Des revêtements céramiques sont obtenus par un procédé de dépôt chimique en phase vapeur assisté par injection liquide pulsée (DLICVD) de précurseurs organométalliques. Des dépôts de carbure de chrome (CrCx) sont élaborés dans un réacteur tubulaire à paroi chaude à partir d’une solution de bis(benzène) chrome dans du toluène pour des températures de 475 °C et sous pression partielle d’azote (pression totale 50 Torr). Une couche d’accroche pouvant être nécessaire pour revêtir des pièces métalliques, tels des aciers et alliages, par un revêtement céramique non-oxyde de type CrCx, des couches de chrome métallique (Cr) et des carbures mixtes Cr-Si-C ont également été élaborées par ce procédé DLICVD. Ainsi, l’ajout d’un additif à base de chlore ou de soufre (par exemple l’hexachlorobenzène ou le thiophénol) dans la solution BBC/toluène permet la déposition de films de chrome métallique (Cr) à 475 °C. De plus, l’utilisation d’une solution de précurseur contenant simultanément du Si et du Cr tel que le tetrakis(trimethylsilylmethyl)chromium dans du toluène mène au dépôt d’un carbure mixte Cr-Si-C pouvant jouer le rôle d’interphase dans des assemblage céramique-métal. Des films de carbure de silicium (SiC) sont obtenus à partir de deux précurseurs (1,3 disilabutane et polysilyléthylène) injectés purs ou en solution également dans du toluène. Les dépôts sont faits dans une gamme de température comprise entre 700 et 800 °C, sous pression partielle d’azote (pression totale 50 Torr). Les films obtenus sont des films amorphes de SiC contenant une faible quantité d’hydrogène (provenant du mécanisme de décomposition des précurseurs) : a-SiC:H. Les films sont stœchiométriques dans le cas de l’injection de précurseur pur, et quasi stœchiométrique lorsque les précurseurs sont dilués dans du toluène. Les films amorphes tels que déposés deviennent nanocristallins en présentant la structure cubique du SiC après recuit sous vide à 1000 °C. L’influence du solvant (toluène) sur la composition, la morphologie et la vitesse de croissance des dépôts est discutée en fonction des systèmes chimiques étudiés et des conditions expérimentales, en particulier les conditions locales dans le réacteur DLICVD telles que les gradients de température et de concentration. Des films de carbure de hafnium (HfC) sont également élaborés par le même procédé à partir d’une solution de bis(cyclopentadiényl)diméthyl hafnium dans du toluène après avoir testé plusieurs précurseurs. Une température de 750 °C est utilisée et l’utilité d’une pression partielle de dihydrogène dans le gaz vecteur azote est démontrée (pression totale 50 Torr, 423 sccm de N2 et 77 sccm de H2). Tels que déposés, ces films sont riches en carbone (C-rich HfCx) et ont une structure quasi-amorphe. Ils deviennent nanocristallins après recuit sous vide à 1000 °C. Enfin, la mise en œuvre de films multicouches céramiques par DLICVD à paroi chaude est mise en évidence par l’élaboration de revêtements multicouches HfC/SiC à 750 °C, sous pression partielle d’un mélange de gaz vecteur N2/H2. Le contrôle du procédé permet une nano structuration de ces revêtements multicouches jusqu’à une bi-période de 100 nm (empilement de 100 couches d’environ 50 nm chacune). La stabilité thermique de ces architectures et des tests préliminaires de résistance à l’oxydation à haute température des films de SiC et HfC/SiC sont discutés. / Ceramic coatings are made from metalorganic precursors by a chemical vapour deposition process assisted by pulsed liquid injection (DLICVD). Chromium carbide (CrCx) films are grown in a tubular hot wall reactor from a solution of bis(benzene)chromium in toluene under partial pressure of nitrogen at 475 °C (total pressure set at 50 Torr). Bonding layers are useful on metallic components, such as steels and alloys, with non-oxide ceramic films such as CrCx, to that purpose metallic chromium (Cr) and mixed carbides Cr-Si-C have been made by DLICVD. Furthermore, adding a chlorinated or sulfur based additive (e.g. hexachlorobenzene or thiophenol) in the BBC/toluene solution allows depositing metallic chromium (Cr) at 475 °C. Moreover, using a precursor containing Si and Cr as tetrakis(trimethylsilylmethyl)-chromium in toluene leads to the deposition of Cr-Si-C mixed carbide. Silicon carbide films are made from two precursors (1,3-disilabutane and polysilylethylene) that have been injected either pure or diluted in toluene. A temperature range of 700 to 800 °C has been used under a partial pressure of nitrogen (total pressure of 50 Torr). SiC films are amorphous and contain a small quantity of hydrogen (hydrogen comes from precursor pyrolysis mechanism): a-SiC:H. Films are stoichiometric when pure precursors are injected, and quasi stoichiometric when precursors are diluted in toluene. As deposited coatings are amorphous and become nanocristalline (cubic SiC structure) after annealing at 1000 °C under vacuum. The influences of the solvent (toluene) on the composition, morphology and growth rate are discussed as a function of the chemical system and experimental conditions, in particular reactor gradient conditions such as temperature and precursors concentration in gas phase. Hafnium carbide films are also made using a solution of bis(cyclopentadiényl)diméthyl hafnium in toluene by the same process. Temperature is set to 750 °C and hydrogen partial pressure has been shown useful (total pressure of 50 Torr, 423 sccm of N2 and 77 sccm of H2). As-deposited films are C-rich HfCx and quasi amorphous. They become nanocristalline after annealing at 1000 °C under vacuum. Finally, ceramics multilayer HfC/SiC coatings were deposited by DLICVD at 750 °C under a partial pressure of a mixture of N2/H2. The process allows a good control of the multilayer nanostructure. Thermal stability and high temperature oxidation preliminary tests on SiC and HfC/SiC films are discussed.

Master of Science / Department of Civil Engineering / Robert J. Peterman / Epoxy polymer overlays have been used for decades on existing bridge decks to protect the deck and extend its service life. The polymer overlay’s ability to seal a bridge deck is now being specified for new construction. Questions exist about the amount of drying time needed to achieve an acceptable concrete moisture content to ensure an adequate bond to the polymer overlay. Current Kansas Department of Transportation (KDOT) specifications for new bridge decks call a 14 day wet curing period followed by 21 days of drying (Kansas DOT, 2007) If not enough drying is provided, the moisture within the concrete can form water vapor pressure at the overlay interface and induce delamination. If too much drying time is provided projects are delayed, which can increase the total project cost or even delay overlay placement until the next spring. A testing procedure was developed to simulate a bridge deck in order to test the concrete moisture content and bonding strength of the overlay. Concrete slabs were cast to test typical concrete and curing conditions for a new bridge deck. Three concrete mixtures were tested to see what effect the water –cement ratio and the addition of fly ash might have on the overlay bond strength. Wet curing occurred at 3 different temperatures (40°F, 73°F, and 100°F) to see if temperature played a part in the bond strength as well. The concrete was then allowed to dry for 3, 7, 14, or 21 days. Five epoxy-polymer overlay systems that had been preapproved by KDOT were each used in conjunction with the previously mentioned concrete and curing conditions. After, the slabs were setup to perform pull-off tests to test the tensile rupture strength. The concrete slabs with the different epoxy overlays were heated to 122-125°F to replicate summer bridge deck temperatures. Half of the pull-off tests were performed when the slabs were heated and half were performed once the slabs had cooled back down to 73°±5°F. Results from the pull-off tests as well as results from a moisture meter taken on the concrete prior to the overlay placement were compared and analyzed. Testing conditions were compared with each other to see which had a larger effect on the epoxy polymer overlay’s bond strength.

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Douglas McGregor / The effect of polyethylene addition on the growth of mercuric iodide (HgI[supscript]2) tetragonal prismatic crystals is examined. Three types of polyethylene powder are utilized: low molecular weight (¯Mw ~ 4 x 103), ultra high molecular weight (¯Mw ~ 3 x 6 106), and spectrophotometric grade polyethylenes. Among these types of polyethylene, the low molecular weight polyethylene produces the most significant change in HgI[supscript]2 morphology, with {110} being the most prominent crystal faces. Thermal desorption - gas chromatography/mass spectroscopy (TD-GC/MS) studies show that thermal desorption of the low molecular weight polyethylene at 100°C and 150°C produce isomers of alkynes, odd nalkanes, and methyl (even-n) alkyl ketones. HgI[supscript]2 growth runs with n-alkanes, with either neicosane, n-tetracosane, or n-hexatriacontane, cannot replicate the crystal shapes produced during growth with the low molecular weight polyethylene, whereas HgI[supscript]2 growth runs with ketones, with either 3-hexadecanone or 14-heptacosanone, produce HgI[supscript]2 tetragonal prismatic crystals, similar to the crystals grown with the low molecular weight polyethylene. C-O double bond contained in any ketone is a polar bond and this polar bond may be attracted to the mercury atoms on the top-most layer of the {110} faces through dipoledipole interaction. As a result, the growth of the {110} faces is impeded, with the crystals elongated in the [001] direction and bounded by the {001} faces along with large, prismatic {110} faces.

<p>Large scale and cost-efficient synthesis of carbon nanostructured materials has garnered tremendous interest over the last decade owing to their plethora of engineering and bio-science applications. One promising method is roll-to-roll radio frequency chemical vapor deposition and this work presents a computational investigation of the capacitively coupled radio frequency plasma in such a system. The system operates at moderate pressures (less than 30 mbar) with an 80 kHz square wave voltage input. The computational model aids the understanding of plasma properties and α-γ transition parameters which strongly influence the nanostructure deposition characteristics in the system. One dimensional argon and hydrogen plasma models are developed to characterize the effects of input voltage, gas pressure, frequency, and waveform on the plasma properties. A hybrid mode which displays the characteristics of both α and γ discharges is found to exist for the low cycle frequency 80 kHz square wave voltage input due to the high frequency harmonics associated with a square waveform. The threshold voltage at which the transition between the different regimes occurs is higher for hydrogen than for argon owing to its diatomic nature. Collision radiative modeling is performed to predict the argon emission intensity in the discharge gap. The results are found to lie within 16% of the optical emission spectroscopy measurements with better agreement at the center of the discharge, where the measurement uncertainty is low and the emission by ions is not significant. A quasi-zero dimensional steady state chemistry model which uses the hydrogen plasma properties as inputs predicts high concentrations of C₂H, C₂H₂, C₂H₃⁺, C₂H₄⁺and C₂H₆⁺during carbon nanostructure deposition.</p> <p> </p> <p>Carbon nanostructures are popularly used as field emitters. Field emission based microplasma actuators generate highly non-neutral surface discharges that can be used to heat, pump, and mix the flow through microchannels and offer an innovative solution to the problems associated with microcombustion. They provide a constant source of heat to counter the large heat loss through the combustor surface, they aid in flow transport at low Reynolds numbers without the use of moving parts, and they provide a constant supply of radicals to promote chain branching reactions. This work presents two actuator concepts for the generation of field emission microplasma, one with offset electrodes and the other with planar electrodes. They operate at input voltages in the 275 to 325 V range at a frequency of 1 GHz which is found to be the most suitable value for flow enhancement. The momentum and energy imparted by the charged particles to the neutrals as modeled by 2D Particle-In-Cell with Monte Carlo Collisions (PIC/MCC) are applied to actuate flow in microchannels using 2D Computational Fluid Dynamics modeling. The planar electrode configuration is found to be more suitable for the purpose of heating, igniting and mixing the flow, as well as improving its residence time through a 10 mm long microcombustor. The combustion of hydrogen and air with the help of 4 such actuators, each with a power consumption of 47.5 mW/cm, generates power with an efficiency of 28.8%. Coating the electrode surface with carbon nanostructures improves the combustion efficiency by a factor of 2.5 and reduces the input voltage by a factor of 6.5. Such microcombustors can be applied to all battery based systems requiring micropower generation with the ultimate goal of “generating power on a chip'”.</p>

Dans un contexte général de réduction de la pollution atmosphérique, l’industrie automobile cherche à augmenter le rendement des moteurs thermiques pour en limiter la consommation et les émissions. Pour satisfaire cet objectif, les températures de combustion sont en constante augmentation, ce qui entraîne une augmentation de la sollicitation thermique de la face d’échappement de ces moteurs. Ces pièces n’étant pas refroidies, elles sont exposées à des températures toujours plus élevées, ce qui nécessite une durabilité à haute température accrue des matériaux. Cette thèse a pour objectif d’évaluer la durabilité des pièces de fonderie de la face échappement telles que les collecteurs, corps de turbine ou turbo collecteurs réalisées en fonte GSSiMo+ et en acier inoxydable moulé 1.4826Nb à des températures supérieures à leur température maximale actuelle d’utilisation. Une première étape a porté sur l’effet de la vapeur d’eau sur l’oxydation de la surface pendant des traitements thermiques continus et cycliques et sur l’évolution associée de la microstructure. La seconde étape a porté sur l’effet de ces traitements thermiques sur les propriétés mécaniques à température ambiante. Enfin, un montage de fatigue thermomécanique par dilatation différentielle entre un support en carbure de silicium et une éprouvette métallique en V a été conçu pour être utilisé sur un banc d’oxydation cyclique sous atmosphère contrôlée afin d’étudier les mécanismes de fissuration et d’endommagement en fatigue thermomécanique ainsi que l’effet de l’environnement sur l’initiation de fissures dans ces conditions. L’augmentation de la température maximale des cycles thermiques appliqués de 700 à 800°C pour la fonte GS SiMo+ et de 850 à 950°C pour l’acier 1.4826Nb a pour principale conséquence une accélération de la perte de section par oxydation et une diminution des propriétés mécaniques du fait de l’évolution de la microstructure. Cette perte de section paroxydation est fortement accélérée en présence de vapeur d’eau. Les essais préliminaires réalisés avec le montage de fatigue thermomécanique ont permis de valider son dimensionnement et de mettre en avant les cycles thermomécaniques pour lesquels l’initiation et la propagation de fissures étaient les plus rapides sur des cycles 300-800°C pour la fonte et 300-950°C pour l’acier.Une plus ample campagne d’essai reste à réaliser pour évaluer les mécanismes de fissuration et l’effet de l’environnement en fonction de la température maximale / Due to tightening environmental standards, the automotive industry is constantly trying to improvethe efficiency of the internal combustion engines in order to increase their fuel economy andreduce their carbon emissions. The main way to meet this goal on a turbocharged engine is toincrease the combustion temperature. This leads to increasing exhaust gas temperature andincreasing thermal loads on exhaust manifolds and turbine housings. These components beinguncooled, their maximum temperature is increasing and require better durability at hightemperature. The main objective of this thesis is to evaluate the durability of SiMo spheroidalgraphite iron (SGI) and 1.4826Nb cast stainless steel (CSS) at higher temperature than the actualmaximum operating temperature in order to evaluate their use on engines with higher power. Thefirst part of the study focuses on the effect of water vapor on high temperature oxidation duringcontinuous and cyclic heat treatments and on the underlying microstructure evolution. The secondpart focuses on the effect of these heat treatments on the tensile properties at room temperature.At last, a thermomechanical fatigue test setup has been designed to study the effect ofenvironment on crack initiation during thermomechanical fatigue (TMF). This setup uses thedifference in thermal expansion between silicon carbide and metallic materials to generatemechanical strain and stress in a V-shaped specimen during thermal cycling in a controlledatmosphere cyclic oxidation test bench. Increasing maximum temperature during thermal cyclingfrom 700 to 800°C for SiMo SGI and from 850 to 950°C for 1.4826Nb CSS leads to acceleratedwall thickness loss due to increased oxidation and to a drop in mechanical properties duemicrostructure evolution. The wall thickness loss is further accelerated in humid atmosphere.Preliminary tests performed with the TMF setup demonstrated the design is valid and enabled toidentify the thermomechanical loads leading to faster crack initiation and propagation for 300-800°C thermal cycling of SiMo SGI and 300-950°C thermal cycling of 1.4826Nb CSS. More testsare necessary to identify the crack initiation mechanisms according to the maximum temperatureof the thermal cycle and the atmosphere

School of Chemical and Metallurgical Engineering, Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, South Africa 26 February 2016 / Many reports in the open literature have focused on Fischer-Tropsch (FT) kinetics, yet none of them appear to be able to explain FTS completely. Few of the FT models consider the production of olefins and paraffins separately. To study whether the selectivity to olefins and paraffins follows similar trends and if kinetics alone suffices to explain FT phenomena, a series of FT experiments were conducted in a fixed bed reactor loaded with 10% Co/TiO2. FT feeds were periodically switched from syngas to syngas + N2 by adjusting the total reactor pressure so that the reactant partial pressures (PCO and PH2) remained constant. During the initial deactivation (the first 1200 hours), it was found that the formation rates of olefins remained fairly constant (in some cases they increased) while those of paraffins decreased. This indicates the deactivation is mainly caused by the decrease in the paraffin formation rate. Currently, none of the published kinetic models can explain the phenomenon that the decay of the reaction rates of olefins and paraffins were not the same during the deactivation. At steady state (1055 to 2700 hours, overall reaction rate fairly constant), adding extra N2 decreased the selectivity to the light hydrocarbons. These results suggest that by feeding the extra N2 there could be an increase in selectivity and formation rates to long chain hydrocarbons (C5+). Plotting molar ratios of paraffin to olefin (P/O) with carbon number n+1 versus the ratio with carbon number n revealed linear relationships which are independent of feed gases, catalyst activity and reaction temperature. These results imply that product distributions might be determined by some sort of equilibrium. Another plot of normalised mole fractions of CnH2n, Cn+1H2n+2, and CnH2n+2 in ternary diagrams showed that after disturbances these product distributions tended to stable points. It is suggested that this could be due to slow changes in the liquid composition after the disturbances. Although not all the results are explained, the researcher emphasises that normal kinetics alone cannot explain these results completely. There might be factors, iii including vapour-liquid equilibrium or reactive distillation, which are worthy of consideration to explain FTS. / MT2016

Orientador: Steven Frederick Durant / Banca: Antonio Riul Júnior / Banca: Rogério Valentim Gelamo / Resumo: Neste trabalho, filmes finos amorfos de carbono hidrogenado também contendo bromo foram produzidos por duas técnicas: Deposição e Implantação iônica por Imersão em Plasma (DIII). As deposições foram feitas em plasmas alimentados com diferentes proporções de bromofórmico (CHBr3) e acetileno (C2H2), variando também o tempo de deposição, a potência de radiofrequencia aplicada e a pressão dentro do reator. Para medição de espessura e rugosidade, e molhabilidade, filmes depositados em substratos de vidro foram analisados por perfilometria e geniometria (medidas de ângulo de contato), respectivamente. A estrutura e composição química dos filmes foram examinadas por Espectroscopia de Reflexão-Absorção no Infravermelho (IRRAS) e Espectroscopia de Raios X (XPS) em amostras depositadas em aço inoxidável polido. Para obter espectros de trasmitância no Ultravioleta-visível e infravermelho-próximo, filmes foram depositados em substratos de quartzo. A partir destes espectros e das espessuras dos filmes, propriedades ópticas como o índice de refração, coeficiente de absorção e gap óptico dos materiais foram calculados. Taxas de deposição dos filmes contendo bromo foram tipicamente no itervalo de 33 a 108 nm.min-1 pelo processo de PECVD, e de 13 a 56 nm.min-1 pelo processo de DIIIP. Rugosidades entre 24 e 37 nm foram observadas em ambos os métodos. As medidas de ângulo de contato revelaram que os filmes bromados são hidrofólicos. Espectros IRRAS revelaram a presença de grupos contendo bromo em 1430-1410 com-1 devido à deformação angular de grupos CH2-Br e CH3-BR, e em 1210 cm-1 também referente à deformação angular de CH2-Br nos filmes produzidos com bromofórmio na alimentação do reator. As análises de XPS comprovaram a incorporação de bromo nos filmes em até... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In this work, amorphous hydrogenated carbon this films also containing were produced by two techiniques: Plasma Enhanceb Chemical Vapor Deposition (PECVD) and Plasma Immersion Ion Implantation and Deposition(PIIID). Deposition were realized in plasmas fed with different proportions of bromoform (CHBr3) and acetylene (C2H2), the parameters deposition time, applied radio frequency power, and reactor pressure were also varied. The film thickness and thickness and roughness, and wettability were measured, for films deposited onto glass substrates using perfilometry and goniometry (contact-angle measurements), respectvely. infrared Reflections-Absorption Spectroscopy (IRRAS) and X-Ray Photoelectron Spectroscopy (XPS) were employed to study the chemical structure and composition of films deposited onto polished stainless-steel substrates. Transmission ultraviolet-visible-near infrared spectroscopy (UVS) was used to characterized films deposited onto quartz substrates. From the UVS spectra and film thicknesses, optical properties such as refractive index, absorption coefficient and optical gap were calculated. Bromine-containing film deposition rates ranged from 33 to nm.min-1 for PECVD, and from 13 to nm.min-1 for PIIID. Roughnesses of between 24 e 37 nm were observed for both techniques. Contact angle measurement revealed that brominated films are hydrofobic. Characteritic absorptions owing to the presence in the films of bromine-containing groups at 1430-1410 cm-1 due to asymmetric bending of CH2-Br e CH3-Br groups, and at 1210 cm-1 also due to asymmetric bending of CH2-Br were observed in IRRAS spectra of the brominated films. As confirmed by XPS analyses, bromine was incorporated at up to 43% at in films deposited in CHBr3 plasmas. The refractive index decreased from 2.38 for plasma-polymerized C2H2 film... (Complete abstract click electronic access below) / Mestre

Os tubos de Geradores de Vapor em Reatores Nucleares do tipo PWR são submetidos a diferentes níveis de tensões e carregamento em altas temperaturas, reduzindo sua vida útil devido o surgimento de defeitos e corrosão. A inspeção por Correntes Parasitas é um ensaio não destrutivo usado para diagnosticar defeitos de corrosão e descontinuidades na superfície externa e interna em tubos de trocadores de calor. Esses tubos estão sujeitos a danos por diferentes mecanismos de degradação mecânica e química, tais como trincas por fadiga e corrosão sob tensão. Os sinais de inspeção por Correntes Parasitas são afetados por diferentes ruídos dificultando sua análise pelo inspetor. Esse trabalho apresenta os resultados da análise dos sinais de Correntes Parasitas usando a Transformada de Hilbert-Huang (THH) funcionando como filtro de ruídos (De-noising), como uma técnica alternativa de processamento e análise de sinais. A Transformada de Hilbert-Huang teve esse nome atribuído pela agência espacial norte-americana (NASA) para o resultado da reunião de dois processos, um método de decomposição empiricamente modal (Empirical Mode Decomposition EMD), seguido da análise espectral de Hilbert (Hilbert Spectral Analysis HSA). Os sinais de inspeção por correntes parasitas possuem características de transiente, não estacionário e não linear. A transformada de Hilbert-Huang aplicada neste trabalho forneceu dois recursos alternativos em processamento de sinais; o pré-processamento que funcionou como filtro de ruídos, e outro de análise de sinais, responsável pela identificação das características tempo-frequência-energia do sinal. / The nuclear power plant steam generator tubes are subjected to different levels of stress and loading at high temperatures, reducing its lifetime due to the development of defects and corrosion. The Eddy Current Testing (ECT) is a nondestructive testing used to diagnose defects of corrosion and discontinuities in the inner and outer surface of heat exchanger tubes. These tubes are subject to failure by different mechanisms of chemical and mechanical degradation such as fatigue and stress corrosion crack. The ECT signals are affected by different noises making the analysis a difficult task to the inspector. This dissertation presents the results of the main characteristics from the ECT signals using the Hilbert-Huang Transform (HHT) as an alternative method for the processing and signal analysis. The Hilbert-Huang Transform has its name given by the American National Aeronautics and Space Administration, NASA, as the result of Empirical Mode Decomposition (EMD) and the Hilbert Spectral Analysis (HSA) methods. The Eddy Current signals are transient, nonstationary and nonlinear. The Hilbert-Huang Transform applied in this work provided two alternative proceedings in signal processing, one in signal pre-processing acting as noise filter (De-noising) and another as signal analysis, which identifies the characteristics of signal time-frequency-energy.

Catalisadores de Ni (10% em massa) suportado em matrizes mistas MgO-SiO2 foram aplicados na rea&ccedil;&atilde;o de reforma a vapor de glicerol. Os efeitos do teor de MgO como aditivo e do m&eacute;todo de prepara&ccedil;&atilde;o foram avaliados frente &agrave;s propriedades f&iacute;sico-qu&iacute;micas e texturais dos materiais; assim como &agrave; atividade, seletividade, estabilidade e forma&ccedil;&atilde;o de carbono na reforma a vapor do glicerol. Os catalisadores foram preparados com diferentes teores m&aacute;ssicos de MgO (10%, 30% e 50%) sobre SiO2 comercial, utilizando processo via seca (mistura f&iacute;sica) e via &uacute;mida (impregna&ccedil;&atilde;o sequencial com diferentes solventes: &aacute;gua, etanol e acetona). Foram utilizadas as t&eacute;cnicas de caracteriza&ccedil;&atilde;o de espectroscopia de energia dispersiva de raios X, fisissor&ccedil;&atilde;o de nitrog&ecirc;nio, difratometria de raios X, termogravimetria, difratometria de raios X in situ com O2, redu&ccedil;&atilde;o a temperatura programada com H2, difratometria de raios X in situ com H2, dessor&ccedil;&atilde;o a temperatura programada com H2 e microscopia eletr&ocirc;nica de varredura. Foi observado que o Ni(II) interage de forma variada com os suportes com diferentes teores de MgO, e que a polaridade do solvente de impregna&ccedil;&atilde;o utilizado no processo de prepara&ccedil;&atilde;o influencia as propriedades dos catalisadores. A fim de verificar a atividade, seletividade e deposi&ccedil;&atilde;o de carbono; os catalisadores foram testados na rea&ccedil;&atilde;o de reforma a vapor de glicerol a 600oC, por um per&iacute;odo de 5h e raz&atilde;o molar &aacute;gua:glicerol de 12:1. Ap&oacute;s as rea&ccedil;&otilde;es, os catalisadores foram novamente submetidos &agrave;s an&aacute;lises de termogravimetria, difratometria de raios X e microscopia eletr&ocirc;nica de varredura, visando a caracteriza&ccedil;&atilde;o dos dep&oacute;sitos de carbono obtidos durante o processo catal&iacute;tico. Os catalisadores de matrizes mistas se mostraram ativos e apresentaram seletividades similares para os produtos gasosos CH4, CO e CO2, al&eacute;m de um alto rendimento em H2. Observou-se que a adi&ccedil;&atilde;o de MgO no suporte, aumentou a dispers&atilde;o do Ni(II) no material, que por sua vez, influenciou na quantidade de carbono depositado ao longo da rea&ccedil;&atilde;o. A polaridade do solvente de impregna&ccedil;&atilde;o tamb&eacute;m teve influ&ecirc;ncia na dispers&atilde;o met&aacute;lica, sendo que, quanto menor a polaridade do solvente, maior foi a dispers&atilde;o obtida no catalisador, e menor a deposi&ccedil;&atilde;o de carbono na rea&ccedil;&atilde;o. O material que apresentou o melhor desempenho catal&iacute;tico frente ao rendimento de H2 e &agrave; deposi&ccedil;&atilde;o de carbono, foi o catalisador preparado com 30% de MgO com etanol como solvente de impregna&ccedil;&atilde;o. / Ni catalysts (10wt%) supported on MgO-SiO2 were assessed in glycerol steam reforming reaction. The effects of MgO as additive and preparation method were evaluated on physico-chemical and textural materials properties; as their activity, selectivity, stability and carbon formation in glycerol steam reforming. The catalysts were prepared with different amounts of MgO (10wt%, 30wt% and 50wt%) on commercial SiO2 by dry process (physical mixture) and wet process (sequential impregnation with water, ethanol and acetone as solvents). Samples were characterized by energy dispersive X-ray spectroscopy, nitrogen physisorption, X-ray diffraction, thermogravimetry, in situ X-ray diffraction with O2, temperature programmed reduction with H2, in situ X-ray diffraction with H2, temperature programmed desorption with H2 and scanning electron microscopy. It was observed that the Ni(II) interacts differently with supports with different MgO content, and the polarity of impregnation solvent used in preparation process influences on catalysts properties. In order to evaluated the activity, selectivity and carbon deposition, the catalysts were tested in glycerol steam reforming reaction at 600oC for 5h and water:glycerol molar ratio of 12:1. After reaction, carbon deposits obtained during the catalytic process were characterized by thermogravimetry, X-ray diffraction and scanning electron microscopy. Mixed matrices catalysts were active in glycerol steam reforming and showed similar selectivity for the gaseous products (H2, CH4, CO and CO2), with a high H2 yield. It was observed that the addition of MgO increased Ni(II) dispersion on material, which influenced on the quantity of carbon deposited during reaction. Polarity of impregnation solvent had also influence on metallic dispersion, and smaller the solvent polarity, higher the dispersion obtained in the catalyst, and lower the carbon deposition on reaction. The material that showed the best catalytic performance in H2 yield and carbon deposition, was the catalyst prepared with 30wt% of MgO with ethanol as impregnation solvent.

A crescente busca por fontes alternativas de energia tem despertado o interesse no uso do hidrogênio e do gás de síntese obtidos a partir de fontes renováveis. Dentre essas fontes destacam-se o etanol, produzido no Brasil a partir da cana-de-açúcar e com uma rede de abastecimento já desenvolvida, e o glicerol, obtido como subproduto na produção do biodiesel. Hidrogênio e gás de síntese podem ser obtidos a partir da reação de reforma a vapor de etanol e glicerol (RVE e RVG), levando assim a crescente interesse no desenvolvimento de catalisadores eficientes no processo de produção de H2 e gás de síntese a partir desses álcoois. <br />Na presente tese foram estudados catalisadores de níquel suportados em soluções sólidas de CexZr1-xO2, visando avaliar o desempenho dos mesmos nas reações de RVE e RVG. Os suportes foram preparados através do método Pechini e os catalisadores foram preparados por impregnação e polimerização em única etapa, variando-se o teor metálico em 5, 10 e 15% em massa. Sobre o catalisador com melhor desempenho catalítico foram adicionados, por impregnação, os seguintes metais nobres (promotores): Rh, Ru, Pt e Au (1% em massa). <br />Os suportes e catalisadores foram caracterizados por difração de Raios X (DRX); espectroscopia Raman, redução a temperatura programada com H2 (RTP H2), capacidade de estocagem de oxigênio (OSC); fisissorção de N2 (método B.E.T.); espectroscopia na região do infravermelho com reflectância difusa com CO (DRIFTS - CO), espectrocospia de absorção de Raios X (XAS - XANES RTP-H2), espectroscopia fotoeletrônica de raios X (XPS), espectroscopia dispersiva de Raios X (EDX) e microscopia eletrônica de varredura (MEV). <br />Os ensaios catalíticos foram realizados nas temperaturas de 600 e 700&deg;C para a RVG e a 400, 500 e 600&deg;C para a RVE, utilizando uma razão água:álcool de 3:1. Foram realizados também análises de DRIFTS acoplado a um espectrômetro de massas visando identificar os intermediários formados durante a reação de RVE. A partir dos ensaios catalíticos observou-se que a composição do suporte, o teor metálico e o método de preparação influenciam na seletividade em produtos gasosos devido a mudanças estruturais causadas, principalmente na dispersão da fase ativa sobre o suporte. Além disso, observou-se que a adição de metais nobres favoreceu uma menor deposição de carbono sobre os catalisadores. / The growing interest for alternative energy sources has stimulated the interest in the use of hydrogen and syngas obtained from renewable sources. Among these sources, the use of ethanol produced in Brazil from sugar cane and with a supply network already developed, and glycerol obtained as a byproduct in the biodiesel production have been highlighted in the last years. <br />Hydrogen and syngas can be produced from steam reforming of ethanol and glycerol reactions (SRE and SRG), leading to a growing interest in the development of efficient catalysts for the production of H2 and syngas from these alcohols. <br />In the present thesis, catalysts of nickel supported on CexZr1-xO2 solid solution were studied, with the goal of evaluating the performance of those in the SRE and SRG reactions. The supports were prepared by Pechini method and the catalysts were synthesized by impregnation and polymerization method in one step, with nickel loads of 5 wt.%, 10 wt.% and 15 wt.%. On the catalyst with better catalytic performance, it was impregnated 1wt% of Rh, Ru, Pt or Au as promoter. <br />Supports and catalysts were characterized by X-ray diffraction (XRD), Raman spectroscopy, temperature-programmed reduction (TPR), oxygen storage capacity (OSC), N2 physisorption (B.E.T. method), Diffuse Reflectance Infrared Spectroscopy with CO (DRIFTS - CO), X-ray absorption near edge structure (XANES - TPR H2), X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy (EDX) and Scanning electron microscopy (SEM). <br />The catalytic tests of SRG were performed at 600 and 700&deg;C and for SRE at the tests were carried out at 400, 500 and 600&deg;C. The feed of water:alcohol was in the molar ratio of 3:1. DRIFTS coupled to a mass spectrometer analyzes was also carried out to identify the intermediates formed during the SRE. From the catalytic tests it was possible to observe that the support composition, metal load and preparation method influenced the selectivity to gaseous products, probably due to structural changes caused, mainly in the dispersion of the active phase on the support. Also, it was observed that the addition of noble metals favored a lower carbon deposition on the catalysts.