Dentre os principais avanços na área de ciência ou tecnologia dos materiais podemos ressaltar as atuais técnicas de produção, manipulação e análise de estruturas de tamanho muito reduzido, os quais possuem propriedades físicas (magnéticas, eletrônicas e óticas) diferentes das apresentadas pelos mesmos materiais em estruturas maiores. Nanopartículas (NPs) de metais nobres, principalmente ouro e prata, estão sendo utilizadas e incorporadas em diversas tecnologias que tiram proveito de suas características óticas ou condutivas Neste trabalho apresentamos uma metodologia de preparação de NPs de metais nobres, com a possibilidade de incorporá-las em um material dielétrico. As amostras, produzidas a partir da técnica de agregação gasosa, foram preparadas em um gerador de NPs, construído em um dos canhões de um sistema de magnetron sputtering comercial (AJA Internacional). No gerador, átomos são removidos do alvo e termalizados pelo fluxo do gás de trabalho, se condensando na forma de NPs. As NPs são extraídas do gerador aerodinamicamente e seguem em direção ao substrato. Utilizando um dos outros canhões do nosso sistema de sputtering podemos codepositar as NPs produzidas em uma matriz dielétrica ou metálica. Podemos também depositar camadas de filmes finos sobre o material produzido pelo gerador de NPs. As amostras de nanopartículas de ouro e prata produzidas foram caracterizadas a partir de técnicas de microscopia eletrônica de varredura (MEV), retroespalhamento Rutheford (RBS), espectrofotometria de UV-Visível e microscopia ótica em campo próximo (SNOM). A partir das imagens de MEV, podemos inferir a presença da matriz dielétrica a partir da separação das NPs e essa presença pode ser confirmada pela análise dos resultados de RBS. Por fim a análise do espectro de absorbância das amostras em conjunto com as imagens de SNOM demonstrou o comportamento plasmônico das amostras produzidas, sobretudo das NPs codepositadas em matriz dielétrica. / In the midst of main advances in material science and technology we can highlight the new techniques of preparation, manipulation and analyses of structures of very small size. They have physical properties (magnetic, electronic and optical) different from those presented by the same material, but in bigger dimension. Noble metal nanoparticles, mainly gold and silver, are incorporated into various technologies in order to take advantage of their optical or electric properties. In this work, we present a technique to produce noble metal nanoparticles by a physical method that also permits to imbed them in a dielectric material matrix. The samples, produced using the gas aggregation technique, were prepared in a nanoparticle gun, developed on one of the guns of a commercial magnetron sputtering system (AJA International). In the nanoparticles generator, atoms are removed from the target and thermalized by the flow of the sputtering working gas, and they are also condensed to form the nanoparticles. The nanoparticles are extracted from the generator aerodynamically and then they proceed to the substrate. Using another gun of the sputtering system we can deposit the nanoparticles produced in a dielectric or metallic matrix. We can also deposit under and capping layers of thin films on the nanoparticles layer produced. The samples of gold and silver nanoparticles produced were characterized by scanning electron microscopy (SEM), Rutherford backscattering analysis (RBS), UV-Visible spectrophotometry and near field optical microscopy (SNOM). In the SEM images, from the distribution and morphology of the nanoparticles it was possible infer the presence of the dielectric matrix, and this was also confirmed by the RBS measurements. Finally, absorbance spectrum of the samples together with the SNOM images have demonstrated the plasmonic character of the samples produced, specially for the NPs co-deposited in the dielectric matrix.

Atualmente, a nanociência e nanotecnologia são consideradas como um campo emergente onde, continuamente, as barreiras entre as disciplinas são rompidas. Seu principal foco de estudo consiste em buscar o controle estrutural ao nível molecular, arranjando os átomos de modo a se conseguir um entendimento e controle das propriedades fundamentais da matéria. Neste estudo foram propostas modificações moleculares e, consequentemente, na morfologia, propriedades ópticas e cristalinas em filmes finos de TiO2 com o objetivo de aumentar sua eficiência fotônica. Os filmes finos de TiO2 foram preparados pelo processo sol-gel avaliando a influência de diferentes ácidos e agente direcionador para a obtenção dos arranjos nanoestruturados. A seguir, os filmes que apresentaram maior eficiência fotônica foram incorporados com nanopartículas metálicas (Au, Ag, Pd e Pt) com objetivo de minimizar os processos de recombinação eletrônica do par lacuna/elétron. Das diversas rotas estudadas, os filmes finos de TiO2 preparados com ácido acético obtiveram maior eficiência fotônica devido à pouca aglomeração dos grãos de titânia, o que pode ter favorecido uma maior exposição dos sítios fotocatalíticos. A presença do agente direcionador na formulação teve pouco efeito na eficiência fotônica, possivelmente devido à maior aglomeração dos grãos nos filmes finos de TiO2. Com a adição de nanopartículas metálicas, os filmes finos de TiO2 com nanopartículas de platina e ouro apresentaram maior eficiência fotônica. A presença de hexamina nos filmes finos de TiO2 com nanopartículas metálicas teve pouca influência na eficiência fotônica, exceto com nanopartículas de platina e ouro. A melhora da eficiência fotônica, nestes casos, pode ser atribuída a uma possível diminuição da velocidade de recombinação do par lacuna/elétron. Dessa forma, com o presente trabalho pôde-se comprovar a grande influência das condições de preparação do TiO2 nas propriedades ópticas, morfológicas e na eficiência fotônica. Futuramente, com o maior entendimento do mecanismo desta influência poder-se-ão delinear de forma mais precisas a morfologia e eficiência fotônica destes filmes finos de TiO2, conforme a aplicação a qual serão destinados. / Currently, nanoscience and nanotechnology are considered an emerging field and continuously breaking the barrier among various disciplines. The main focus of study involves controlling structures at molecular level, arranging the atoms in order to achieve an understanding and controlling the fundamental properties of matter. In this study, molecular changes on the basis of morphology, optical and crystalline properties of TiO2 thin films in order to increase their photon efficiency were proposed. The TiO2 thin films were prepared by solgel process evaluating the influence of different acids and templates to obtain the nanostructured arrangements. Then, metal nanoparticles like Au, Ag, Pd and Pt were incorporated on TiO2 thin films. This incorporation might minimize the electron-hole recombination, so it could improve the photon efficiency. From the several routes studied, the TiO2 thin films prepared with acetic acid showed the best performance by the reason of low agglomeration of TiO2 grains, which favors the exposure of the photoactive sites. The presence of template in the formulation had a slightly effect on photon efficiency, possible due to the higher agglomeration of the grains on the TiO2 thin films. The addition of Pt and Au nanoparticles on TiO2 thin films showed superior photon efficiency. The TiO2 thin films with hexamine and metallic nanoparticles did not show the improvement on photon efficiency except for Pt and Au nanoparticles. On these situations, the improvement on photon efficiency is might be due to a possible decrease at the electron-hole recombinations velocity. Thus, the present work demonstrates the great influence of preparation conditions on the optical, morphological properties and the photon efficiency. In the future, with greater understanding of the mechanism of this influence, the properties of TiO2 thin films will be able tailoring depending on the application.

Atualmente, a nanociência e nanotecnologia são consideradas como um campo emergente onde, continuamente, as barreiras entre as disciplinas são rompidas. Seu principal foco de estudo consiste em buscar o controle estrutural ao nível molecular, arranjando os átomos de modo a se conseguir um entendimento e controle das propriedades fundamentais da matéria. Neste estudo foram propostas modificações moleculares e, consequentemente, na morfologia, propriedades ópticas e cristalinas em filmes finos de TiO2 com o objetivo de aumentar sua eficiência fotônica. Os filmes finos de TiO2 foram preparados pelo processo sol-gel avaliando a influência de diferentes ácidos e agente direcionador para a obtenção dos arranjos nanoestruturados. A seguir, os filmes que apresentaram maior eficiência fotônica foram incorporados com nanopartículas metálicas (Au, Ag, Pd e Pt) com objetivo de minimizar os processos de recombinação eletrônica do par lacuna/elétron. Das diversas rotas estudadas, os filmes finos de TiO2 preparados com ácido acético obtiveram maior eficiência fotônica devido à pouca aglomeração dos grãos de titânia, o que pode ter favorecido uma maior exposição dos sítios fotocatalíticos. A presença do agente direcionador na formulação teve pouco efeito na eficiência fotônica, possivelmente devido à maior aglomeração dos grãos nos filmes finos de TiO2. Com a adição de nanopartículas metálicas, os filmes finos de TiO2 com nanopartículas de platina e ouro apresentaram maior eficiência fotônica. A presença de hexamina nos filmes finos de TiO2 com nanopartículas metálicas teve pouca influência na eficiência fotônica, exceto com nanopartículas de platina e ouro. A melhora da eficiência fotônica, nestes casos, pode ser atribuída a uma possível diminuição da velocidade de recombinação do par lacuna/elétron. Dessa forma, com o presente trabalho pôde-se comprovar a grande influência das condições de preparação do TiO2 nas propriedades ópticas, morfológicas e na eficiência fotônica. Futuramente, com o maior entendimento do mecanismo desta influência poder-se-ão delinear de forma mais precisas a morfologia e eficiência fotônica destes filmes finos de TiO2, conforme a aplicação a qual serão destinados. / Currently, nanoscience and nanotechnology are considered an emerging field and continuously breaking the barrier among various disciplines. The main focus of study involves controlling structures at molecular level, arranging the atoms in order to achieve an understanding and controlling the fundamental properties of matter. In this study, molecular changes on the basis of morphology, optical and crystalline properties of TiO2 thin films in order to increase their photon efficiency were proposed. The TiO2 thin films were prepared by solgel process evaluating the influence of different acids and templates to obtain the nanostructured arrangements. Then, metal nanoparticles like Au, Ag, Pd and Pt were incorporated on TiO2 thin films. This incorporation might minimize the electron-hole recombination, so it could improve the photon efficiency. From the several routes studied, the TiO2 thin films prepared with acetic acid showed the best performance by the reason of low agglomeration of TiO2 grains, which favors the exposure of the photoactive sites. The presence of template in the formulation had a slightly effect on photon efficiency, possible due to the higher agglomeration of the grains on the TiO2 thin films. The addition of Pt and Au nanoparticles on TiO2 thin films showed superior photon efficiency. The TiO2 thin films with hexamine and metallic nanoparticles did not show the improvement on photon efficiency except for Pt and Au nanoparticles. On these situations, the improvement on photon efficiency is might be due to a possible decrease at the electron-hole recombinations velocity. Thus, the present work demonstrates the great influence of preparation conditions on the optical, morphological properties and the photon efficiency. In the future, with greater understanding of the mechanism of this influence, the properties of TiO2 thin films will be able tailoring depending on the application.

For the selective separation of Noble Metals, different new chelating polymers with the same functional group, based on tri-isobutylphosphine sulphide, have been synthesised. Different spacers between the polymeric matrix and the functional group were introduced during the synthetic process, varying the length and number of heteroatoms (O, S) in the spacer molecule. These polymers show a good affinity towards gold and silver ions and a lower adsorption capacity towards palladium, and do not adsorb all other noble and base metals tested / Nuevos polímeros quelatantes con el mismo grupo funcional, basado en el sulfuro de tri-isobutilfosfina, han sido sintetizados para la separación selectiva de los Metales Nobles. Se han introducido diferentes espaciadores entre la matriz polimérica y los grupos funcionales, variando su longitud y el número de heteroátomos (O, S) presentes. Estos polímeros muestran una buena afinidad para los iones oro y plata, y una capacidad de adsorción inferior para los iones paladio, mientras que no adsorben al resto de Metales Nobles y metales base evaluados / Nous polímers quelatants amb el mateix grup funcional, basat en el sulfur de tri-isobutilfosfina, han estat sintetitzats per a la separació selectiva dels Metalls Nobles. S’han introduit diferents espaiadors entre la matriu polimèrica i els grups funcionals, variant la seva longitud i el nombre d’heteroàtoms (O, S) presents. Aquests polímers mostren una bona afinitat per als ions or i plata, i una capacitat d’adsorció inferior per als ions paladi, mentre que no adsorbeixen la resta de Metalls Nobles i metalls base avaluats

Dentre os principais avanços na área de ciência ou tecnologia dos materiais podemos ressaltar as atuais técnicas de produção, manipulação e análise de estruturas de tamanho muito reduzido, os quais possuem propriedades físicas (magnéticas, eletrônicas e óticas) diferentes das apresentadas pelos mesmos materiais em estruturas maiores. Nanopartículas (NPs) de metais nobres, principalmente ouro e prata, estão sendo utilizadas e incorporadas em diversas tecnologias que tiram proveito de suas características óticas ou condutivas Neste trabalho apresentamos uma metodologia de preparação de NPs de metais nobres, com a possibilidade de incorporá-las em um material dielétrico. As amostras, produzidas a partir da técnica de agregação gasosa, foram preparadas em um gerador de NPs, construído em um dos canhões de um sistema de magnetron sputtering comercial (AJA Internacional). No gerador, átomos são removidos do alvo e termalizados pelo fluxo do gás de trabalho, se condensando na forma de NPs. As NPs são extraídas do gerador aerodinamicamente e seguem em direção ao substrato. Utilizando um dos outros canhões do nosso sistema de sputtering podemos codepositar as NPs produzidas em uma matriz dielétrica ou metálica. Podemos também depositar camadas de filmes finos sobre o material produzido pelo gerador de NPs. As amostras de nanopartículas de ouro e prata produzidas foram caracterizadas a partir de técnicas de microscopia eletrônica de varredura (MEV), retroespalhamento Rutheford (RBS), espectrofotometria de UV-Visível e microscopia ótica em campo próximo (SNOM). A partir das imagens de MEV, podemos inferir a presença da matriz dielétrica a partir da separação das NPs e essa presença pode ser confirmada pela análise dos resultados de RBS. Por fim a análise do espectro de absorbância das amostras em conjunto com as imagens de SNOM demonstrou o comportamento plasmônico das amostras produzidas, sobretudo das NPs codepositadas em matriz dielétrica. / In the midst of main advances in material science and technology we can highlight the new techniques of preparation, manipulation and analyses of structures of very small size. They have physical properties (magnetic, electronic and optical) different from those presented by the same material, but in bigger dimension. Noble metal nanoparticles, mainly gold and silver, are incorporated into various technologies in order to take advantage of their optical or electric properties. In this work, we present a technique to produce noble metal nanoparticles by a physical method that also permits to imbed them in a dielectric material matrix. The samples, produced using the gas aggregation technique, were prepared in a nanoparticle gun, developed on one of the guns of a commercial magnetron sputtering system (AJA International). In the nanoparticles generator, atoms are removed from the target and thermalized by the flow of the sputtering working gas, and they are also condensed to form the nanoparticles. The nanoparticles are extracted from the generator aerodynamically and then they proceed to the substrate. Using another gun of the sputtering system we can deposit the nanoparticles produced in a dielectric or metallic matrix. We can also deposit under and capping layers of thin films on the nanoparticles layer produced. The samples of gold and silver nanoparticles produced were characterized by scanning electron microscopy (SEM), Rutherford backscattering analysis (RBS), UV-Visible spectrophotometry and near field optical microscopy (SNOM). In the SEM images, from the distribution and morphology of the nanoparticles it was possible infer the presence of the dielectric matrix, and this was also confirmed by the RBS measurements. Finally, absorbance spectrum of the samples together with the SNOM images have demonstrated the plasmonic character of the samples produced, specially for the NPs co-deposited in the dielectric matrix.

Les nanoparticules (NPs) métalliques ont fait l’objet d’un intérêt important ses dernières années dans des domaines variées tels que la santé, l’environnement ou l’électronique. Dans cette thèse, nous nous sommes particulièrement intéressés à l'application de NPs de métaux nobles mono ou bimétalliques dans le domaine de la plasmonique. Pour cela, nous avons synthétisé par voie organométallique des nanoparticules monométalliques d'or, d'argent et de cuivre d'une taille comprise entre 5 et 11 nm et caractérisées par une distribution en taille étroite. Après dépôt sur un substrat solide, elles s’organisent ainsi spontanément à 3D formant des supercristaux individuels. Nous avons étudié les propriétés optiques de ces supercristaux, en mesurant leurs spectres d'absorbances en fonction de leur épaisseur et de la nature des nanoparticules. Nous avons ensuite montré que ces supercristaux pouvaient être utilisés comme substrats SERS. La taille moyenne des nanoparticules étant beaucoup plus petites que celles reportées dans la littérature, ces substrats présentent un plus grand nombre de points chauds. On observe de plus un signal uniforme et reproductible d’un supercristal à l’autre. Les spectres Raman des ligands (alcanethiols ou alkylamines) ont été enregistrés et des facteurs d’exaltations entre 103 et 104 ont été calculés. Après vérification par electroreflectance de la stabilité des NPs sur une large gamme de potentiels, nous avons couplé le SERS à l'électrochimie en utilisant comme électrode une monocouche ordonnée de NPs d'or. Les taux de couvertures pour deux molécules différentes adsorbées sur les NPs ont été ainsi calculés. De plus nous avons pu suivre et confirmer la formation des espèces au cours des réactions d'oxydoréduction des molécules adsorbées en surface par SERS. Finalement nous avons synthétisé des NPs cœur-coquille Au@Ag, Ag@Au et d'alliage Cu-Au en utilisant comme germes les nanoparticules d’or, d’argent et de cuivre. Les structures et compositions chimiques de ces particules ont été étudiées. Leurs spectres optiques ont été mesurés par spectroscopie UV-Visible et simulés par calcul DDA (Discrete Dipole Approximation). Ils confirment la formation soient de structures cœur-coquille soient d’alliage. Par spectroscopie Raman basse fréquence, pour les NPs Au@Ag, nous montrons un couplage entre le cœur et la coquille en accord avec un modèle core shell développé dans la littérature. Pour les nanoparticules Cu-Au, le signal Raman basse fréquence est en accord avec la formation d’un alliage. / Metallic nanoparticles (NPs) have been subjected to a growing interest these last years in various domains such as healthcare, environment or electronics. In this thesis, we were particularly interested in the application of NPs mono or bimetallic made of noble metals in plasmonic domain. In this way, we synthesized by organometallic route, monometallic NPs of gold, silver and copper with a diameter ranging from 5 to 11 nm and characterized by a narrow polydispersity. After deposition on a solid substrate, they organized themselves spontaneously in 3D forming individual supercrystals. We studied the optical properties of these supercrystals, by measuring their absorbance spectra in function of their thicknesses and the nature of the NPs. Then, we showed that these supercrystals can be used as SERS substrates. The mean diameter of the NPs is way smaller than the ones reported in the literature. These substrates display a uniform and reproductible signal from a supercrystal to another. The Raman spectra of coating agent (alkanethiols or alkylamines) have been collected and enhancement factor ranging from 103 to 104 have been calculated. After verification by electroreflectance of NPs stability over a wide potential range, we coupled SERS with electrochemistry by using a monolayer of organized gold NPs as an electrode. Coverage rates for two different molecules adsorbed on the NPs have been calculated. Moreover, we could follow and confirm the species formation during the oxydoreduction reactions of the adsorbed molecules by SERS. Finally, we synthesized core-shell NPs Au@Ag, Ag@Au and alloy NPs Cu-Au by using gold, silver and copper NPs as seeds. Their structures and chemical compositions have been studied. Their optical spectra have been measured by UV-Visible spectroscopy and simulated by DDA (Discrete Dipole Approximation). They confirmed the core-shell and alloy structures. By low frequency Raman spectroscopy, for the Au@Ag NPs, we showed a coupling between the core and the shell in accordance with the core-shell model developed in the literature. For the Cu-Au NPs, low-frequency Raman signal is in agreement with the formation of an alloy.

Nanostructures have potential for use in state-of-the-art applications such as sensing, imaging, therapeutics, drug delivery, and electronics. The ability to fabricate and engineer these nanoscale materials is essential for the continued development of such devices. Because the morphological features of nanomaterials play a key role in determining chemical and physical properties, there is great interest in developing and improving methods capable of controlling their size, shape, and composition. While noble nanoparticles have opened the door to promising applications in fields such as imaging, cancer targeting, photothermal treatment, drug delivery, catalysis and sensing, the synthetic processes required to form these nanoparticles on surfaces are not well-developed. Herein is a detailed account on efforts for adapting established solution-based seed-mediated synthetic protocols to structure in a substrate-based platform. These syntheses start by (i) defining heteroepitaxially oriented nanostructured seeds at site-specific locations using lithographic or directed-assembly techniques, and then (ii) transforming the seeds using either a solution or vapor phase processing route to activate kinetically- or thermodynamically-driven growth modes, to arrive at nanocrystals with complex and useful geometries. The first series of investigations highlight synthesis-routes based on heterogeneous nucleation, where templates serve as nucleation sites for metal atoms arriving in the vapor phase. In the first research direction, the vapor-phase heterogeneous nucleation of Ag on Au was carried out at high temperatures, where the Ag vapor was sourced from a sublimating foil onto adjacent Au templates. This process transformed both the composition and morphology of the initial Au Wulff-shaped nanocrystals to a homogeneous AuAg nanoprism. In the second case, the vapor-phase heterogeneous nucleation of Cu atoms on Au nanocrystal templates was investigated by placing a Cu foil next to Au templates and heating, which caused the Cu atoms from the foil to sublimate from the foil and heterogeneously nucleation on the surface of the immobilized Au seeds. This process caused the composition and morphology of the Au Wulff-shape to transform into a homogeneous AuCu nanotriangle. Lastly, we characterized the morphological features and composition, optical properties, and also the catalytic and photocatalytic performance toward hydrogenation of 4-nitrophenolate. The second series of investigations highlight synthetic routes utilizing competencies of substrate-based techniques with colloidal chemistry. We have demonstrated two substrate-based syntheses yielding bimetallic nanostructures where shape control was achieved through (i) facet-selective capping agents and (ii) additive and subtractive process. In the first case a citrate-based cubic structure has been synthesized in the presence or absence of ascorbic acid and the role of each has been considered in shape control. Reactions were carried out in which Ag+ ions were reduced onto substrate-immobilized Ag, Au, Pd, and Pt seeds. It was discovered that for syntheses lacking ascorbic acid, citrate acts as both the capping and the reducing agent, resulting in a robust nanocube growth mode; however, when ascorbic acid was included in these syntheses, then the growth mode reverted to one that advances the octahedral geometry. The conclusion of these results was that citrate, or one of its oxidation products, selectively caps (100) facets, but where this capability was compromised by ascorbic acid. In the second case, galvanic replacement reactions have been carried out on immobilized cubic and Wulff structures to create the substrate-based nanoshells and nanocages, where the prepositioned templates were chemically transformed into hollow structures. In this novel research, Wulff-shaped templates of Au, Pt, or Pd, formed through the dewetting of ultrathin films, were first transformed into core−shell structures through the reduction of Ag+ ions onto their surface and then further transformed through the galvanic replacement of Ag with Au. Detailed studies were provided highlighting discoveries related to (i) alloying, (ii) dealloying, (iii) hollowing, (iv) crystal structure and (vi) the localized surface plasmon resonance (LSPR). Overall, a series of synthetic strategies based on physical and chemical vapor deposition were devised and validated to achieve novel substrate- based nanomaterials with different shapes and compositions for a variety of applications such as sensing, plasmonics, catalysis, and photocatalysis. The novel research in this dissertation also takes advantage of competencies of substrate-based techniques with colloidal chemistry and, brings this rich and exciting chemistry and its associated functionalities to the substrate surface. / Mechanical Engineering

A síntese de Fischer-Tropsch é um processo de conversão do gás de síntese (CO + H2) em hidrocarbonetos de cadeias longas. Os catalisadores clássicos para a hidrogenação do CO são, principalmente, o Fe e o Co suportados em diferentes óxidos. O desempenho catalítico do catalisador é influenciado pelo tamanho, dispersão e grau de redução das partículas metálicas. Estudos recentes mostram uma promissora aplicação de materiais à base de nanofibras de carbono na catálise heterogênea. Estes materiais apresentam algumas vantagens em relação aos suportes catalíticos tradicionais, tais como: uma baixa interação metal-suporte, elevada área superficial, ausência de poros fechados, alta condutividade térmica, elevada inércia química e hidrofobicidade. Neste trabalho foram fabricados suportes catalíticos macroscópicos à base de nanofibras de carbono, empregando o método de vapor deposição, a partir da decomposição do etano. Os catalisadores foram preparados pela impregnação incipiente do Co e de promotores na superfície do suporte. Foram empregados os metais nobres, Ir, Pt e Ru, como promotores catalíticos, com o objetivo de incrementar a redutibilidade e a atividade do catalisador. Todos os catalisadores foram caracterizados por Quimissorção de CO, Fisissorção de N2, Redução a Temperatura Programada (TPR), Espectroscopia Fotoeletrônica de Raios X (XPS) e Microscopia Eletrônica de Transmissão (MET). Os catalisadores foram, então, testados na síntese de Fischer-Tropsch, utilizando um reator de leito fixo e fluxo contínuo, com análise simultânea dos produtos gasosos e controle sistemático da temperatura, pressão e vazão dos reagentes. Finalmente, foram analisados os produtos líquidos obtidos na reação com objetivo de conhecer a influência dos promotores na seletividade dos hidrocarbonetos formados. / Fischer-Tropsch synthesis is a process of converting the syngas (CO + H2) to long-chain hydrocarbons. The traditional catalysts for the CO hydrogenation are Fe and Co supported on different oxides. Catalytic performance of the catalyst is influenced by size, dispersion and degree of reduction of metal particles. Recent studies show a promising application of materials based on carbon nanofibers in heterogeneous catalysis. These materials have some advantages compared to traditional catalyst supports, such as a low metal support interaction, high surface area, no closed pores, high thermal conductivity, high chemical resistance, and hydrophobicity. In this work, based on macroscopic carbon nanofiber catalyst supports have been manufactured by employing the method of chemical vapor deposition from ethane decomposition. Catalysts were prepared by incipient wetness impregnation of Co and promoters on the support surface. Noble metals, Ir, Pt and Ru were used as catalytic promoters, with the aim of increasing the reductibility and catalyst activity. All catalysts were characterized by CO Chemisorption, N2 Physisorption, Temperature Programmed Reduction (TPR), X-ray Photoelectron Spectroscopy (XPS), and Transmission Electron Microscopy (TEM). The catalysts were then tested in the Fischer-Tropsch synthesis using a fixed bed reactor, continuous flow, with simultaneous analysis of gaseous products and systematic temperature control, pressure, and flow rate of the reactants. Finally, the liquid products obtained in the reaction were analyzed in order to determine the influence of promoters on the selectivity of hydrocarbons formed.

Pollution from automobile exhaust is one of the most major environmental problems because of increasing usage of engine technologies. Diesel and lean burn gasoline engines operate under oxygen rich (lean) conditions and they emit harmfull gases to the atmosphere (CO,CO2, NO, NO2). The control of NOx emission from exhaust has become a challenging issue in engine industry because of the worldwide environmental regulations. Therefore lean-burn NOx emission control technologies have been developed to reduce emission of harmfull gases from exhausts, and the NOx storage/reduction (NSR) catalysts is one of the most promising candidates to reduce the pollution caused by lean-burn engines. In NSR systems, NO from the emission is first oxidized to NO2 over noble metal sites (Pt, Rh, Pd) during lean-burn engine operation. After that NO2 is stored as nitrites and nitrates in alkali earth oxides (BaO,MgO, CaO) particles or monolayer which is well dispersed on a substrate (Gamma-Al2O3, TiO2, SiO2). Finally, stored NOx compound are broken into N2 and O2 on noble metal sites. The Pt/BaO/Gamma-Al2O3 system is one of the most popular subjects in literature both experimentally and theoretically since this system is known to be catalytically more active and ecient in interactions between NOx and Pt-BaO components are still not clearly explained. For this reason, in this thesis, the interaction between catalytic redox components, Pt and Rh, and the support material Gamma-Al2O3 and the eects of Pt and Rh in atomic and diatomic clusters forms on the adsorption of the NO2 molecule on the Gamma-Al2O3(100) surface have been investigated by using density functional theory (DFT).

A síntese de Fischer-Tropsch é um processo de conversão do gás de síntese (CO + H2) em hidrocarbonetos de cadeias longas. Os catalisadores clássicos para a hidrogenação do CO são, principalmente, o Fe e o Co suportados em diferentes óxidos. O desempenho catalítico do catalisador é influenciado pelo tamanho, dispersão e grau de redução das partículas metálicas. Estudos recentes mostram uma promissora aplicação de materiais à base de nanofibras de carbono na catálise heterogênea. Estes materiais apresentam algumas vantagens em relação aos suportes catalíticos tradicionais, tais como: uma baixa interação metal-suporte, elevada área superficial, ausência de poros fechados, alta condutividade térmica, elevada inércia química e hidrofobicidade. Neste trabalho foram fabricados suportes catalíticos macroscópicos à base de nanofibras de carbono, empregando o método de vapor deposição, a partir da decomposição do etano. Os catalisadores foram preparados pela impregnação incipiente do Co e de promotores na superfície do suporte. Foram empregados os metais nobres, Ir, Pt e Ru, como promotores catalíticos, com o objetivo de incrementar a redutibilidade e a atividade do catalisador. Todos os catalisadores foram caracterizados por Quimissorção de CO, Fisissorção de N2, Redução a Temperatura Programada (TPR), Espectroscopia Fotoeletrônica de Raios X (XPS) e Microscopia Eletrônica de Transmissão (MET). Os catalisadores foram, então, testados na síntese de Fischer-Tropsch, utilizando um reator de leito fixo e fluxo contínuo, com análise simultânea dos produtos gasosos e controle sistemático da temperatura, pressão e vazão dos reagentes. Finalmente, foram analisados os produtos líquidos obtidos na reação com objetivo de conhecer a influência dos promotores na seletividade dos hidrocarbonetos formados. / Fischer-Tropsch synthesis is a process of converting the syngas (CO + H2) to long-chain hydrocarbons. The traditional catalysts for the CO hydrogenation are Fe and Co supported on different oxides. Catalytic performance of the catalyst is influenced by size, dispersion and degree of reduction of metal particles. Recent studies show a promising application of materials based on carbon nanofibers in heterogeneous catalysis. These materials have some advantages compared to traditional catalyst supports, such as a low metal support interaction, high surface area, no closed pores, high thermal conductivity, high chemical resistance, and hydrophobicity. In this work, based on macroscopic carbon nanofiber catalyst supports have been manufactured by employing the method of chemical vapor deposition from ethane decomposition. Catalysts were prepared by incipient wetness impregnation of Co and promoters on the support surface. Noble metals, Ir, Pt and Ru were used as catalytic promoters, with the aim of increasing the reductibility and catalyst activity. All catalysts were characterized by CO Chemisorption, N2 Physisorption, Temperature Programmed Reduction (TPR), X-ray Photoelectron Spectroscopy (XPS), and Transmission Electron Microscopy (TEM). The catalysts were then tested in the Fischer-Tropsch synthesis using a fixed bed reactor, continuous flow, with simultaneous analysis of gaseous products and systematic temperature control, pressure, and flow rate of the reactants. Finally, the liquid products obtained in the reaction were analyzed in order to determine the influence of promoters on the selectivity of hydrocarbons formed.