Dissertations / Theses on the topic 'Metal catalyst nanoparticles'

Thesis (Ph. D.)--Chemical and Biomolecular Engineering, Georgia Institute of Technology, 2007.
Teja, Amyn, Committee Chair ; Kohl, Paul, Committee Member ; Liu, Meilin, Committee Member ; Nair,Sankar, Committee Member ; Rousseau, Ronald, Committee Member.

Sodium borohydride is stable in alkaline solution, however, it hydrolyses and generates hydrogen gas in the presence of suitable catalyst. By this way hydrogen can be generated safely for the fuel cells. All of the catalyst having been used in the hydrolysis of sodium borohydride, with one exception, are heterogeneous. The limited surface area of the heterogeneous and therefore, have limited activity because of the surface area. Thus, the use of metal nanoclusters as catalyst with large surface area is expected to provide a potential route to increase the catalytic activity. In this dissertation we report for the first time the use of ruthenium(0) nanoparticles as catalyst in the hydrolysis of sodium borohydride. The water dispersible ruthenium(0) nanoparticles were prepared by the reduction of RuCl3.xH2O with sodium borohydride and were stabilized by three different ligands dodecanethiol, ethylenediamine and acetate. Among these three colloidal materials the acetate stabilized ruthenium(0) nanoparticles were found to have the highest catalytic activity in catalyzing the hydrolysis of sodium borohydride. The acetate stabilized ruthenium(0) nanoparticles were characterized by tranmission electron microscopy (TEM), X-ray photoelectron spectroscopy and FT-IR spectroscopy. The particle size of the acetate stabilized ruthenium(0) nanoparticles was determined to be 2.62±
1.18 nm from the TEM analysis. The kinetic of the ruthenium(0) nanoparticles catalyzed hydrolysis of sodium borohydride was studied depending on the catalyst concentration, substrate concentration and temperature. The activation parameters of this reaction were also determined from the evaluation of the kinetic data. This catalyst provides the lowest activation energy ever found for the hydrolysis of sodium borohydride.

Nanomaterial’s applications have expanded greatly in the last few decades due to their interesting properties. Example of nanomaterials are metal nanoparticles NP. NP have interesting physical and optical properties that make them different and more useful than their bulk counterpart. Some of these properties are the large surface area to mass ratio and their ability to absorb light. NP have been applied in the health, environment, and catalysis fields The main focus of this thesis will be on the applications of nanomaterials in medicine and catalysis. In the first part of the thesis, coated polydispersed and polymorphic silver nanostructures AgNS were synthesized using seed mediated method. The synthesized AgNS were characterized using SEM, TEM, and UV-VIS. The stability of these AgNS were determined by measuring the shift in the plasmon band over time and by measuring their zeta potential. Moreover, the bactericidal properties of coated AgNS were tested on gram negative bacteria such as Escherichia coli and Pseudomonas aeruginosa and gram positive bacteria such as Methicillin- Resistant Staphylococcus aureus (MRSA) and Staphylococcus aureus. The second part of the thesis discusses the field of nanocatalysis where different supported metal nanoparticles on TiO2 were synthesized and characterized by TEM, diffuse reflectance DR, XPS and ICP. The activity of the synthesized catalysts was tested for Ullmann C-C cross coupling reaction. The use of the photoresponisve Pd@TiO2 under the combination of UVA 368 and visible light 465nm irradiation offered the highest selectivity toward the cross coupling product.

Noble metals notably platinum (Pt), is a major element of heterogeneous catalysts, excel in catalysing an extensive number of important catalytic reactions in chemical and automotive industries. Since the increased use of these metals is severely limited because of their high cost and scarcity’s, there is therefore an urgent need for the search of alternative base metal catalysts that are cheaper and more widely available. This can only be practical if the main drawbacks of base metals such as the agglomeration of particles under high temperatures operational conditions and irreversible sulphur poisoning can be overcome, and their activity enhanced, such that they can directly replace Pt on a weight-to-weight basis. However, most previous studies have been restricted to low temperature reaction conditions and have not compared their activity directly to that of Pt, whether in terms of active sites or on a weight-to-weight basis. Moreover, most researchers have not investigated extensively the long-term stability of their base metal catalysts, since the longest was at most around 200 hours and at relatively low temperatures, for example at room temperature. It is proposed that long term stability can be achieved by producing uniformly distributed nano-sized socketed and strained base metal particles via the exsolution method. The main objective of this thesis is to produce exsolved base metals catalyst systems rivalling Pt on a weight-to-weight basis in two base reactions; CO and NO oxidation. NO oxidation was also chosen as our model reaction in this research since most Pt in the automotive industry are used in the lean NOx trap (LNT) or a combination of LNT and selective catalytic reduction (SCR), which demand the high conversion of NO to NO2 at low temperatures to work effectively. Initial screening experiments were performed to evaluate the potential CO oxidation activities and long-term stability at 520 °C of two different exsolved metal pellet systems namely lanthanum-doped ceria nickel titanates to exsolve nickel (Ni) metal (La0.8Ce0.1Ni0.4Ti0.6O3) and lanthanum-doped strontium iron nickel titanates to exsolve iron-nickel (FeNi) alloy (La0.5Sr0.4Fe0.1Ni0.1Ti0.6O3). Exsolved FeNi pellet system gives high and stable turnover frequencies (TOFs) of 103 s-1 at 520 °C for almost 170 hours, which confirms the potential of these stable exsolved metal systems for CO oxidation. Sixty exsolved metal powder systems with various metal formulations were produced to enable direct activity comparison to Pt on a weight-to-weight basis. Most exsolved metal systems displayed increasing CO2 production rates with increasing CO partial pressures (PCO) and reversible sulphur poisoning with exsolved CoNi powder system showing remarkable stability at 200 °C for 655 hours (one month). This exsolved CoNi system also showed enhanced activity for CO oxidation upon exposure to CO-rich environment, as a result of the restructuring of particles iv into metal oxide nanocubes anchored onto nanosockets within the support surface. The CO2 production rates of the activated exsolved CoNi powder system at 200 and 520 °C were 0.13 x 10-4 and 1.5 x 10-4 mol s-1 g-1 compared to its initial rate of around 0 (below the detected limit of 0.007 x10-4 mol s-1 g-1) and 0.8 x 10-4 mol s-1 g-1 prior to activation. These active spinel (CoNi)3O4 cubic structures were seen planted at an angle of ~55°, at the edge of an empty socket with mediocre features for CO oxidation, such as rich in Co2+ with exposed (100) planes that had only 44 cubes μm-2 compared to its initial 144 particles μm-2 particle population. Above 450 °C, the main active sites for CO oxidation were thought to be close to or at the metal-support interface of the exsolved CoNi systems. Comparable NO2 production rates to those of commercial Pt catalyst was achieved with only ± 5 % of difference at each measured point within the temperature range used (100-440 °C) over exsolved CoNi system by exploiting the effect of having two particle size ranges (10 and 30 nm). These results confirm the dual functionality of the activated exsolved CoNi system and its huge potential to be commercialised as an alternative catalyst to Pt in two oxidation reactions; CO and NO oxidation. In general, a simple procedure that induces high, long-lasting activity in a base metal catalyst, rivalling platinum for CO and NO oxidation on a weight-to-weight basis was demonstrated. The nature of this activation by tracking individual nanoparticles was successfully elucidated to link their microstructural evolution to their catalytic and kinetic behaviour. This research also illustrates new strategies for enhancing and tailoring the catalytic activity of base metal systems towards replacing platinum.

Les catalyseurs à base de zéolite ont été largement utilisés dans la conversion de la biomasse. Les rendements catalytiques des produits recherchés sont fortement limités en raison de la taille relativement petite des pores dans les zéolithes et la préparation du catalyseur par imprégnation conduit généralement à des nanoparticules métalliques relativement grosses et à un faible contact entre les sites métalliques et acides. Le but de ce travail est la conception de catalyseurs nanocomposites métal-zéolithe contenant des nanoparticules de ruthénium uniformément réparties dans les zéolithes hiérarchiques BEA et ZSM-5. L'utilisation de ruthénium évite la formation de silicates et d'aluminates métalliques inertes difficilement réductibles, tandis que les nanotubes de carbone avec des nanoparticules d'oxyde métallique supportées jouent un rôle de gabarit sacrificiel, ce qui permet de créer une mésoporosité et d'apporter une fonctionnalité métallique à l'intérieur de la matrice zéolithique. Par rapport aux catalyseurs métalliques supportés par des zéolites classiques, les zéolites ruthénium hiérarchiques synthétisées présentaient une activité beaucoup plus élevée et une sélectivité en méthane plus faible dans la synthèse Fischer-Tropsch. La caractérisation des catalyseurs préparés a indiqué l'initiation de la cristallisation des zéolites sur des nanoparticules métalliques. Cet effet a en outre été utilisé pour augmenter la dispersion de nanoparticules métalliques par cristallisation secondaire de Ru supporté sur ZSM-5. Nos résultats montrent une redispersion significative des nanoparticules d'oxyde métallique incorporées et une augmentation de l'activité des réactions modèles. De plus, une stratégie de synthèse a été développée pour la préparation de catalyseurs nanocomposites métalliques et zéolithiques hiérarchiques pour la synthèse directe d'iso-paraffines à partir de gaz de synthèse. Les nanocomposites sont synthétisés en trois étapes. Dans la première étape, la zéolite mère (noyau) est gravée avec une solution de fluorure d'ammonium. La gravure crée de petits mésopores à l'intérieur des cristaux de zéolite. Dans la deuxième étape, les nanoparticules de Ru préparées à l'aide de microémulsion eau-dans-huile sont déposées dans les mésopores de la zéolithe. Dans la troisième étape, une enveloppe de zéolite de zéolites de type MFI (silicalite-1 ou ZSM-5) est cultivée sur les cristaux de zéolite parent recouvrant à la fois la surface gravée et les nanoparticules métalliques. Ainsi, les nanoparticules métalliques deviennent entièrement encapsulées à l'intérieur de la matrice zéolithique. Les paramètres les plus importants tels que la teneur en ruthénium, la mésoporosité de la zéolite, et plus particulièrement, l'acidité de l'enveloppe du catalyseur, qui affectent les performances catalytiques des matériaux nanocomposites synthétisés dans la synthèse Fischer-Tropsch à basse température ont été identifiés dans ce travail. La quantité relative plus élevée d'iso-paraffines a été observée sur les catalyseurs contenant une enveloppe de ZSM-5. La proximité entre les sites métalliques et acides dans l'enveloppe zéolithique des catalyseurs nanocomposites est un paramètre crucial pour la conception de catalyseurs bifonctionnels zéolithiques métalliques efficaces pour la synthèse sélective de carburants de type essence via la synthèse Fischer-Tropsch, tandis que l'acidité du cœur du catalyseur a qu'un impact limité sur les performances catalytiques
Zeolite-based catalysts have been widely used in the conversion of biomass. The catalytic yields of the desired products are strongly limited due to the relatively small size of the pores in zeolites and the catalyst preparation by impregnation usually leads to relatively large metal nanoparticles and low contact between metal and acid sites. The purpose of this work is the design of metal-zeolite nanocomposite catalysts containing ruthenium nanoparticles uniformly distributed in the hierarchical BEA and ZSM-5 zeolites. Use of ruthenium avoids formation of inert hardly reducible inert metal silicates and metal aluminates, while carbon nanotubes with supported metal oxide nanoparticles play a role of sacrificial template, which allows creating mesoporosity and bringing metallic functionality inside the zeolite matrix. Compared to the conventional zeolite supported metal catalysts the synthesized hierarchical ruthenium-zeolites exhibited much higher activity and lower methane selectivity in Fischer-Tropsch synthesis. Characterization of the prepared catalysts has indicated initiation of crystallization of zeolites over metal nanoparticles. This effect has been further used to increase the dispersion of metal nanoparticles by secondary crystallization of Ru supported over ZSM-5. Our results show significant re-dispersion of embedded metal oxide nanoparticles and increase in the activity of model reactions. In addition, a synthetic strategy was developed for the preparation of hierarchical metal and zeolite nanocomposite catalysts for direct synthesis of iso-paraffins from syngas. The nanocomposites are synthesized in three steps. In the first step, the parent (core) zeolite is etched with an ammonium fluoride solution. The etching creates small mesopores inside the zeolite crystals. In the second step, the Ru nanoparticles prepared using water-in-oil microemulsion are deposited in the mesopores of the zeolite. In the third step, a zeolite shell of MFI-type zeolites (silicalite-1 or ZSM-5) is grown on the parent zeolite crystals coating both the etched surface and metallic nanoparticles. Thus, the metal nanoparticles become entirely encapsulated inside the zeolite matrix. Most important parameters such as ruthenium content, zeolite mesoporosity, and more particularly, the acidity of the catalyst shell, which affect the catalytic performance of the synthesized nanocomposite materials in low-temperature Fischer−Tropsch synthesis were identified in this work. The higher relative amount of iso-paraffins was observed on the catalysts containing a shell of ZSM-5. The proximity between metal and acid sites in the zeolite shell of the nanocomposite catalysts is a crucial parameter for the design of efficient metal zeolite bifunctional catalysts for selective synthesis of gasoline-type fuels via Fischer−Tropsch synthesis, while the acidity of the catalyst core has only a limited impact on the catalytic performance

La catalyse constitue un élément clé en synthèse chimique et la recherche actuelle tend à rendre les procédés catalytiques plus propres dans le contexte de la chimie verte. Dans cet esprit, cette thèse a impliqué la recherche de catalyseurs nanoparticulaires utilisés en milieu aqueux, sans ligand toxique et en très faible quantité. La synthèse des nanoparticules (NPs) catalytiques a utilisé des ions des éléments de transition de la droite du tableau périodique et des réducteurs capables de réduire rapidement ces cations en atomes de degré d’oxydation nul s’agrégeant en petites NPs métalliques très actives en catalyse. Les réducteurs choisis ont été des composés réservoirs d’électron organique (naphthyl sodium) ou organométalliques (complexes sandwichs à 19 électrons de valence du fer tel que [Fe(I)Cp*(ŋ6-C6Me6)] ou du cobalt tel que [Co(II)Cp*2], (Cp* = ŋ5-C5Me5)). Les supports limitant l’agrégation des NPs métalliques ont été le solvant (polyéthylène glycol, 1ère partie de la thèse), les cations des réservoirs d’électron organométalliques (2ème partie de la thèse) ou un réseau zéolitique imidazolate (MOF de type ZIF-8, 3ème partie de la thèse). Au lieu d’un cation métallique, il a aussi été possible d’utiliser un cluster tel que [Au25(SR)18] (R = CH2CH2Ph) comme précurseur, auquel cas la réduction peut se limiter à un simple transfer d’électron produisant un cluster anionique stabilisé par le contre-cation sandwich encombré du réservoir d’électron. Les petites NPs ainsi stabilisées se sont avérées d’excellents catalyseurs “verts” de plusieurs réactions de couplage C-C ou C-N et de production d’hydrogène par hydrolyse d’hydrures métalliques en milieu aqueux dans des conditions très douces. Cette dernière réaction a été efficacement catalysée par des NPs bimétalliques Ni2Pt NP@ZIF-8 avec une synergie spectaculaire entre les deux métaux
Catalysis is a key element in chemical synthesis, and current research is focusing on making catalytic processes cleaner in the context of green chemistry. In this spirit, this thesis involves the research of nanoparticle (NP) catalysts used in aqueous medium, without toxic ligand and in very small quantities toward a variety of useful processes. The synthesis of the catalytic NPs used cations of the transition elements of the right of the periodic table and of reducing agents capable of rapidly reducing these cations to atoms of zero oxidation state aggregating into small catalytically active metal NPs. The chosen reducing agents were organic (naphthyl sodium) or organometallic (19-electron) sandwich complexes of iron such as [Fe(I)Cp*(ŋ6-C6Me6)] or cobalt such as [Co(II)Cp*2], (Cp* = ŋ5-C5Me5)) used as electron reservoirs. The supports limiting the aggregation of the metal NPs were the solvent (polyethylene glycol, first part of the thesis), the cations of the organometallic electron reservoirs (2nd part of the thesis) or a zeolitic imidazolate framework (MOF of ZIF-8 type, 3rd part of the thesis). Instead of a metal cation, it has also been possible to use a cluster such as [Au25(SR) 18] (R = CH2CH2Ph) as a precursor, in which case the reduction was limited to a simple electron transfer producing an anionic cluster stabilized by the congested sandwich counter cation of the electron reservoir. The small NPs thus stabilized proved to be excellent "green" catalysts for several C-C or C-N reactions and hydrogen production by hydrolysis of metal hydrides in an aqueous medium under very mild conditions. This latter reaction was efficiently catalyzed by Ni2Pt@ZIF-8 bimetallic NPs with a spectacular synergy between the two metals

L'hydrosilylation des alcènes est une méthode cruciale de formation de liaisons carbone-silicium. Elle est utilisée industriellement pour la production de fluides silicones fonctionnels et d'élastomères silicones. Les procédés actuels d'hydrosilylation des alcènes utilisent des complexes de platine comme catalyseurs. Bien que ces complexes soient extrêmement efficients, ils ne sont d'habitude pas récupérés en fin de réaction, ce qui rend leur utilisation coûteuse et peu durable, étant donnée la rareté du platine. Dans ce projet, nous avons synthétisé et testé plusieurs types de nanoparticules métalliques comme catalyseurs pour l'hydrosilylation des alcènes, dans un effort vers des catalyseurs durables. D'abord, nous avons synthétisé des nanoparticules de platine de 2 nm de diamètre et les avons comparées avec le complexe de Karstedt, le catalyseur de référence en hydrosilylation des alcènes. Nous avons montré que les nanoparticules de platine étaient aussi efficientes que le complexe de Karstedt dans des conditions proches des conditions industrielles, malgré leur dispersion métallique plus faible. Ces observations ont réactivé le débat sur la nature réellement homogène ou colloïdale du complexe de Karstedt pendant la catalyse. Ensuite, un catalyseur hétérogène à base de platine, résistant à la lixiviation, a été développé, basé sur l'encapsulation de nanoparticules de platine dans la matrice d'une silice mésostructurée, la SBA-15. Enfin, d'autres catalyseurs alternatifs ont été développés, basés sur d'autres métaux
Alkene hydrosilylation is a crucial method of forming carbon-silicon bonds. It is used industrially for the production of functional silicone fluids and silicone elastomers. The current industrial alkene hydrosilylation processes use platinum complexes as catalysts. Although these complexes are extremely efficient, they are usually not recovered at the end of the synthesis, making their use expensive and unsustainable, given the scarcity of platinum. In this work, we have synthesized and evaluated several kinds of metal nanoparticles as catalysts for alkene hydrosilylation, in a quest towards sustainable catalyts. First, we have synthesized platinum nanoparticles of 2 nm diameter and compared them with Karstedt's complex, the benchmark catatalyst in alkene hydrosilylation. It was shown that platinum nanoparticles were as efficient as Karstedt's complex in industrially relevant hydrosilylation conditions, despite their lower metal dispersion. These findings reactivated the debate on whether's Karstedt's complex was truly homogeneous or colloidal during catalysis. Then, a leaching-resistant heterogeneous platinum catalyst was developed, based on the embedding of platinum nanoparticles in the matrix of a mesostructured silica, SBA-15. Finally, other alternative catalytic systems were developed, based on other metals

L'objectif principal de ce travail est la préparation de nanoparticules d'argent (AgNPs) stabilisées par des oligo-et polysaccharides et leur application en catalyse et pour la détection de lectines. Pour atteindre cet objectif, deux stratégies ont été utilisées, l'une utilisant le polysaccharide dextran comme stabilisant et l'autre utilisant des composés amphiphiles oligosaccharidiques dérivés du maltose, lactose, maltoheptaose et du xyloglucane. Dans les deux stratégies, la préparation des nanoparticules AgNPs a été optimisée en réalisant une analyse multifactorielle basée sur l'étude de la bande de résonance plasmonique de surface (SPR) des nanoparticules. Toutes les suspensions colloïdales stables de nanoparticules ont été caractérisées par spectroscopie ultraviolet-visible (UV-vis), microscopie électronique à transmission (TEM), diffraction des rayons X aux petits angles (SAXS) et par diffusion dynamique de lumière (DLS). Les activités catalytiques des nanoparticules ont été déterminées pour la réaction de réduction du p-nitrophénol (Nip) par NaBH4, dans l'eau ou dans des mélanges eau-éthanol. Parmi les différentes nanoparticules préparées, celles stabilisées par du dextran ou par le dérivé de maltoheptaose Mal7NAcC12 ont montré les meilleures propriétés catalytiques pour la réduction du Nip par NaBH4 avec des constantes de vitesse respectives de 1,41 et 1,11 s-1 m-2 L. Ces valeurs sont parmi les plus élevées de la littérature. L'effet du solvant et notamment de la présence d'éthanol sur les propriétés catalytiques des nanoparticules a également été évalué. Il a été montré que la présence d'éthanol inhibe l'activité des nanoparticules, probablement par formation d'une couche de solvant à la surface des particules entrant en compétition avec le réducteur. Enfin, trois systèmes différents (Ag-Mal7NAcC12 Ag-XGONAcC12 et Ag-LacNAcC12) ont été évalués comme biocapteurs potentiels pour la détection de lectines. Les nanoparticules Ag-Mal7NAcC12 en particulier ont permis la détection colorimétrique et sans marquage de la Concanavaline A.

The sol-immobilisation method, in which metal nanoparticles are ‘preformed’ (stabilised by the polymer, polyvinyl alcohol) before they are anchored to a support material, was adapted in order to prepare monometallic Au/TiO2 and Pd/TiO2 catalysts, with tailored properties. Varied temperature and solvent environments (H2O, mixed H2O:EtOH and EtOH) were employed during colloidal metal formation, generating metal particles with distinct characteristics (metal particle diameter and available metal sites). The metal nanoparticle properties in the resulting catalysts were fully characterised using a range of spectroscopic (XAFS, IR and UV-Vis) and imaging techniques (TEM and HAADF STEM). It was determined that the preparation of metal nanoparticles at −30°C, in a mixed H2O:EtOH solvent afforded the smallest average particle diameter, regardless of the choice of metal (2.0 nm for Au, 1.4 nm for Pd). However, when prepared at 1°C in H2O, a higher population of small Au (< 5 atoms) or Pd clusters (< 20 atoms) existed, compared with any other environment. The performance of the catalysts were tested in three different reactions; Au/TiO2 for the oxidation of glycerol, and Pd/TiO2 for the hydrogenation of furfural and pnitrophenol. For the two former reactions, it was established that metal particle size is not the only factor influencing performance; the highly active isolated metal clusters, as well as the solvent-PVA-metal interaction, are considered very important factors, and are discussed. Understanding colloidal metal formation, including nucleation and growth phenomena, is vital in the future design of metal nanoparticle properties, and was investigated by means of in situ XAFS. A continuous flow method of nanoparticle synthesis was first explored and developed, before a synchrotron based experiment was performed to monitor the nanoparticle generation (colloidal reduction) in a range of reactors fabricated from different materials (silicon/glass, PTFE and PEEK).

Les matériaux poreux basés sur les polymères font l’objet de recherches nombreuses et variées depuis leur découvertes et jusqu’à aujourd’hui encore. Leurs propriétés uniques et remarquables, comme par exemple une fonctionnalisation aisée ou une large gamme de porosité accessibles, couplées à leur faible coût de production les rendent attrayant pour de nombreuses applications. Parmi elles, la catalyse supportée est en plein essor, spécialement depuis l’avènement des nanoparticules. Durant ce travail de thèse, nous avons développé différents matériaux polymères pouvant servir de support, se focalisant majoritairement sur trois types de matériaux : des matériaux polymères massiques, des matrices polymères poreuses en capillaire ainsi que des polystyrènes poreux provenant de la dégradation sélective de copolymères diblocs.Dans un premier temps, différentes stratégies ont été employées pour l’immobilisation et la génération de nanoparticules sur les matériaux massiques. L’un a consisté en la synthèse d’un monomère contenant un pont disulfure qui, après réduction, a permis la libération de groupement thiol permettant l’accrochage de nanoparticules d’or. La seconde a consisté à réduire de manière originale les nanoparticules en utilisant un gaz, l’hydrogène. Dans un seconde partie, la synthèse de différentes matrices polymères dans des capillaires a été réalisée. Tout d’abord, une matrice déjà connue de la littérature à base de N-acryloxysuccinimide a été utilisée, après modification via thiol-ène et substitution nucléophile par différentes amines, pour immobiliser des nanoparticules de cuivre ainsi que d’or, respectivement. D’autre part, une nouvelle matrice à partir de carbonate cyclique aura, elle, été utilisée après modification, pour l’immobilisation de nanoparticules de platine. Enfin à partir de copolymères diblocs possédant différentes jonctions entre chaque bloc (un pont disulfure ainsi qu’un acétal), différents polystyrènes poreux ont été obtenus. Les copolymères possédant une jonction acétal à lui été utilisé pour l’immobilisation de nanoparticules d’or, permettant la mise en place des réactions de réduction de nitro, d’homocouplage boronique ainsi que de la mise en cascade de ces deux réactions
Porous materials based on polymers have been the subject of intense and various researches since their discovery until now. Their unique and remarkable properties, like their easy functionalization or their large porosity range reachable for instance, coupled with their low production cost makes them attractive for numerous applications. Among them, supported catalysis is booming, especially since the rising of nanoparticles. During this Ph.D. contribution, we have developed different polymeric materials, which could be used as support, focusing mainly onto three types: bulky materials, porous polymeric matrixes into capillaries and porous polystyrene arising from the selective degradation of diblocks copolymers.Firstly, different strategies have been employed for the immobilization and the generation of nanoparticles onto bulk materials. On the one hand, the synthesis of a monomer, bearing a disulphide bridge which can, after a reduction step, free a thiol moiety allowing us to anchor gold nanoparticles. On the other hand, a new route to reduce nanoparticle has been employed using gaseous hydrogen. In another part, the syntheses of different polymeric matrixes into capillaries have been made. First, we used an already known matrix, based on N-acryloxysuccinimide -after modification step via thiol-ene reaction and nucleophilic substitution by amines- to anchor copper or gold nanoparticles, respectively. Also, a new matrix based on cyclic carbonates has been used, after modification, to immobilized platinum nanoparticles. Finally, starting from diblocks copolymers possessing different junctions between both blocks (disulphide bridge or acetal), porous polystyrenes have been obtained. The copolymers bearing an acetal have been implemented to immobilized gold nanoparticles, catalysing several reactions like nitro reduction, boronic homocoupling as well as the cascade reaction of both

From catalytic studies in surface science, it has been shown that the catalytic activity is dependent on the type of metal facet used. Nanocrystals of different shapes have different facets. This raises the possibility that the use of metal nanoparticles of different shapes could catalyze different reactions with different efficiencies. The catalytic activity is found to correlate with the fraction of surface atoms located on the corners and edges of the tetrahedral, cubic, and spherical platinum nanoparticles. It is observed that for nanoparticles of comparable size, the tetrahedral nanoparticles have the highest fraction of surface atoms located on the corners and edges and also have the lowest activation energy, making them the most catalytically active. Nanoparticles have a high surface-to-volume ratio, which makes them attractive to use compared to bulk catalytic materials. However, their surface atoms are also very active due to their high surface energy. As a result, it is possible that the surface atoms are so active that their size and shape could change during the course of their catalytic function. It is found that dissolution of corner and edge atoms occurs for both the tetrahedral and cubic platinum nanoparticles during the full course of the mild electron transfer reaction and that there is a corresponding change in the activation energy in which both kinds of nanoparticles strive to behave like spherical nanoparticles. When spherical palladium nanoparticles are used as catalysts for the Suzuki reaction, it is found that the nanoparticles grow larger after the first cycle of the reaction due to the Ostwald ripening process since it is a relatively harsh reaction due to the need to reflux the reaction mixture for 12 hours at 100 oC. When the tetrahedral Pt nanoparticles are used to catalyze this reaction, the tetrahedral nanoparticles transform to spherical ones, which grow larger during the second cycle. In addition, studies on the effect of the individual reactant have also provided clues to the surface catalytic process that is taking place. In the case of the electron transfer reaction, the surface catalytic process involves the thiosulfate ions binding to the nanoparticle surface and reacting with the hexacyanoferrate (III) ions in solution. In the case of the Suzuki reaction, the surface catalytic mechanism of the Suzuki reaction involves the phenylboronic acid binding to the nanoparticle surface and reacting with iodobenzene via collisional processes.

The development of clean, sustainable chemical processes is a key priority towards meeting the growing demand for synthetic functional chemicals, while balancing rapidly depleting natural resources. The selective oxidation (selox) of crotyl alcohol to crotonaldehyde and the selective hydrogenation of benzyl cyanide to phenylethylamine are two specific systems for which, it is proposed, new heterogeneous catalysts and deeper mechanistic insight will improve. In this thesis the rational design of palladium catalysts is investigated for these systems, via synthesis of palladium nanoparticles with tailored morphology and palladium-gold nanoparticles with tuneable surface composition. Pd icosahedra, nanorods and nanocubes were synthesised and characterised extensively to confirm the size and morphology of the nanoparticles. Pd icosahedra are revealed to be three times more active for crotyl alcohol selox than the nanocubes, and ten times faster than the nanorods, while maintaining good selectivity. An Au-shell, Pd-core structure was synthesised, progressively annealed to induce alloying and characterised using various in situ spectroscopies. Surface Au was found to enhance crotyl alcohol selox activity and selectivity towards crotonaldehyde, in accordance with model predictions. An optimum crotonaldehyde yield was obtained for an Au40Pd60 surface alloy. By employing in situ and time-resolved spectroscopies the active site of Pd selox catalysts is examined, and the role of oxygen in this system and the catalyst’s kinetic behaviour is defined. Reversible redox cycling of the catalyst dependent on its environment was observed, and it was possible to identify PdOx as the active catalytic species responsible for selectively oxidising crotyl alcohol to crotonaldehyde, with high temperatures suppressing catalytic selectivity. Systematic characterisation of an industrial carbon supported Pd catalyst, used in nitrile hydrogenation, reveals potential sources of deactivation including surface poisoning by CN species. Solutions to improve catalyst performance are proposed using the knowledge acquired from the nanoparticle catalysts’ studies.

Acrylic monomers are important materials that represent a large portion of the economy. The current industrial synthesis hydrates cyanohydrins with sulfuric acid, a process which results in large amounts of waste and significant energy costs. A transition metal catalyzed, acid free hydration of cyanohydrins would be beneficial from both economic and environmental standpoints. However, this reaction is challenging, as many catalysts are poisoned by the cyanide released when cyanohydrins degrade. Therefore the development of a catalyst that is resistant to cyanide poisoning is the ideal method to circumvent these difficulties. This dissertation describes several cyanohydrin hydration catalysts, with an emphasis on nanoparticle catalysts. These are at the interface between the homogeneous and heterogeneous catalysts that have been explored previously for this reaction. Chapter I surveys previous studies on nanoparticle catalysts for nitrile hydration and their implications for the hydration of cyanohydrins. Chapter II reports on the homogeneous platinum catalysts [PtHCl(P(NMe2)3)2] and [PtH2(P(NMe2)3)2], exploring secondary coordination sphere effects to enhance nitrile hydration. Chapter III describes another example of this type of complex, [PtH2(P(OMe)3)2], that forms catalytically active nanoparticles under reaction conditions. Explorations of the reactivity of this catalyst with nitriles and cyanohydrins are also described in this chapter. Chapter IV investigates a silver nanoparticle catalyst with a water soluble phosphine (1,3,5-triaza-7-phosphaadamantane) ligand for its activity towards the hydration of nitriles and cyanohydrins. The results of the degradation of the nanoparticles in the presence of cyanide are also described. Chapter V reports on the preparation and examination of a solid supported nickel catalyst for cyanohydrin hydration. Finally, Chapter VI describes how these investigations have made progress towards the development of a cyanide resistant nitrile hydration catalyst. This dissertation includes previously published and unpublished co-authored material.
2015-09-29

Powerful tools have emerged in the past few years to allow the sensing, imaging and modulation of biological processes in living systems. Bioorthogonal organometallic reactions are transformations catalysed by transition metals, which are compatible within a biological environment. Palladium-mediated cross-coupling and decaging reactions, for example, have been successfully applied to catalyse non-natural chemical transformations within a biological milieu. Up until now, copper-catalysed cycloaddition reactions have been used extensively for the conjugation, immobilisation, and purification of biomolecules, but their further application in vivo has been limited by the inherent toxicity of copper. Herein, different transition metal catalysts were designed and applied in cellular and in vivo manipulations. Polymeric solid supports were functionalised with palladium nanoparticles and used as biocompatible, heterogeneous catalysts in selective decaging and cross-coupling reactions to activate fluorescent probes and synthesise cytotoxic anticancer drugs in situ. In order to gain tumour selectively, targeting functionalities were incorporated into the particles to allow the spatial control of the selective activation of labelling probes. The simultaneous synthesis of two different anticancer agents intracellularly, by two totally different mechanisms (in situ synthesis and decaging), is reported. The cellular toxicity of copper was addressed by entrapping copper nanoparticles on a polymeric solid support, allowing the activation of labelling probes, as well as the synthesis of an anticancer agent from two benign components through the well-known copper catalysed azide-alkyne cycloaddition. The biocompatibility of the copper catalysts in vivo was shown by implantation in zebrafish embryos.

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

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2018
Cataloged from PDF version of thesis. Page 157 blank. Vita.
Includes bibliographical references (pages 137-153).
Core-shell nanostructures represent a promising and versatile design platform for enhancing the performance of noble metal catalysts while reducing the cost. Early transition metal carbides (TMCs) and nitrides (TMNs) have been identified as ideal core materials for supporting noble metal shells owing to their earth-abundance, thermal and chemical stability, electrical conductivity, and their ability to bind strongly to noble metals while still being immiscible with them. Unfortunately, the formation of surface oxides or carbon on TMCs and TMNs presents a difficult synthetic challenge for the deposition of atomically thin, uniform noble metal layers. Recent advances have enabled the synthesis of TMC core nanoparticles with noble metal shells (denoted as NM/TMC), although applicability toward TMN cores has not been previously demonstrated. Furthermore, the complete properties of these unique materials are still unknown.
This thesis conducts a detailed investigation of the synthesis, characterization, and catalytic performance of NM/TMC and NM/TMN core-shell nanoparticles to provide a comprehensive understanding of their material properties and the underlying phenomena. First, in-situ studies yielded insight into the mechanism behind the high temperature self-assembly of NM/TMC particles, indicating the presence of a metallic alloy phase preceding the formation of the core-shell structure upon insertion of carbon into the lattice. Next, the synthesis of NM/TMN nanoparticles was demonstrated via nitridation of a parent NM/TMC, and the structural and electronic properties of both core-shell materials were examined through in-situ X-ray absorption spectroscopy (XAS). The analysis revealed significant alterations to the electronic structure of the noble metal shell due to bonding interactions with the TMC and TMN cores, which led to weakened adsorbate binding energies.
Finally, the materials displayed improved performance for the oxygen reduction reaction (ORR), a critical challenge for fuel cell technologies. Notably, particles with complete, uniform shells exhibited unprecedented stability during electrochemical ageing at highly oxidizing conditions, highlighting the great potential of core-shell architectures with earth-abundant TMC and TMN cores for future ORR applications. Overall, this work will provide new opportunities toward the design of enhanced noble metal catalysts and enable further optimization of their performance.
by Aaron R. Garg.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Chemical Engineering

The synthesis, characterization and structure-function relationships of mono- and bimetallic dendrimerencapsulated nanoparticles (DENs) are described. Control over the factors influencing the structure of bimetallic DENs has been attained for PdAu and AuAg systems. The bimetallic DENs are characterized by UV-vis, HRTEM, and single-particle energy dispersive x-ray spectroscopy (EDS). In addition, we use catalysis and selective extraction to chemically probe the surface structure. The fabrication of TiO2-supported Pd, Au and PdAu nanocomposites from DEN precursors is shown to be a viable route for the synthesis of catalytically active, reasonably monodisperse heterogeneous catalysts. Using the dendrimer-templating synthesis, tight control over the size of 1- 2 nm Pd DEN catalysts has led to the observation of a particle-size effect for the hydrogenation of allyl alcohol. We have proposed that for particles with diameters between 1.5“ 1.9 nm the reaction occurs preferentially on the exposed face atoms.

Las especies de metal con diferentes tamaños (átomos individuales, nanocristales y nanopartículas) muestran un comportamiento catalítico diferente para diversas reacciones catalíticas heterogéneas. Se ha demostrado en la bibliografía que muchos factores que incluyen el tamaño de partícula, la forma, la composición química, la interacción metal-soporte, la interacción metal-reactivo / disolvente, pueden tener influencias significativas sobre las propiedades catalíticas de los catalizadores metálicos. Los desarrollos recientes de metodologías de síntesis bien controladas y herramientas de caracterización avanzada permiten correlacionar las relaciones a nivel molecular. En esta tesis, he llevado a cabo estudios sobre catalizadores metálicos desde átomos individuales hasta nanoclusters y nanopartículas. Al desarrollar nuevas metodologías de síntesis, el tamaño de las especies metálicas puede modularse y usarse como catalizadores modelo para estudiar el efecto del tamaño sobre el comportamiento catalítico de los catalizadores metálicos para la oxidación del CO, la hidrogenación selectiva, la oxidación selectiva y la fotocatálisis. Se ha encontrado que, los átomos metálicos dispersados por separado y los grupos subnanométricos de metal pueden aglomerarse en nanoclusters o nanopartículas más grandes en condiciones de reacción. Para mejorar la estabilidad de los catalizadores subnanométricos de metal, he desarrollado una nueva estrategia para la generación de átomos individuales y clusters en zeolitas. Esas especies subnanométricas de metales son estables en tratamientos de oxidación-reducción a 550 oC. Siguiendo esta nueva metodología de síntesis, este nuevo tipo de materiales puede servir como catalizador modelo para estudiar la evolución de especies subnanométricas de metales en condiciones de reacción. La transformación estructural de las especies subnanométricas de Pt ha sido estudiada mediante microscopía electrónica de transmisión in situ. Se ha demostrado que el tamaño de las especies de Pt está fuertemente relacionado con las condiciones de reacción, que proporcionan importantes conocimientos para comprender el comportamiento de los catalizadores de metales subnanométricos en condiciones de reacción. En la otra línea de investigación para catalizadores de metales no nobles, he desarrollado varias estrategias generales para obtener catalizadores de metales no nobles, ya sea soportados sobre óxidos metálicos o protegidos por capas delgadas de carbono. Estos materiales muestran un rendimiento excelente para varias reacciones importantes, como la hidrogenación quimioselectiva de nitroarenos, incluso cuando se comparan con los catalizadores de metales nobles convencionales. En algunos casos, los catalizadores de metales no nobles pueden incluso alcanzar selectividades para productos inviables que no ha sido posible conseguir en catalizadores de metales nobles convencionales, que es causado por la diferente ruta de reacción en catalizadores de metales no nobles. Sin embargo, la espectroscopía fotoelectrónica de rayos X a presión ambiente ha revelado que la irradiación de la luz puede modular la selectividad a los alcoholes y los hidrocarburos C2 +, lo que abre una nueva posibilidad para ajustar el comportamiento catalítico de los catalizadores metálicos. Con base en los trabajos anteriores de diferentes aspectos relacionados con catalizadores metálicos heterogéneos, las perspectivas sobre las direcciones futuras hacia una mejor comprensión del comportamiento catalítico de diferentes entidades metálicas (átomos individuales, nanoagrupamientos y nanopartículas) de una manera unificadora también se han dado en esta tesis.
Les espècies metàl·liques de diferents dimensions (àtoms individuals, nanoclusters i nanopartícules) mostren diferents comportaments catalítics per a diverses reaccions catalítiques heterogènies. S'ha demostrat a la literatura que, molts factors que inclouen la mida de la partícula, la forma, la composició química, la interacció amb el suport metàl·lic, la reacció metàl·lica i la interacció amb dissolvents poden tenir influències significatives sobre les propietats catalítiques dels catalitzadors metàl·lics. Els desenvolupaments recents de metodologies de síntesi ben controlades i eines de caracterització avançada permeten relacionar les relacions a nivell molecular. En aquesta tesi, he realitzat estudis sobre catalitzadors metàl·lics d'àtoms únics a nanoclústers i nanopartícules. Mitjançant el desenvolupament de noves metodologies de síntesi, la mida de les espècies metàl·liques es pot modular i utilitzar com a catalitzadors model per estudiar l'efecte de mida sobre el comportament catalític dels catalitzadors metàl·lics per a l'oxidació de CO, hidrogenació selectiva, oxidació selectiva i fotocatàlisi. S'ha trobat que, els àtoms metàl·lics dispersos individualment i els clústers metàl·lics subnanomètrics poden aglomerar-se en nanoclústeres o nanopartícules més grans en condicions de reacció. Per millorar l'estabilitat dels catalitzadors subnanomètrics de metall, he desenvolupat una nova estratègia per a la generació d'àtoms i racimos en zeolites. Aquestes espècies metàl·liques subnanométricas són estables en tractaments de reducció d'oxidació a 550 oC. Després d'aquesta nova metodologia de síntesi, aquest nou tipus de materials poden servir com a model de catalitzador per estudiar l'evolució de les espècies metàl·liques subnanométricas en condicions de reacció. La transformació estructural de l'espècie Pn subnanométrica ha estat estudiada per microscòpia electrònica de transmissió in situ. S'ha demostrat que la mida de les espècies de Pt està fortament relacionada amb les condicions de reacció, que proporcionen idees importants per comprendre el comportament dels catalitzadors de subnanometria en condicions de reacció. En l'altra línia de recerca dels catalitzadors de metalls no nobles, he desenvolupat diverses estratègies generals per obtenir catalizadors de metalls no nobles recolzats en òxids metàl·lics o protegits per capes de carboni primes. Aquests materials presenten un excel·lent rendiment per a diverses reaccions importants, com la hidrogenació quimioelectiva de nitroarenes, fins i tot quan es comparen amb els catalitzadors convencionals de metall noble. En alguns casos, els catalitzadors de metalls no nobles poden fins i tot aconseguir selectivitats a productes no factibles que no s'han pogut assolir en catalitzadors de metall noble convencionals, que es deuen a la via de reacció diferent en catalitzadors de metalls no nobles. No obstant això, s'ha observat una espectroscòpia de fotoelèctria de raigs X amb pressió d'atmosfera que la irradiació lleugera pot modular la selectivitat als alcohols i hidrocarburs C2 +, la qual cosa obre una nova possibilitat per sintonitzar el comportament catalític dels catalitzadors metàl·lics. A partir d'aquests treballs de diferents aspectes relacionats amb els catalitzadors metàl·lics heterogenis, també s'ha donat en aquesta tesi perspectives sobre les futures orientacions cap a una millor comprensió del comportament catalític de diferents entitats metàl·liques (àtoms individuals, nanoclústers i nanopartícules).
Metal species with different size (single atoms, nanoclusters and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that, many factors including the particle size, shape, chemical composition, metal-support interaction, metal-reactant/solvent interaction, can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow to correlate the relationships at molecular level. In this thesis, I have carried out studies on metal catalysts from single atoms to nanoclusters and nanoparticles. By developing new synthesis methodologies, the size of metal species can be modulated and used as model catalysts to study the size effect on the catalytic behavior of metal catalysts for CO oxidation, selective hydrogenation, selective oxidation and photocatalysis. It has been found that, singly dispersed metal atoms and subnanometric metal clusters may agglomerate into larger nanoclusters or nanoparticles under reaction conditions. To improve the stability of subnanometric metal catalysts, I have developed a new strategy for the generation of single atoms and clusters in zeolites. Those subnanometric metal species are stable in oxidation-reduction treatments at 550 oC. Following this new synthesis methodology, this new type of materials can serve as model catalyst to study the evolution of subnanometric metal species under reaction conditions. The structural transformation of subnanometric Pt species has been studied by in situ transmission electron microscopy. It has been shown that the size of Pt species is strongly related with the reaction conditions, which provide important insights for understanding the behavior of subnanometric metal catalysts under reaction conditions. In the other research line for non-noble metal catalysts, I have developed several general strategies to obtain non-noble metal catalysts either supported on metal oxides or protected by thin carbon layers. These materials show excellent performance for several important reactions, such as chemoselective hydrogenation of nitroarenes, even when compared with conventional noble metal catalysts. In some cases, non-noble metal catalysts can even achieve selectivities to unfeasible products which has not been possible to achieve on conventional noble metal catalysts, which is caused by the different reaction pathway on non-noble metal catalysts. Nevertheless, it has been revealed by ambient-pressure X-ray photoelectron spectroscopy that light irradiation can modulate the selectivity to alcohols and C2+ hydrocarbons, which opens a new possibility for tuning the catalytic behavior of metal catalysts. Based on the above works from different aspects related with heterogeneous metal catalysts, perspectives on the future directions towards better understanding on the catalytic behavior of different metal entities (single atoms, nanoclusters and nanoparticles) in a unifying manner have also been given in this thesis.
Liu, L. (2018). Heterogeneous Metal Catalysts: From Single Atoms to Nanoclusters and Nanoparticles [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/113169
TESIS

Due to its unique properties and high surface area, Graphene has become a good candidate as an effective solid support for metal catalysts. The Nobel Prize in Physics for 2010 was awarded to Andre Geim and Konstantin Novoselov "for groundbreaking experiments regarding the two-dimensional material graphene". Microwave-assisted synthesis of various metallic nanostructured materials was investigated for CO oxidation applications. These metallic nanostructured materials were used to convert CO to CO2 as an effective approach for carbon monoxide elimination due to its harmful effect on health and environment. In particular, this dissertation is focusing on palladium as a transition metal that has a unique ability to activate various organic compounds to form new bonds. The prepared graphene-supported metallic nanostructured materials were successfully used to investigate Suzuki cross-coupling reaction as an important reaction in the field of pharmaceutical applications. In this research, nanostructured materials were used as solid support catalysts which showed remarkable improvements in the aspects of size, surface structure, catalytic selectivity, shape and recyclability. The nano porous structure and superparamagnetic behavior of (Fe3O4) nano particles that were used as an effective ingredient in graphene-supported palladium catalyst improved the catalytic activity and the catalyst recyclability simply by using an external magnetic field. This research has been divided into two main categories; the first category is to investigate other metal oxides as a solid support for palladium to be used in CO oxidation catalysis. The second category will focus on improving of solid support systems of palladium – magnetite catalyst to increase recyclability. The final stage of this investigation will study the use of these solid supported metal catalysts in continuous heterogeneous processes under flow reaction conditions. The structural, morphological and physical properties of graphene-based nanocomposites described herein were studied using standard characterization tools such as TEM, SEM, X-ray diffraction, XPS and Raman spectroscopy.

This thesis describes in a first part the synthesis of new mixed-metal clusters of ruthenium in association with palladium, platinum and tin. The use of monometallic dichloro complexes of Pd or Pt in reactions with negatively charged penta- or hexaruthenium clusters in the presence of a chlorine scavenger has been moderately successful in the case of Pd, but highly successful in the case of Pt. High yields were obtained in many instances. The mixed clusters [Ru₅C(CO)₁₄Pt(COD)], [Ru₆C(CO)₁₆Pt(COD)], [Ru₆C(CO)₁₅(Pt(COD))₂] and [{Ru₆C(CO)₁₆}₂Pt(MeCN)₂] were characterised by X-ray crystallography. On the other hand, the use of [Pt(PPh₃)₄] allowed the isolation and structure determination of [Ru₆C(CO)₁₆PPh₃] rather than mixed species. The reactivity of [Ru₅C(CO)₁₄Pt(COD)] and [Ru₆C(CO)₁₆Pt(COD)] with CO, PPh₃ and dppm was investigated, and led to the isolation of other mixed-metal and homometallic compounds. The crystal structures of the clusters [Ru₅C(CO)₁₁Pt(CO)(dppm)₂], [Ru₆C(CO)₁₃(dppm)₂] and [Ru₆C(CO)₁₆Pt₃(dppm)₂] were determined. Several Ru-Sn mixed clusters were also synthesised, and in particular reactions involving [PPN]₂[Ru₆C(CO)₁₆] and SnCl₄ led to the isolation of [PPN][Ru₆C(CO)₁₆SnCl₃] and [Ru₆C(CO)₁₆SnCl₂], which were characterised crystallographically. In a second part, some of the new mixed-metal clusters were used as precursors for nanoparticle heterogeneous catalysts, using the mesoporous silica MCM-41 or carbon nanotubes as supports. A Ru-Pd/MCM-41 catalyst derived from a Pd₆Ru₆ cluster was shown to be extremely active for the hydrogenation of alkenes to alkanes and of naphthalene to cis-decalin selectively. This material was characterised by STEM and in situ FTIR and EXAFS, which confirmed the bimetallic nature of the nanoparticles and their homogeneous small sizes and dispersion on the support. The shape of the nanoparticles was further assessed by theoretical calculations. A Ru-Sn/MCM-41 catalyst was prepared from [PPN][Ru₆C(CO)₁₆SnCl₃] and shown to hydrogenate selectively cyclic poly-enes to their mono-enes, under solvent-free and low temperature conditions. This catalyst was also characterised by STEM and in situ FTIR and EXAFS, which indicated that the tin atom is the anchoring point for the bimetallic nanoparticles on the siliceous walls of MCM-41. Finally, the clusters [Ru₅C(CO)₁₄Pt(COD)], [Ru₆C(CO)₁₆Pt(COD)], [PPN][Ru₆C(CO)₁₆SnCl₃] and [Ru₆C(CO)₁₆SnCl₂] were used as ideal precursors for small-sized and evenly dispersed bimetallic nanoparticles supported on carbon nanotubes.

Durant les darreres dècades, el disseny de processos en el marc de la química sostenible ha anat creixent de forma exponencial. La recerca constant de processos mes benignes amb el medi ambient ha implicat un gran esforç per obtenir millors rendiments mitjançant l'activació de llocs específics, i possant especial èmfasi amb el control de la quimio-, la regio- i la enantioselectivitat, punts crucials per a l'economia atómica. En aquest sentit, els dissolvents juguen un paper crític, i com podrà veure's al llarg d'aquesta memòria..
Aquesta Tesi s'enfoca en l'ús de mitjans de reacció alternatius i sostenibles, com són els líquids iònics (ILs), el diòxid de carboni supercrític (scCO2) i la barreja de ambdós dissolvents, amb l'objectiu de disminuir l'ús de dissolvents orgànics convencionals i la seva aplicació en els següents processos catalítics: hidrogenació asimètrica, reacció de Suzuki d'acoblament creuat C-C, reacció d'alquilació al·lílica asimètrica i la hidrogenació de arens.
In the last decades, the design of processes in the framework of the sustainable chemistry has been exponentially growing. The constant searching of cleaner processes has led to a lot of effort to obtain higher yields by activation of specific sites, and improving chemo-, regio- and enantio-selectivities, which are crucial from a point of view of an atom economy strategy. In this sense, solvents play a critical role.
This PhD thesis focuses on the use of alternative sustainable reaction media such as ionic liquids (ILs), supercritical carbon dioxide (scCO2) and mixtures of both solvents in different catalytic processes, with the aim of decreasing the use of conventional organic solvents applied in the following catalytic reactions: homogeneous and supported rhodium catalysed asymmetric hydrogenation, biphasic palladium catalysed Suzuki C-C cross-coupling, homogeneous palladium catalysed asymmetric allylic alkylation, and ruthenium and rhodium nanoparticles catalysed arene hydrogenation were tested.

Silver nanoparticles (sub 10 nm), supported on, or in, cellulose, have been demonstrated to be well stabilised and immobilised during application in a model continuous reaction: the reduction of 4-nitrophenol (4-NP) to 4-aminophenol with sodium borohydride. The production of these silver nanoparticles (NP), within the cellulose supports, was carried out by either in situ reduction of silver precursors absorbed into the preformed cellulose supports, or, by inclusion of ex situ synthesised NPs (prepared in DMSO solutions) in the dissolution of cellulose and trapping upon subsequent coagulation of cellulose. The effects of NP synthesis method (affecting particle size and agglomeration) and the cellulose morphology and porous structure were examined with respect to the catalytic activity of the materials. The in situ reduction of a silver salt with aqueous NaBH4 solutions (0.03 to 1.0 wt. %) led to tuneable Ag NP sizes with mean diameters of 5 to 11 nm (TEM) and metal loadings of 0.5-1.0 wt. %. The catalytic activity of these samples in the 4-NP reduction reaction (0.05 mM, 0.167 M NaBH4, 30 °C) was demonstrated to increase upon decreasing NP size: TOF values of 22–356 h-1, consistent with a Langmuir-Hinshelwood mechanism. The porous structure of these Ag-cellulose materials (0.2 to 294 m2 g-1) was demonstrated to be variable and dependent on drying treatments of the regenerated cellulose hydrogel. Thermal drying, freeze-drying and critical point drying resulted in materials with different bulk structure and porosity. In turn the different porosities resulted in extremely different catalyst activities, e.g. Ag-cellulose catalyst (0.3 mm disks) thin film, hydrogel and cryogel phases exhibited TOF values of 2, 12 and 178 h-1, respectively. In addition, the NP synthesis could be carried out in either the cellulose hydrogel or cryogel, which led to different extents of Ag NP catalyst stabilisation against agglomeration during the 4-NP reaction and catalyst recovery and recycling. The Ag NPs synthesised in the cryogel cellulose disks were observed to undergo agglomeration (TEM) after use in 4 repeat batch reductions, whilst those NPs synthesised in the hydrogel cellulose, prior to freeze-drying to the final cryogel catalyst material, did not exhibit any agglomeration upon 4 repeat reduction reactions. The ex situ reduction of Ag and Au NPs was carried out by the reduction of AgOAc and Au(OAc)3 by DMSO and variation of the NP synthesis parameters, such as time (10 min – 1h) and temperature (50 – 80 °C), allowed for control of the NP sizes (3 to 6 nm Ag NPs and 4 to 11 nm Au NPs, TEM). It was demonstrated that the addition of the polysaccharide starch (0.42 wt. % in DMSO) allowed for consistent Ag NP size (ca. 4 nm) to be achieved throughout the 8 h synthesis, the starch acting as both the reducing and capping agent, maintaining the small sizes and narrow particle size distributions of the NPs upon aging (72 h). A kinetic model with a bimolecular nucleation step was developed to describe this reduction of the silver acetate by the starch/DMSO system. However, contact of the NPs with solutions of imidazolium ILs, 1-Ethyl-3-methylimidazolium acetate (EmimOAc) and 1-Butyl-3-methylimidazolium chloride (BmimCl) in DMSO, used in the dissolution of cellulose, led to the oxidation of the Ag(0) and Au(0) NPs. Thus, when these NP solutions were mixed in cellulose solutions regeneration by phase inversion with the aim of preparing cellulose/NP composites led to materials with negligible metal loadings (AAS). This oxidation, of the metal NPS, was partially overcome by stabilisation of the starch capped Ag NPs by pre-treatment with cellulose (1:1 mixture of α and MC cellulose). However, the activity of the resulting Ag-cellulose catalyst (0.5 wt. % AAS, 6.7 nm TEM) was much lower than the Ag-cellulose catalysts prepared by in situ reduction of silver in the cellulose hydrogel, despite the comparable NP sizes. This was presumed to be a result of encapsulation of the Ag NPs by the cellulose, leading to a decrease in the accessible surface of the NPs. Finally, the use of Ag NP / cellulose composites, prepared by in situ reduction of silver in cellulose hydrogel beads (0.19 wt. %, 6.4 nm), were demonstrated in the continuous reduction of 4-NP in a packed bed reactor (τ’ 100 g s dm-3). The activation energies of the reactions of 4-NP catalysed by the Ag-cellulose catalyst materials were determined (3.2 to 9.4 kJ mol-1) from Arrhenius plots, which demonstrated that above 20 °C the reaction was likely subject to diffusion limitations in the cellulose beads. The high degree of stabilisation of the Ag NPs against agglomeration imparted by the cellulose support was demonstrated: the rate of reaction was observed to be constant over 120 h, treating 45 L of 4-NP solution, with the catalyst material after use demonstrating no significant leaching of silver, or agglomeration, of NPs (AAS, TEM).

The research in this dissertation examines the chemistry and applications of dendrimers in homogeneous catalysis. We examined interactions between dendrimers and charged probe molecules, prepared dendrimer-encapsulated metal nanoparticles in organic solvents, studied size-selectivity of dendrimer-encapsulted catalysts, and designed molecular rulers as in-situ probes to measure the location of dendrimer-encapsulted metal nanoparticles. The intrinsic proton binding constant and a constant that characterizes the strength of electrostatic interactions among occupied binding sites in poly(amidoamine) (PAMAM) dendrimers have been obtained by studying the effect of solution pH on the protonation of the dendrimers. The significant finding is that these two factors are greatly modulated by the unique and hydrophobic microenvironment in the dendrimer interior. Hydrophilic poly(propylene imine) (PPI) dendrimers were modified with various hydrophobic alkyl chains through an amide linkage and were then used as templates for preparing intradendrimer copper nanoclusters. The main driving force for encapsulating metal-ions was found to be the differences in metal-ion solubility between the solvent and the interior of the dendrimer. Nanometer-sized metal particles are synthesized and encapsulated into the interior of dendrimers by first mixing together the dendrimer and metal ion solution and then reducing the composite chemically, and the resulting dendrimer-encapsulated metal nanoparticles can then be used as catalysts. By controlling the packing density on the dendrimer periphery using either different dendrimer generations or dendrimer surface functionalities, it is possible to control access of substrates to the encapsulated catalytic nanoparticle. Molecular rulers consisting of a large molecular "stopper", a reactive probe and a linker were designed as in-situ probes for determining the average distance between the surface of dendrimer-encapsulated palladium nanoparticles and the periphery of their fourth-generation, hydroxyl-terminated PAMAM dendrimer hosts. By doing so, we avoid having to make assumptions about the nanoparticle size and shape. The results suggest that the surface of the encapsulated nanoparticle is situated 0.7 ± 0.2 nm from the surface of the dendrimer.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2016.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 231-249).
The noble metals (NMs) comprise ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), osmium (Os), iridium (Ir), platinum (Pt), and gold (Au). Together, these corrosion-resistant elements serve as nature's universal catalysts by binding reactant molecules neither too strongly nor too weakly. This allows for rapid catalytic transformations of reactants into useful products. Modern society, its current technologies, and its emerging renewable energy technologies are underpinned by precious metal catalysts. However, the noble metals are the least abundant elements in the lithosphere, making them prohibitively scarce and expensive for future global-scale technologies. Furthermore, the traditional catalyst engineering toolkit is ill-equipped to optimize the reactivity, stability, and loading of NM catalysts. The technologies developed in this thesis have two overarching implications. First, a method is developed to engineer non-sintered and metal-terminated transition metal carbide (TMC) nanoparticles. Featuring "noble metal-like" surface reactivity, TMCs are earth-abundant and exhibit many useful catalytic properties, such as carbon monoxide and sulfur tolerance. By designing TMC nanoparticles with controlled surface properties, this thesis offers new avenues for replacing noble metal catalysts with inexpensive alternatives. Second, a method is developed to synthesize TMC nanoparticles coated with atomically-thin noble metal monolayers. This offers new directions for improved catalyst designs by substantially enhancing reactivity and stability while reducing overall noble metal loadings. These synthetic achievements in nanoscale core-shell catalyst engineering were guided by computational quantum chemistry, model thin film studies, and advanced spectroscopic techniques. Examination of the catalytic utility of these new materials was performed in the context of water electrolysis, proton exchange membrane fuel cells, direct methanol fuel cells, and high temperature thermal reforming.
by Sean Thomas Hunt.
Ph. D.

This thesis investigated new metal nanoparticle and semiconductor catalyst and photocatalyst systems for achieving fine chemical synthesis from both fossil-fuel sourced reactants and biomass carbohydrate-derived reactants. Photocatalysts for industrially important organic oxidation reactions were developed that efficiently worked with the aid of solar light irradiation, at low temperature and pressure, that avoided the use of hazardous chemicals. The effects on the organic reaction mechanisms of different noble metal nanoparticle and metal oxide nanostructures were explored for these chemical transformations. Success in developing the nanomaterial photocatalysts has contributed to the field of sustainable green chemical synthesis.

This thesis describes the synthesis, characterisation and catalytic testing of multifunctional immobilised metal nanoparticle in metal-organic framework (MOF) materials. Combining the activity of metal nanoparticles with the porosity and Lewis acidity of metal-organic frameworks provides a single catalytic material which can perform multi-step reactions. Strategies to immobilise the metal nanoparticles within the metal-organic frameworks have been investigated. Immobilisation has been achieved by applying three different methodologies. First, deposition of metal nanoparticle precursors within mesoporous MOFs is discussed. Chapter 3 shows the effectivity of the double solvents deposition technique to achieve dispersed and small nanoparticles of around 2.7 nm. The best system combined Pd nanoparticles with MIL-101(Cr). This system was further investigated in tandem reductive amination catalysis, discussed in Chapter 4, to investigate the activity and selectivity provided by these multifunctional catalysts. Another immobilisation technique was performed by coating Pd decorated SiO2 spheres with a MOF layer. Using this technique, MOF was grown cyclically in solution, providing tuneable shell thicknesses of MOF on the metal nanoparticle decorated oxide spheres. While the homogeneity of the MOF shell needs more optimisation, it was determined that the surface charge on the spheres played an important role in the growth of MOF in the desired location. Finally, the third immobilisation technique is the core-shell growth of MOF on colloidal metal nanoparticles. Polymer-capped metal nanoparticles with well-defined shapes were synthesised and characterised. From here, the optimisation of conditions for core-shell growth of UiO-66 and MIL-100(Sc) were investigated. Conditions which provided the desired core-shell morphology were found for both MOF types. These materials were then subsequently used in tandem reductive amination catalysis and a more straightforward styrene hydrogenation. It was shown that the metal nanoparticles remain active catalysts within either MOF shell and the MOF shell stabilises the metal nanoparticle and acts as a Lewis acid catalyst.

Els carburs de metalls de transició (TMC) exhibeixen propietats químiques i catalítiques similars a les dels costosos metalls nobles. La conversió d'alcohol, hidrogenació d'olefines i altres reaccions importants han demostrat l'aplicabilitat d'aquests compostos en processos industrials. També se sap que nanopartícules de metalls nobles (NMNPs) mostren una alta activitat catalítica tot i la baixa o nul • la reactivitat del metall sòlid. A més, investigacions recents assenyalen que els suports de TMC polaritzen la densitat electrònica de NMNPs adsorbits i augmenten l'activitat catalítica respecte als suports més tradicionals d'òxid metàl • lic. Aquests descobriments recents han inspirat el treball presentat en aquesta tesi, realitzat mitjançant tècniques actuals de la química quàntica. S'ha estudiat CO, CO2, H2, H2O adsorbits sobre TiC i sobre petits clústers d'or adsorbits en el suport. S'ha considerat la superfície (001), terrasses, esglaons monoatòmics i defectes, i també la reactivitat de les molècules adsorbides sobre la superfície neta de TiC (001) i en dos clústers d'or, Au4 i Au6, adsorbits. Les barreres energètiques calculades per a la formació de metà o formaldehid a partir de gas de síntesi, en TiC (001) resulten ser massa altes i aquests processos són inviables sobre el suport net. Sobre els clústers d'or suportats sobre TiC (001) hi ha una major activitat catalítica, però la reacció continua sent altament impedida. No obstant això, la reacció de desplaçament del gas d'aigua es preveu que sigui ràpida en el sistema Au4/TiC (001), superant els catalitzadors utilitzats normalment en la indústria. Experiments recents mostren que els clústers de Ni, Cu i Au estan fortament deformats un cop adsorbits sobre TMC, donant lloc a catalitzadors molt actius. S'ha investigat la interacció dels àtoms amb la fase delta de MoC. La interacció és més forta pel recobriment més baix considerat, la relaxació de la superfície és important i l'activitat es preveu que augmenti en l'ordre Ni> Cu> Au. Finalment, s'han considerat possibles reconstruccions no polars per a la superfície (001) de Mo2C centrant-se en l'energia d’escissió, la qual és proporcional a l'estabilitat de cada tipus de terminació. Les reconstruccions no polars disminueixen l'energia d’escissió, confirmant l'aplicabilitat dels conceptes clàssics de Tasker per a òxids als TMC.
Los carburos de metales de transición (TMC) exhiben propiedades químicas y catalíticas similares a las de los costosos metales nobles. La conversión de alcohol, hidrogenación de olefinas y otras reacciones importantes han demostrado la aplicabilidad de estos compuestos en procesos industriales. También se sabe que nanopartículas de metales nobles (NMNPs) muestran una alta actividad catalítica a pesar de la baja o nula reactividad del metal sólido. Además, investigaciones recientes señalan que los soportes de TMC polarizan la densidad electrónica de NMNPs adsorbidos y aumentan la actividad catalítica respecto a los soportes más tradicionales de óxido metálico. Estos descubrimientos recientes han inspirado el trabajo presentado en esta tesis, realizado mediante técnicas actuales de la química cuántica. Se ha estudiado CO, CO2, H2, H2O adsorbidos sobre TiC y sobre pequeños clusters de oro adsorbidos sobre el suport. Se ha considerado la superficie (001), terrazas, escalones monoatómicos y defectos y, también, la reactividad de las moléculas adsorbidas sobre la superficie limpia de TiC (001) y en dos clusters de oro, Au4 y Au6, adsorbidos. Las barreras energéticas calculadas para la formación de metano o formaldehído a partir de gas de síntesis en la superficie limpia de TiC (001) resultan ser demasiado altas y esos procesos son inviables sobre el soporte limpio. Sobre los clusters de oro soportados sobre TiC (001) hay una mayor actividad catalítica, pero la reacción continúa siendo altamente impedida. Sin embargo la reacción de desplazamiento del gas de agua se prevé que sea rápida en el sistema Au4/TiC (001), superando los catalizadores utilizados normalmente en la industria. Experimentos recientes muestran que los clusters de Ni, Cu y Au están fuertemente deformados una vez adsorbidos sobre TMC dando lugar en catalizadores muy activos. Se ha investigado la interacción de los átomos con la fase delta del catalizador de MoC. La interacción es más fuerte para el recubrimiento más bajo considerado, la relajación de la superficie es importante y la actividad se prevé que aumente en el orden Ni> Cu> Au. Finalmente, se han considerado posibles reconstrucciones no polares para la superficie (001) de Mo2C centrándose en la energía de escisión, que es proporcional a la estabilidad de cada tipo de terminación. Las reconstrucciones no polares disminuyen la energía de escisión, confirmando la aplicabilidad de los conceptos clásicos de Tasker para óxidos a los TMC.
Carbides of the early transition metals (TMC) exhibit chemical and catalytic properties that in many aspects are very similar to those of expensive noble metals. Alcohol conversion, hydrogenation of olefins and many others important reactions demonstrated the applicability of these compounds for industrial processes. It is also known that small noble metal nanoparticles (NMNPs) show high catalytic activity despite of the poor reactivity or inertness of the bulk metal. Additionally, recent investigations pointed out that supporting TMCs polarize the electron density of adsorbed NMNPs increasing the catalytic activity respect to more traditional metal oxide supports. These recent discoveries inspired the work reported in this thesis using state-of-the-art quantum chemical techniques. We studied CO, CO2, H2, H2O molecules adsorbed on TiC and on small gold clusters adsorbed thereon. We considered the (001) extended surface, terraces, monatomic steps and kink defective sites. The reactivity of adsorbed molecules on the clean TiC (001) surface and on two gold clusters, Au4 and Au6, adsorbed thereon were also studied. Energy barriers calculated for methane or formaldehyde formation from syngas, on the clean TiC (001) surface were by far too high and those processes are unviable on the clean support. Gold clusters supported by TiC (001) show higher catalytic activity but the reaction continues to be highly hindered. However water gas shift reaction is predicted to be fast on the Au4/TiC(001) system, overtaking catalysts normally used in industry. Recent experiments show that Ni, Cu and Au clusters are strongly perturbed upon adsorption on TMC resulting in extremely active catalysts. We investigated the interaction of those atoms with the delta phase of the MoC catalyst. The interaction is stronger for the lowest coverage considered, the relaxation of the surface important and the activity is predicted to increase in the order Ni>Cu >Au. Finally, we have studied possible non-polar reconstructions of the (001) surface of Mo2C focusing on the cleavage energy, proportional to the stability of each type of termination. The non-polar reconstructions decreased the calculated cleavage energy, confirming the applicability of the classical Tasker’s concepts for oxides to TMCs.

De nos jours, les matériaux carbonés macroscopiques font face à un nombre croissant d'applications en catalyse, soit en tant que supports, soit directement en tant que catalyseurs sans métal. Cependant, il reste difficile de développer un support de catalyseur hiérarchisé à base de. carbone ou un catalyseur utilisant un procédé de synthèse beaucoup plus simple. À la recherche de nouveaux matériaux carbonés structurés pour la catalyse hétérogène, nous avons exploré le potentiel du feutre de carbone / graphite du commerce (FC / FG). Le but du travail décrit dans cette thèse a été le développement du monolithe FG et FC en tant que catalyseur sans métal pour les réactions d’oxydation en phase gazeuse et en tant que support de catalyseur, notamment pour le palladium, pour les réactions d’hydrogénation en phase liquide, et leur rôle dans la performance de réaction de ces catalyseurs. En raison de leur surface de chimie inerte avec une mouillabilité inappropriée, une telle étude avait pour condition d'activer celles d'origine. Par conséquent, des FG et des FC modifiés bien arrondis ont été synthétisés avec des propriétés physico-chimiques adaptées par une série de procédés de traitement chimique, tels que l'oxydation, l'amination, la thiolation, le dopage à l'azote et au soufre. L’oxydation partielle du sulfure d’hydrogène en soufre élémentaire et l’hydrogénation sélective du cinnamaldéhyde α, β-insaturé, en tant que réactions sensibles à l’effet des propriétés du catalyseur sur l’activité et la sélectivité, combinées à des techniques de caractérisation, ont été choisis pour étudier l’effet de la matériaux carbonés sur le comportement catalytique
Nowadays, macroscopic carbon materials are facing an increasing number of applications in catalysis, either as supports or directly as metal-free catalysts on their own. However, it is still challenging to develop hierarchical carbon-based catalyst support or catalyst using a much simple synthesis process. In the quest for novel structured carbon materials for heterogeneous catalysis we explored the potential of commercial carbon/graphite felt (CF/GF). The aim of the work described in this thesis has been the development of GF and CF monolith as metal-free catalyst for gas-phase oxidation reactions and as catalyst support, notably for palladium, for liquid-phase hydrogenation reactions, and their roles in the reaction performance of these catalysts. Due to their inert chemistry surface with inappropriate wettability, a prerequisite for such a study was to activate the origin ones. Therefore, well-rounded modified GFs and CFs were synthesized with tailored physic-chemical properties by a series of chemical treatment processes, such as oxidation, amination, thiolation, nitrogen- and sulfur-doping. The partial oxidation of hydrogen sulfide into elemental sulfur and selective hydrogenation of α, β-unsaturated cinnamaldehyde, as the sensitive test reactions to the influence of the catalyst properties on activity and selectivity, combined with characterization techniques, were chosen to investigate the effect of functionalized carbon materials on the catalytic behavior

Through employing a combination of complimentary structural, spectroscopic and high-resolution microscopy techniques, the superior properties of a [PtCl4]2- precursor to yield well-defined, isolated nanoparticles (predominantly 2-3 nm) upon microporous framework architectures, have been established. These are prepared via a one-step, in situ methodology, within three-dimensional porous molecular architectures, to afford robust heterogeneous catalysts. The catalytic activity of these materials can be intrinsically linked to the degree of nanoparticle formation. The [PtCl4]2- precursor bestows a greater propensity for nanoparticle formation across a range of activation conditions by comparison to [PdCl4]2- and [AuCl4]- precursors. This, in concert with the surrounding microporous architecture, donates superior catalytic performance for the aerobic oxidation of KA oil to cyclohexanone (precursor for adipic acid and ε-caprolactam), under continuous flow conditions. It is able to approach unrivalled yields of >90% by adapting a ‘closed-loop’ system. Detailed spectroscopic investigations into the nature of the active sites at the molecular level, coupled with high-resolution electron microscopy, reveal that the intricacies of the synthetic methodology and associated activation procedures play a vital role in regulating the locality, morphology and size of the metal nanoparticles produced. Theseinvestigations also offer insights into the potential consequences of prolonged catalytic exposure. All three (Au, Pt & Pd) nanoparticle systems demonstrate a profound influence on the activation of molecular oxygen and alkyl peroxides for a plethora of selective catalytic oxidations. Furthermore, this design strategy offers adequate scope for the creation of multi-metallic (e.g. Pd-Cu, Au-Cu & Au-Pt), multifunctional heterogeneous catalysts, in the continued quest for the activation of molecular oxygen in sustainable catalytic processes.

Copper-based materials are one of the most promising catalysts for performing transformations of important organic compounds in both academic and industrial operations. However, it is challenging to consistently synthesize highly active and stable copper species as heterogeneous catalysts due to their relatively high surface energy. As a result, agglomeration usually occurs, which limits the catalytic activities of the copper species. The work presented in this dissertation shows different synthetic strategies for obtaining active and stable copper-based materials by modifying chemical/physical properties of copper nanoparticles (NPs). Emphasis is placed on discussing specific catalytic systems, including carbon-supported catalysts (monometallic and bimetallic copper-based heterogeneous catalysts) and titania-supported catalysts, and their advantages in terms of catalytic performance. In recent years, there has been increasing interest in using metal-organic frameworks (MOFs) as a sacrificial template to obtain carbon-supported NPs via a thermolysis process. The advantages of using MOFs to prepare carbon supported nanomaterials are a fine distribution of active particles on carbon matrix without post-synthesis treatments and corresponding increased catalytic activity and stability in many reaction conditions. To better understand the potential of this synthetic approach, MOF pyrolyzed products have been characterized. Then, they were applied as heterogeneous catalysts for several chemical reactions. In particular, the high energy copper-based MOF, CuNbO-1, was decomposed to obtain an amorphous copper species supported on carbon (a-Cu@C). This catalyst was found to be highly active for reduction, oxidation, and N-arylation reactions without further tuning or optimization. Higher catalyst turnover numbers for each of these transformations were obtained when comparing a-Cu@C activity to that of similar Cu-based materials. To improve catalyst performance, a secondary metal can be introduced to create synergistic effects with the parent copper species. In order to gain insights into the role of the second metal, a well-known Cu-MOF, HKUST-1, was doped with nickel, cobalt, and silver solutions, followed by a decomposition process with 2,4,6-trinitrotoluene (TNT) as additive. This additive was used to enhance the rapid thermolysis of the bimetallic MOFs. In these bimetallic systems, the addition of a second metal was found to help in dispersing both metals over the carbon composite support and in influencing the particle size and oxidation state of the metals. Catalytic performance showed that even <1% of a secondary metal increased the rate for nitrophenol reduction. Optimal catalytic performance was achieved using a Ni-CuO@C bimetallic catalyst. Another synthetic strategy for Cu-catalyst preparation involves using the deposition-precipitation method, in which a copper catalyst anchored on a titania support was synthesized at low weight % in order to obtain a single atom catalyst (1-Cu/TiO2). The higher copper loading catalyst, 5-Cu/TiO2, was synthesized as a benchmark catalyst for comparison. The copper structure in the synthesized catalysts was investigated by powder X-ray diffraction (PXRD), Raman, scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX), X-ray photoelectron spectroscopy (XPS), N2 physisorption and inductively coupled plasma mass spectrometry (ICP-MS) in order to characterize physical and chemical properties. STEM-EDX observations showed single atom copper species less than 0.75 nm in size, as well as nanoparticles with an average diameter of ~1.31 nm. This catalyst was highly active in the reduction of nitro-aromatic compounds with NaBH4 at room temperature. The small to atomic level sizes of the Cu species and multiple oxidation states of Ti species were found to play a crucial role in the catalytic activity.

L'épuisement progressif des matières premières d'origine fossile et la nécessité de réduire les émissions de gaz à effets de serre ont conduit la communauté scientifique à rechercher de nouveaux matériaux dont la production ne dépendra pas de ressources non renouvelables. Dans un autre temps ces matériaux pourront déjà être introduits sur le marché afin de substituer des produits déjà existant qui proviennent de matières premières fossiles. Par exemple, l'acide 2,5-furandicarboxylique (FDCA) obtenu par valorisation de la biomasse lignocellulosique est un potentiel substituant de l'acide téréphtalique actuellement utilisé pour la production de polyesters. En effet, le FDCA peut être obtenu par oxydation sélective du 5-hydroxyméthylfurfural (HMF) synthétisé à partir de la biomasse lignocellulosique. Ainsi, ce travail de thèse peut être défini par deux problématiques principales : (1) Le développement de catalyseurs pour l'oxydation de HMF en FDCA sans utiliser de bases inorganiques et (2) Développement de membranes catalytiques de polymères pour la future adaptation du procédé d'oxydation en réacteur à flux continu. Pour ce qui concerne l'oxydation de HMF dans des conditions neutres, une première étude s'est intéressée à la possibilité d'utiliser de l'oxyde de nickel nanométrique comme support pour des nanoparticules. Ensuite, la possibilité d'utiliser des nanoparticules de Pt supportées sur du TiO2 obtenues par décomposition contrôlée de clusters carbonyliques a été étudiée. Ainsi, des membranes de polymère obtenues par électrospinning, contenant les nanoparticules métalliques étudiées précédemment, ont été appliquées comme système catalytique pour l'oxydation du HMF
The depletion of fossil-derived resources and the need to decrease the emission of green-house gases led scientists to look for sustainable materials to replace the already existing fossil-derived ones. For instance, 2,5-furandicarboxylic acid (FDCA) has been pointed out as the bioderived counterpart of terephthalic acid for the synthesis of polyesters. In fact, FDCA could be obtained by means of selective oxidation of 5-hydroxymethylfurfural (HMF), a bio-derived platform molecule produced by glucose hydrolysis. This reaction is known to be catalyzed by supported metal nanoparticle systems in presence of inorganic bases under batch conditions. This work deals with the development of catalytic systems able to perform the base-free HMF oxidation, since the possibility to circumvent base addition leads more sustainable processes. In particular, two different sets of catalytic systems have been studied: mono- and bimetallic Au and Pd nanoparticles on nano-sized NiO, and mono- and bimetallic Pt/Sn systems on titania, prepared via cluster precursor decomposition. Another topic that will be discussed in this thesis focuses on the development of catalytically active polymeric membranes obtained via electrospinning and their application as catalytic system for HMF oxidation either under basic and neutral aqueous conditions. In details, polyacrylonitrile and nylon have been tested as electrospun polymeric matrixes for the embedding of Au-based nanoparticles and Pt clusters

Les liquides ioniques (LIs) à base d’imidazolium présentent une très grande organisation en réseaux 3D et sont constitués de microdomaines polaires et apolaires, dû à la présence des canaux ioniques et au regroupement des chaînes alkyles lipophiles. L’objectif de ce travail est d’utiliser leurs propriétés de solvatation, liées à cette organisation, pour générer et stabiliser in situ des nanoparticules métalliques (NPs) d’une taille contrôlée et prévisible. Cette approche a trouvé de nombreuses applications dans des domaines tels que la catalyse et la microélectronique. Le phénomène de croissance cristalline des NPs (ruthénium, nickel et tantale) générées in situ lors de la décomposition sous H2 des complexes organométalliques, est contrôlé i) par la taille des poches apolaires, dans lesquelles le complexe se dissout, ii) par les conditions expérimentales (température, agitation) et iii) par la nature du métal et du complexe précurseur. Le mécanisme de stabilisation des NPs, jusqu'alors mal compris, dépend du mécanisme de formation des NPs, qui pourrait entraîner la présence de ligands hydrures ou carbènes N-hétérocycliques (NHC) à leur surface. Cette présence a été démontrée par marquage isotopique et analysée en RMN ainsi qu’en spectrométrie de masse. Les LIs sont également des milieux intéressants en catalyse. Des études sur l’influence du LI sur l’activité des catalyseurs homogènes ont souligné l’importance cruciale des paramètres physico-chimiques des LIs, et particulièrement de la viscosité, qui intervient ainsi dans la loi cinétique. Enfin, une étude approfondie de l’effet de la taille des NPs sur l’activité catalytique et la sélectivité pour l’hydrogénation, réalisée en milieu LI, a confirmé l’importance du contrôle de la taille des NPs pour les applications catalytiques
Imidazolium based ionic liquids (ILs) consist of a continuous 3-D network of ionic channels, coexisting with non polar domains created by the grouping of lipophilic alkyl chains, forming dispersed or continuous microphases. The aim of this work is to use the specific solvation properties of ILs, related to this 3-D organisation, to generate and stabilise in situ metal nanoparticles (NPs) of a controlled and predictable size. This approach has found application in fields such as catalysis and microelectronics. The phenomenon of crystal growth of NPs (ruthenium, nickel, tantalum) generated in situ in ILs from the decomposition of organometallic complexes under molecular hydrogen, is found not only to be controlled by i) the size of non-polar domains, in which the complexes dissolve, but also by ii) the experimental conditions (temperature, stirring) and iii) the nature of the metal and its precursor complex. The previously unexplained stabilisation mechanism of NPs in ILs is found to depend on the mechanism of formation of NPs, which may lead to the presence of either hydrides or N-heterocyclic carbenes (NHC) at their surface. These have both been evidenced through isotopic labelling experiments analysed by NMR and mass spectrometry. Another advantage of ILs is that they provide an interesting medium for catalytic reactions. Studies on the influence of the IL on the catalytic performance in homogeneous catalysis have highlighted the crucial importance of the physical-chemical parameters of ILs, in particular the viscosity, for which a term must be included in the kinetic rate law. Using these findings, a thorough investigation of the effect of the NP size on catalytic activity and selectivity in hydrogenation in ILs was undertaken, confirming the importance of controlling NP size for catalytic applications

Small particles of gold (< 100 nm) have attracted great interest among researchers due to the unique combination of their physicochemical properties. Among various research areas catalysis and bio-nanotechnology represent the largest areas of growth for gold nanoparticle research. Catalysts play a crucial role in the life of the modern society. More than 85 % of all chemical processes are catalytic, and this number is increasing every year. There is a constant demand to develop more efficient and durable catalysts in order to address increasing energy demands and environmental requirements. The first part of the thesis is focused on the study of catalytic activity of supported gold and mixed-metal catalysts, derived from atomically precise phosphine-stabilised gold and mixed-metal clusters in the liquid-phase oxidation of cyclohexene and one-pot synthesis of imines. Various characterisation techniques (TEM, diffuse-reflectance UV-vis, XPS, etc.) as well as kinetic studies were used in order to establish the optimal structure of gold catalysts. The effect of catalytic support, nature of hetero-metal atom for mixed metal-systems and type of catalyst pre-treatment were also examined. Gold nanoparticles are actively studied in various biomedical applications as they are offering new approaches to the detection and treatment of life-threatening diseases, such as cancer. The second part of this work discusses our preliminary investigations of biological activity of gold nanoparticles, stabilised with cancer-targeting molecules. In particular, the cytotoxicity of gold nanoparticles was studied using 11 different cancer and normal cell types. Gold uptake and particle localisation inside the cells were also investigated.

Les matériaux « coeur-coquille » composés d’une nanoparticule métallique encapsulée à l'intérieur de coquilles inorganiques (oxydes, carbone …) attirent de plus en plus l'attention par leurs propriétés particulières, en particulier dans le domaine de la catalyse. Les particules métalliques sont protégées par la coquille, qui empêche entre autres le frittage et la croissance des particules à haute température. Cependant, les coquilles sont généralement méso à macroporeuses et elles ne peuvent pas jouer le rôle de tamis moléculaire pour les molécules de taille nanométrique. En revanche, les zéolithes sont des solides cristallins microporeux dont les pores bien définis permettent une forte discrimination des réactifs basée sur la taille, la forme ou leur coefficient de diffusion. L’objectif de cette thèse visait à la synthèse de catalyseurs de type coeur-coquille dans lesquels la coquille est une zéolite microporeuse de structure MFI (silicalite-1 et ZSM-5), le coeur étant soit une particule de métal noble (Au, Ag, Pt, Pd), soit des alliages de ces différents métaux, soit enfin un métal de transition (Co, Ni, Cu). Ces catalyseurs ont été appliqués dans des réactions d'hydrogénation sélective (aromatiques substitués) et l'oxydation sélective de CO en présence d'hydrocarbures. Nous avons ainsi montré que la coquille zéolithique, tout en protégeant les particules du frittage, modifie la sélectivité des réactions en interdisant aux réactifs volumineux d’atteindre les sites catalytiques
Nanostructured yolk-shell materials, which consist of metal nanoparticle cores encapsulated inside hollow shells, attract more and more attention in material science and catalyst applications during the last two decades. Metal particles are usually highly mono-dispersed in size and isolated from each other by the shell, which prevents growth by sintering at high temperature. Because they are generally made of meso/macroporous oxides or amorphous carbon, shells cannot carry out molecular sieve-type separation of molecules at the nanometric scale. The aim of the present thesis was to synthesize yolk-shell catalyst with microporous zeolite shells (silicalite-1 and ZSM-5), containing noble (Au, Pt, Pd) transition (Co, Ni, Cu) and alloy metal nanoparticles. Zeolites are crystalline microporous solids with well-defined pores capable of discriminating nanometric reactants on the basis of size, shape and diffusion rate. Zeolite-based yolk-shell catalysts have been applied in selective hydrogenation (toluene and mesitylene) and oxidation (CO) reactions in the presence of hydrocarbons. Zeolite shells not only plaid a key role as membranes, thus changing selectivities as compared to conventional supported catalysts, but they also protected metal nanoparticles from sintering under reaction conditions

Durant la darrera dècada, les nanopartícules de sílice han trobat aplicacions en catàlisi, depuració d’aigua, camps biomèdics, agrícoles i industrials ... per les seves característiques físiques i químiques úniques, com ara una gran superfície, una excel·lent biocompatibilitat, una bona estabilitat tèrmica, mecànica i química, mida i forma de porus regulable, riquesa en grups silanol a la superfície que permeten una fàcil modificació superficial. La nostra recerca en aquesta tesi s’ha centrat en la preparació i caracterització de diversos tipus de nanopartícules de sílice funcionalitzades i la seva aplicació en catàlisi, biomedicina i recuperació d’elements de terres rares. Es van preparar noves nanopartícules de sílice mesoporoses derivades d’amides de prolina-valinol mono i disililades i es van utilitzar com a catalitzadors reciclables per a la reacció aldòlica asimètrica amb elevada activitat i selectivitat. Aquests nanomaterials es poden recuperar i reutilitzar amb èxit fins a sis vegades (capítol 2). Per contra, els nostres esforços en la preparació de nanopartícules d’organosílice reciclables com a catalitzadors quirals o lligands per a la α-trifuorometilació i α-fluorinació enantioselectives de compostos carbonílics no van tenir èxit (capítol 2). Es van preparar una sèrie de nanopartícules d’organosílice mesoporoses periòdiques mixtes que posseïen grups Boc i tert-butil èster com a agents potencials per ultrasons focalitzat d’alta intensitat (High Intensity Focused Ultrasound, HIFU). Es preveia que aquests nanomaterials alliberessin CO2 i / o isobutè del grup COOtBu sensible a la temperatura. Tanmateix, es va trobar que el grup Boc era bastant estable i no es podia eliminar en condicions de HIFU a 80 ºC, requerint l’addició d’àcid. El concepte no deixa de ser prometedor per futurs agents de contrast per a teràpies basades en HIFU (Capítol 3). Medicaments antiinflamatoris no esteroides com l’ibuprofè i el diclofenac es van unir de forma covalent a nanopartícules de sílice a través d’un grup funcional amida per a aplicacions potencials en formulacions tòpiques (pomades i cremes). A més, el recobriment de teixits de cotó amb aquestes nanopartícules de sílice funcionalitzades va proporcionar teixits hidrofòbics per a potencials aplicacions cutànies tòpiques en apòsits destinats a tractar ferides cròniques. El medicament antiinflamatori corresponent s’allibera in situ mitjançant el trencament enzimàtic selectiu de l’enllaç amida en presència de proteases (capítol 4). Es van preparar nanopartícules de sílice mesoporoses amb nucli magnètic funcionalitzades amb fragments de cyclen com a adsorbents nous per a la recuperació específica i selectiva de diferents ions de terres rares (RE) de les aigües residuals (Capítol 5).
Durante la última década, las nanopartículas de sílice han encontrado aplicaciones en catálisis, purificación de agua, campos biomédicos, agrícolas e industriales ... debido a sus características químicas y físicas únicas, tales como alta superficie, excelente biocompatibilidad, buena estabilidad térmica, mecánica y química, tamaño y forma de poro ajustable, superficie enriquecida con grupos silanol que permiten una fácil modificación superficial. Nuestra investigación en esta tesis se ha centrado en la preparación y caracterización de varios tipos de nanopartículas de sílice funcionalizadas novedosas, así como su aplicación en catálisis, biomedicina y recuperación de elementos de tierras raras. Se prepararon nuevas nanopartículas de sílice mesoporosa derivadas de amidas de prolina-valinol mono y disililadas y se usaron como catalizadores reciclables para la reacción aldólica asimétrica con elevada actividad y selectividad. Estos nanomateriales se pueden recuperar con éxito y reutilizar hasta seis veces (Capítulo 2). Por el contrario, nuestros esfuerzos en la preparación de nanopartículas de organosílice reciclables como catalizadores o ligandos quirales para la α-trifuorometilación y α-fluoración enantioselectivas de compuestos carbonílicos no tuvieron éxito (Capítulo 2). Se preparó una serie de nanopartículas de organosilica mesoporosas mixtas periódicas que poseen grupos Boc y éster de terc-butilo como posibles agentes sensibles al ultrasonido focalizado de alta intensidad (High Intensity Focused Ultrasound, HIFU). Se esperaba que estos nanomateriales liberaran CO2 y / o isobuteno del grupo COOtBu sensible a la temperatura. Sin embargo, se encontró que el grupo Boc era bastante estable y no podía eliminarse en condiciones HIFU a 80 ºC, sino que se requería además la adición de ácido. Sin embargo, el concepto es prometedor para futuros agentes de contraste para terapias basadas en HIFU (Capítulo 3). Fármacos antiinflamatorios no esteroideos como ibuprofeno y diclofenaco se unieron de forma covalente a nanopartículas de sílice a través de un grupo funcional amida para su posible aplicación en formulaciones tópicas (pomadas y cremas). Además, el recubrimiento de telas de algodón con estas nanopartículas de sílice funcionalizadas proporcionó telas hidrófobas para posibles aplicaciones cutáneas tópicas en apósitos destinados a tratar heridas crónicas. El fármaco antiinflamatorio correspondiente se libera in situ mediante la escisión enzimática selectiva del enlace amida en presencia de proteasas (Capítulo 4). Se prepararon nanopartículas de sílice mesoporosas con núcleo magnético funcionalizadas con fragmentos de cyclen como adsorbentes novedosos para la recuperación específica y selectiva de diferentes iones de tierras raras (RE) del agua residual (Capítulo 5).
During the last decade, silica nanoparticles have found applications in catalysis, water purification, biomedical, agricultural and industrial fields… due to their unique chemical and physical characteristics, such as high surface area, excellent biocompatibility, good thermal, mechanical and chemical stability, adjustable pore size and shape, enriched surface silanol groups with easy surface modification. Our research in this thesis has been focused on the preparation and characterization of various types of novel functionalized silica nanoparticles, as well as their application in catalysis, biomedicine and rare earth elements recovery. Novel mesoporous silica nanoparticles derived from mono- and bis-silylated proline-valinol amides were prepared and used as recyclable catalysts for the asymmetric aldol reaction with high activity and selectivity. These nanomaterials can be successfully recovered and reused for up to six runs (Chapter 2). Conversely, our efforts in the preparation of recyclable organosilica nanoparticles as chiral catalysts or ligands for the enantioselective α-trifuoromethylation and α-fluorination of carbonyl compounds were not successful (Chapter 2). A series of mixed periodic mesoporous organosilica nanoparticles possessing Boc and tert-butyl ester groups were prepared as potential high intensity focused ultrasound (HIFU) responsive agents. These nanomaterials were expected to release CO2 and/or isobutene from the temperature-sensitive COOtBu group. However, Boc group was found to be quite stable and could not be removed under HIFU conditions at 80 ºC, requiring the addition of acid. The concept is nevertheless promising for future contrast agents for HIFU based therapies (Chapter 3). Non-steroidal anti-inflammatory drugs such as ibuprofen and diclofenac were grafted to silica nanoparticles through an amide functional group for potential application in ointment and cream topical formulations. Furthermore, coating of cotton fabrics with these functionalized silica nanoparticles provided hydrophobic fabrics for potential topical cutaneous applications in dressings intended to treat chronic wounds. The corresponding anti-inflammatory drug is released in situ by the selective enzymatic cleavage of the amide bond in the presence of proteases (Chapter 4). Two functionalized magnetic core-shell mesoporous silica nanoparticles containing cyclen moieties were prepared as novel adsorbents for the specific and selective recovery of different rare earth (REs) ions from wastewater (Chapter 5).

Thesis advisor: Chia-Kuang (Frank) Tsung
The core-shell hybrid structure is the simplest motif of two-component systems which consists of an inner core coated by an outer shell. Core-shell composite materials are attractive for their biomedical, electronic and catalytic applications in which interface between core and shell is critical for various functionalities. However, it is still challenging to study the exact role that interface plays during the formation of the core-shell structures and in the properties of the resulted materials. By studying the formation mechanism of a well interface controlled one-to-one metal nanoparticle (NP)@zeolite imidazolate framework-8 (ZIF-8) core-shell material, we found that the dissociation of capping agents on the NP surface results in direct contact between NP and ZIF-8, which is essential for the formation of core-shell structure. And the amount of capping agents on the NP surface has a significant effect to the crystallinity and stability of ZIF-8 coating shell. Guided by our understanding to the interface, one-to-one NP@UiO-66 core-shell structure has also been achieved for the first time. We believe that our research will help the development of rational design and synthesis of core-shell structures, particularly in those requiring good interface controls
Thesis (MS) — Boston College, 2017
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry

Gegenstand dieser Arbeit ist die Synthese neuer funktioneller Materialien unter Zuhilfenahme von Blockcopolymerpartikeln als „soft templates“ und die Untersuchung ihrer Anwendungsmöglichkeiten als Katalysator- und Energiespeichermaterialien. Drei Arten von Kompositpartikeln mit komplexen Strukturen wurden synthetisiert: Palladium@poly(styrol-b-2-vinylpyridin)@Dodecanthiol-Gold (Pd@PS-P2VP@DT-Au) Hybridpartikel, Polydopamin@Gold (PDA@Au) Nanoreaktoren und poröse Ti4O7 Partikel mit verbundener Porenstruktur. Im ersten Teil der Arbeit wurden Pd@PS-P2VP@Au Kern-Schale Partikel, bestehend aus DT-Au Aggregaten als Kern, umgeben von mit Palladium Nanopartikeln beschichtetem PS-P2VP als Schale hergestellt. Die auf die strukturierte P2VP Schale aufgebrachten Palladium Nanopartikel weisen im Vergleich mit anderen bekannten Systemen gute katalytische Eigenschaften für die Reduktion von 4-Nitrophenol mit NaBH4 auf. Im zweiten Teil wurden zum ersten Mal PDA@Au Nanoreaktoren mit verbundener Porenstruktur unter Verwendung einer „soft template“-Methode synthetisiert. Dabei wurden poröse PS-P2VP Partikel als Template verwendet. Mittels Elektronentomografie (ET) konnte die verbundene Porenstruktur mit den darin gleichmäßig verteilten Gold Nanopartikeln direkt abgebildet werden. Die PDA@Au Partikel wurden mithilfe der katalytischen Reduktion von 4-Nitrophenol kinetisch untersucht. Im dritten Teil wurden poröse Ti4O7 Partikel mit verbundener Porenstruktur als neuer Typ von Schwefel Wirtsmaterial für Lithium-Schwefel Batterien unter Zuhilfenahme von porösen PS-P2VP Templatpartikeln entwickelt. Die elektrochemische Untersuchung von Ti4O7/S und kohlenstoffbeschichtetem Ti4O7/S beim Einsatz als Kathodenmaterial ergab hervorragende Leistungsdaten von 1219 mAhg−1 bzw. 1411 mAhg−1 für die Anfangskapazität und eine Kapazitätserhaltung von 74% bzw. 77% nach 200 Zyklen.
The present thesis focuses on the synthesis of novel functional materials by using block copolymer particles as soft templates. Three types of particles with complex structures have been synthesized, involving palladium@poly(styrene-b-2-vinylpyridine)@dodecanethiol-gold (DT-Au) (Pd@PS-P2VP@DT-Au) hybrid particles, polydopamine@gold (PDA@Au) nanoreactors with Au nanoparticles immobilized in PDA channels, and porous Ti4O7 particles with interconnected-pore structure. Their possible applications as catalyst and energy storage materials have been studied. In the first part of the thesis, Pd@PS-P2VP@DT-Au core-shell particles, which consist of dodecanethiol-gold (DT-Au) aggregation as core and Pd coated PS-P2VP as shell, have been fabricated based on the Rayleigh instability of polymer nanotubes inside Anodic Aluminium Oxide (AAO) porous membranes. The hybrid particles show efficient catalytic activity for the reduction of 4-nitrophenol by NaBH4. The catalytic activity has been compared with other reported systems. In the second part, PDA@Au nanoreactors with interconnected channel structures have been synthesized for the first time by using porous PS-P2VP particles as soft template. Electron tomography (ET) provides direct visualization of the interconnected pore structure of the nanoreactors, inside of which Au nanoparticles are homogeneously embedded. Such PDA@Au particles have been explored as nanoreactors for kinetic studies using the reduction of 4-nitrophenol as the model reaction. In the third part, porous Ti4O7 and carbon-coated Ti4O7 particles with interconnected-pore structure have been developed as efficient sulfur-host material for lithium-sulfur batteries by using porous PS-P2VP particles as template. The Ti4O7/S and carbon-coated Ti4O7/S composites show excellent electrochemical performance with initial capacities of 1219 mAh g−1 and 1411 mAh g−1, capacity retentions of 74% and 77% after 200 cycles, respectively.

L'énergie, le développement durable et la santé sont au cœur des préoccupations actuelles de la planète. La disparition inéluctable des énergies fossiles, les conséquences graves des émissions de gaz carbonique sur l'environnement et la santé appellent des solutions rapides et efficaces pour suppléer aux premières et minimiser les autres.Parmi les solutions envisagées la catalyse hétérogènes représentés par les matériaux poreux, ces derniers ont prouvé leur efficacité, néanmoins des obstacles sont à corriger ou à contourner tel que le problème d'inaccessibilité des molécules encombrantes dans sites des micropores de ce matériau. Dans cette thèse nous avons essayé de trouver la solution à ce problème en travaillant sur des nanostructures ZSM-5.Dans une première étape, nous avons optimisé ce matériau en l'occurrence ZSM-5, avec une réduction de la taille des particules, d'une échelle microscopique vers une autre nanométrique, ce qui nous a permis d'augmenter la surface externe après une modification de certains paramètres. Dans la deuxième étape, et afin de donner une entité catalytique à notre support (la zéolithe), nous avons activé ce matériau par l'incorporation des cations, choisis en fonction d'une réaction bien spécifique, qui est celle d'oxydation des méthylènes benzéniques. Pour ce fait nous avons élaboré différents catalyseurs pour nos réactions.Nous avons conclu cette thèse par la catalyse avec la M-ZSM-5 (M = Cu, Cr et Fe) et une étude comparative est faite avec les MOFs qui portent les mêmes cations actifs dans leur partie minérale
Energy, sustainable development, and health are at the heart of contemporary concerns of the planet. The inevitable disappearance of fossil fuels, the severe consequences of carbon emissions on the environment and health require quick and effective solutions to supplement the first and minimize others. Among the solutions proposed, there are porous materials which have proven their effectiveness; however, there are still obstacles to be corrected or circumvented. In this thesis, we focus on the problem of bulky molecules' inaccessibility in micro pores of the materials we wish to study. In the first part, we optimize the material in this case, ZSM-5, with a reduction in particle size to a microscopic scale to another nano, which allows us to increase the external surface after changing certain parameters. In the second step, in order to give a catalytic entity to our support (zeolite), we activate with this material incorporating cations selected according to a specific property of the benzyl methylenes oxidation reaction. For this reason we developed different method of preparation. We conclude this thesis by catalysis with M-ZSM-5 (M = Cu, Cr and Fe) and a comparative study on the method of preparation and the MOFs that bears the same cations as mineral part which constitutes the materials

Recent advances in surface science technology have opened new opportunities for atomic scale studies in the field of nanoparticle (NP) catalysis. The 2007 Nobel Prize of Chemistry awarded to Prof. G. Ertl, a pioneer in introducing surface science techniques to the field of heterogeneous catalysis, shows the importance of the field and revealed some of the fundamental processes of how chemical reactions take place at extended surfaces. However, after several decades of intense research, fundamental understanding on the factors that dominate the activity, selectivity, and stability (life-time) of nanoscale catalysts are still not well understood. This dissertation aims to explore the basic processes taking place in NP catalyzed chemical reactions by systematically changing their size, shape, oxide support, and composition, one factor at a time. Low temperature oxidation of CO over gold NPs supported on different metal oxides and carbides (SiO2, TiO2, TiC, etc.) has been used as a model reaction. The fabrication of nanocatalysts with a narrow size and shape distribution is essential for the microscopic understanding of reaction kinetics on complex catalyst systems ("real-world" systems). Our NP synthesis tools are based on self-assembly techniques such as diblock-copolymer encapsulation and nanosphere lithography. The morphological, electronic and chemical properties of these nanocatalysts have been investigated by atomic force microscopy (AFM), scanning tunneling microscopy (STM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and temperature-programmed desorption (TPD). Chapter 1 describes briefly the basic principles of the instrumentation used within this experimental dissertation. Since most of the state-of-art surface science characterization tools provide ensemble-averaged information, catalyst samples with well defined morphology and structure must be available to be able to extract meaningful information on how size and shape affect the physical and chemical properties of these structures. In chapter 2, the inverse-micelle encapsulation and nanosphere lithography methods used in this dissertation for synthesizing uniformly arranged and narrow size- and shape-selected spherical and triangular NPs are described. Chapter 3 describes morphological changes on individual Au NPs supported on SiO2 as function of the annealing temperature and gaseous environment. In addition, NP mobility is monitored. Chapter 4 explores size-effects on the electronic and catalytic properties of size-selected Au NPs supported on a transition metal carbide, TiC. The effect of interparticle interactions on the reactivity and stability (catalyst lifetime) of Au NPs deposited on TiC is discussed in chapter 5. Size and support effects on the formation and thermal stability of Au2O3, PtO and PtO2 on Au and Pt NPs supported on SiO2, TiO2 and ZrO2 is investigated in chapter 6. Emphasis is given to gaining insight into the role of the NP/support interface and that played by oxygen vacancies on the stability of the above metal oxides. Chapter 7 reports on the formation, thermal stability, and vibrational properties of mono- and bimetallic AuxFe1-x (x = 1, 0.8, 0.5, 0.2, 0) NPs supported on TiO2(110). At the end of the thesis, a brief summary describes the main highlights of this 5-year research program.
Ph.D.
Department of Physics
Sciences
Physics PhD