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The work presented in this dissertation focuses on the study of post deposition spatial and temporal evolution of adatom islands and molecules on surfaces using ab initio and semiemperical methods. It is a microscopic study of the phenomena of diffusion and reaction on nanostructured surfaces for which we have developed appropriate computational tools, as well as implemented others that are available. To map out the potential energy surface on which the adatom islands and molecules move, we have carried out ab initio electronic structure calculations based on density functional theory (DFT) for selected systems. For others, we have relied on semiempirical interatomic potentials derived from the embedded atom method. To calculate the activation energy barriers, we have employed the "drag" method in most cases and verified its reliability by employing the more accurate nudged elastic band method for selected systems. Temporal and spatial evolution of the systems of interest have been calculated using the kinetic Monte Carlo (KMC), or the more accurate (complete) Self Learning kinetic Monte Carlo (SLKMC) method in the majority of cases, and ab initio molecular dynamics simulations in others. We have significantly enhanced the range of applicability of the SLKMC method by introducing a new pattern recognition scheme which by allowing occupancy of the "fcc" and "hcp" sites (and inclusion of "top" site in the pattern recognition as well) is capable of simulating the morphological evolution of iii three dimensional adatom islands, a feature not feasible via the earlier - proposed SLKMC method. Using SLKMC (which allows only fcc site occupancy on fcc(111) surface), our results of the coarsening of Ag islands on the Ag(111) surface show that during early stages, coarsening proceeds as a sequence of selected island sizes, creating peaks and valleys in the island-size distribution. This island size selectivity is independent of initial conditions and results from the formation of kinetically stable islands for certain sizes as dictated by the relative energetics of edge atom detachment/attachment processes together with the large activation barrier for kink detachment. On applying the new method, SLKMC-II, to examine the self diffusion of small adatom islands (1-10 atoms) of Cu on Cu(111), Ag on Ag(111) and Ni on Ni(111), we find that for the case of Cu and Ni islands, diffusion is dominated by concerted processes (motion of island as a whole), whereas in the case of Ag, islands of size 2-9 atoms diffuse through concerted motion whereas the 10-atom island diffuses through single atom processes. Effective energy barriers for the self diffusion of these small Cu islands is 0.045 eV/atom, for Ni it is 0.060 eV/atom and for Ag it is 0.049 eV/atom, increasing almost linearly with island size. Application of DFT based techniques have allowed us to address a few issues stemming from experimental observations on the effect of adsorbates such as CO on the structure iv and stability of bimetallic systems (nanoparticles and surfaces). Total energy calculations of Ni-Au nanoparticles show Ni atoms to prefer to be in the interior of the nanoparticle. CO molecules, however, prefer to bind to a Ni atom if present on the surface. Using ab initio molecular dynamics simulations, we confirm that the presence of CO molecule induces diffusion of Ni atom from the core of the Ni-Au nanoparticle to its surface, making the nanoparticle more reactive. These results which help explain a set of experimental data are rationalized through charge transfer analysis. Similar to the case of Ni-Au system, it is found that methoxy (CH3O) may also induce diffusion of inner atoms to the surface on bimetallic Au-Pt systems. Our total energy DFT calculations show that it is more favorable for methoxy to bind to a Pt atom in the top Au layer than to a Au atom in Au-Pt system thereby explaining experimental observations. To understand questions related to the dependence of product selectivity on ambient pressure for ammonia decomposition on RuO2(110), we have carried out an extensive calculation of the reaction pathways and energy barriers for a large number of intermediate products. On combining the reaction energetics from DFT, with KMC simulations, we show that under UHV conditions, selectivity switches from N2 ( ∼ 100 % selectivity) at T = 373K to NO at T = 630K, whereas under ambient conditions, N2 is still the dominant product but maximum selectivity is only 60%. An analysis based on thermodynamics alone shows a contradiction between experimental data at UHV with those under ambient pressure. Our calculations of the reaction rates which are essential for KMC simulations removes this apv parent inconsistency and stresses the need to incorporate kinetics of processes in order to extract information on reaction selectivity.

Células a combustível de membrana polimérica têm cada vez mais se destacado como meio na obtenção de energia, pela sua alta eficiência e potencial para fazê-la de modo sustentável. Entretanto muitos ainda são os desafios para consolidá-la comercialmente. Dentre eles, a aglomeração e a perda de área ativa em catalisadores suportados em carbono recebem um destaque especial, principalmente em células PEM de temperatura elevada de operação. Eletrocatalisadores não suportados, baseados em nanoarquiteturas de geometria controlada, têm se tornado uma tendência em diversas frentes de pesquisa. Tal fato se deve à alta eficiência e estabilidade atingidas por sistemas nanométricos organizados, além da possibilidade em se criar superfícies funcionais adaptadas a reações específicas. O trabalho de pesquisa buscou o desenvolvimento de sistemas catalíticos não suportados, de alta área superficial, como alternativa a eletrocatalisadores nanoparticulados suportados em carbono, a fim de se reduzir a perda sobre a área ativa quando submetidos às condições de operação em células a combustível. O trabalho explorou dois conceitos, a confecção de nanotubos de platina e a confecção de nanofios nanoporosos à base de platina vítrea. Para este desenvolvimento foram estudados e caracterizados os efeitos da dissolução seletiva, em escala nanométrica, acoplados à conformabilidade de metais amorfos e à utilização da troca galvânica como ferramenta de síntese de superfícies. Tais estudos foram utilizados como base para o projeto de sistemas catalíticos não suportados. Os materiais propostos foram avaliados quanto a sua atividade e estabilidade frente a reações comuns em células a combustível. Tais sistemas demonstraram uma alta estabilidade em relação à sua área ativa, em ensaios de durabilidade, assim como uma alta utilização do metal nobre, tornando-os promissores para a tecnologia de células a combustível. / PEM Fuel cells have recently been excelled as energy conversion devices, due to their high efficiency and the potential of performing in a sustainable fashion. However, there are many issues still to be addressed before large scale commercialization. Among them, nanoparticle agglomeration and the loss over the active area in carbon supported catalysts, receive special attention, particularly in high temperature PEM fuel cells. Unsupported catalysts based on nanoarchitectures of controlled geometry, have became a new trend on several research lines. The reason underneath lies on the high efficiency and stability obtained by organized hierarchical nanostructures, furthermore, they have also the possibility of tailored made surfaces designed for specific reactions. This research work sought to develop unsupported catalytic systems, with high surface area, as an alternative to carbon supported nanoparticle catalysts, in order to overcome the loss over the active surface area when under the operational environment of fuel cells. The work explored two concepts; the synthesis of platinum nanotubes, and the synthesis of nanoporous nanowires on amorphous platinum alloys. For this development, the effects of selective dissolution, on nanometer scale, coupled with vitreous plastic conformation, were studied and characterized, as well as the employment of galvanic displacement as a tool on tailored made surfaces. Those studies provided a base for the design of unsupported catalytic systems. The proposed materials were evaluated according to their catalytic activity and stability towards common fuel cell reactions. The unsupported systems presented a high stability regarding its active surface area, on durability studies, as well as high noble metal utilization, making them promising materials for future electrode designs.

Células a combustível de membrana polimérica têm cada vez mais se destacado como meio na obtenção de energia, pela sua alta eficiência e potencial para fazê-la de modo sustentável. Entretanto muitos ainda são os desafios para consolidá-la comercialmente. Dentre eles, a aglomeração e a perda de área ativa em catalisadores suportados em carbono recebem um destaque especial, principalmente em células PEM de temperatura elevada de operação. Eletrocatalisadores não suportados, baseados em nanoarquiteturas de geometria controlada, têm se tornado uma tendência em diversas frentes de pesquisa. Tal fato se deve à alta eficiência e estabilidade atingidas por sistemas nanométricos organizados, além da possibilidade em se criar superfícies funcionais adaptadas a reações específicas. O trabalho de pesquisa buscou o desenvolvimento de sistemas catalíticos não suportados, de alta área superficial, como alternativa a eletrocatalisadores nanoparticulados suportados em carbono, a fim de se reduzir a perda sobre a área ativa quando submetidos às condições de operação em células a combustível. O trabalho explorou dois conceitos, a confecção de nanotubos de platina e a confecção de nanofios nanoporosos à base de platina vítrea. Para este desenvolvimento foram estudados e caracterizados os efeitos da dissolução seletiva, em escala nanométrica, acoplados à conformabilidade de metais amorfos e à utilização da troca galvânica como ferramenta de síntese de superfícies. Tais estudos foram utilizados como base para o projeto de sistemas catalíticos não suportados. Os materiais propostos foram avaliados quanto a sua atividade e estabilidade frente a reações comuns em células a combustível. Tais sistemas demonstraram uma alta estabilidade em relação à sua área ativa, em ensaios de durabilidade, assim como uma alta utilização do metal nobre, tornando-os promissores para a tecnologia de células a combustível. / PEM Fuel cells have recently been excelled as energy conversion devices, due to their high efficiency and the potential of performing in a sustainable fashion. However, there are many issues still to be addressed before large scale commercialization. Among them, nanoparticle agglomeration and the loss over the active area in carbon supported catalysts, receive special attention, particularly in high temperature PEM fuel cells. Unsupported catalysts based on nanoarchitectures of controlled geometry, have became a new trend on several research lines. The reason underneath lies on the high efficiency and stability obtained by organized hierarchical nanostructures, furthermore, they have also the possibility of tailored made surfaces designed for specific reactions. This research work sought to develop unsupported catalytic systems, with high surface area, as an alternative to carbon supported nanoparticle catalysts, in order to overcome the loss over the active surface area when under the operational environment of fuel cells. The work explored two concepts; the synthesis of platinum nanotubes, and the synthesis of nanoporous nanowires on amorphous platinum alloys. For this development, the effects of selective dissolution, on nanometer scale, coupled with vitreous plastic conformation, were studied and characterized, as well as the employment of galvanic displacement as a tool on tailored made surfaces. Those studies provided a base for the design of unsupported catalytic systems. The proposed materials were evaluated according to their catalytic activity and stability towards common fuel cell reactions. The unsupported systems presented a high stability regarding its active surface area, on durability studies, as well as high noble metal utilization, making them promising materials for future electrode designs.

Comme le naphtalène a récemment émergé comme un socle fondamental en chimie médicinale, le développement de méthodologies menant à des plateformes fonctionnalisées basées sur du naphtalène est devenu un centre d’intérêt majeur de la communauté scientifique. En effet, des conditions expérimentales optimisées sur le benzène ou d’autre noyaux aromatiques ne peuvent pas toujours être transposées au naphtalène. Ces dernières peuvent parfois conduire à des résultats différents, possiblement dû à l’aromaticité plus faible de ce bicycle aromatique.Dans ce contexte, cette thèse s’articule autour du naphtalène et de ses dérivés. Des méthodes variées permettant une fonctionnalisation sélective de différentes positions de cette plateforme, ainsi que des stratégies de synthèses d’architectures polycycliques ont été développées.Notre attention s’est ensuite portée sur des précurseurs du naphtalène, en particulier sur les tetralones. En utilisant une méthode basée sur l’utilisation d’un groupe directeur éphémère, la position 8 de ce bicycle a été arylée, et les différents composés ainsi obtenus ont pu être convertis en d’autre plateformes polycycliques. En complément, des calculs DFT ont permis d’expliquer la régiosélectivité observée lors de la synthèse de fluorenones étendues, et d’étudier le mécanisme d’arylation dirigée des tetralones. / Because naphthalene has recently emerged as a fundamental platform in medicinal chemistry, the development of methodologies leading to diversely functionalised naphthalene-based platforms has become a prime concern of the scientific community. Indeed, experimental conditions previously optimised for benzene and other aromatic rings cannot always be applied to naphthalene. These methods can sometimes lead to different results, as a consequence of the lower aromaticity of the naphthalene core.In this context, this thesis is dedicated to the naphthalene and its derivatives. Various methods to selectively functionalise the different positions of the naphthalene core and synthetic pathways to extended polycyclic architectures were developed.Next, we focused on naphthalene precursors, especially on tetralones. Using a strategy involving a transient directing group, the position 8 of these bicycles was successfully arylated and the resulting compounds were successfully converted into other polycyclic platforms. In addition, DFT calculation have been used to explain the regioselectivity observed during the synthesis of extended fluorenones, and to study the mechanism of directed arylation of tetralones.