the solution and the diffusion resistances were reduced as well due to the increase in mass transfer. It is also believed that the solubility of H2, the reacting gas was also enhanced in hexane containing CO2 allowing for more H2 to bind to the surface of the iron nanoparticles. The effects of three individual operation variables namely, temperature, CO2 pressure and time and their interactions on the hydrotreatment of oleic acid were studied using a central composite design. The results showed that all these three variables were significant factors for increasing the yield of octadecane while CO2 pressure was the most significant variable in decreasing the yield of heptadecane, the major decarboxylation/decarbonylation product.

碩士
靜宜大學
應用化學系
106
This study presents Pd-Au/TiO2-WO3 nanoparticle prepared by a hydrothermal and sol-gel method as a CO2 conversion photocatalysts. The catalysts were characterized by X-ray diffraction (XRD), Scan electron microscope (SEM), Tunneling electron microscope (TEM), XPS, BET, UV-visible and Photoluminescence (PL) instruments. The appropriate amounts of Pd and Au on TiO2-WO3 composites exhibited enhanced photocatalytic activity for CO2 reduction compared with commercial TiO2 (P25). It showed the photocatalytic CH4 production rate (39.1 μmol g-1 h-1) was 100 fold that of TiO2 (P25); moreover, a large amount of CO was produced (at a rate of 271.3 μmol g-1 h-1) was 300 fold that of TiO2 (P25). The significantly improved photocatalytic activity was not only due to the increased specific surface area (72.9 m2g-1) but also UV-vis showed a remarkable enhancement of light absorption. It owes to the incorporation Pd-Au with TiO2 the visiblelight active the UV light-responsive for increased solar energy utilization. Furthermore, PL spectra revealed that the Pd-Au content can influence the charge transfer efficiency of the Pd-Au/TiO2-WO3 composites. The quantum yield of CH4 production was calculated as 1.05 %. A CO2 reduction reaction mechanism was proposed on Pd-Au/TiO2-WO3. This study can bring new insights into designing TiO2 nanostructures for applications such as solar energy conversion and storage.

In the agri-food industry, carbon dioxide sensors can be used for process control, monitoring quality, and assessing safety. A carbon dioxide sensor was developed using poly aniline boronic acid (PABA) conducting polymer as the electrically conductive region of the sensor for use in the agri-food industry and was demonstrated for use in detecting incipient or ongoing spoilage in stored grain. The developed sensor dynamically detected up to 2455 ppm CO2 concentration levels. The performance of the sensor in measurements of low concentrations of dissolved CO2 was characterized using standard solutions of NAHCO3. The dynamic range for the detection of H2CO3 was 4.91X10-4 to 9.81X10-3 mol L-1. The dc resistance values decreased with increasing CO2 concentration indicating an increase of conductivity due to increase in the amount of protonation. The developed CO2 sensor was evaluated for the influence of temperature (by storing it at – 20°C and 0°C as well as at operating temperatures of +10°C to 55°C) and relative humidity (from 20 to 70%). Temperature dependence of sensor's resistance values were observed possibly due to the change in conduction mechanism at different temperatures. The variation in the resistance with humidity was curvi-linear and repeatable, indicating that humidity has a less pronounced effect on the sensor’s performance. The sensor’s response to changes in CO2 concentrations at various humidity and temperature levels was stable indicating that the sensor can detect CO2 levels under fluctuating environmental conditions. The response of the PABA film to CO2 concentration was not affected by the presence of alcohols and ketones, proving that the developed CO2 sensor is not cross-sensitive to these compounds which may be present in spoiling grain. The sensor packaging components were selected and built in such a way to avoid contamination of the sensing material and the substrate by undesirable components including grain dust and chaff. The developed conducting polymer CO2 sensor exhibited dynamic performance in its response, recovery times, sensitivity, selectivity, stability and response slope when exposed to various CO2 levels inside simulated grain bulk conditions.

The thesis has been presented in two parts. The 1st part of the thesis focuses on the fundamental understanding of room temperature CO2 adsorption on iron-oxide based NP surfaces. The 2nd part describes the understanding of an interesting catalytic reaction dynamics, namely of metalized energetic molecules. The content of the thesis is presented in the following way. In Chapter 2, fabrication, structural elucidation and CO2 surface chemistry of supported iron-oxide (α-Fe2O3) NPs are discussed. In Chapter 3, the same on the supported Fe-Pd-oxide(shell)@Pd(core) NP surfaces is presented where the bimetallization by introducing Pd+2 doping in iron-oxide (α-Fe2O3) NPs, leads to CO2 adsorption at the room temperature. A periodic density functional theory (DFT) results for the CO2 adsorption on the model pristine α-Fe2O3(0001) and on the model Pd+2 doped α-Fe2O3(0001) surfaces are discussed in Chapter 4. In Chapter 5, femtosecond pulse induced chemistry of CO2 on Pd(core)@Fe-Pd-oxide(shell) NP surfaces is discussed. In Chapter 6 I have presented conical intersection-mediated nonadiabatic chemical dynamics of a simple analogue nitramine (containing one N-NO2 energetic group) molecule, dimethylnitramine (DMNA) and its complex with an iron atom (DMNA-Fe). Finally, in Chapter 7, general conclusions and future directions are presented

abstract: The applications utilizing nanoparticles have grown in both industrial and academic areas because of the very large surface area to volume ratios of these particles. One of the best ways to process and control these nanoparticles is fluidization. In this work, a new microjet and vibration assisted (MVA) fluidized bed system was developed in order to fluidize nanoparticles. The system was tested and the parameters optimized using two commercially available TiO2 nanoparticles: P25 and P90. The fluidization quality was assessed by determining the non-dimensional bed height as well as the non-dimensional pressure drop. The non-dimensional bed height for the nanosized TiO2 in the MVA system optimized at about 5 and 7 for P25 and P90 TiO2, respectively, at a resonance frequency of 50 Hz. The non-dimensional pressure drop was also determined and showed that the MVA system exhibited a lower minimum fluidization velocity for both of the TiO2 types as compared to fluidization that employed only vibration assistance. Additional experiments were performed with the MVA to characterize the synergistic effects of vibrational intensity and gas velocity on the TiO2 P25 and P90 fluidized bed heights. Mathematical relationships were developed to correlate vibrational intensity, gas velocity, and fluidized bed height in the MVA. The non-dimensional bed height in the MVA system is comparable to previously published P25 TiO2 fluidization work that employed an alcohol in order to minimize the electrostatic attractions within the bed. However, the MVA system achieved similar results without the addition of a chemical, thereby expanding the potential chemical reaction engineering and environmental remediation opportunities for fluidized nanoparticle systems. In order to aid future scaling up of the MVA process, the agglomerate size distribution in the MVA system was predicted by utilizing a force balance model coupled with a two-fluid model (TFM) simulation. The particle agglomerate size that was predicted using the computer simulation was validated with experimental data and found to be in good agreement. Lastly, in order to demonstrate the utility of the MVA system in an air revitalization application, the capture of CO2 was examined. CO2 breakthrough time and adsorption capacities were tested in the MVA system and compared to a vibrating fluidized bed (VFB) system. Experimental results showed that the improved fluidity in the MVA system enhanced CO2 adsorption capacity.
Dissertation/Thesis
Doctoral Dissertation Mechanical Engineering 2019

博士
國立清華大學
化學工程學系
99
The main purpose of this study was to develop the techniques of the preparation of nanocrystals. In this dissertation, three techniques including (I) the deaggregation of silver powders assisted by supercritical CO2, (II) the synthesis of silver nanoparticles in CO2-expanded liquids, and (III) the synthesis of metal sulfide nanocrystals using wet-chemical method had been studied. System I. The deaggregation of silver powders assisted by supercritical CO2 The mixture of silver particles/organic solvent/dispersing agent in the reactor was pressurized with CO2 ranging from 800 to 2000 psi for a period of time, followed by the depressurization through a nozzle rapidly. The organic solvents of toluene, hexane and ethyl acetate and the dispersing agents of isostearic acid and dodecanethiol were used. The process temperature was ranged from 25 to 50°C. After the process of depressurization, the silver particles solution was investigated by dynamic laser scattering (DLS). It was found that the operation with the pressurized CO2, especially in the supercritical condition, could help the deaggregation of silver powders and the size of deaggregated silver particles was less than 1000 nm. However, part of the deaggregated silver particles tended to assemble into thin films on the surface of solution and the wall of receiver. The anti-solvent effect induced by adding CO2 or insufficient amount of dispersing agent to cap the surface of silver particles might be the reasons. In addition, during depressurization through nozzle, the volume of gas expanded greatly leading to the nebulization of organic solvent. Thus, the huge receiver to collect the nebulizing solvent droplets was required. System II. The synthesis of silver nanoparticles in CO2-expanded liquids A soluble form of silver carboxylate, silver isostearate (AgISt), was synthesized and characterized. The results of ATR-FTIR, 1H-NMR, XRD, DSC and TGA indicated that the methylated branched alky chains in AgISt exhibited a steric hindrance to impede the growth of layered structure of AgISt molecules, which led to the high solubility of AgISt in non-polar solvents. A novel technique to synthesize silver nanoparticles (AgNPs) using CO2-expanded liquids as the processing medium was proposed. AgISt and hydrogen (H2) were utilized as silver precursor and reducing agent, respectively. The operative pressure of H2 and CO2 were ranged from 14 to 800 psi and from 200 to 800 psi, respectively. At 40°C, the averaged size of synthesized AgNPs was ranged from 2 to 7 nm. While the applied pressures of H2 and CO2 were increased, the size distribution of AgNPs was narrower and the formation rate of AgNPs was increased. The investigations of HRTEM, SAED, ATR-FTIR showed that AgNPs were grown in face-centered cubic phase and capped with isostearic acid, which was derived from the reduction of AgISt with H2. Further increase the reaction temperature to 60 or 80°C, the formation rate of AgNPs was reduced and the size distribution of AgNPs became broader. The reason might be that the resistance of mass transfer of H2 in CO2-expanded liquids limited the reduction reaction of AgISt and H2 as temperature was increased. System III. The synthesis of metal sulfide nanocrystals using wet-chemical method Metal isostearates including zinc isostearate (ZnISt2), cadmium isostearate (CdISt2), and copper isostearate (CuISt2) were synthesized by the cation exchange reaction of sodium isostearate with the corresponding metal ions. The results of XRD and DSC indicated that no layered structure was form in metal isostearate, which led to their high solubility in non-polar solvents. Metal isostearates were employed as precursors to react with H2S to synthesis metal sulfide nanocrystals in wet-chemical method. By using ZnISt2 as precursor, ZnS nanowires were formed at 40~120°C, whereas nanorods were formed at 160°C. By using CdISt2 as precursor, rod, bipod, tripod, and tetrapod shapes of CdS nanocrystals were formed at 40~120°C. The investigation of HRTEM indicated that the arms and cores of multipod-shaped CdS were grown in wurtzite phase and zinc blende phase, respectively. Further increased the temperature to 160°C, spherical, rod-like and warm-like CdS nanocrystals were formed. By using CuISt2 as precursor, irregular aggregated CuS were form at 40°C, whereas circular, triangular, and hexagonal CuS nanocrystals were form at 80~160°C. The XRD pattern indicated that CuS nanocrystals were grown in covellite phase.