This thesis is based on the study of ammonia oxidation on platinum group metals. The objectives of this thesis are accept or discard the diverse mechanisms proposed. Even suggest the most appropriate according to the data obtained. To carry out this work is necessary to know the geometry of each species that may exist on the surface of the catalyst and the transition states of the reactions that lead from one species (or combination of species) to another. This is know the key points of a reaction (activation energy and reaction enthalpy). With all data obtained was proposed a microkinetic model of the process and analysis this to obtain a reduced model, equivalent to a mechanism. With this model it is possible to obtain a simulation of the temporal evolution of each species, both in gas phase on the surface, depending on initial conditions. All this information is useful to know how the mechanism works and the evolution of products depending on the temperature or the oxygen-ammonia ratio. To carry out this thesis has used the density functional theory (DFT) implemented in VASP code on a model of a periodic cell of 2 ¡Á 2 with four layers of metal where the two more superficial are entirely free, being able to deform and adapt the molecule adsorbed. The Encut and k-points used are 400 eV and 5 ¡Á 5 ¡Á 1, respectively.This thesis is divided in three chapters. The first examines and compares the dehydrogenation of ammonia on platinum in the faces 100 and 111. The second chapter examines and compares the dehydrogenation on platinum, palladium and rhodium on both sides, 100 and 111. And the third chapter examines the process of ammonia oxidation on Pt(100).The first part has been carried out a systematic study of adsorption and the relative stability of the ammonia and the species of dehydrogenation on the surfaces of Pt (111) and Pt (100). Different adsorption geometries and positions have been studied. The vibrational spectra of various fragments of ammonia have been calculated and were compared with the experimental data available. The adsorption of NH3 is on top position and for the NH2 is on bridge and it is the most stable on Pt (100) than on Pt (111). For the NH and N are adsorbed on the hollow site. There is a considerable difference in the energy of adsorption of NH2 on both sides. This difference is mainly explained by the geometry that takes the kind on both sides. Being much more stable on the 100 side than on the face 111. Accordingly, the platinum surface determines the most stable species NHx: On Pt(100) has more affinity NH2 species, whereas species prefer NH Pt(111).The second part extends the study of the dehydrogenation to other metals such as Palladium and Rhodium. The different adsorption geometries and positions have been studied for the intermediate of ammonia dehydrogenation (NHx, x=0-2). The six surfaces studied, the NH3 adsorbs preferably on the top position, the NH2 on bridge, NH and N on hollow. However, the adsorption energies of the fragments NHx fluctuate considerably from one surface to another. All species absorbs more strongly on the face 100 than on face 111. The Rh(100) is the surface that provides maximum stability for the different NHx species. The reaction energy, the activation energy and the geometry of the transition state for the successive of ammonia dehydrogenation (NHx ¡ú NHx-1) have been determined, which allows calculating the rate coefficients. Our results prove that the reaction is structure sensitive. As a general trend, the first step of dehydrogenation is the limiting step, especially for palladium. According to the experimental data Rhodium is a good catalyst for the decomposition of NH3 compared to Pt and Pd. It has also been observed a linear relationship between the potential energy of the transition state and the adsorption energy of the products. The third part studies the ammonia oxidation on Pt(100). The conversion of NH3 leading to NHx intermediate species that reacts with adsorbed oxygen species and ultimately the formation of the products (NO, N2O, N2 and H2O) that it has been systematically calculated. The reaction comes through an imine mechanism, while the classical mechanisms postulated by Bodenstein and Andrussow (nytroxyl and hydroxilamine, respectively) as reaction intermediates can be discarded. The activation energy for the oxidative ammonia dehydrogenation on Pt(100) has been drastically reduced compared to the non-oxidative ammonia dehydrogenation. The barriers of ammonia dehydrogenation are greatly favored by the O-assisted way than the OH-assisted way. The final products are formed by recombination of adsorbed Nitrogen with N (N2), O (NO) and NO (N2O). The water is formed through the recombination of two adsorbed OH, regenerating adsorbed oxygen. The limiting step in the oxidative ammonia dehydrogenation is the first step, abstraction of the first proton of ammonia (NH3¡úNH2+H). While the nitric oxide desorption is the rate determining step (rds) of the process. We calculated the reaction rate coefficients of elementary steps involved in the reaction mechanism allows doing a microkinetic analysis. The simulations carried out with the microkinetic model describe well the experimental distribution of products obtained at different temperatures, depending on the time and the ratio of initial NH3/O2. Getting a temporal distribution of each species in gas phase and on the surface. / Esta tesis se basa en el estudio de la oxidación de amoniaco sobre el grupo del platino. El objetivo de esta tesis es descartar o aceptar los diversos mecanismos propuestos. Incluso proponer el más correcto según los datos obtenidos. Para llevar a cabo esta acometida es necesario conocer cada geometría de las diferentes especies que pueden existir sobre la superficie del catalizador, así como los estados de transición entre las reacciones que lleven de una especie (o combinación de especies) a otras. Es decir conocer los puntos claves de una reacción (energía de activación y entalpía de reacción). Con los datos obtenidos se ha realizado la microcin¨¦tica del proceso completo y se ha realizado un análisis microcinético, llegando a obtener un modelo reducido, el equivalente a un mecanismo de reacción. Con este modelo es posible obtener una simulación de la evolución temporal de cada especie, tanto en fase gas como sobre la superficie, en función de unas condiciones iniciales. Toda esta información es de gran utilidad para conocer el funcionamiento del mecanismo y conocer la evolución de los productos en función de la temperatura, o de la relación de amoniaco-oxigeno. Para realizar esta tesis se ha usado la Teoría del funcional de la Densidad (DFT), el programa VASP usa esta teoría con ondas planas para realizar los cílculos sobre un modelo periódico de una celda de 2¡Á2 con cuatro capas de metal donde las dos más superficiales están totalmente libres, pudiéndose deformar y adaptar al adsorbato. El Encut y los k-points usados son de 400 eV y 5¡Á5¡Á1, respectivamente. La tesis se ha dividido en tres capítulos. En el primero se estudia y compara la deshidrogenación del amoniaco sobre Platino en las caras 100 y 111. En el segundo capitulo se estudia y compara la deshidrogenación sobre Platino, Paladio y Rodio en las dos caras, 100 y 111. Y en el tercer capítulo se estudia el proceso de la oxidación de amoniaco sobre Platino en la cara 100.En la primera parte se han llevado a cabo una estudio sistemático de la adsorción y la estabilidad relativa del amoniaco y de las especies de la deshidrogenación sobre las superficies de Pt (111) y Pt (100). Diferentes geometrías y posiciones de adsorción han sido estudiadas. Los espectros vibracionales de los diversos fragmentos de amoníaco se han calculado y se han comparado con los datos experimentales disponibles. La adsorción de NH3 se realiza sobre la posici¨®n top el NH2 sobre la posición bridge y es la más estable sobre Pt (100) que sobre Pt (111). Para el NH y el N se adsorben sobre el hollow. Existe una diferencia considerable en la energía de adsorción del NH2 sobre las dos caras. Esta diferencia se explica principalmente por la geometría que adopta la especie sobre las dos caras. Siendo mucho más estable sobre la cara 100 que sobre la cara 111. En consecuencia, la superficie de platino determina la especie NHx más estable: Sobre Pt(100) tiene más afinidad la especie NH2, mientras que la especie NH prefiere el Pt (111). En la segunda parte el estudio de la deshidrogenación se ha ampliado a otros metales como el Paladio y el Rodio. Diferentes geometrías de adsorción y posiciones han sido estudiados para NH3 y los intermedios de la deshidrogenación del amoniaco (NHx, x = 0 - 2). En las seis superficies investigadas, el NH3 adsorbe preferentemente sobre la posición top, el NH2 en bridge, el NH y el N lo hacen sobre el hollow. Sin embargo, las energías de adsorción los fragmentos NHx difieren considerablemente de una superficie a otra. Todas las especies de absorber con más fuerza en la cara 100 que en el la cara 111. El Rh(100) es la superficie que proporciona la máxima estabilidad para las diferentes especies. La energía de reacción, la geometría del estado de transición y la barrera de activación de los sucesivos pasos de reacción de la deshidrogenación (NHx ¡ú NHx-1) se han determinado, lo que permite calcular los coeficientes de las velocidades de reacción. Nuestros cálculos demuestran que la reacción es sensible a la estructura de la superficie. Como tendencia general, el primer paso de la deshidrogenación es el paso limitante, especialmente para Paladio. De acuerdo con los datos experimentales el Rodio es un buen catalizador para la descomposición de NH3 frente al Pt y el Pd. También se ha observado una relación lineal entre la energía potencial del estado de transición y la energía de adsorción de los productos. En la tercera parte se ha estudiado el proceso de oxidación de amoniaco sobre Pt(100). La conversión de NH3 que lleva a especies intermedias de NHx que reacciona con especies que contienen oxígeno adsorbido y en última instancia la formación de los productos de reacción (NO, N2O, N2 y H2O), han sido calculadas sistemáticamente. La reacción procede a través de un mecanismo de amina, mientras que los mecanismos clásicos postulados por Andrussow y Bodenstein (nitroxilo y hidroxilamina, respectivamente) como productos intermedios de reacción pueden ser descartados. Las barreras de activación para la deshidrogenación oxidativa del amoniaco sobre Pt(100) se han reducido drásticamente con respecto a la deshidrogenación no-oxidativa. La energía de activación de la deshidrogenación de amoniaco y de las subsiguientes deshidrogenaciones (NHx) son en gran medida favorecidas por el oxigeno adsorbido con respecto al hidróxido adsorbido. Los productos finales están formados por recombinación de N adsorbido con N (N2), O (NO) y NO (N2O). El agua se forma a través de la recombinación de OH adsorbido, regenerando un oxígeno.La etapa limitante en la deshidrogenación oxidativa del amoniaco es la primera etapa, la abstracción del primer protón del NH3. Mientras que desorción del NO es la etapa limitante del proceso en general. Se han calculado los coeficientes de velocidad de reacción de los pasos elementales que participan en el mecanismo de reacción, permitiendo obtener un análisis microcinético. Las simulaciones realizadas con el modelo microcinético describen bien la distribución de productos obtenidos experimentalmente a diferentes temperaturas, en función del tiempo y del ratio de NH3/O2 iniciales. Obteniendo una distribución temporal de cada especie, en fase gas y sobre la superficie.

Made available in DSpace on 2014-10-09T12:35:34Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:01Z (GMT). No. of bitstreams: 0 / 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. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

L'objectif de ce travail est la synthèse et l'étude des propriétés acido-basiques de nanotubes de carbone (CNT) dopés à l’azote pour les utiliser comme catalyseurs ou supports de catalyseurs. Pour ce faire, trois types de nanotubes de carbone dopés à l'azote ont été synthétisés, caractérisés et testés dans la conversion de l'alcool isopropylique. Les nanotubes de carbone dopés diffèrent par le taux d’azote et la présence ou non d'une section non dopée dans leur structure. Pour les matériaux à faible teneur en azote, la réaction conduit à la formation d'acétone indiquant la présence de sites basiques. À plus forte teneur en azote, les catalyseurs dopés conduisent à la formation d'acétone et de propène, mettant en évidence la présence de sites basiques et acides. La caractérisation par XPS nous a permis de proposer que les sites basiques sont constitués de groupes de surface pyridiniques et les sites acides sont des groupements sulfoniques formés au cours de la purification de ces matériaux avec de l'acide sulfurique. Des catalyseurs au ruthénium et au palladium supportés (2%) sur des nanotubes de carbone non dopés et dopés à l'azote (N-CNT), ont été préparés et évalués dans la réaction de décomposition de l'alcool isopropylique comme réaction test. La présence de fonctionnalités azotées (azote pyridinique, pyrrolique et quaternaire) sur le support dopé à l'azote induit une plus grande dispersion du métal. En ce qui concerne les catalyseurs supportés, ceux de palladium étaient plus actifs et plus sélectifs que ceux au ruthénium. De plus, les catalyseurs au Pd sont sélectifs en acétone, tandis que les catalyseurs au Ru conduisent à la déshydratation et la déshydrogénation. Le dopage des nanotubes de carbone par l’azote conduit aussi à l'apparition de propriétés d'oxydo-réduction. Enfin, nous avons montré que des nanotubes de carbone, constitués de deux sections différentes : une partie non dopée hydrophobe reliée à un segment hydrophile, sont amphiphiles. Nous les avons utilisés comme supports tensioactif de catalyseur au palladium. Ces nouveaux catalyseurs à base de Pd supporté ont été testés dans la réaction d'oxydation de plusieurs alcools en utilisant l'oxygène moléculaire en phase liquide. L'oxydation du 2- heptanol produit sélectivement la cétone correspondante, alors que l'oxydation de l'alcool benzylique est très sélective vis-à-vis de l'aldéhyde. Par ailleurs, l'oxydation de l'éthanol produit de l'acide acétique de manière sélective. / The objective of this work is the synthesis and the investigation of the acid and basicproperties of nitrogen doped carbon nanotubes (CNTs) able to be used as catalysts or catalystsupports. For this, three types of purified nitrogen doped CNTs were synthesized,characterized and tested for isopropyl alcohol conversion under nitrogen or air atmosphere,and compared to undoped CNTs. The N-doped CNTs differ from their nitrogen content andfrom the presence or not of undoped section in their structure. The reaction lead to theformation of acetone as the sole product on catalysts presenting no nitrogen or low nitrogencontent (< 2.8% w/w), pointing to the presence of basic sites. At higher nitrogen content, Ndopedcatalysts lead to the formation of acetone and propene, highlighting the presence ofboth basic and acids sites on such material. XPS characterization allow us to propose that thebasic sites consist in pyridinic surface groups and the acidic sites in sulfonic surface groupsformed during the purification of these material with sulfuric acid. Ruthenium and palladiumsupported catalysts (2% w/w) were prepared on nitrogen-doped and non-doped carbonnanotubes (N-CNT), and evaluated for the reaction of decomposition of isopropyl alcohol asprobe reaction. The presence of nitrogen functionalities (pyridinic, pyrrolic and quaternarynitrogen) on the nitrogen doped support induces a higher metal dispersion: 1.8 nm (Pd/NCNT)< 4.9 nm (Pd/CNT), and 2.4 nm (Ru/N-CNT) < 3.0 nm (Ru/CNT). As far as thesupported catalysts are concerned, the palladium ones were more active and more selectivethan the ruthenium ones. The Pd catalysts were selective towards acetone, whereas Rucatalysts lead to dehydration and dehydrogenation products. The nitrogen doping induces theappearance of redox properties, which appear when oxygen is present in the reaction mixture.Finally, we have shown that unique amphiphilic magnetic hybrid carbon nanotubes thatcontain on the same nanotube two different sections: a hydrophobic undoped part connectedto a hydrophilic N-doped segment are synthesized and used as tensioactive supports forpalladium catalysts. These new Pd-supported catalysts have been used in the alcoholoxidation reaction using molecular oxygen in the liquid phase. The oxidation of 2-heptanolproduces selectively the ketone, the oxidation of benzyl alcohol is very selective towards thealdehyde, and ethanol oxidation produces selectively acetic acid.

The aim of the thesis is to clarify the importance of diversifying investment portfolios with the help of precious metals at the present time and to analyze the fluctuation of precious metals market in terms of demand, supply and price developments. The core of the thesis focuses on analysis of the market of precious metals from 1998 to 2011 The used work method is comparison of precious metals between themselves and the world stock indices, the method of analysis in separate calculations of indicators, the method of deduction from the results of calculations.

Thin metallic films are particularly interesting as potential hydrogen storage materials as well as hydrogen sensitive optical sensors. Thin films with various microstructure from nanocrystalline to epitaxial can be relatively easily prepared by varying the deposition parameters. Deposition of multi-layers enables preparation of thin films with arbitrary composition. Defects structure plays a key role in hydrogen absorption. Hydrogen atoms segregated at open volume defects reduce their formation energy leading to enhan- ced concentration of hydrogen-induced defects in the material. Moreover hydrogen diffusion along dislocations and grain boundaries facilitates hydrogen absorption in the metal lattice. Thin films clamped to the stiff substrate undergo anisotropic volume expansion during the hydrogen loading. As a consequence high stresses are induced in the film and can result in detachment of the film from the substrate. In this work hydrogen absorption in Gd and Pd films and Pd-Mg multi-layers was studied. Development of the defect structure of hydrogen-loaded films was investigated by means of variable energy positron annihilation spectroscopy com- bined with X-ray diffraction, atomic force microscopy and optical transmittance measurement. Complementary studies of interaction of hydrogen with defects in...

Made available in DSpace on 2014-10-09T12:35:34Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:01Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

The oxidation of Pd single crystals: Pd(111), Pd(100) and Pd(110) was studied using Temperature Programmed Desorption (TPD), X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES), Low Electron Energy Diffraction (LEED) and Scanning Tunneling Microscopy (STM) as they were subjected to O2 in the pressure range between 1 and 150 Torr at temperatures 600-900 K. The oxygen species formed during oxidation, the oxygen uptake dependence on the sample history, the Pd single crystal surface morphology transformations, and the catalytic methane combustion over Pd single crystals were investigated in detail. The Pd single crystal oxidation proceeded through a three-step mechanism. Namely, (1) oxygen dissociatively adsorbed on Pd surface, forming chemisorbed oxygen and then surface oxide; (2) atomic oxygen diffused through a thin surface oxide layer into Pd metal, forming near surface and bulk oxygen; (3) bulk PdO formed when a critical oxygen concentration was reached in the near surface region. The diffusion of oxygen through thin surface oxide layer into Pd metal decreased in the order: Pd(110)>Pd(100)>Pd(111). The oxygen diffusion coefficient was estimated to be around 10-16 cm2 s-1 at 600 K, with an activation energy of 80 kJ mol-1. Once bulk PdO was formed, the diffusion of oxygen through the bulk oxide layer was the rate-determining step for the palladium oxidation. The diffusion coefficient was equal to 10-18 cm2 s-1 at 600 K and the activation energy was approximately 120 kJ mol-1. The oxygen diffusion through thin surface oxide layer and bulk PdO followed the Mott-Cabrera parabolic diffusion law. The oxygen uptake on Pd single crystals depended on the sample history. The uptake amount increased with the population of the bulk oxygen species, which was achieved by high oxygen exposure at elevated temperatures, for example in 1 Torr O2 at above 820 K. Ar+ sputtering or annealing in vacuum at 1300 K depleted the bulk oxygen. The Pd single crystal surface morphology was determined by the oxidation conditions: O2 pressure, treatment temperature and exposure time. When bulk PdO was formed, the single crystal surface was covered with semi-spherical agglomerates 2-4 nm in size, which tended to aggregate to form a“cauliflower-like" superstructure. The single crystal surface area during oxidation, determined by integrating the STM image, experienced three major expansions in consistent with a three-step oxidation mechanism. The surface area on the oxidized single crystals increased in the order: Pd(110)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The present work describes the synthesis of a new catalyst of palladium nanoparticles supported on multi-walled carbon nanotubes containing nitrogen (Pd@CNxNCPM) 1 and its use in carbon-carbon coupling reactions (Suzuki and Heck) as well as reactions catalytic hydrogenation (reduction of double C-C bonds and nitro compounds reduction). The synthetic strategy employed afforded the simple way to obtain the catalyst with reaction in a short time and efficiently. To this was employed as the palladium precursor, the salt potassium hexacloropalladate IV and hydrazine monohydrate as the reducing agent, without the need for stabilizing agents for the control of nucleation and size of nanoparticle. The catalyst system was characterized as its morphology: dispersion, size and shape of nanoparticles by scanning electron microscopy. Also the catalyst was performed Raman spectroscopy and determination of amount of palladium. After characterization the catalyst, it was tested for coupling reactions of carbon-carbon: Suzuki and Heck leading to the formation of their products with 70-> 95% for Suzuki coupling and 75-> 95% for Heck. For the synthesis in question were used 0.5 mol% of catalyst (based amount of palladium) for Suzuki and 10 mol% for Heck. It should be noted that the catalyst shown stable in the reaction conditions tested, and observed the possibility of reuse of this system for additional reaction cycles without loss of efficiency for the Suzuki coupling. Also, the catalyst was efficient and chemoselectiv for catalytic hydrogenations of unsaturated carbon-carbon bonds and nitro compounds leading to their products in good yields. Thus, the synthesized catalyst proved versatile and can be used in reactions of carbon-carbon coupling well as in catalytic reduction may also be recovered and reused, which provides an environmentally friendly at the same characteristic. / O presente trabalho apresenta a síntese de um novo catalisador de nanopartículas de paládio suportadas em nanotubos de carbono de paredes múltiplas contendo nitrogênio (Pd@CNxNCPM) 1 e sua utilização em reações de acoplamento carbono-carbono (Suzuki e Heck) bem como em reações de Hidrogenações catalíticas (reduções de duplas ligações C-C e redução de nitrocompostos). A estratégia sintética utilizada permitiu a obtenção do catalisador de maneira simples, em curto tempo reacional e de maneira eficiente e sem a presença de agentes estabilizantes externos. Para isso foi empregado como precursor de paládio o sal hexacloropaladato IV de potássio e como agente redutor, hidrazina monohidratada sem a necessidade de agentes estabilizantes para o controle da nucleação e tamanho de nanopartículas. O sistema catalítico foi caracterizado quanto sua morfologia: dispersão, tamanho e forma de nanopartículas através de microscopia eletrônica de varredura. Também foi realizada espectroscopia Raman do catalisador bem como determinação do teor de paládio. Após devidamente analisado o catalisador, o mesmo foi testado para reações de acoplamento carbono-carbono de Suzuki e Heck levando a formação dos respectivos produtos com rendimentos de 70-> 95% para os acoplamentos de Suzuki e 75-> 95% para Heck. Para as sínteses em questão foram usados 0,5 mol% de catalisador (baseados na massa de paládio) para Suzuki e 10 mol% para Heck. Cabe salientar que o catalisador se mostra estável nas condições reacionais testadas, sendo observada a possibilidade de reuso deste sistema por ciclos reacionais adicionais, sem perdas de eficiência para o acoplamento de Suzuki. Ainda, o catalisador se mostrou eficiente para hidrogenações catalíticas quimiosseletivas de ligações de carbono-carbono insaturadas e nitrocompostos levando aos respectivos produtos em bons rendimentos. Dessa forma o catalisador sintetizado se mostrou versátil, sendo possível ser utilizado em reações de acoplamento carbono-carbono bem como em reduções catalíticas, também pode ser recuperado e reutilizado, o que confere ao mesmo uma característica ambientalmente correta.

This work presents a theoretical study of stability of phases in selected metallic systems. We propose a model of structural transformations in transition metal disilicides MoSi2, CrSi2, VSi2 and TiSi2 and in Pd thin films grown on cubic substrates W(001) and Nb(001). The obtained results yield the total energy proles for the structural transformations studied, the activation energies needed for each individual transformation and an estimate of the temperature at which the structure can transform. The total energies are calculated by full-potential linearized augmented plane waves (FLAPW) method incorporated in the WIEN2k code. Both generalized gradient approximation (GGA) and local density approximation (LDA) are employed for the exchange-correlation term. It turns out that temperatures corresponding to the activation energies of structural transformations in transition metal disilicides exceed their melting temperatures. Comparing the resulting total energy proles to those obtained by the semiempirical Bond Order interatomic potentials (BOP) substantially helps to adjust the fitting parameters of the BOPs. The estimated temperature of 168 K needed to transform the hcp structure of an innite Pd crystal into the dhcp structure explains the behavior of the Pd thin lm on W(001) and Nb(001) substrates. Pd lms deposited on W(001) substrate and thicker than about 100 monolayers undergo this transformation already at room temperature. Thinner lms need to be annealed at 400 K rst, due to their stronger interaction with the substrate. The difference between the computed result and a real temperature at which the hcp Pd lm transforms its structure to the dhcp can be explained by both the interaction between the lm and the substrate and by the inuence of the domain topology of the lm. Analyzing different models of transformation of the initial hcp Pd structure to the ground state fcc structure, we identied the optimum model that respects the domain topology of the Pd lm.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Triazenes are a class of compounds characterized by the presence of a diazoamino functional group (N=N N) showing remarkable ability to support the stereochemical requisites of a wide variety of metal transition complexes. They act as versatile ligands in coordination chemistry when deprotonated and have relevant biological and synthetic porperties. This work presents the synthesis and investigation of molecular and crystal structure of a new series of monotriazenes [3-(4-phenyldiazenyl)-1-(2-fluorophenyl)triazene (2b); 1-(2-chlorophenyl)-3-(4-phenyldiazenyl)triazeno (2c), 1-(2-bromophenyl)-3-(4-phenyldiazenyl)triazene (2d); 3-(4-phenyldiazenyl)-1-(2-iodophenyl) triazene (2e); 1,3-bis-(3-methoxy-4-methylbenzoate)triazene (2g)] and substituted 1,4-bis (phenyltriazenyl)butanes, C6H5N(H)=N-N(CH2)4-N=NN(H)C6H5, [1,4-bis(4-ethyl-benzoato triazenyl) butane (5a), 1,4-bis(2-fluorophenyltriazenyl)butane (5b), 1,4-bis(2-clorophenyltriazenyl)butane (5c), 1,4-bis(2-bromophenyltriazenyl)butane (5d), 1,4-bis(2-iodophenyltriazenyl)butane (5e), 1,4-bis(4-amidophenyltriazenyll)butane (5f)]. The insertion of groups on phenyl rings attached to the triazene chains makes the environment significantly more interesting coordination providing the supramolecular array through noncovalent intermolecular interactions and self-organizatinal units of primary molecule. The metal ions used for complexation are salts of Ni2+, Cu2+ and Pd2+ and they were chosen due to the attracting biological relevance, magnetic properties, catalytic yielding. Nine metal complexes unpublished were synthesized [trans-[PdII(C6H5NNC6H4NNNC6H4Cl)2(C5H5N)2] (3c) [(PdII (R1R2C6H3NNNC6H3R1R2)(PPh3)2Cl) DMSO] [R1 = 4-C(O)OCH3, R2 = 3-OCH3] (3g) [CuII (RC6H5NNN(CH2)4NNNC6H5R)]2 [R = C2H5C(O)O (6a), R = F (6b), R = NH2C(O) (6f)], [NiII (RC6H5NNN(CH2)4NNNC6H5R)]2 [R = F (7b) R = Cl (7c) R = Br (7d) R = NH2C(O) (7f)]. The synthesis and characterization of these compounds is justified by the exploration of the reactivity, the coordinative behavior and by the understanding of the interactions between different ligands and metal centers. The structural analysis of the synthesized compounds by X-ray diffraction on single crystal in the solid state were performed for characterization of interactions in the crystal. Thus, a thorough understanding of the relationship between the crystal structure and supramolecular organization is analyzed. Besides the structural analysis of compounds, elemental analysis CHN, infrared, nuclear magnetic resonance and ultraviolet-visible spectroscopies and mass spectrometry were also carried out for characterization. The physical chemical properties were investigated through thermogravimetric analysis and magnetic susceptibility. / Triazenos são importantes membros da família de compostos nitrogenados de cadeia aberta, caracterizados por conter o grupo funcional [N═N─N] e apresentam diferentes propriedades de coordenação a metais de transição. São compostos fracamente ácidos e quando desprotonados atuam como ótimos ligantes na química de coordenação apresentando grande importância sintética e biológica. Nessa tese, foi inicialmente desenvolvida a síntese de uma série inédita de compostos triazenos monocatenados [3-(4-fenildiazenil)-1-(2-fluorofenil)triazeno (2b); 1-(2-clorofenil)-3-(4-fenildiazenil)triazeno (2c); 1-(2-bromofenil)-3-(4-fenildiazenil)triazeno (2d); 3-(4-fenildiazenil)-1-(2-iodofenil)triazeno (2e); 1,3-bis(3-metoxi-4-metilbenzoato)triazeno (2g)] e de compostos triazenos biscatenados derivados do 1,4-bis(feniltriazenido)butano, C6H5N(H)N=N-(CH2)4-N=N-N(H)C6H5, [1,4-bis(etil-4-benzoatotriazenil) butano (5a); 1,4-bis(2-fluorofeniltriazenido)butano (5b); 1,4-bis(2-clorofeniltriazenido)butano (5c); 1,4-bis(2-bromofeniltriazenido)butano (5d); 1,4-bis(2-iodofeniltriazenido)butano (5e); 1,4-bis(4-amidofeniltriazenido)butano (5f)]. A inserção de grupamentos substituintes nos anéis fenila na cadeia triazenídica tornam o ambiente de coordenação significativamente mais interessante, propiciando o aumento da ocorrência de interações intermoleculares não covalentes e impondo a auto-organização de unidades moleculares primárias no estado sólido. Os metais escolhidos para complexação foram sais de Ni2+, Cu2+ e Pd2+ em virtude de atraírem atenção como objeto de estudos relacionados com medicina, propriedades magnéticas e catálise obtendo-se como resultados deste trabalho nove complexos metálicos inéditos [trans-[PdII(C6H5NNC6H4NNNC6H4Cl)2(C5H5N)2] (3c); [(PdII(R1R2C6H3NNNC6H3R1R2)(PPh3)2Cl)·DMSO] [R1 = 4-C(O)OCH3, R2 = 3-OCH3] (3g); [CuII(RC6H5NNN(CH2)4NNNC6H5R)]2 [R = C2H5C(O)O (6a); R = F (6b); R = NH2C(O) (6f)] ; [NiII(RC6H5NNN(CH2)4NNNC6H5R)]2 [R = F (7b); R = Cl (7c); R = Br (7d); R = NH2C(O) (7f)]. A síntese, e a caracterização desses novos compostos estão relacionadas à exploração da reatividade, ao comportamento coordenativo e a compreensão das interações entre os diferentes centros metálicos e os ligantes. Efetuou-se um estudo estrutural no estado sólido para a caracterização das interações presentes nas estruturas cristalinas dos compostos sintetizados e a ferramenta utilizada foi à difração de raios X em monocristal. Dessa forma aprofundou-se a compreensão da relação entre a estrutura cristalina e sua organização supramolecular. Além do método de difração de raios X de monocristal os compostos foram caracterizados por espectroscopia de infravermelho, espectroscopia de ressonância magnética nuclear, 1H e 13C, espectroscopia ultravioleta e visível, espectrometria de massas e análise elementar CHN. As propriedades físico-químicas foram investigadas através de análise termogravimétrica e susceptibilidade magnética.