Esse tese experimental versa sobre reações eletroquímicas que ocorrem sobre estado termodinâmico afastado do equilíbrio. O sistema químico escolhido é o mais fundamental em eletrocatálise, a oxidação de monóxipdo de carbono (CO), cujo mecanismo fundamental envolve a remoção do CO por uma etapa Langmuir-Hinshelwood. A cinética complexa da oxidação do CO é um sistema biestável e corresponde a assinatura característica da oxidação do CO-bulk em um voltamograma cíclico. Se contanto, uma reação paralela é adicionada, por exemplo a oxidação de hidrogênio ou equivalentemente a adsorção/dessorção de íons cloreto, tal reação paralela quebra o vínculo conservativo entre os sítios livres e as respectivas coberturas de CO e espécie oxigenadas; o que permite o surgimento de oscilações autossustentáveis no tempo como resultado da passagem pela bifurcação de Hopf. Nesse sentido, o sistema H2/CO torna-se de crucial interessante pois mimetiza o oscilador mais corriqueiro em eletroquímica, o HNDR (acrônimo que traduzido para português lê \"Resistência Diferencial Negativa Escondida\"). Essa questão mecanística foi esclarecida nos experimentos com o sistema fundamental de três eletrodos onde foi testado diferentes geometrias e as variáveis mecanísticas essenciais reveladas. Nessa tese, há um segundo aspecto da dinâmica oscilatória da oxidação do H2/CO que consiste em tratar o mecanismo oscilatório sobre uma superfície espacialmente estendida, e nesse intuito foi escolhido usar uma célula a combustível (CaC), que é, em essência, um reator eletroquímico com grande área superficial. A cinética complexa da oxidação do H2/CO em uma CaC, apresentou transições dinâmicas de p1 → p2 → aperiodics. Suspeita-se de duas rotas para o caos: rota Feigenbaum (dobramento de período) e sobreposição de diferentes regiões de MMOs. O espaço de fase da dinâmica obtidas na CaC apresentou uma ordem quanto a distribuição dos períodos e amplitudes de uma séries caótica que permite predizer o comportamento a um curto alcance, e é uma prova indubitável de caos determinístico. A presença de caos foi diretamente atribuído à presença de pelo menos uma variável espacial. Apesar de nenhuma medida espacial ter sido realizada, inferências sobre acoplamentos espaciais são discutidos com base em argumentos lógicos, e sugere-se que exista acoplamento pela fase gasosa porém é improvável haver acoplamento elétrico exceto entre o anodo e o cátodo. A energia de ativação da CaC oscilante revelou que a condução protônica é a etapa determinante do período de oscilação. Diretamente indica que a variação espacial da condutividade da membrana pode ser considerado como uma variável espacial. Por fim, o terceiro aspecto dessa tese refere-se ao cálculo de eficiência para o estado oscilatório, experimental e teórico. Experimentalmente, o balanco energético de um sistema oscilante indicou uma maior eficiência que o respectivo estado estacionário. Teoricamente, a produção de entropia no ponto de bifurcação de Hopf deve ser maior que o respectivo estado estacionário devido a uma defasagem entre a força e potencial termodinâmico. Uma boa prova de que um estado oscilatório é um sistema dissipativo por promover uma conversão mais eficiente entre dois estados energéticos. / This thesis deals with an experimental electrochemical reactions that occur on thermodynamic state far from equilibrium. The chemical system selected is the most fundamental in electrocatalysis, the carbon monoxide (CO) oxidation, whose fundamental mechanism involves the removal of CO by a Langmuir-Hinshelwood step. The kinetics of the complex oxidation of CO is a bistable system and corresponds to the characteristic signature of CO-bulk oxidation in a cyclic voltammogram. If a parallel reaction is added, for instance the hydrogen oxidation or the chloride ion adsorption / desorption, this parallel reaction breaks the conservative link between the free sites and the coverage of both CO and oxygen species; which allows the appearance of self-sustaining oscillations in time as a result of passage through the Hopf bifurcation. In this sense, the system H2/CO becomes crucially interesting because it mimics the oscillator more commonplace in electrochemistry, the HNDR (\"Hidden Negative Differential Resistance\"). This mechanistic issue was cleared mainly in the experiments with the fundamental system in which different geometries were tested thus reavealing the essential mechanistic variables. In this thesis, there is a second aspect of the oscillatory oxidation of H2/CO which consists in treating the oscillating mechanism of a surface spatially extended, and to this end a fuel cell (FC), which is essentially an electrochemical reactor with a large surface area, was chosen to be used. The kinetics of the complex oxidation of H2/CO in a FC, showed dynamic transitions p1 → p2 → aperiodics. Two routes to chaos are suspected: Feigenbaum route (folding time) and different overlapping regions of MMOs. The FC phase space presented an order regarding the distribution of periods and amplitudes of a chaotic series that allows predicting the behavior in a short range, and it is an undoubtable proof of deterministic chaos. The presence of chaos was directly attributed to the presence of at least one spatial variable. Although no spatial measurement has been performed, inferences about spatial couplings are discussed based on logical arguments and suggests that there is coupling through the gas phase and whereas a electrical coupling between the anode and cathode is the unique with relevance with respect to the coupling by electrical field. The activation energy of the oscillating FC revealed that the proton conduction is a decisive step of the oscillation period. This directly indicates that the spatial variation of the conductivity of the membrane can be considered as a spacial variable. Finally, the third aspect of this thesis refers to the efficiency calculation from both experimental and theoretical points of view. Experimentally, the energy balance of an oscillating system indicated a higher efficiency than the repective steady state. Theoretically, the entropy production at the point of Hopf bifurcation must be greater than the steady state due to a lag between the thermodynamic force and potential. This is a good proof that an oscillatory state is a dissipative system becouse it promote a more efficient conversion between two energetic states.

The presented thesis focuses on studying the interaction between rhodium and cerium oxide and its impact on the reactivity. We investigated two different systems, Rh/CeOx and Rh-CeOx, by means of the photoelectron spectroscopy and the temperature programmed reactions. Rh/CeOx stands for rhodium nanoparticles supported by cerium oxide thin film. We show that there is an electronic metal-substrate interaction between rhodium and cerium oxide. The type of the interaction depends on a degree of cerium oxide reduction and it has a tremendous impact on the reactivity of the system. On the other hand, Rh-CeOx represents cerium oxide thin films doped by rhodium. We characterized the properties of the films with various concentration of rhodium. We show that the morphology, chemical composition and reactivity of the samples strongly depend on the concentration of the rhodium dopant. Powered by TCPDF (www.tcpdf.org)

Thesis advisor: Dunwei Wang / Atomically dispersed catalysts refer to substrate-supported heterogeneous catalysts featuring one or a few active metal atoms that are separated from one another. They represent an important class of materials ranging from single atom catalysts (SACs) and nanoparticles (NPs). The study of SACs has brought an attention of understanding the reaction mechanism at the molecular level. SACs is a promising field, however, there are still many challenges and opportunities in developing the next generation of catalysts. Catalysts featuring two atoms with well-defined structures as active sites are poorly studied. It is expected that this class of catalysts will show uniqueness in activity, selectivity, and stability. However, the difficulty in synthesizing such structures has been a critical challenge. I tackled this challenge by using a facile photochemical method to generate active metal centers consisting of two iridium metal atoms bridged by O ligands and bound to a support by stripping the ligands of the organometallic complex. My research also unveiled the structure of this dinuclear heterogeneous catalysts (DHCs) by integrating various characterization resources. Direct evidence unambiguously supporting the dinuclear nature of catalysts anchored on metal oxides is obtained by aberration-corrected scanning transmission electron microscopy. In addition, different binding modes have been achieved on two categories of metal oxides with distinguishable surface oxygen densities and interatomic distances of binding sites. Side-on bound DHCs was demonstrated on iron oxide and ceria where both Ir atoms are affixed to the surface with similar coordination environment. The binding sites on the OH-terminated surface of Fe2O3 and CeO2 anchor the catalysts to provide outstanding stability against detachment, diffusion and aggregation. The competing end-on binding mode, where only one Ir atom is attached to the substrate and the other one is dangling was observed on WO3. Evidence supporting the binding modes was obtained by in situ diffuse reflectance infrared Fourier transform spectroscopy. In addition, the synergistic effect between two adjacent Ir atoms and the uniqueness of different coordinative oxygen atoms around Ir atoms were investigated by a series of operando spectroscopy such as X-ray absorption spectroscopy and microscopy at atomic level under the reaction condition. The resulting catalysts exhibit high activities and stabilities toward H2O photo-oxidation and preferential CO oxidation. Density functional theory calculations provide additional support for atomic structure, binding sites modes on metal oxides, as well as insights into how DHCs may be beneficial for these catalytic reactions. This research has important implications for future studies of highly effective heterogeneous catalysts for complex chemical reactions. / Thesis (PhD) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Chemical warfare agents are a toxic class of compounds that are incredibly harmful to human health. Methods of detoxification and decontamination currently exist, however they all suffer from problems that involve logistical transport or involve technologies that directly address liquid threats instead of vapors. One promising method of detoxification involves the oxidation of these compounds into less-harmful species. The relatively large chemical size and complexity of modern-day chemical warfare agents, however, precludes a straightforward analysis of the chemical transformations that take place on novel decontaminating materials. Additionally, a fundamental understanding of reaction mechanisms that occur on novel material surfaces is required before improved materials can be developed. To this end, the oxidation of three simpler, smaller organic molecules were studied over a variety of materials in order to build up a chemical understanding of the systems under study. The photoepoxidation of propene into propene oxide was observed to readily occur over an in-house developed dual titania-silica catalyst created by atomic layer deposition. The subsequent photoinduced degradation of produced propene oxide was observed to occur over the novel catalyst. Next, the oxidation of CO was studied over a Pt/TiO2 catalyst while in the presence of humidity. The addition of water was shown to enable an alternative, low energy pathway that closely followed the water gas shift, but ended upon the production of stable surface-bound formates. Gaseous oxygen was found to subsequently oxidize these surface formates into the full oxidation product, CO2. Next, the oxidation of methanol was studied over the same Pt/TiO2 catalyst. It was discovered that the water produced when methanol initially adsorbs to the catalyst surface is responsible for unlocking the oxidative capacity of the material. Finally, a custom packedbed reactor was designed and built that enabled unique experimental capabilities not yet available in commercial systems, and will be used in the future to directly test the oxidative capabilities of novel materials for chemical warfare agent destruction. / Doctor of Philosophy / The chemical interactions and reactions that occur between gases and surfaces are incredibly important for a multitude of technologies employed by governments, militaries, and citizens alike. The precise methods in which these gases interact with materials of interest determine whether said material can be used in a catalytic fashion. Much like how an automobile catalytic converter does not have to be replaced each time the vehicle is started; a catalyst is able to be used repeatedly without loss of function. Catalysts in general are unique in that they function to create or allow for chemical reactions to proceed through alternative, lower energy pathways that are more likely to occur under milder environmental conditions. In order to understand the chemical reactions that occur on a catalyst, a combination of specialized spectroscopic methods was used that allowed for tracking the precise chemical bonds that were formed or broken during reaction. A few different model chemical reactions are explored in this work, ranging from the conversion of carbon monoxide into CO2, and the oxidation of methanol, a small alcohol commonly found in fuel cells. The experimental techniques employed herein allowed for precise chemical mechanisms to be tracked, and the information gained will certainly be useful for the design of next-generation materials by future research.

The experimental data and results demonstrated here illustrate the preparation and application of mesoporous metal oxides in energy storage, adsorption, and catalysis. First, a new method of controlling the pore size and wall thickness of mesoporous silica was developed by controlling the calcination temperature. A series of such silica were used as hard templates to prepare the mesoporous metal oxide Co₃O₄. Using other methods, such as varying the silica template hydrothermal treatment temperature, using colloid silica, varying the materials ratio etc., a series of mesoporous β-MnO₂ with different pore size and wall thickness were prepared. By using these materials it has been possible to explore the influence of pore size and wall thickness on the rate of lithium intercalation into mesoporous electrode. There is intense interest in lithium intercalation into titanates due to their potential advantages (safety, rate) replacing graphite for new generation Li-ion battery. After the preparation of an ordered 3D mesoporous anatase the lithium intercalation as anode material has been investigated. To the best of our knowledge, there are no reports of ordered crystalline mesoporous metal oxides with microporous walls. Here, for the first time, the preparation and characterization of three dimensional ordered crystalline mesoporous α-MnO₂ with microporous wall was described, in which K+ and KIT-6 mesoporous silica act to template the micropores and mesopores, respectively. It was used as a cathode material for Li-ion battery. Its adsorption behavior and magnetic property was also surveyed. Following this we described the preparation and characterization of mesoporous CuO and reduced Cu[subscript(x)]O, and demonstrated their application in NO adsorption and delivery. Finally a series of crystalline mesoporous metal oxides were prepared and evaluated as catalysts for the CO oxidation.

Les nanoparticules présentent des propriétés liées à la taille qui diffèrent fortement de celles observées dans des matériaux massifs. D'intenses recherches sur les nanoparticules sont actuellement en cours du fait de leurs grandes potentialités. Il a été montré que certaines nanoparticules métalliques sont catalytiquement actives et efficaces, comme par exemple le Palladium. L'objectif de la thèse est d'étudier la formation de nanoparticules de Pd déposées sur des surfaces pré-structurées de HOPG (Highly Ordered Pyrolytic Graphite) afin d'en optimiser la taille, la densité de surface et la stabilité. Trois étapes principales ont été menées dans nos études : la préparation des substrats, le dépôt de Pd et la caractérisation des échantillons par microscopie à effet tunnel (STM). La préparation des substrats contient elle-même deux étapes : la création de défauts par l'implantation d'agrégats Aun+ ou le bombardement de Co2, suivie d'une oxydation thermique. On obtient ainsi la formation de trous contrôlés en profondeur et en diamètre, qui serviront de sites d'ancrage pour les nanoparticules de Pd. Les mesures STM nous ont permis d'établir la relation entre la quantité de Pd déposée et la taille des nanoparticules de Pd formées à la surface du HOPG. Deux modes de croissance ont clairement été mis en évidence. Ils sont liés à la taille des défauts dans le HOPG. Les nanoparticules se présentent soit sous la forme de colliers soit sous la forme de particules isolées. Ces échantillons ont ensuite été caractérisés par des mesures de catalyse en chimie organique (Heck) ainsi qu'en catalyse gaz (oxydation du CO). / Nanoparticles exhibit size-related properties that different from those observed in bulk materials. Nanoparticle research has attracted intense interest due to its great potential applications. It has been shown that some metallic nanoparticles are catalytically active and effective, such as-Palladium.The aim of this thesis is to study the formation of Pd nanoparticles deposited on pre-structured HOPG (Highly Ordered Pyrolytic Graphite) surfaces in order to optimize their size, density and surface stability. Three major steps were taken in our studies: preparation of substrates, deposition of Pd and characterization of samples by scanning tunneling microscopy (STM). Substrats preparations itself contains two steps : the creation of defects by Aun+ clusters implantation or by bombardment of Co2 ions, followed by thermal oxidation. These steps give the formation of hales with controlled depth and diameter, which serve as anchoring sites for Pd nanoparticles.The STM measurements have allowed us to establish the relationships between the quantity of deposited Pd and the size of Pd nanoparticles formed on the HOPG surface. Two growth modes were clearly observed which are related to the defect sizes created on the HOPG surface. Nanoparticles are present either in the form of pearl necklace or in the form of isolated particles. These samples were then characterized by catalytic measurements in organic synthesis (Heck) and gas catalysis (CO oxidation).

A molecular-level understanding of a heterogeneous catalytic reaction is the key goal of heterogeneous catalysis. A surface science approach enables the realization of this goal. However, the working conditions (ultrahigh vacuum (UHV) conditions) of traditional surface science techniques restrict the investigations of heterogeneous catalysis system under industrial working conditions (atmospheric pressures). Polarization Modulation Infrared Reflection-Absorption Spectroscopy (PM-IRAS) can be operated in both UHV and atmospheric pressure conditions with a wide temperature span while providing high resolution (4 cm-1 is used in this dissertation) spectra. In this dissertation, PM-IRAS has been employed as a major technique to: 1) obtain both electronic and chemical information of catalysts from UHV to elevated pressure conditions; 2) explore reaction mechanisms by in situ monitoring surface species with concurrent kinetic measurements. In this dissertation, NO adsorption and dissociation on Rh(111) have been studied. Our PM-IRAS spectra show a transition of NO adsorption on three-fold hollow sites to atop sites occurs at low temperatures (<275 K). NO dissociation is found to account for this transition. The results indicated the dissociation of NO occurs well below the temperature previously reported. Characterizations of highly catalytically active Au films have also been carried out. Electronic and chemical properties of (1 x 1)- and (1 x 3)-Au/TiOx/Mo(112) films are investigated by PM-IRAS using CO as a probe molecule. The Au overlayers are found to be electron-rich and to have significantly different electronic properties compared with bulk Au. The exceptionally high catalytic activity of the Au bilayer structure is related to its unique electronic properties. CO oxidation reactions on Rh, Pd, and Pt single crystals are explored from low CO pressures under steady-state conditions (less than 1 x 10-4 Torr) to high pressures (0.01-10 Torr) at various gaseous reactant compositions. Surface CO species are probed with in situ PM-IRAS to elucidate the surface phases under reaction conditions. These experimental results are used to correlate reaction kinetics and surface reactant species. It is evident that there is a continuum over the pressure range studied with respect to the reaction mechanism. The most active phase has been shown to be an oxygen-dominant surface. The formation of a subsurface oxygen layer is found to deactivate the reaction.

During the last decades the specific manipulation of matter on the (sub-) nanometer scale, also known as nanoscience, became possible by technologies such as the scanning tunneling microscope. Nanocatalysts, i.e. catalytic active structures of up to a few nanometers in size, belong to this rather new class of materials. Unlike ordinary ’macroscopic’ catalytic materials, the performance of nanocatalysts does not simply scale, for instance, with the surface to volume ratio of the active material. In this Thesis model nanocatalysts are investigated by means of ab-initio density functional theory calculations. In paper I, we explain the experimentally observed catalytic characteristics of small gold clusters, Au1-4, on a regular magnesium oxide terrace towards the oxidation of carbon monoxide by thoroughly studying the adsorption of CO and O2 on these clusters. In the subsequent paper II, we study the feasibility of a catalytic water-mediated CO oxidation reaction on Au1-4/MgO and find that this reaction mechanism is not assessable for Au2,4/MgO and unlikely for Au1,3/MgO. Papers III and IV concentrate on the reactivity of clusters in the gas phase. Particularly, we focus on the relative stability of Au13 isomers and its potential for O2 dissociation (paper III). We find the lowest energy isomers, which contain a triangular prism at their center surrounded by a ring of the remaining seven atoms, to be generally stable upon O2 adsorption. The dissociation of O2 at certain sites of Au13 is found to be exothermic. In paper IV we performed scans of the Born-Oppenheimer potential energy surfaces of neutral and charged Cu3, Ag3, and Au3 to explore the thermally excited vibrations of these trimers. While the Born-Oppenheimer surface of Cu3 exhibits one fairly deep energy minimum, it is comparatively flat with two shallow minima in the case of Ag3. Hence for Ag3 there exist many thermally accessible geometries in a wide range of angles and bond lengths. For Au3, two distinct energy minima appear, being well-separated by a barrier of 180 meV. Already at room temperature, we find bond lengths changes of up to 5% for the studied trimers. Choosing Au3 as a case study for the changed reactivity of thermally excited modes, we find CO to bind up to 150 meV stronger to the excited cluster. Gold deposited on graphene and graphite was observed to form larger aggregates. In paper V, we study the electronic structures, high mobility, and substrate-mediated clustering processes of Au1-4 on graphene. Already in the 1970s is was speculated that dispersion forces, i.e. van der Waals forces, significantly contribute to the adsorption energies of gold atoms on graphite. We accounted for van der Waals interactions in our density functional theory calculations (paper VI) and investigated the influence of these dispersion forces on the binding of copper, silver, and gold adatoms on graphene. While copper and gold show a mixed adsorption mechanism, i.e. chemical binding plus attraction due to the van der Waals forces, silver is purely physisorbed on graphene. / Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 719

Made available in DSpace on 2016-06-02T19:56:59Z (GMT). No. of bitstreams: 1 6783.pdf: 3853594 bytes, checksum: 5c76462cb2ede47f0f6638372f3f2364 (MD5) Previous issue date: 2015-02-18 / Financiadora de Estudos e Projetos / The fluid catalytic cracking (FCC) is one of the most important process in the petroleum refining industry, being responsible for the increase of the yield of the most valuable light hydrocarbons. On the other hand, the FCC process generates big amounts of CO, NOx and SOx emissions. The CO emissions from the most of pollution sources are abatement using noble metal based catalysts. However, the growing demand and scarcity of those metals have caused an increase in the process cost and consequently promoting studies to find alternative catalysts with comparable efficiency and lower in cost. In this respect, the literature had presented interesting results with transitions metal catalysts. Thus, the objective of this work was to prepare exchanged or impregnated Fe or Mn on H-mordenite or Ce-mordenite, which were evaluated between 150 and 550 oC in the CO oxidation with O2, in the presence or absence of interfering compounds (water steam or SO2). The catalysts were characterized by ICP-OES, DRX, DRS-UV-VIS and Mössbauer spectroscopy. The results showed that the preparation procedures of the interchanged or impregnated Fe or Mn catalysts were adequate, and no mordenite crystallinity loss was observed. Contrary to the exchanged Fe or Mn based catalysts, those based on impregnated Fe or Mn oxides showed a important potential as catalysts in the CO oxidation with O2. Then, in the applied operational conditions the Ce-MOR/Fe10, Ce-MOR/Mn5, Ce-MOR/Mn10 e H-MOR/Mn5 catalysts were able to produce an effluent with CO content lower than 500 ppm, which is the allowed limit by the environmental regulations related with FCC units. In the presence of water steam the evaluated Fe or Mn catalysts presented activity loss that was recovered after the elimination of that interfering from the feed. Nevertheless, in the presence of SO2, the tested catalysts showed an irreversible and significantly activity loss. / O craqueamento catalítico fluido (FCC) é uma das etapas mais importantes no refino de petróleo, sendo responsável pelo aumento do rendimento em frações leves, de maior valor agregado. Por outro lado, o FCC é responsável na refinaria por uma grande parcela das emissões de monóxido de carbono (CO), óxidos de nitrogênio (NOx) e óxidos de enxofre (SOx). O CO, em particular, na maioria das fontes poluidoras é eliminado via oxidação sobre catalisadores à base de metais nobres. Porém, o aumento na demanda desses metais e sua baixa disponibilidade criam um forte impacto no custo do processo, surgindo a necessidade de buscar catalisadores alternativos, com eficiência comparável e de menor custo. Assim, o objetivo deste trabalho foi preparar catalisadores à base de ferro ou manganês impregnados ou trocados em H-mordenita ou Ce-mordenita e avaliá-los entre 150 e 550 oC na oxidação de CO com oxigênio (O2), na ausência ou presença de compostos interferentes à reação como vapor de água e dióxido de enxofre (SO2). Os catalisadores foram caracterizados por espectroscopia de emissão atômica (ICP-OES), difração de raios X (DRX), espectroscopia de reflectância difusa (DRS-UV-VIS), redução com H2 à temperatura programada (RTP-H2) e espectroscopia Mössbauer (MOSS). Os resultados mostraram que os procedimentos de preparação dos catalisadores, trocados ou suportados, foram eficientes, não se observando perda de cristalinidade da mordenita. Os catalisadores com óxidos de Fe ou Mn suportados na mordenita apresentaram um importante potencial para serem utilizados como catalisadores na oxidação de CO com O2, contrário ao que ocorreu com cátions de Fe ou Mn em sítios de troca. Assim, nas condições operacionais utilizadas, os catalisadores Ce-MOR/Fe10, Ce-MOR/Mn5, Ce-MOR/Mn10 e H-MOR/Mn5 foram capazes de converter CO suficiente para produzir um efluente gasoso com teor menor que 500 ppm de CO, sendo essa a concentração limite permitida pela legislação que rege as emissões de unidades FCC. Os catalisadores impregnados com Fe e Mn, quando avaliados na presença de vapor de água e de SO2, ocorreu perda da atividade, a que foi recuperada somente no caso do vapor de água.

Made available in DSpace on 2016-06-02T19:55:24Z (GMT). No. of bitstreams: 1 2075.pdf: 4577723 bytes, checksum: 80abdc876165c000f61328875ff2a061 (MD5) Previous issue date: 2008-10-20 / Financiadora de Estudos e Projetos / Mixed oxides with perovskite structure have high potential as catalysts in gas depollution processes and particularly in the abatement of nitrogen oxides (NOx). Such solids could be considered as a promising alternative for the replacement of noble metals based catalysts, whose use is predominant. Great flexibility of composition, easy synthesis, low cost and high thermal stability justify the special interest in these materials. However, the low specific surface areas (<10 m2/g) of these solids, when prepared by conventional methods, limit your use in catalytic processes. Some efforts have been made in order to overcome that disadvantage. Nevertheless, the preparation of high surface area ternary or multinary oxides is not easy once their synthesis is associated with solid state reactions carried out at high temperatures. Considering the discussed context, perovskites were obtained in this work by means of a conventional method or via sequencial nanocasting. In the first case, perovskites with LaFe1-xCoxO3 (x = 0, 0.2, 0.3, 0.4, 0.5 and 1) nominal compositions were prepared using the citrate method and nitrate salts as inorganic precursors. In the second case, LaFeO3 and LaFe0.6Co0.4O3 perovskites were obtained by nanocasting using Fluka 05120 activated carbon, Black Pearls 2000 black carbon (Cabot Corporation), and porous carbons nanocasted in Aerosil 200 pyrogenic silica and sílica-SBA-15 mesoporous molecular sieve. X-ray diffraction (XRD), N2 sorption measurements, X-ray fluorescence (XRF), hydrogen temperature programmed reduction (H2-TPR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transformed infrared spectroscopy (FTIR) and thermogravimetry (TG) were used to characterize the studied solids. The catalytic activity of the prepared perovskites was evaluated in the reduction of NO to N2 with CO and in the oxidation of the latter compound to CO2. According to the obtained results, it was evident that in comparison with the conventional route, the nanocasting technique using carbons as hard template was efficient to obtain the pure perovskite phase with specific surface areas substantially higher (25 a 49 m2/g). The prepared perovskites were highly active and selective in the reduction of NO to N2 with CO, as well as in the oxidation of the latter compound to CO2. The most active samples were those whose B sites contain up to about 30 % Co. However, the activity of these catalysts decreases strongly with the presence of O2 or water steam. The La-Fe nanocasted binary perovskites showed, in the studied reactions, remarkable higher catalytic activity than the perovskite with the same composition prepared using the conventional method. The higher activity of these materials was related with the increase of their specific surface area. The nanocasted ternary perovskites with LaFe0.6Co0.4O3 composition, despite of the significant increase in their specific surface area, did not show a considerable increase in their activity. This result is in agreement with the behaviour of La-Fe-Co ternary perovskites, in which Co occupies a proportion of B sites greater than 30 %. / Óxidos mistos com estrutura perovskita apresentam alto potencial como catalisadores em processos de despoluição de gases e particularmente no abatimento de óxidos de nitrogênio (NOx). Tais sólidos são uma alternativa promissora para substituição de catalisadores à base de metais nobres, cujo uso é predominante. Vantagens como grande flexibilidade de composição, fácil síntese, baixo custo e elevada estabilidade térmica justificam o especial interesse por esses materiais. Contudo, as baixas áreas superficiais específicas desses sólidos (< 10 m2/g), quando sintetizados por métodos convencionais, limitam o seu uso em processos catalíticos. Algumas tentativas têm sido feitas no sentido de contornar essa desvantagem. No entanto, a obtenção de óxidos ternários ou multinários de alta área superficial específica é especialmente difícil, uma vez que sua síntese está associada a reações no estado sólido realizadas em temperaturas elevadas. Considerando o contexto discutido, neste trabalho foram obtidas perovskitas através de método convencional ou via nanomoldagem seqüencial. No primeiro caso, perovskitas com composição nominal LaFe1-xCoxO3 (x = 0; 0,2; 0,3; 0,4; 0,5 e 1) foram preparadas utilizando o método do citrato e sais de nitratos como precursores inorgânicos. No segundo caso, perovskitas LaFeO3 e LaFe0,6Co0,4O3 foram obtidas por nanomoldagem utilizando carbono ativado Fluka 05120, negro de fumo Black Pearls 2000 (Cabot Corporation), e carbonos porosos nanomoldados em sílica pirogênica Aerosil 200 e peneira molecular mesoporosa sílica-SBA-15. Difração de raios X (DRX), medidas de adsorção/dessorção de N2, fluorescência de raios X (FRX), redução com hidrogênio a temperatura programada (RTP-H2), microscopia eletrônica de varredura (MEV), microscopia eletrônica de transmissão (MET), espectroscopia no infravermelho por transformada de Fourier (IV) e termogravimetria (TG) foram utilizadas para caracterizar os sólidos estudados. A atividade catalítica das perovskitas preparadas foi avaliada na redução de NO a N2 com CO e na oxidação desse último composto a CO2. De acordo com os resultados obtidos, ficou evidente que em comparação com a rota convencional, a técnica de nanomoldagem utilizando moldes de carbono foi eficiente na obtenção da fase perovskita pura com área superficial específica substancialmente maior (25 a 49 m2/g). As perovskitas preparadas foram altamente ativas e seletivas na redução de NO a N2 com CO, bem como na oxidação desse último composto a CO2, sendo mais ativas aquelas cujos sítios B contêm até cerca de 30 % de Co. A presença de O2 ou vapor de água, entretanto, reduz fortemente a atividade desses catalisadores. As perovskitas binárias La-Fe nanomoldadas apresentaram, nas reações estudadas, atividade catalítica consideravelmente superior a da perovskita com a mesma composição preparada pelo método convencional. A maior atividade desses materiais foi relacionada com o aumento da sua área superficial específica. As perovskitas nanomoldadas ternárias com composição LaFe0,6Co0,4O3, apesar do significativo aumento na sua área superficial específica, não apresentaram um aumento considerável na atividade, fato esse condizente com o comportamento de perovskitas ternárias La-Fe-Co, nas quais o Co ocupa uma proporção de sítios B superior a 30 %.