Catalisador é uma substância que altera a velocidade de uma reação. Na indústria do petróleo os catalisadores mais utilizados são os catalisadores de Fluid Catalytic Cracking (FCC) e Hidrocatalytic Cracking (HCC) cada qual utilizado em uma determinada etapa do processo. Esses catalisadores são usados para facilitar a quebra das cadeias moleculares que darão origem a uma mistura de hidrocarbonetos. Contudo, o catalisador perde progressivamente sua atividade, seja pela mudança de sua estrutura molecular original ou pela sua contaminação provenientes de outras moléculas do petróleo. A aplicação das radiações ionizantes (feixe de elétrons e raios gama) nesses catalisadores desativados foi estudada para auxiliar na extração de metais ou terras-raras de alto valor agregado. Nos ensaios realizados com os catalisadores de FCC utilizaram-se das técnicas de irradiação por 60Co e por feixe de elétrons (EB) e tiveram como estudo a extração do lantânio (La2O3), a regeneração e utilização desses catalisadores. Entretanto, o uso da radiação ionizante não contribuiu nesses processos. Já nos catalisadores de HCC foi utilizado a irradiação por feixe de elétrons e como estudo a extração do molibdênio (MoO3). Na temperatura em torno de 750°C nesses catalisadores irradiados do leito inferior obteve-se um rendimento de extração duas vezes maior em comparação aos não irradiados, ou seja de 57,65% e 26,24% respectivamente. / Catalyst is a substance that changes the rate of a reaction. In the petroleum industry the commonly catalysts are used for Fluid Catalytic Cracking (FCC) and Hidrocatalytic Cracking (HCC), which one applied in a specific stage. These catalysts are used to facilitate the molecular chains cracking which will generate a mixture of hydrocarbons. However, the catalyst gradually loses its activity, either by changing its original molecular structure or by its contamination from other petroleum molecules. The application of ionizing radiation (electron beam and gamma rays) over these spent catalysts was studied to contribute with the extraction of metals or rare-earths of high added-value. Tests carried out with FCC catalysts were used the techniques of 60Co irradiation and electron beam (EB) and had as a subject the extraction of lanthanum (La2O3), regeneration and utilization of these catalysts. However, the use of ionizing radiation has not contributed in these processes. Meanwhile with HCC catalysts the irradiation used was electron beam and had as a subject the extraction of molybdenum (MoO3). In temperature around 750°C, these irradiated catalysts of the lower region have an extraction yield twice higher compared to non-irradiated ones, in other words 57.65% and 26.24% respectively.

Catalisador é uma substância que altera a velocidade de uma reação. Na indústria do petróleo os catalisadores mais utilizados são os catalisadores de Fluid Catalytic Cracking (FCC) e Hidrocatalytic Cracking (HCC) cada qual utilizado em uma determinada etapa do processo. Esses catalisadores são usados para facilitar a quebra das cadeias moleculares que darão origem a uma mistura de hidrocarbonetos. Contudo, o catalisador perde progressivamente sua atividade, seja pela mudança de sua estrutura molecular original ou pela sua contaminação provenientes de outras moléculas do petróleo. A aplicação das radiações ionizantes (feixe de elétrons e raios gama) nesses catalisadores desativados foi estudada para auxiliar na extração de metais ou terras-raras de alto valor agregado. Nos ensaios realizados com os catalisadores de FCC utilizaram-se das técnicas de irradiação por 60Co e por feixe de elétrons (EB) e tiveram como estudo a extração do lantânio (La2O3), a regeneração e utilização desses catalisadores. Entretanto, o uso da radiação ionizante não contribuiu nesses processos. Já nos catalisadores de HCC foi utilizado a irradiação por feixe de elétrons e como estudo a extração do molibdênio (MoO3). Na temperatura em torno de 750°C nesses catalisadores irradiados do leito inferior obteve-se um rendimento de extração duas vezes maior em comparação aos não irradiados, ou seja de 57,65% e 26,24% respectivamente. / Catalyst is a substance that changes the rate of a reaction. In the petroleum industry the commonly catalysts are used for Fluid Catalytic Cracking (FCC) and Hidrocatalytic Cracking (HCC), which one applied in a specific stage. These catalysts are used to facilitate the molecular chains cracking which will generate a mixture of hydrocarbons. However, the catalyst gradually loses its activity, either by changing its original molecular structure or by its contamination from other petroleum molecules. The application of ionizing radiation (electron beam and gamma rays) over these spent catalysts was studied to contribute with the extraction of metals or rare-earths of high added-value. Tests carried out with FCC catalysts were used the techniques of 60Co irradiation and electron beam (EB) and had as a subject the extraction of lanthanum (La2O3), regeneration and utilization of these catalysts. However, the use of ionizing radiation has not contributed in these processes. Meanwhile with HCC catalysts the irradiation used was electron beam and had as a subject the extraction of molybdenum (MoO3). In temperature around 750°C, these irradiated catalysts of the lower region have an extraction yield twice higher compared to non-irradiated ones, in other words 57.65% and 26.24% respectively.

Les nanoparticules bimétalliques supportées sont des catalyseurs particulièrement attractifs en raison d’une activité et d’une stabilité accrues par rapport à leurs homologues monométalliques. Dans cette thèse des solides à base d'or ont été étudiés en tant que catalyseurs de l'oxydation sélective du glucose en absence de base. Il a été mis en évidence que la variation du ratio molaire entre l’or et le second métal (Pd, Pt, or Cu) a un impact différent sur les performances catalytiques en fonction de la nature du second métal, du support et de la méthode de préparation. Les séries Au-Pd supportés sur TiO2 et préparés par la méthode de sol-immobilisation et Au-Cu supportés sur TiO2 et préparés par la méthode de précipitation-réduction ont montré un effet synergique important, en particulier lorsque le rapport entre les deux métaux était de 1. Ces catalyseurs convertissent sélectivement le glucose en acide gluconique et leur activité a été trouvée supérieure à celle des contreparties monométalliques. L'analyse XPS a démontré que les espèces Au+δ, Pd+2 et CuOH jouent alors un rôle important dans la réaction étudiée en absence de base. Le bismuth en tant que second métal n'a montré aucun effet bénéfique, au contraire du palladium et du cuivre. Les catalyseurs à base d’Au et de Pt supportés sur ZrO2 se sont avérés quant à eux très stables lorsque la teneur en or était inférieure à 0,3% en masse. La nature du support a un impact très important sur le mécanisme de la réaction conduite en absence base sur des catalyseurs à base d’or. La raison réside dans les interactions que ce support développe avec la phase bimétallique favorisant ainsi la formation des espèces actives / The supported bimetallic nanoparticles are particularly attractive catalysts due to the increased activity and stability over their monometallic counterparts. In this thesis, gold-based solids have been studied as catalysts for the selective base-free oxidation of glucose. It has been demonstrated that the variation of the molar ratio between gold and the second metal (Pd, Pt, or Cu) has a different impact on the catalytic performances depending on the nature of the second metal, the support and the method of preparation. TiO2 supported Au-Pd series prepared by the sol-immobilization method and Au-Cu series prepared by the precipitation-reduction method showed a significant synergistic effect, particularly when the ratio of the two metals was 1. Under the reaction conditions used (T = 60 °C or 80 °C, P = 5 bar air, t = 5 h), these catalysts selectivity to gluconic acid and their activity was found to be greater than that of monometallic counterparts, especially when the catalyst is supported on TiO2. XPS analysis showed that the Au+δ, Pd+2 and CuOH species played an important role in the base-free reaction. Bismuth as the second metal showed no beneficial effect, unlike palladium and copper. The Au-Pt catalysts supported on ZrO2 proved to be still active when the gold content was less than 0.3 wt.%. Ultimately, the nature of the support has a very important impact on the mechanism of the base-free reaction conducted on gold-based catalysts (formation of H2O2 in situ). The reason lies in the interactions of the support with the bimetallic phase thus favoring the formation of the active species

Record high CO2 emissions in the atmosphere and the need to find alternative energy sources to fossil fuels are major global challenges. Conversion of CO2 into useful fuels like methanol and methane can in principle tackle both these environment and energy concerns. One of the routes to convert CO2 into useful fuels is by using supported metal catalyst. Specifically, metal atoms or clusters (few atoms large in size) supported on oxide materials are promising catalysts. Experiments have successfully converted CO2 to products like methanol, using TiO2 supported Cu atoms or clusters. How this catalyst works and how CO2 conversion could be improved is an area of much research. We used a quantum mechanical tool called density functional theory (DFT) to obtain atomic and electronic level insights in the CO2 reduction processes on TiO2 supported metal atoms and clusters. We modeled small Cu clusters on TiO2 surface, which are experimentally synthesizable. Our results show that the interfacial sites in TiO2 supported Cu are able to activate CO2 into a bent configuration that can be further reduced. The Cu dimer was found to be the most reactive for CO2 activation but were unstable catalysts. Following Cu, we also identified other potential metal atoms that can activate CO2. Compared to expensive and rare elements like Pt, Au, and Ir, we found several early and mid transition metals to be potentially active catalysts for CO2 reduction. Because the supported metal atom or cluster is a reactive catalyst, under reaction conditions they tend to undergo aggregation and/or oxidation to form larger less active catalysts. We chose Co, Ni, and Cu group elements to study their catalyst stability under oxidizing reaction conditions. Based on the thermodynamics of Cu oxidation and kinetics of O2 dissociation, we found that TiO2 supported Cu atom or a larger Cu tetramer cluster were the likely species observed in experiments. Our work provides valuable atomic-level insights into improving the CO2 reduction activities and predicts potential catalysts for CO2 reduction to valuable fuels.

Cette étude présente la préparation et l’évaluation de l’activité d’un nouveau catalyseur monolithique en microréacteur. La réaction d’hydrogénation du p-nitrophénol par transfert d’hydrogène avec l’acide formique a été choisie comme réaction modèle pour comparer les performances du monolithe à celles d’un catalyseur commercial en lit fixe.Cette thèse comporte une partie expérimentale importante. D’un côté, un montage expérimental et des protocoles d’analyse en ligne ont été mis au point pour faire une étude quantitative précise de la réaction modèle. De l’autre côté, les conditions de préparation d’un monolithe de silice fonctionnalisée dans le tube-réacteur en acier chemisé de verre ont été optimisées. Il a été chargé en nanoparticules de Pd par une méthode en écoulement. Le monolithe comporte un réseau de macropores pour l’écoulement et une organisation hexagonale typique de mésopores et micropores, et cela presque sans retrait au séchage. L’activité des 2 types de catalyseurs dans la réaction modèle a été comparée par leur cinétique de réaction et leur comportement dynamique dans la phase de mise en régime du microréacteur. Une partie théorique présente la modélisation du microréacteur en régime stationnaire pour l’établissement des cinétiques et en régime transitoire pour rationaliser les observations expérimentales. Le monolithe Pd@silice et le catalyseur commercial Pd@alumine ont des comportements différents et obéissent à des lois cinétiques différentes. Un modèle réactionnel impliquant un changement de propriétés de la surface catalytique pourrait expliquer le profil de concentration inhabituel observé avec le catalyseur commercial. La comparaison démontre la supériorité du nouveau catalyseur monolithe, et lui ouvre de bonnes perspectives industrielles. / This study presents the preparation and the evaluation of performance of a new monolithic catalyst in microreactor. The transfer hydrogenation of p-nitrophenol by formic acid is chosen as the model reaction for the comparison of the monolith with a traditional packed-bed microreactor containing commercial catalyst.This thesis includes an important experimental part. On the one hand, experimental set-up and protocols involving on-line analysis have been developed in order to study quantitatively the model reaction; On the other hand, the conditions of preparation of functionalized silica monolith in a stainless steel tube with the inner wall pre-coated by glass were optimized, and the palladium nanoparticles were immobilized by a continuous flow method. The monolith possesses the flow-through macropores, typical hexagonal organization of mesopores and micropores, and scarcely any shrinkage. The comparison of the two types of catalysts mainly focuses on the activity of catalysts in the model reaction, their kinetic model and their dynamic behavior in the start-up phase of the flow microreactor. In the theoretical part, the modelisation of reactor has been investigated both under stationary conditions for kinetics determination and under transient conditions for the rationalization of experimental observations. Pd@silica monolith and commercial Pd@alumina powder have different behavior and gives different kinetic laws. A reaction model with change in the catalytic surface properties could explain the unusual profile of concentrations observed with commercial catalyst. The superior performance of monolithic catalyst is demonstrated, which also exhibits particular industrial interests.

Neste trabalho foram preparados e caracterizados catalisadores de platina suportados em g-alumina (g-Al2O3), óxido de zircônio (ZrO2) e em suportes mistos de óxido de zircônio e g-alumina. Os suportes bi-componente contendo (15%) ZrO2/g-Al2O3 foram preparados por dois métodos distintos: no primeiro, utilizou-se uma suspensão ácida de óxido de zircônio comercial e no segundo, óxido de zircônio precipitado a partir do acetato. Os catalisadores foram submetidos a ensaios catalíticos de reforma a vapor de etanol a fim de verificar o efeito do suporte sobre a distribuição dos produtos. As técnicas de caracterização utilizadas foram área superficial específica (B.E.T), redução a temperatura programada (RTP), difração de raios-X (DRX) e espectroscopia de absorção molecular na região UV-VI, que identificou a espécie [PtOxCly]s2-. A conversão do etanol e a distribuição dos produtos variaram para cada suporte testado e para os diferentes tempos de contatos (W/F) utilizados. O catalisador (1%) Pt/g-Al2O3 apresentou a melhor seletividade para a produção de hidrogênio e a menor conversão para o etanol. Os catalisadores que utilizaram o suporte bi-componente (15%) ZrO2/g-Al2O3 e ZrO2 pura apresentaram alta conversão de etanol e baixa seletividade para hidrogênio, além de alta tendência à formação de bio-produtos. / In this work catalysts of platinum supported on g-alumina (g-Al2O3), oxide of zirconium (ZrO2) and mixed oxide of zirconium and g-alumina had been prepared and characterized. The bi-component supports containing ( 15%) ZrO2/g-Al2O3 had been prepared by two different methods : in the first, an acid suspension of comercial oxide of zirconium was used and in the second, oxide of zirconium was precipitated from acetate. The catalysts were tested in ethanol steam reforming reaction to verify the effect of the support on the distribution of the products. For the characterization, the following techniques were used. Superficial specific area (B.E.T,), temperature programmed reduction (TPR.), X-ray powder diffraction (XRD) and spectroscopy of molecular absorption in the UV-vis, for identification of [PtOxCly]s 2- species. The ethanol conversion and product distribution were different for each support tested and for different time of contact (W/F) used. The catalyst (1%) Pt/g-Al2O3 presented the best selectivity for the hydrogen production and the lower conversion for ethanol. The catalysts with bi-component support (15%) ZrO2/ g-Al2O3 and pure ZrO2 presented high ethanol conversion and lower selectivity for hydrogen production with high selectivity and formation of bio-products.

<p>In recent years, first principles periodic Density Functional Theory (DFT) calculation</p><p>has been used to investigate heterogeneous catalytic reactions and examine catalyst</p><p>structures as well as adsorption properties in a variety of systems. The increasing</p><p>contribution to give detailed understanding of elementary reaction mechanism is critical to</p><p>provide fundamental insights into the catalyst design. It is a link to the fundamental</p><p>knowledge and a bridge to the practical application. DFT calculations is also a powerful</p><p>tool to predict and yield promising catalysts which is time- and cost-saving in the practical</p><p>end.</p><p>Because of the recent boom in natural shale gas deposit, there is an increasing interest</p><p>in developing more efficient ways to transform light alkanes into desired and high-value</p><p>chemicals, such as propylene. Propylene is a valuable raw material in the petrochemical</p><p>application to make value-added commodities, such as plastics, paints, and fibers, etc. The</p><p>conventional cracking, steam cracking (SC) and fluid catalytic cracking (FCC), could not</p><p>meet the growing demand of propylene. Thus, it has motivated extensive research of</p><p>production technologies. On the other hand, the abundance of light alkanes extracted from</p><p>the shale gas makes on-purpose production an appealing method which is economically</p><p>competitive. Non-oxidative dehydrogenation of propane (PDH) is a one of ways to make</p><p>up the supply and solve the issue.</p><p>xiii</p><p>According to the current research and industrial work, platinum (Pt) shows promising</p><p>performance for the PDH. However, it suffered from some major drawbacks, such as</p><p>thermodynamic limitation, rapid deactivation leading to poor catalytic performance and</p><p>frequent regeneration. In addition, it is a relatively high cost noble metal. Consequently,</p><p>many efforts have been devoted to the enhancement of the catalytic performance. It was</p><p>found that the stability and the selectivity of Pt-based catalysts can be improved via</p><p>modifying its properties with transition metals as promoters.</p><p>In this thesis, DFT calculations were performed for propane dehydrogenation over</p><p>two different catalyst systems, bimetallic platinum-zinc alloy and monometallic platinum</p><p>catalysts. The work provides insights into the catalyst crystal structures, the adsorption</p><p>characteristics of diverse adsorbates as well as the energy profiles regarding to the</p><p>selectivity of the propane dehydrogenation. Bulk calculation signifies a stable tetragonal</p><p>configuration of the PtZn catalyst which is in accordance with the experimental result. The</p><p>thermodynamic stability regarding to the stability of bulk and surface alloys are studied</p><p>with the consideration of physical constrains. We have identified the thermodynamic</p><p>stability of several PtZn low-index surface facets, (101), (110), (001), (100) flat surfaces</p><p>and stepped surface (111), at certain chemical potential environmental conditions through</p><p>the surface energy phase diagram. Stoichiometric and symmetric (101) slab is</p><p>thermodynamically stable under the region of high Pt chemical potential, and the offstoichiometric</p><p>and symmetric (100 Zn-rich) slab under the low Pt chemical potential.</p><p>In this work, PtZn(101) is used as a model surface to demonstrate the effect on the</p><p>catalytic performance with zinc promotion of platinum. In comparison with Pt(111) surface,</p><p>an elimination of 3-fold Pt hollow site on PtZn(101) is of important and it leads to the</p><p>xiv</p><p>change of binding site preferences. The divalent groups (1-propenyl, 2-propenyl) change</p><p>from Pt top site on PtZn(101) to 3-fold site on Pt(111), which is because of the lack of Pt</p><p>3-fold site on alloyed surface. As for propylene, it changes from di-σ site on PtZn to 𝜋 site</p><p>on Pt. The surface reaction intermediates are found to bond more weakly on PtZn(101)</p><p>than on the Pt surface. Especially, the binding energy of propylene reduces from -1.09 to -</p><p>0.16 eV. The weaker binding strength facilitates the activity of propylene on alloyed</p><p>surfaces.</p><p>Through a complete and classic reaction network analysis, the introduction of Zn</p><p>shows an increase in the endothermicity and the energy barrier of each elementary reaction</p><p>on the alloy surface. With the consideration of entropy for kinetic under real experimental</p><p>condition, the alloying of Zn is found to lower the energy barrier for the propylene product</p><p>desorption and increases that for propylene dehydrogenation. Meanwhile, the competition</p><p>between desired C-H and undesired C-C cleavages is investigated. It is found that the</p><p>cleavage of C-H is energetically favorable than that of C-C. These positive factors</p><p>potentially lead to a high selectivity toward propylene production on PtZn(101).</p><p>Subsequently, Microkinetic modeling is performed to estimate kinetic parameters</p><p>including the reaction order, rate-determining step to build a possible reaction mechanism.</p><p>Finally, conclusions brought out about the comparison between bimetallic and</p><p>monometallic catalyst, and suggestions for future work are presented.</p>

The global population is constantly rising and with the consequent increase in demand for clean water, the planet is facing a looming freshwater shortage. At the current rate, cities around the globe could lose as much as two thirds of their freshwater supply by 2050. To tackle this, there has been a huge surge on the investigation of novel wastewater treatment technologies. Advanced oxidation processes (AOPs) have shown great promise in this regard. Recently using microwaves with AOPs has been proven to exhibit improved reaction rates and thus there is a push towards developing processes involving microwaves and AOPs to achieve high water treatment efficiencies. However no methodical studies have been conducted to the best of our knowledge, to take the lab scale improvements successfully on to the pilot scale wastewater treatment system. To design such a system by coupling microwaves with Fenton process is the objective of this microwave assisted catalytic treatment of wastewater (MICROCAT) research project. Multiphysics simulation was used for cavity design optimisation and common pesticides found in agricultural wastewater were used as candidate impurities. A heterogeneous Fenton catalyst was prepared by a multi-stage thermal and chemical treatment of polyacrylonitrile (PAN) mesh on polypropylene support structure in collaboration with De Montfort University (DMU). The PAN meshes, after each stage of the treatment process, have been characterised using the field emission gun scanning electron microscope (FEGSEM) and electron dispersive X-ray spectroscopy (EDX) for microstructure and composition. The catalyst was used to study the decomposition of a model compound (e.g., carbetamide) using microwave radiation as well as conventional heating. Two kinds of trials were carried out constant power and constant temperature to observe the effect of variation of process parameters on the reaction rates. It was seen that the use of microwave heating enhanced the rate of decomposition compared to conventional heating in both scenarios. Attempts were also made to modify the composition of the catalyst and the support structure using polyvinylidene fluoride (PVDF) and carbon based additives (graphite and carbon black) to improve the microwave absorption characteristics. The combination of additive and PAN/PVDF mixtures has the potential to help in designing a suitable fabric support for catalyst that could be more receptive to microwaves, thereby helping to improve the energy efficiency of the process. Thorough investigation of dielectric properties and microwave absorption characteristics of the catalyst and support materials were performed independently. The heating rates of the meshes were monitored using an infrared thermal imaging camera. The absorption efficiencies of materials commonly used to build water treatment reactors such as polypropylene (PP), Fibreglass reinforced plastic (FRP), polyvinyl chloride (PVC), glass, PTFE, and fused quartz were assessed by subjecting them to constant microwave power experiments to ascertain their utility for making the reactor parts To take the successful lab scale results (100 ml) to scalable levels (80000 ml) for field trails, a new microwave reactor system was designed and tested. The cavity design was aided by multiphysics simulation of the electromagnetic field and temperature distribution inside the cavity. The model was created using COMSOL and provided valuable insight in making several design choices and improvements. The material data used in the model was determined both from our characterisation results and from corroborative literature data. The cavity itself was fully constructed using aluminium and the internal components were made using polypropylene and PTFE within the project timeline. The cavity was commissioned and initial testing at end user sites involved experiments measuring the rate of decomposition of carbetamide and other pesticides the results again emphasising that microwave treatment improves the reaction rates both from lab scale and in pilot scale water treatment situations in comparison to conventional treatment systems. This augers well for the generic applicability of the microwave assisted catalytic reactor system and its potential for the efficient treatment of contaminated water from hard to treat agricultural. Industrial, medical and defence waste/pollutants in future. An added advantage is that the developed microwave treatment system is mobile (on an ISO-container) and hence can reach the remote, contaminated site and treat it then and there rather than transporting the contaminated fluid to the treatment plant in a faraway location.

Neste trabalho foram preparados materiais constituídos por Al2O3 e Nb2O5, na forma de grãos esferoidais para serem usados como suporte de catalisadores aplicados à propulsão. Os suportes foram preparados por quatro diferentes métodos: impregnação úmida do óxido de alumínio moldado por uma solução alcoólica de cloreto de nióbio (NbCl5); impregnação seca do óxido de alumínio por uma solução alcoólica de NbCl5; co-precipitação dos precursores de óxido de alumínio e óxido de nióbio; e mistura física dos precursores desses óxidos previamente autoclavados separadamente. Entre esses métodos, os suportes que apresentaram melhores características para aplicação em propulsão a monopropelente hidrazina (N2H4) foram aqueles preparados por mistura física, contendo 20% m/m de óxido de nióbio (Su20MF) e por impregnações secas sucessivas, contendo 10% m/m de óxido de nióbio (Su10IS). A adição do óxido de nióbio ao óxido de alumínio resultou em acentuado aumento da resistência mecânica à compressão, mas não causou variação significativa do número e força dos sítios ácidos de Lewis, em função dos tratamentos de calcinação efetuados a 873 K por 5 horas. Todos os suportes foram impregnados com solução de H2IrCl6 e após tratamentos de redução sob H2, obteve-se catalisadores de irídio suportados, com elevados teores metálicos, CAT-20Ir, contendo aproximadamente 20% m/m de Ir disperso na superfície do suporte Su10IS, e CAT-27Ir, contendo aproximadamente 27% m/m de Ir disperso na superfície do suporte Su20MF. Caracterizações por quimissorção de H2 e por MET/EDS mostraram que o irídio fixou-se quase que exclusivamente sobre o óxido de alumínio, gerando partículas metálicas com diâmetros médios tanto maiores quanto menores as áreas superficiais expostas desse óxido. Testes efetuados em bancada com as reações de decomposição de hidrazina e de amônia revelaram que a reação com hidrazina ocorre de forma completa em temperaturas acima de 393 K, gerando exclusivamente amônia e nitrogênio, enquanto que a decomposição da amônia inicia-se em temperaturas superiores e diferenciadas, dependendo do catalisador. Durante a reação da hidrazina, a reação de decomposição da amônia formada, produzindo hidrogênio foi acompanhada, sendo tanto menor quanto maior o diâmetro médio das partículas de irídio, sendo que a seletividade ao hidrogênio mostrou ser uma função linear do diâmetro médio, ao menos entre 24 Å e 40 Å. Esse comportamento se deve ao fato de que a decomposição da amônia é uma reação sensível à estrutura da fase ativa destes catalisadores. Já os testes efetuados em propulsores de 5 N de empuxo no Banco de Teste com Simulação de Altitude (BTSA), evidenciaram um aumento da temperatura, da pressão de câmara e também da força de empuxo, devido à menor decomposição da amônia e maiores tempos para o início da decomposição da hidrazina, efeito este relacionado ao número específico de sítios ativos presentes nas superfícies dos catalisadores. / In this work were prepared supports consisting of Al2O3 and Nb2O5, in the form of spheroidal grains by four different methods: wet impregnation of the aluminum oxide molded an alcoholic solution of niobium chloride (NbCl5); dry impregnation of aluminum oxide in an alcoholic solution of NbCl5; co-precipitation of the precursor of aluminum oxide and niobium oxide; and physical mixing of precursors of these oxides previously autoclaved separately. Among these methods, the supports that showed the best characteristics for application in propulsion monopropellant hydrazine were those prepared by physical mixture containing 20 wt % niobium oxide (Su20MF) and successive dry impregnations, containing 10 wt % niobium oxide (Su10IS).The addition of niobium oxide in aluminum oxide resulted in a significant increase in compressive strength of these selected supports, but caused no significant change in the number and strength of Lewis acid site, which was attributed to the calcination treatment carried out at 873 K by 5 hours. These supports were impregnated with H2IrCl6 solution and after reduction treatment under H2, were obtained supported iridium catalysts with high metal contents, named CAT-20Ir containing approximately 20 wt % of Ir dispersed on the support Su10IS and CAT-27Ir containing approximately 27 wt % of Ir Su20MF dispersed on the support. Characterization by chemisorption of H2 and by TEM/EDS showed that the iridium was anchored almost exclusively on aluminum oxide, generating metal particles with average diameters greater. Tests carried out in laboratory with decomposition of hydrazine and ammonia revealed that the reaction with hydrazine is completely in temperatures above 393 K, generating only ammonia and nitrogen, while the decomposition of ammonia, the reaction initiation above different temperatures depending on the catalyst. During decomposition hydrazine another accompanied reaction was the decomposition of ammonia generated, producing hydrogen. The selectivity to hydrogen showed to be a linear function of the mean diameter particle of iridium, least between 24 Å and 40 Å , these results were attributed to the fact that the decomposition of ammonia is a sensitive reaction to the structure of the active phase of these catalysts. Tests carried out at the Altitude Simulation Test Facility (BTSA/INPE) showed the following effects caused by Nb2O5 addition to iridium catalyst supports: increase of temperature, chamber pressure and thrust power, due to a smaller ammonia decomposition; and increase of time for hydrazine decomposition when there is an excessive reduction of the specific number of active sites.

O presente trabalho teve como objetivo estudar a síntese do biodiesel por transesterificação etílica de diferentes matérias-primas lipídicas empregando catalisadores heterogêneos (químico e bioquímico). Para cumprir com os objetivos propostos foram selecionadas matérias-primas lipídicas de baixo impacto no setor alimentício, entre as quais destacam-se: óleos vegetais (andiroba, babaçu, macaúba, palma e pinhão manso) e gordura residual (sebo bovino) e catalisadores de comprovada potencialidade como óxido de nióbio impregnado com sódio (químico) e a lipase de Burkholderia cepacia imobilizada em suporte híbrido sílicaalcool polivinílico (bioquímico). O trabalho foi desenvolvido em três etapas. Inicialmente, foram determinadas as propriedades físico-químicas das diferentes matérias-primas lipídicas, algumas ainda pouco exploradas, para verificar se apresentavam potencial para serem utilizadas na reação de transesterificação. Em seguida foram preparados os catalisadores propostos por protocolos já estabelecidos, sendo obtido para o catalisador químico elevado teor de sódio impregnado no óxido de nióbio (25,43 ± 0,29%) e para catalisador bioquímico elevada atividade hidrolítica (1814 ??281 U/g). Na segunda etapa, as reações de transesterificação foram conduzidas em regime de batelada em condições adequadas para cada catalisador em termos de temperatura, tempo e proporção de catalisador. Na terceira etapa, os produtos obtidos foram purificados e quantificados por cromatografia gasosa, RMN 1H, viscosimetria e análise termogravimétrica (TGA). O conjunto de dados obtidos demonstrou que a formação de ésteres etílicos a partir das diferentes matérias-primas é viável para os catalisadores testados. Ambos os catalisadores (químico e bioquímico) atuaram de forma eficiente convertendo os ácidos graxos presentes nas matérias-primas lipídicas nos ésteres etílicos correspondentes e apresentaram elevada estabilidade em bateladas consecutivas, com destaque para o catalisador bioquímico que revelou um tempo de meiavida de 290 h. Entretanto, a qualidade da matéria-prima lipídica interferiu a atuação dos catalisadores de maneira diferenciada. Enquanto, o catalisador químico foi sensível a presença de níveis elevados de acidez, como o constatado no óleo de macaúba, a atuação do catalisador bioquímico sofreu influência da presença de peróxidos indicativo de oxidação apresentada pelo óleo de andiroba. Com exceção dos óleos de macaúba e andiroba que apresentaram qualidade comprometida, todas as matérias-primas lipídicas originaram amostras de biodiesel com características adequadas para serem usadas como combustível, incluindo valores de viscosidade entre 3,9 a 6,0 (cSt) que atendem as especificações estabelecidas na ASTM 6751- 02. Apesar do desempenho similar dos catalisadores testados, a via química foi superior em termos de produtividade em relação à via bioquímica. Entretanto, essa baixa produtividade pode ser incrementada utilizando métodos não convencionais de aquecimento, como por exemplo, irradiação de micro-ondas e ultrassom. Os resultados obtidos neste trabalho demonstram ainda que os catalisadores heterogêneos testados possuem potencial para substituir os sistemas homogêneos normalmente empregados na síntese do biodiesel. Essa substituição oferece vantagens, que podem propiciar um aumento considerável nas perspectivas de sustentabilidade sócio-ambiental de todo o processo de produção. / The present work aimed at studying the biodiesel synthesis by transesterification reaction from several lipidic feedstocks via ethyl route employing heterogeneous catalysts (chemical and biochemical). To attain the proposed objectives non-edible feedstock having low impact in the food segment, among which stand out: vegetable oils (andiroba, babassu, macauba, palm and Jatropha curcas) and residual fat (beef tallow) and potential catalysts as niobium oxide impregnated with sodium (chemical) and lipase from Burkholderia cepacia immobilized on silica-polyvinyl alcohol matrix (biochemical) were previously selected. The work was developed in three steps. Initially, the physico-chemical properties of the different lipidic feedstocks were investigated, some of them still little explored, to identify their potential as reactants in the transesterification reactions. Then the proposed catalysts were prepared by protocols already established, being obtained for the chemical catalyst high level of sodium impregnated in the niobium oxide (25.43 ± 0.29%) and for the biochemical catalyst high hydrolytic activity (1,814± 281 U/g). In the second step, the transesterification reactions were carried out in batch reactors under appropriated conditions for each catalyst in terms of temperature, time and catalyst proportion. In the third step, the obtained products were purified and quantified by gas chromatography, 1H NMR spectroscopy, viscosimetry and thermogravimetric analysis (TGA). The dataset obtained demonstrated that the formation of ethyl esters from the different feedstocks was feasible for the tested catalysts. Both catalysts (chemical and biochemical) were efficient in converting all fatty acids present in the lipidic feedstock into the corresponding ethyl esters and showed high stability under consecutive batch runs, with emphasis for the biochemical catalyst with a half-life time of 290 h. However, the poor quality of the feedstocks strong affected the performance of the catalysts in a different way. While the chemical catalyst was sensitive to high acidity levels, as verified in the macauba oil, the biochemical catalyst performance was influenced by the presence of peroxides indicating oxidation as showed in the andiroba oil. Except for these oils, all the other feedstocks originated biodiesel samples with appropriate characteristics to be used as fuel, including viscosity values between 3.9 to 6.0 (cSt) that are in accordance with specifications recommended by ASTM 6751-02. Even though the catalysts showed similar performances, the chemical route gave higher productivity than that attained by biochemical route. However, such lower productivity can be increased using non conventional heating systems as for instance, micro-wave irradiation and ultrasound. The results obtained in this work demonstrated that the selected heterogeneous catalysts possess potential to replace the homogeneous systems usually employed in the biodiesel synthesis. Such replacement offers advantages that can provided a considerable increase in the perspectives to attain an environmental sustainability of process as a whole.