A eletro-oxidação de metanol e etanol é um tema ativamente estudado em eletrocatálise. O motivo da grande atenção dada à investigação da atividade eletrocatalítica destes álcoois é devido à procura de novos sistemas conversores de energia mais eficientes e menos poluidores. As pesquisas em eletrocatálise têm sido direcionadas também ao estudo de sistemas nanoparticulados. Partículas metálicas de tamanho nanométrico oferecem aspectos interessantes no estudo de efeitos estruturais em eletrocatalisadores dispersos. O decréscimo do tamanho de partícula promove uma utilização mais eficiente do catalisador, uma vez que a razão do número de átomos superficiais pelo número de átomos total é favorecida. Neste trabalho, investigou-se a oxidação eletroquímica de metanol e etanol sobre catalisadores de Pt e catalisadores de PtRh através da técnica de espectrometria de massas eletroquímica diferencial (DEMS). Nos catalisadores PtRh/C foi estudado o efeito da composição atômica do catalisador na reação de oxidação destes álcoois e nos catalisadores comerciais Pt/C E-Tek o efeito de tamanho de partícula na reação de oxidação de metanol. Na eletro-oxidação dos álcoois metanol e etanol sobre os catalisadores PtRh/C observou-se que a corrente faradáica decresceu em função do aumento de ródio no catalisador bimetálico. Por outro lado, a eficiência na oxidação completa do álcool a CO2 aumentou com a adição de ródio ao catalisador de platina. Atribuiu-se aos resultados obtidos com o catalisador PtRh/C, que o efeito eletrônico deve ter um papel importante no mecanismo de oxidação dos álcoois sobre estes catalisadores bimetálicos. No caso dos catalisadores Pt/C E-Tek o efeito do tamanho de partícula na reação de oxidação de metanol foi evidente. As medidas de eletro-oxidação de metanol mostraram uma eficiência alta na oxidação completa do álcool a CO2 sobre os catalisadores de carga metálica 30 e 40 %. Inferiu-se neste caso, que deve ser considerado não somente a morfologia da partícula, mas também o acoplamento entre partículas de tamanhos diferentes via produtos solúveis a fim de se obter um entendimento melhor do mecanismo global da reação. Sugeriu-se que há uma faixa de tamanho de partícula ótimo para a eletro-oxidação eficiente de metanol a CO2, de 3 a 10 nm. A perda em eficiência pode ser devido tanto a partículas muito pequenas quanto muito grandes conduzindo principalmente a oxidação parcial de metanol a formaldeído. / The methanol and ethanol electrooxidation is a subject of intense studies in electrocatalysis. The aim of such attention concerning this alcohol electrooxidation activity is due to development of new energy converter systems more efficient and less pollutant. The electrocatalysis research has been also directed to nanoparticle systems. Metallic particles in nanometric size offer interesting aspects for structural effects studies in supported electrocatalysts. The particle size decrease could promote efficient catalyst use, once the ratio number of superficial atoms/total atoms raises. In this work, the electrochemical oxidation of methanol and ethanol on Pt/C and PtRh/C catalysts through differential electrochemical mass spectrometry (DEMS) was investigated. The atomic composition effect in the alcohol oxidation was studied on PtRh/C catalysts. The particle size effect on methanol oxidation reaction was studied on Pt/C E-Tek catalysts. It has been observed in this bimetallic catalysts that the higher rhodium content, the lower faradaic current. On the other hand, the efficiency for complete methanol electrooxidation to CO2 increased with rhodium addition in the platinum catalyst. To these results were assigned that electronic effect plays a key role in the mechanism of alcohol oxidation on bimetallic catalysts. For Pt/C E-Tek catalysts ones, the particle size effect in the methanol oxidation reaction was more evident. Methanol electrooxidation measurements have shown a high efficiency for complete alcohol oxidation to CO2 on the 30 and 40 % wt. Pt/C catalysts. It was inferred, in this case, that must be consider not only the particle morphology but also the coupling between different size particles via soluble products in order to improve a better understanding of global reaction mechanism. It was suggested that there is an optimum particle size range for efficient methanol electrooxidation to CO2, that is, 3 to 10 nm range. The loss of efficiency could be due to very small particles or very great particles resulting in methanol partial oxidation mainly to formaldehyde.

O ouro foi considerado um metal pouco interessante do ponto de vista catalítico por muito tempo, devido ao fato de não quimiossorver moléculas como hidrogênio e oxigênio. Entretanto, suas propriedades catalíticas são reveladas quando suas dimensões são reduzidas a poucos nanômetros, particularmente menores do que 10 nm. Assim, nanocatalisadores de ouro vêm recebendo atenção devido as suas excelentes propriedades catalíticas e alta seletividade em reações de oxidação e redução. O presente trabalho descreve a síntese e caracterização de nanopartículas de ouro suportadas e sua aplicação em reações de oxidação de alcoóis para produção de aldeídos, cetonas e ésteres. Para facilitar a separação do catalisador, um suporte magnético composto de magnetita revestida com sílica foi desenvolvido. A síntese das nanopartículas de ouro suportadas foi realizada de duas maneiras: (I) pela impregnação do suporte com espécies aniônicas de ouro seguido de redução e (II) pela impregnação de nanopartículas de ouro pré-sintetizadas. Em todos os casos nanopartículas de ouro na faixa de 5 nm foram obtidas. A etapa de redução do metal impregnado no suporte foi investigada em detalhe através de duas estratégias: a redução térmica e a redução por hidrogênio. Os testes catalíticos para as reações de oxidação de alcoóis mostraram que os catalisadores sintetizados apresentam altas taxas de conversão e seletividade, porém dependentes do método de preparação utilizado / Gold in the bulk form has been regarded to be an uninteresting metal from the point of view of catalysis, as it is chemically inert towards chemisorption of reactive molecules such as oxygen and hydrogen. However, the catalytic properties of gold are revealed when the size is reduced to few nanometers, particularly with dimension less than 10 nm. Therefore, gold nanocatalysts have received great attention due to the excellent catalytic properties and high selectivity in oxidation and reduction reactions. This master thesis describes the synthesis and characterization of supported gold nanoparticles and their application in alcohol oxidation reaction to produce aldehydes, ketones and esters. In order to improve the catalyst separation and recovery, a magnetic support comprised of magnetite coated by silica was developed. The supported gold nanoparticles were synthesized in two different ways: (I) by impregnation of anionic gold species on silica surface followed by metal reduction, and (II) by impregnation of pre-synthesized gold nanoparticles on the support. In all examples supported gold nanoparticles of about 5 nm were obtained. The reduction step (of the metal impreganted on the support) was investigated in detail by two different strategies: thermal reduction and reduction by hydrogen. The synthesized catalysts showed high conversion rates and selectivity in the catalytic reactions of alcohol oxidation, but those are dependent on the preparation method

Choline oxidase catalyzes the four-electron oxidation of choline to glycine betaine, a limited number of compounds that accumulate to high levels in cytoplasm to prevent dehydration and plasmolysis in adverse hyperosmotic environments. With this respect, the study of choline oxidase has potential for the development of therapeutic agents that inhibit the biosynthesis of glycine betaine, thereby rendering pathogenic bacteria susceptible to either conventional treatments or the immune system. In this study, the highly GC rich codA gene encoding for choline oxidase was cloned, expressed. The resulting enzyme was purified to high levels, allowing for detailed biochemical, mechanistic and structural characterizations. A chemical mechanism for the reaction catalyzed by choline oxidase was established by using kinetic isotope effects and viscosity effects as probes, in which the choline hydroxyl proton is not in flight in the transition state for CH bond cleavage. Furthermore, these experiments indicated that chemical steps of flavin reduction by choline and betaine aldehyde are rate limiting for the overall turnover of the enzyme. Further mechanistic characterization clearly suggested a hydride transfer mechanism that is fully quantum mechanical. The structure of choline oxidase was resolved at 1.86 Å resolution in collaboration with the group of Dr. Allen O. Orville, at the Georgia Institute of Technology, providing a structural framework that is consistent with the mechanistic studies. The results of these studies will be presented and discussed in the context of the Glucose-Methanol-Choline oxidoreductase enzyme superfamily, of which choline oxidase is a member. Previous structural and mechanistic studies of alcohol- and aldehyde-oxidizing enzymes with different cofactors, as well as the biotechnological and biomedical relevance of choline oxidase are presented in Chapter 1. Chapter 3-8 illustrate my studies on choline oxidase, including cloning, expression, purification and preliminary characterizations (Chapter 3), spectroscopic and steady state kinetics (Chapter 4), the determination of the chemical mechanism for alcohol oxidation and the investigation of the involvement of quantum mechanical tunneling (Chapter 5 and 6), the study of aldehyde oxidation (Chapter 7), and the structural determination of choline oxidase by x-ray crystallography (Chapter 8). Chapter 9 presents a general discussion of the data presented.

Transition metal nanoclusters are more active and selective catalysts than their bulk counterparts as the fraction of surface atoms increases with the decreasing particle size. When stabilized in organic or aqueous solutions, they can catalyze many reactions. The catalytic activity of metal nanoclusters depends on the particle size and size distribution. Particle size can be controlled by encapsulating the nanoclusters in the cavities of highly ordered porous materials such as zeolites. In this project, osmium(0) nanoclusters were formed within the void spaces of zeolite. Thus, nanoclusters of certain size were prepared as supported catalyst. Osmium(III) cations were introduced into the cavities of zeolite by ion exchange and were reduced partially or completely to form intrazeolite osmium(0) nanoclusters. The intrazeolite osmium(0) nanocusters were characterized by HRTEM, TEM, EDX, XPS, XRD, ICP-OES spectroscopic methods and N2 adsorption-desorption technique. Intrazeolite osmium(0) nanoclusters were employed as catalyst in the aerobic oxidation of alcohols in organic solution.

This report summarises the work done on monohydroxy aliphatic alcohol upgrading using Au/TiO2 catalysis. The catalysts were initially tested using a plug-flow CO oxidation reactor; complete conversion of a stream of CO flowing over the catalyst bed at a GHSV of approximately 79,500 hr-1 was typically achieved without any required external heating. TEM analysis showed that the freshly prepared catalyst does not contain detectable Aunano clusters, while the spent CO oxidation catalyst had clearly visible nanoparticles with an average size of approximately 1.6 nm. XRD analyses showed that the final pH to which the deposition-precipitation procedure was adjusted had a major role in determining the average nanocluster size. Alcohols were oxidised using the 1% Au/TiO2 catalyst in a plug-flow reactor, with the alcohol vapour being produced by sparging a blended stream of helium and oxygen (typically made up to a total flowrate of 100 ml min-1). The temperature of the alcohol could be adjusted, thereby controlling the vapour mole fraction of alcohol. For methanol oxidation, the primary reaction pathway across the entire range of studied feed compositions was combustion. The onset of combustion occurred dramatically, in the range of 140-160°C. For ethanol oxidation, acetaldehyde selectivity increases and overall conversion decreases as the oxygen content of the feed stream decreases. The kinetics of the catalysed ethanol oxidation showed a compensation effect, described by the equation ln(A) = 0.2032EA + 2.6102 (EA in kJ mol-1). Propanol oxidation demonstrated the highest selectivity towards a value added product (propanaldehyde), with propanaldehyde being formed in significant quantities. However, combustion was still favoured at high temperatures when large excesses oxygen were present. The thermokinetic data calculated for n-propanol oxidation did not exhibit the compensation effect observed in ethanol oxidation; the EA for this reaction was stable at approximately 38 kJ mol-1. In the anaerobic catalysed reactions of ethanol and n-propanol, an oily layer was collected above the water meniscus in a cold trap. This oil could potentially be formed via poly-aldol condensation reactions of the aldehydes produced during oxidation. Though other researchers suggest these condensation reactions typically end in a cyclic dehydration into aromatic compounds, electrospray mass spectrometry found no indication of such products. Control reactions performed using unloaded TiO2 and porous Au (obtained by in-situ reduction of Au2O3) produced different product distributions, all requiring substantially higher reaction temperatures. This suggests that there must be a synergistic effect between the Au and TiO2 substrate which facilitates reactions. Furthermore, the product distributions of the 1% Au/TiO2 catalysed reactions were significantly different from results published by other researchers performing similar oxidations on Au(111) single crystals, where substantially higher selectivity towards value-added products (formaldehyde, acetaldehyde, and propanaldehyde) is typically observed.

A eletro-oxidação de metanol e etanol é um tema ativamente estudado em eletrocatálise. O motivo da grande atenção dada à investigação da atividade eletrocatalítica destes álcoois é devido à procura de novos sistemas conversores de energia mais eficientes e menos poluidores. As pesquisas em eletrocatálise têm sido direcionadas também ao estudo de sistemas nanoparticulados. Partículas metálicas de tamanho nanométrico oferecem aspectos interessantes no estudo de efeitos estruturais em eletrocatalisadores dispersos. O decréscimo do tamanho de partícula promove uma utilização mais eficiente do catalisador, uma vez que a razão do número de átomos superficiais pelo número de átomos total é favorecida. Neste trabalho, investigou-se a oxidação eletroquímica de metanol e etanol sobre catalisadores de Pt e catalisadores de PtRh através da técnica de espectrometria de massas eletroquímica diferencial (DEMS). Nos catalisadores PtRh/C foi estudado o efeito da composição atômica do catalisador na reação de oxidação destes álcoois e nos catalisadores comerciais Pt/C E-Tek o efeito de tamanho de partícula na reação de oxidação de metanol. Na eletro-oxidação dos álcoois metanol e etanol sobre os catalisadores PtRh/C observou-se que a corrente faradáica decresceu em função do aumento de ródio no catalisador bimetálico. Por outro lado, a eficiência na oxidação completa do álcool a CO2 aumentou com a adição de ródio ao catalisador de platina. Atribuiu-se aos resultados obtidos com o catalisador PtRh/C, que o efeito eletrônico deve ter um papel importante no mecanismo de oxidação dos álcoois sobre estes catalisadores bimetálicos. No caso dos catalisadores Pt/C E-Tek o efeito do tamanho de partícula na reação de oxidação de metanol foi evidente. As medidas de eletro-oxidação de metanol mostraram uma eficiência alta na oxidação completa do álcool a CO2 sobre os catalisadores de carga metálica 30 e 40 %. Inferiu-se neste caso, que deve ser considerado não somente a morfologia da partícula, mas também o acoplamento entre partículas de tamanhos diferentes via produtos solúveis a fim de se obter um entendimento melhor do mecanismo global da reação. Sugeriu-se que há uma faixa de tamanho de partícula ótimo para a eletro-oxidação eficiente de metanol a CO2, de 3 a 10 nm. A perda em eficiência pode ser devido tanto a partículas muito pequenas quanto muito grandes conduzindo principalmente a oxidação parcial de metanol a formaldeído. / The methanol and ethanol electrooxidation is a subject of intense studies in electrocatalysis. The aim of such attention concerning this alcohol electrooxidation activity is due to development of new energy converter systems more efficient and less pollutant. The electrocatalysis research has been also directed to nanoparticle systems. Metallic particles in nanometric size offer interesting aspects for structural effects studies in supported electrocatalysts. The particle size decrease could promote efficient catalyst use, once the ratio number of superficial atoms/total atoms raises. In this work, the electrochemical oxidation of methanol and ethanol on Pt/C and PtRh/C catalysts through differential electrochemical mass spectrometry (DEMS) was investigated. The atomic composition effect in the alcohol oxidation was studied on PtRh/C catalysts. The particle size effect on methanol oxidation reaction was studied on Pt/C E-Tek catalysts. It has been observed in this bimetallic catalysts that the higher rhodium content, the lower faradaic current. On the other hand, the efficiency for complete methanol electrooxidation to CO2 increased with rhodium addition in the platinum catalyst. To these results were assigned that electronic effect plays a key role in the mechanism of alcohol oxidation on bimetallic catalysts. For Pt/C E-Tek catalysts ones, the particle size effect in the methanol oxidation reaction was more evident. Methanol electrooxidation measurements have shown a high efficiency for complete alcohol oxidation to CO2 on the 30 and 40 % wt. Pt/C catalysts. It was inferred, in this case, that must be consider not only the particle morphology but also the coupling between different size particles via soluble products in order to improve a better understanding of global reaction mechanism. It was suggested that there is an optimum particle size range for efficient methanol electrooxidation to CO2, that is, 3 to 10 nm range. The loss of efficiency could be due to very small particles or very great particles resulting in methanol partial oxidation mainly to formaldehyde.

Neste trabalho foram produzidos eletrocatalisadores Pd/C, Au/C, PdAu/C, PdAuPt/C, PdAuBi/C e PdAuIr/C a partir do método de redução por borohidreto para oxidação eletroquímica de metanol, etanol e etilenoglicol. No método de redução por borohidreto, adiciona-se de uma só vez uma solução alcalina contendo borohidreto de sódio a uma mistura contendo água/2-propanol, precursores metálicos e o suporte de carbono Vulcan XC72. Os eletrocatalisadores obtidos foram caracterizados por espectroscopia de energia dispersiva de raios-X (EDX), difração de raios-X (DRX), microscopia eletrônica de transmissão (MET) e voltametria cíclica. A oxidação eletroquímica do metanol, etanol e etilenoglicol foi estudada por cronoamperometria utilizando a técnica do eletrodo de camada fina porosa. O estudo do mecanismo de oxidação eletroquímica do etanol foi estudado por meio da técnica de espectroscopia no infravermelho com transformada de Fourier (FTIR) in situ. Os melhores eletrocatalisadores foram testados em células alcalinas unitárias alimentadas diretamente por metanol, etanol e etilenoglicol. Estudos preliminares mostraram que a composição atômica adequada para preparar catalisadores ternários é igual a 50:45:05. De acordo com os experimentos eletroquímicos em meio básico, o eletrocatalisador PdAuPt/C (50:45:05) apresentou a maior atividade para oxidação eletroquímica de metanol, enquanto que, nas mesmas condições, o PdAuIr/C foi mais ativo para oxidação do etanol e o PdAuBi/C mais ativo para a oxidação do etilenoglicol. Estes resultados indicam que a adição de ouro na composição dos eletrocatalisadores contribui para uma maior atividade catalítica dos mesmos. Os resultados de FTIR mostraram que o mecanismo da oxidação do etanol se processa de modo indireto, ou seja, a ligação CC não é rompida, formando acetato. / In this study Pd/C, Au/C, PdAu/C, PdAuPt/C, PdAuBi/C and PdAuIr/C electrocatalysts were prepared by the sodium borohydride reduction method for the electrochemical oxidation of methanol, ethanol and ethylene glycol. This methodology consists in mix an alkaline solution of sodium borohydride to a mixture containing water/isopropyl alcohol, metallic precursors and the Vulcan XC 72 carbon support. The electrocatalysts were characterized by energy dispersive X-ray (EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM) and cyclic voltammetry. The electrochemical oxidation of the alcohols was studied by chronoamperometry using a thin porous coating technique. The mechanism of ethanol electro-oxidation was studied by Fourier Transformed Infrared (FTIR) in situ. The most effective electrocatalysts were tested in alkaline single cells directly fed with methanol, ethanol or etylene glycol. Preliminary studies showed that the most suitable atomic composition for preparing the ternary catalysts is 50:45:05. Electrochemical data in alkaline medium show that the electrocatalyst PdAuPt/C (50:45:05) showed the better activity for methanol electrooxidation, while PdAuIr/C was the most active for ethanol oxidation and PdAuBi/C (50:45:05) was the most effective for ethylene glycol oxidation in alkaline medium. These results show that the addition of gold in the composition of electrocatalysts increases their catalytic activities. The spectroelectrochemical FTIR in situ data permitted to conclude that C-C bond is not broken and the acetate is formed.

L'objectif de cette thèse était d'évaluer des nitroxydes chiraux à squelette imidazolidin-4-one comme catalyseurs d'oxydation énantiosélective d'alcools par le dioxygène. Pour cela, plusieurs nitroxydes avec différents substituants en position α ont été synthétisés afin de voir les effets possibles de chacun des groupements. Différents co-catalyseurs décrits dans la bibliographie ont été testés afin de faire ces réactions qui ont lieu à température ambiante et pression atmosphérique. Ces systèmes catalytiques peuvent se différencier selon s'ils utilisent ou pas de métal comme additif.La stratégie utilisée pour la synthèse des catalyseurs a été développée au laboratoire à partir de travaux sur des nitrones réalisés précédemment. Grâce à cette stratégie et à l'utilisation de différentes nitrones de départ, des analogues différemment substitués en position α peuvent être synthétisés rapidement en seulement deux étapes. En particulier, l'utilisation d'une nitrone chirale nous permettra l'obtention de catalyseurs énantiopurs qui pourront être utilisés pour les réactions d'oxydation énantiosélectives.Dans la première partie de notre étude, différents systèmes catalytiques ont été testés avec nos catalyseurs sur un substrat modèle : l'alcool benzylique. Les résultats obtenus nous ont aidé à déterminer : (1) la capacité des nitroxydes de type imidazolidin-4-one à agir en tant que catalyseurs pour les réactions d'oxydation aérobie ; (2) la différence de réactivité selon la substitution en position α ; (3) les systèmes catalytiques les plus efficaces avec nos catalyseurs ; (4) le type de substrats qui pourront être envisagés lors de l'oxydation énantiosélective.C'est ainsi la désymétrisation de diols conduisant à la formation d'atropoisomères qui a été envisagée. L'oxydation par le dioxygène de trois substrats a ainsi été testée avec plusieurs catalyseurs énantiopurs et un système catalytique à base de cuivre. Les résultats d'énantiosélectivité obtenus ont été variables selon le substrat et le catalyseur utilisés. Des résultats très encourageants ont été obtenus pour l'un des substrats, avec des excès enantiomériques d'environ 60 %.En parallèle avec les différentes réactions d'oxydation, des études de voltammétrie cyclique et de résonance paramagnétique électronique (RPE) ont aussi été réalisées. La voltammétrie cyclique nous a servi surtout pour expliquer la différence de réactivité de différents analogues selon leur substitution en position α. Avec la RPE, nous avons essayé de comprendre un peu plus l'organisation autour du cuivre des différents éléments qui font partie du système catalytique à base de cuivre utilisé pour les oxydations énantiosélectives.Grâce à tous ces travaux, nous avons démontré que les nitroxydes à squelette imidazolidin-4-one peuvent être utilisés en tant que catalyseurs pour l'oxydation aérobie d'alcools. Nous avons noté l'importance des substituants en position α qui jouent un rôle important sur la stabilité de l'espèce active, ce qui pourra faire varier l'efficacité de chaque composé. Les nitroxydes contenant le squelette imidazolidin-4-one ont aussi donné des bons résultats dans des réactions d'oxydation énantioséletive de diols benzyliques. / The aim of this thesis was to evaluate the use of chiral nitroxides containing an imidazolidin-4-one squeletton as enantioselective catalysts for the aerobic oxidation of alcohols. In this view, several nitroxides with different α substituents have been synthesized to investigate the influence of these groups. Several co-catalysts reported in the literature have been tested for the oxidation reactions that take place at room temperature and atmospheric pressure. These catalytic systems can be classified relatively to the presence or the absence of metal as additive.The strategy used for the catalyst synthesis has been developped in the laboratory from previous studies about nitrones. Using this strategy and different starting nitrones, several α-substituted analogues can be rapidly synthesized in only two steps. Particularly, the use of a chiral nitrone will permit the obtention of enantiopur catalysts that will be able used for the enantioselective oxidations.In the first part of our study, several catalytic systems have been tested with our catalysts with a reference substrate: benzylic alcohol. According to the results, we have been able to determine: (1) the capacity of imidazolidin-4-one nitroxides to behave as catalysts for the aerobic oxidations; (2) the difference of reactivity depending on the α substituents; (3) the more effective catalytic systems for our catalysts; (4) the scope of the reaction in order to determine the suitable substrates for enantioselective reactions.With all these results in hand, diol desymmetrization for the synthesis of atropoisomers has been considered. Dioxygen oxidation of three diols has been tested using different enantiopur catalysts with a copper-based catalytic system. The enantioselectivity obtained proved variable depending on the substrate and the catalyst used. Very encouraging results have been obtained for one of the substrate, with enantiomeric excess of about 60 %.At the same time as the oxidation reactions, cyclic voltammetry and electron paramagnetic resonance (EPR) studies have been carried out. Cyclic voltammetry has been useful to explain the difference of reactivity of the catalysts according the α substituents. Using the EPR, we have tried to understand the organisation around copper for the different species from the catalytic system used for the enantioselective oxidations.By means of this study, we have demonstrated that imidazolidin-4-one nitroxides can be used as catalysts for the aerobic oxidation of alcohols. The α substituents play an important role in the stability of the active species that can change the efficacity of each compound. Imidazolidin-4-one nitroxides have also given encouraging results in the enantioselective oxidation of benzylic diols.

Neste trabalho foram produzidos eletrocatalisadores Pd/C, Au/C, PdAu/C, PdAuPt/C, PdAuBi/C e PdAuIr/C a partir do método de redução por borohidreto para oxidação eletroquímica de metanol, etanol e etilenoglicol. No método de redução por borohidreto, adiciona-se de uma só vez uma solução alcalina contendo borohidreto de sódio a uma mistura contendo água/2-propanol, precursores metálicos e o suporte de carbono Vulcan XC72. Os eletrocatalisadores obtidos foram caracterizados por espectroscopia de energia dispersiva de raios-X (EDX), difração de raios-X (DRX), microscopia eletrônica de transmissão (MET) e voltametria cíclica. A oxidação eletroquímica do metanol, etanol e etilenoglicol foi estudada por cronoamperometria utilizando a técnica do eletrodo de camada fina porosa. O estudo do mecanismo de oxidação eletroquímica do etanol foi estudado por meio da técnica de espectroscopia no infravermelho com transformada de Fourier (FTIR) in situ. Os melhores eletrocatalisadores foram testados em células alcalinas unitárias alimentadas diretamente por metanol, etanol e etilenoglicol. Estudos preliminares mostraram que a composição atômica adequada para preparar catalisadores ternários é igual a 50:45:05. De acordo com os experimentos eletroquímicos em meio básico, o eletrocatalisador PdAuPt/C (50:45:05) apresentou a maior atividade para oxidação eletroquímica de metanol, enquanto que, nas mesmas condições, o PdAuIr/C foi mais ativo para oxidação do etanol e o PdAuBi/C mais ativo para a oxidação do etilenoglicol. Estes resultados indicam que a adição de ouro na composição dos eletrocatalisadores contribui para uma maior atividade catalítica dos mesmos. Os resultados de FTIR mostraram que o mecanismo da oxidação do etanol se processa de modo indireto, ou seja, a ligação CC não é rompida, formando acetato. / In this study Pd/C, Au/C, PdAu/C, PdAuPt/C, PdAuBi/C and PdAuIr/C electrocatalysts were prepared by the sodium borohydride reduction method for the electrochemical oxidation of methanol, ethanol and ethylene glycol. This methodology consists in mix an alkaline solution of sodium borohydride to a mixture containing water/isopropyl alcohol, metallic precursors and the Vulcan XC 72 carbon support. The electrocatalysts were characterized by energy dispersive X-ray (EDX), X-ray diffraction (XRD), transmission electron microscopy (TEM) and cyclic voltammetry. The electrochemical oxidation of the alcohols was studied by chronoamperometry using a thin porous coating technique. The mechanism of ethanol electro-oxidation was studied by Fourier Transformed Infrared (FTIR) in situ. The most effective electrocatalysts were tested in alkaline single cells directly fed with methanol, ethanol or etylene glycol. Preliminary studies showed that the most suitable atomic composition for preparing the ternary catalysts is 50:45:05. Electrochemical data in alkaline medium show that the electrocatalyst PdAuPt/C (50:45:05) showed the better activity for methanol electrooxidation, while PdAuIr/C was the most active for ethanol oxidation and PdAuBi/C (50:45:05) was the most effective for ethylene glycol oxidation in alkaline medium. These results show that the addition of gold in the composition of electrocatalysts increases their catalytic activities. The spectroelectrochemical FTIR in situ data permitted to conclude that C-C bond is not broken and the acetate is formed.

Uma das principais fronteiras de desenvolvimento em catálise heterogênea envolve o uso de suportes de carbono grafitizados como vetores para modificação da estrutura eletrônica de catalisadores em reações catalíticas. Neste contexto os nanotubos de carbono (CNTs) são promissores, permitem boa dispersão e estabilização de nanopartículas (NPs) devido morfologia, defeitos superficiais, curvatura e geometria oca que resultam em interações específicas com catalisadores. Os CNTs podem apresentar uma distribuição variada de diâmetros, com presença de defeitos (vacâncias, pentágonos), podem ser dopados, intercalados com espécies que afetam a densidade eletrônica das suas paredes que podem ser funcionalizadas com uma variedade de moléculas, apresentando novas propriedades que podem influenciar na atividade catalítica de NPs. Apesar do potencial os CNTs quando usados na forma de material particulado, estes podem apresentar problemas em aplicações catalíticas associadas à sua aglomeração afetando a dispersão das NPs e principalmente suas propriedades eletrônicas, além de problemas de filtragem, contaminação dos produtos reacionais e limitações de fluxo. Uma alternativa para explorar os CNTs em catálise heterogênea são os materiais micrométricos com superfície nanoestruturada, baseado em CNTs, que constitui um material compósito cujas propriedades dependem da natureza dos CNTs e do substrato. Nesses compósitos, várias das propriedades dos CNTs podem ser mantidas, porém com uma aglomeração fixa, moldada pela superfície do material micrométrico que podem ser facilmente removidos do meio reacional e também usados em colunas sem comprometimento do fluxo. Neste trabalho foi desenvolvido um suporte catalítico baseado em carvão ativado (AC) e CNTs resultantes da decomposição catalítica de etanol constituindo um compósito micro-nanoestruturado (CNT/AC). Sobre o compósito foram suportadas NPs metálicas de rutênio preparadas por microemulsão com diferentes teores de rutênio. O comportamento catalítico deste novo material catalítico foi investigado frente as reações de oxidação do álcool benzílico e hidrogenação do cinamaldeído. Os resultados dos ensaios catalíticos quando foi utilizado o catalisador baseado em CNTs com um teor de rutênio de 3,2% foram comparados com um catalisador comercial contendo um teor de 5% de rutênio, se mostraram positivos para a reação de oxidação do álcool benzílico apresentando elevada conversão e seletividade para um carregamento de rutênio inferior ao catalisador comercial, com conversão superior a 99% e seletividade para benzaldeído de 100%, enquanto o comercial apresentou conversão de 91% e seletividade também de 100%. Na reação de hidrogenação do cinamaldeído utilizando o catalisador desenvolvido com um teor de 2% de rutênio, observou-se uma conversão de 45% com seletividade distribuída entre hidrocinamaldeído (25%), álcool hidrocinâmico (18%) e álcool cinâmico (2%). Quando se utilizou o catalisador comercial com teor de 5% de rutênio a conversão do cinamaldeído foi de 43% e seletividade para hidrocinamaldeído (37%), álcool hidrocinâmico (3,4%) e álcool cinâmico (3,3%). O catalisador micro-nanoestruturado contendo um carregamento de 1,3% de rutênio foi caracterizado por espectroscopia Raman que indicou a presença das bandas de segunda ordem na faixa de 2500-3200 cm-1 devido a presença dos CNTs, que após a incorporação das NPs de rutênio apresentou um deslocamento da banda G localizada em 1580 cm-1 em cerca de 2 eV, indicando um processo de transferência de carga entre as NPs e os CNTs. Os resultados de absorção de N2 indicou natureza mesoporosa dos catalisadores baseados em CNTs e os teores de rutênio contidos nas amostras destes catalisadores foram medidos por espectroscopia de absorção atômica e apresentaram uma proporção em massa de 1,3; 2,3 e 3,2% de rutênio em relação ao compósito, dados estes confirmados por espectroscopia de energia dispersiva quando utilizada para mapear a composição química do catalisador. Em conclusão, o compósito micro-nanoestruturado desenvolvido neste estudo apresenta um grande potencial para aplicações catalíticas, pois em testes de reciclagem, o catalisador apresentou baixa lixiviação das NPs e baixo desprendimento de CNTs do substrato apresentando desta forma boa estabilidade, além de apresentar uma excelente atividade catalítica na conversão do álcool benzílico acima de 95% após 4 ciclos catalíticos sucessivos e principalmente a seletividade máxima ao benzaldeído. / One of the main frontiers in the development of heterogeneous catalysis involves the use of graphitized carbon supports as vectors for the modification of the electronic structure of the catalysts utilized in catalytic reactions. In this sense, carbon nanotubes (CNTs) are promising materials because their morphology, surface defects, curvature, and hollow geometry allow for good dispersion and stabilization of nanoparticles (NPs), which culminates in specific interactions. CNTs can have a wide distribution of diameters, with the presence of defects (vacancies, pentagons) for this reason, they can be doped and then interspersed with species that affect the electron density of their walls, which can be functionalized with a variety of molecules. As a result, new properties that influence the catalytic activity of NPs arise. Despite their potential application, use of CNTs as particulate matter. This is because can propose problems to their application, due to their agglomeration. This is because the dispersion of NPs and their electronic properties can be affected, and problems contamination of the reaction, and flow limitations appear. An alternative for the use of CNTs in heterogeneous catalysis is the utilization of CNT-based materials with micrometric nanostructured surface. These are composite materials whose properties depend on the nature of the CNTs and the substrate. Various of the properties of CNTs can be maintained in composites, such as fixed clustering, shape of the surface of the micrometric material, which can be easily removed from the reaction medium and used in columns without compromising the flow. This work was based on a catalytic activated carbon (AC) support and CNTs, resulting from the catalytic decomposition of ethanol, which resulted in a micronanostructured composite (CNT/AC). Ruthenium metal NPs prepared by microemulsion and containing different amounts of ruthenium were supported onto the CNT/AC composite. The catalytic behavior of this new material was investigated for the oxidation of benzyl alcohol and hydrogenation of cinnamaldehyde. The obtained results were compared with those achieved with a commercial catalyst. Positive results were obtained for the oxidation of benzyl alcohol, with high substrate conversion and product selectivity having been achieved for a lower ruthenium load than the one present in the commercial catalyst (99% conversion and selectivity of 100 %. toward benzaldehyde. As for the hydrogenation of cinnamaldehyde, 45%, hydrocinnamaldehyde, hydrocinnamyl alcohol and cinnamyl alcohol, selectivities of 25, 18, and 2%, respectively. The micronanostructured catalyst was characterized by Raman spectroscopy, which indicated the presence of second-order bands in the range of 2500-3200 cm-1, due to the presence of CNTs. After incorporation of the ruthenium NPs, there was a shift in the G band located at 1580 cm-1 of about 2 eV, indicating a charge transfer process between the NPs and the CNTs. The results from N2 absorption indicated the mesoporous nature of the catalyst. The concentration of ruthenium catalysts present in the samples was measured by atomic absorption spectrometry. Ruthenium mass ratios of 1.3, 2.3, and 3.2% in relation to the composite, were detected. The composites were tested in various reuses experiments. There was low lixiviation of the NPs and low detachment of CNTs from the substrate. These data were confirmed by energy dispersive spectroscopy, which was used for mapping the chemical composition of the catalyst. In conclusion, the composite developed in this study has great potential for catalytic investigations, since the interaction between the carbon composite and the NPs was effective, and the catalytic activity was maintained for several cycles.