Esta tese teve como objetivo avaliar o desempenho de catalisadores de Rh suportados em cério-zircônio (CZ) e em óxido misto de magnésio e alumínio (HT) derivado de hidrotalcita na reação de redução do NO pelo CO em meio estequiométrico. Os suportes puros e impregnados com Rh foram nomeados CZ, RhCZ, HT e RhHT. Os suportes foram preparados por coprecipitação e o metal nobre foi adicionado no teor de 0,15% (m/m) por impregnação a seco. Foram realizados testes de caracterização como fisissorção de N2, DRX, TPR, espectroscopia Raman, DRIFTS, TGA-DTA e TPD-CO/NO. Para a avaliação catalítica, foi utilizada uma mistura de 1%NO + 1%CO em He e a atividade e seletividade foram expressas através das concentrações dos gases envolvidos ao longo de uma rampa de temperatura desde a temperatura ambiente até 500C. Os resultados de caracterização indicaram nítidas diferenças estruturais e físico-químicas entre os dois tipos de catalisadores nas isotermas de adsorção de N2, nos perfis de redução e nos difratogramas, já dando indícios de que os mecanismos de reação seriam diferentes. Pelas análises de DRIFTS identifica-se a presença de bandas características de espécies de CO adsorvidas no Rh somente para o catalisador RhCZ a baixa temperatura, ressaltando a interação Rh-CZ, também evidenciadas pelos resultados de Raman, mas que provavelmente não ocorrem com o óxido misto de Al e Mg. Observou-se que o suporte de CZ foi mais ativo a baixas temperaturas que o suporte de HT, porém o catalisador RhHT foi mais seletivo a N2 a 350C e emitiu menos N2O ao longo da faixa de temperatura avaliada do que o catalisador RhCZ. Resultados de TPD de NO e comparações de curvas experimentais e teóricas envolvendo as concentrações de CO, CO2 e NOx durante os testes catalíticos, acompanhados também pelas análises de DRIFTS nas mesmas condições, indicam que a redução do Rh e a afinidade do catalisador pelo NO são importantes para favorecer a maior seletividade da reação de redução do NO pelo CO a N2. / The aim of this work was to evaluate the catalytic performance of cerium-zirconium and hydrotalcite-like Mg-Al mixed oxide as supports in the reduction of NO by CO catalyzed by rhodium. The pure supports and metallic catalysts were named CZ, RhCZ, HT and RhHT. The supports were prepared by coprecipitation and were impregnated with 0,15% wt. of Rh. Characterization tests such as N2 fisisorption, XRD, TPR, Raman spectroscopy, DRIFTS, TGA-DTA and NO/CO TPD were performed. To measure the catalytic activity, a gas mixture containing 1% NO + 1% CO in He was used. Activity and selectivity were expressed by means of the gas concentrations measured all over a temperature range, from room temperature to 500C. The characterization results clearly indicated structural and physicochemical differences between the two supports in N2 adsorption isotherms, XRD and TPR profiles and therefore, they would work through different mechanisms. DRIFTS analyses indicated the presence of bands resulting from the adsorption of CO on Rh at low temperatures on RhCZ catalyst, evidencing the great synergy between Rh and CZ, already indicated by Raman results. This synergic effect probably did not occur in RhHT catalyst. The CZ support was more active at low temperatures than HT, however, RhHT catalyst was more selective to N2 at 350 C and emitted less N2O than RhCZ through the evaluated temperature range.The NO TPD results and the comparison of theoretical and experimental CO, CO2 and NOx curves during catalytic tests, also followed by DRIFTS, indicate that Rh reduction and the affinity with NO are important parameters to achieve higher selectivity to N2 in the reduction of NO by CO.

Submitted by ADONIS COELHO null (adonis.don@hotmail.com) on 2016-04-05T19:14:23Z No. of bitstreams: 1 DISSERTAÇÃO FINAL - Adônis Coelho.pdf: 3593393 bytes, checksum: d9939c50e525b3eae4cc80b3170b6281 (MD5) / Approved for entry into archive by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br) on 2016-04-07T12:23:06Z (GMT) No. of bitstreams: 1 coelho_a_me_sjrp.pdf: 3593393 bytes, checksum: d9939c50e525b3eae4cc80b3170b6281 (MD5) / Made available in DSpace on 2016-04-07T12:23:06Z (GMT). No. of bitstreams: 1 coelho_a_me_sjrp.pdf: 3593393 bytes, checksum: d9939c50e525b3eae4cc80b3170b6281 (MD5) Previous issue date: 2016-02-24 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / A produção e o consumo de biodiesel no Brasil e no mundo vem aumentando a cada ano em decorrência da busca por combustíveis menos poluentes e processos de produção mais baratos. Este biocombustível é produzido pela esterificação ou transesterificação de óleos ou gorduras com álcoois de cadeia curta. A catálise homogênea alcalina é a mais empregada na transesterificação gerando grandes quantidades de resíduos ao final do processo, já os catalisadores heterogêneos, menos usados em razão do custo e eficiência, são facilmente separados do produto final e ainda melhoram a qualidade do glicerol residual. O uso do etanol na produção do biodiesel fortalece a agroindústria brasileira, porém possui como principal desvantagem a sua higroscopicidade, o que pode favorecer a reação de saponificação afetando a qualidade do biodiesel e dificultando seu processo de produção. Neste trabalho, hidróxidos duplos lamelares tipo hidrotalcitas e piroauritas com substituição parcial de Mg e Al por Ba, Cu, Zn e Fe foram estudados como precursores de óxidos metálicos com atividade catalítica transesterificante na produção de biodiesel etílico de óleo de soja e caracterizados por TGA, DSC, FTIR-ATR, BET, XRD e SEM. Cromatografia em fase gasosa (GC-FID) foi empregada na quantificação dos produtos. Foram testadas 40 variações dos catalisadores, sendo 20 em cada temperatura de calcinação (450 e 600ºC). Dentre os materiais estudados, aqueles contendo Ba houve formação de fase secundária e os materiais com zinco e cobre obtiveram alta cristalinidade, maior perda de massa quando calcinados e altas áreas superficiais. Nos testes catalíticos em recipientes fechados com pressão autogerada a 120ºC por 12 horas utilizando razão 1:20 (massa óleo/massa etanol) e com 20% (massa catalisador/massa óleo). Os materiais de referência (hidrotalcita e piroaurita sem modificações calcinadas a 450ºC) proporcionaram conversões em biodiesel de 42 e 26%, respectivamente. Em geral, os materiais tipo piroaurita obtiveram rendimentos menores que os materiais tipo hidrotalcita, com destaque para o material com substituição de 10% de magnésio por zinco e 10% de alumínio por ferro calcinado a 450ºC que atingiu 61% de conversão em biodiesel nas condições testadas, e o pior resultado foi conseguido com o material tipo piroaurita preparado com 10% de cobre em substituição ao magnésio calcinado a 450ºC, que atingiu 15% de conversão. / Both the production and consumption of biodiesel have constantly increased worldwide and in Brazil due to a search for fuels which pollute less and production processes which cost less as well. Such biofuel is produced by means of esterification and transesterification of oils or fat with short-chain alcohols. Alkaline homogeneous catalysis is still widely used in transesterification, even though it generates a massive amount of residues at the end of the process; however, heterogeneous catalysts are not employed so frequently because they are more costly and less efficient. Nevertheless, they can be easily separated from the final product and improve the quality of residual glycerol. Although the use of ethanol in the production of biodiesel strengthens the Brazilian agro-industry, it poses a disadvantage: its hygroscopicity, which can generate a saponification reaction and, thus, affect the quality of the biodiesel and make its production process more difficult. In this study, we analyzed lamellar double hydroxides from hydrotalcite and pyroaurite types, with a partial substitution of Mg and Al for Ba, Cu, Zn, and Fe. We studied as metal oxide precursors with a transesterification catalytic activity on production of ethyl biodiesel from soybean oil and characterized them through TGA, DSC, FTIR-ATR, BET, XRD, and SEM. Gas chromatography (GC-FID) was used for products quantification. We conducted tests with 40 variations of catalysts, 20 for each calcination temperature (450 and 600ºC). Among the studied materials, those with Ba presented a secondary phase formation and materials with zinc and copper showed high crystallinity, high mass loss when calcined and high surface areas. In closed containers with auto-generated pressure at 120ºC for 12h using the ratio 1:20 (oil mass/ ethanol mass) and 20% (catalyst mass/ oil mass), the reference materials (hydrotalcite and pyroaurite, without modifications, calcined at 450ºC) yielded biodiesel conversions between 42 and 26%, respectively. Among all materials, pyroaurite obtained smaller yields compared to those from hydrotalcite materials, especially the material with a 10% substitution of magnesium for zinc and 10% of aluminum for iron calcined at 450ºC, which reached 61% conversion into biodiesel on tested conditions. Pyroaurite material prepared with 10% copper substituting calcined magnesium at 450ºC and reaching 15% conversion showed the worst result. / CNPq: 380625/2014-8

Made available in DSpace on 2016-06-02T19:55:34Z (GMT). No. of bitstreams: 1 4908.pdf: 28467151 bytes, checksum: acd573b22e5893693eada9075393a199 (MD5) Previous issue date: 2013-03-08 / Agência Nacional de Petróleo / This work deals with the investigation on the production of heterogeneous catalysts of base surface properties applied for ethylic transestérification, aiming the biodiesel production. In the first and second chapters of this thesis, oxide catalysts containing Li were prepared from incipient wet impregnation method on different supports [SÍO2, MgO, Y-AI2O3 and Mg(Al)0 obtained from MgAl hydrotalcite], using optimized calcination conditions. The materials were characterized by XRD, N2 Fisissorption, ICP-OES, SEM, XPS and TPD of C02. The Li+ addition to the catalysts caused morphologic changes, surface area reduction and increased the oxides crystallite size. On the other hand, Li+ caused a steep increase in the oxide reactivities due to the increase in the base sites strength. These materials were evaluated as catalysts in the model transestérification reaction between methyl acetate and ethanol, under mild reaction conditions. The higher the lithium content in the Li/Mg(Al)0 catalysts, the higher the activity and the different studied supports deeply affected their performances for transestérification. The lithium reaction with the supports Y-AI2O3 and SÍO2 led to lithium aluminates and silicates, inactive for reaction. However, Li/MgO and Li/Mg(Al)0 showed to be very active, mainly due to the presence of large amounts of strong base sites (low coordination O2' anions). Li/Mg(Al)0 exhibited conversion even higher than that obtained for Li/MgO. Nevertheless, Li+ leaching was detected in the solution, which resulted in some homogeneous reaction. Indeed, the stability of the Li+ containing catalysts must be improved in order to be able to be used in the biodiesel production. In the third chapter of this thesis, Ca based oxides, namely Ca/MgAl, were synthesized by impregnation of different contents of Ca nitrate onto MgAl hidrotalcita, and followed by calcination. These materials were characterized by XRD, N2 Fisissorption, SEM-EDS and TPD of CO2 revealing that they are mainly comprised of a oxides mixture [CaO + Mg(Al)0] and that the surface CaO is partially hydrated and carbonated. These materials were also evaluated as catalysts in the model transestérification reaction between methyl acetate and ethanol. By increasing the Ca content on the catalysts, the activity is enhanced, probably because of the formation of a highly basic CaO, well dispersed over the support matrix. The Ca/Mg(Al)0 catalysts can be reused for at least 5 batch runs, with low Ca2+ leaching to the solution. Therefore, the Ca/Mg(Al)0 revealed to be promising candidates as heterogeneous catalysts for ethylic biodiesel production. / Esse trabalho tem como objetivo principal a obtenção de catalisadores heterogêneos com propriedades básicas para aplicação na reação de transesterificação usando etanol, visando à produção de biodiesel. No primeiro e segundo capítulos da tese, catalisadores óxidos contendo Li+ foram preparados por impregnação de LÍNO3 em diferentes suportes [SÍO2, MgO, Y-AI2O3 e Mg(Al)0 obtido a partir de hidrotalcita de MgAl], otimizando-se as condições de calcinação. Os materiais foram caracterizados DRX, Fisissorção de N2, ICP-OES, MEV, XPS e DTP-CO2. A adição de Li+ nos catalisadores causou modificações na morfologia, redução da área específica e aumento do tamanho de partícula dos óxidos. Por outro lado, a presença de Li+ aumentou de maneira expressiva a reatividade dos óxidos pelo aumento da força dos sítios básicos. Esses materiais foram avaliados como catalisadores na reação modelo de transesterificação entre acetato de metila e etanol, sob condições amenas de reação. O aumento do teor de Li+ nos catalisadores de Li/Mg(Al)0 aumentou consideravelmente a atividade catalítica e a natureza dos diferentes suportes afetou fortemente o desempenho para transesterificação. A reação do íon lítio com os suportes Y-AI2O3 e SÍO2 levou à formação de aluminatos e silicatos de lítio, inativos para a reação. Entretanto, Li/MgO e Li/Mg(Al)0 foram bastante ativos, provavelmente devido à presença de grande quantidade de sítios básicos fortes (ânions O2' de baixa coordenação). Li/Mg(Al)0 apresentou conversão ainda maior que Li/MgO. Entretanto, foi detectada lixiviação de Li+ para a solução, o que resultou em alguma contribuição homogênea. De fato, a estabilidade dos catalisadores contendo Li+ deve ser melhorada a fim de tomá-los adequados para produção de biodiesel em larga escala. No terceiro capítulo da tese, foram sintetizados óxidos baseados em Ca suportado em óxido misto de Mg(Al)0 obtido de hidrotalcita. Foram avaliados diferentes teores de Ca2+ impregnado na hidrotalcita e a obtenção de óxidos Ca/Mg(Al)0 por calcinação. Esses materiais foram caracterizados por DRX, Fisissorção de N2, MEV-EDS e DTP-C02 revelando que são constituídos de uma mistura de óxidos [CaO + Mg(Al)0] e que o CaO superficial se encontra parcialmente hidratado e carbonatado. Esses catalisadores também foram avaliados quanto à atividade e estabilidade na reação modelo de transesterificação entre acetato de metila e etanol. Com o aumento do teor de Ca2+ nos catalisadores, houve um aumento significativo no desempenho catalítico dos materiais. Isso ocorre, provavelmente, devido à formação de um CaO superficial, altamente básico, bastante disperso na matriz do suporte. Os catalisadores de Ca/Mg(Al)0 podem ser reutilizados por pelo menos 5 ciclos de reação, apresentando pequena lixiviação de íons Ca2+ para a solução. Dessa maneira, os catalisadores Ca/Mg(Al)0 revelaram ser candidatos promissores para a produção de biodiesel etílico pela rota heterogênea.

Made available in DSpace on 2016-06-02T19:56:41Z (GMT). No. of bitstreams: 1 3274.pdf: 3373226 bytes, checksum: 0bbe8c76b7e7419d9334c8f4a3cb3b96 (MD5) Previous issue date: 2010-07-29 / Universidade Federal de Minas Gerais / Catalysts obtained by thermal decomposition of the precursors with hydrotalcite-like structure [Mg1-xAlx (OH)2]x+ [CO3]x/n. mH2O and [Ni1-x Mg1-xAlx (OH)2]x+ [CO3]x/n. mH2O were prepared, characterized and tested in the reactions of dry and oxidative reforming of methane. The precursors were modified with the addition of nickel during the precipitation or by impregnation, in order to increase the thermal stability and dispersion of the active metal and the resistance against carbon deposition during the reaction. The catalyst precursors were characterized by X-ray diffraction, thermal and gravimetric analysis, atomic emission spectroscopy, surface area determination (BET method) and temperature programmed reduction. The results indicated that the precipitation method led the formation of the hydrotalcite-type structure and that the variation in the calcination temperature resulted in mixed oxides with the desired structure: at 650 °C the mixed oxides were formed, but when the calcination temperature was increased to 850 °C these oxides had become more stable. It was observed in the catalytic experiments that the addition of different amounts of magnesium influenced the activity and stability of the oxides, when compared with samples that contained only Ni/Al. The mixed oxide with composition 12.67% Ni-Mg1,35/Al was the more active and resistant to deactivation during the reaction. / Catalisadores obtidos através da decomposição térmica dos precursores com estrutura tipo hidrotalcitas [Mg1-xAlx(OH)2]x+ [CO3]x/n . mH2O e [Ni1-x + Mg1-xAlx(OH)2]x+ [CO3]x/n . mH2O, foram preparados, caracterizados e testados na reação de reforma seca e reforma oxidativa do metano. Os precursores foram modificados com a adição de níquel durante a precipitação e através do método de impregnação, visando o aumento da estabilidade térmica, dispersão do metal ativo e resistência à deposição de carbono durante a reforma seca do metano. Todos os óxidos com estrutura tipo hidrotalcita foram preparados pelo método de precipitação a pH constante, com exceção dos óxido impregnados, utilizando sais de nitratos dos metais como sais de partida. Os catalisadores e precursores foram caracterizados por Difração de Raios X, Analise Termogravimétrica, Espectroscopia de Emissão Atômica por Plasma Induzido, Medidas de Área Superficial Método B.E.T. e Redução a Temperatura Programada. Os resultados indicam que o método de precipitação proporcionou a formação da estrutura tipo hidrotalcita e as diferentes temperaturas de tratamento térmico, resultaram em óxidos mistos com a estrutura desejada e com propriedades interessantes do ponto de vista para a aplicação em catalise heterogênea. A partir de 650°C é observada a formação dos óxidos mistos, porém é observada a formação de espécies de níquel com diferentes interações com o suporte, assim quando a temperatura de calcinação foi aumentada para 850°C o óxido obtido tornou-se mais estável, o que determinaram novas propriedades físicas e estruturais a estes óxidos. Verificou-se, nos ensaios catalíticos, que a adição de diferentes quantidades de magnésio, influenciou na atividade e estabilidade dos óxidos formados, quando comparados com amostras que continham apenas Ni/Al. O óxido misto com composição 12,67% Ni-Mg1,35/Al foi a que se mostrou mais ativa e resistente a desativação durante o ensaio reacional, mas outros catalisadores também apresentaram resultados interessantes.

Hidróxidos duplos lamelares (HDL) ou compostos lamelares do tipo da hidrotalcita, são materiais com estrutura formada pelo empilhamento de camadas de hidróxidos mistos de cátions divalentes e trivalentes contendo ânions hidratados nos espaços entre essas camadas. Os HDL apresentam uma grande diversidade de aplicações podendo ser utilizados como catalisadores ou suporte para catalisadores, trocadores iônicos, antiácidos, adsorventes. A adsorção de tensoativos em interfaces sólido/líquido é um fenômeno amplamente estudado devido à sua relação direta com estabilidade de colóides. A adsorção de tensoativo em superfícies de óxidos minerais é um processo importante no estudo de detergência, flotação de minerais, dispersão/floculação, crescimento de partículas em suspensão, melhoria na recuperação de óleos, lubrificação, cromatografia, entre outros processos. Mesmo sendo a adsorção um processo muito estudado em sólidos como carvão mineral, resinas poliméricas, polímeros, fibras naturais e sintéticas e em óxidos minerais, os trabalhos que tratam da adsorção de tensoativos em HDLs são escassos. Este projeto teve como principais objetivos a síntese e caracterização de HDL de magnésio e alumínio intercalado com ânion carbonato e o estudo das propriedades de adsorção de tensoativos aniônicos sulfonados, dodecilbenzenosulfonato e octilbenzenosulfonato, na superfície deste HDL, investigando o efeito da temperatura, do pH e da força iônica do meio e a influência do tamanho da cadeia hidrofóbica, no processo de adsorção. Para a síntese do HDL foi utilizado o método de coprecipitação a pH variável seguido de tratamento hidrotérmico. O material obtido foi caracterizado através das técnicas de difração de raios-X no pó, espectroscopia no infravermelho, análise termogravimétrica, análise térmica diferencial, adsorção de nitrogênio, análise elementar, e espalhamento de luz. A adsorção foi realizada pelo método de batelada, com o controle dos parâmetros envolvidos. Os resultados de adsorção mostraram que para ambos os tensoativos, as variáveis afetam a adsorção de maneira semelhante. Uma diminuição na quantidade de tensoativo adsorvida é observada em maiores temperaturas e em maiores valores de pH. Quando a adsorção é realizada em maior força iônica, uma maior quantidade adsorvida é observada para ambos os tensoativos estudados, exceto para o caso da adsorção de SDBS em concentrações acima da CMC. Uma competição entre a formação de micelas e a adsorção explica estes resultados. / Layered double hydroxides (LDH) or the hydrotalcite-like compounds are a class of material with structure formed by the stacking of positively charged layers of mixed divalent and trivalent cations hydroxides, containing in the interlayer spaces solvated anions. According to their chemical composition, crystallinity, thermal stability and other physical-chemical properties, the LDH can be used in a wide variety of application areas as catalysts or catalysts support, as antacid, as anionic exchanger, as adsorbents. The adsorption of surfactants at the solid/liquid interfaces has been extensively studied due to its direct relationship with colloids stability. The surfactant adsorption on mineral oxides is an important process in the study of detergency, mineral flotation, dispersion/flocculation, particles growth in suspension, oil recovery enhanced, lubrication and chromatography, among others. Even though this is an extensively studied process, few reports concerning to the adsorption of surfactants on LDH are available in the literature. The aim of this project was the synthesis and characterization of HDL of magnesium and aluminum containing carbonate as the intercalated anions and the adsorption study of sulfonated anionic surfactants, dodecylbenzenesulfonate and octylbenzenesulfonate, on this HDL, investigating the influence of the temperature, of the pH, of the ionic strength media and of the hydrophobic chain length on the adsorption process. The adsorbent was synthesized by the co precipitation method and characterized by PXRD analysis, infrared spectroscopy, TG/DT analysis, specific surface area, zeta potential measurements, and elemental chemical analysis. The adsorption was carried out by the batch method, with the control of the involved parameters. The results of the adsorptions showed that for both surfactants the variables affect the adsorption in a similar way. A decrease in the amount of adsorbed surfactant is observed at higher temperature and higher pH values. At higher ionic strength medium, the amount of adsorption increase for both surfactants, except for SDBS at equilibrium concentration higher than CMC. A competition between the micelle formation and adsorption can explain these results.

Les microbialites sont des roches organo-sédimentaires dont les processus de formation restent mal compris. L'objectif central de cette thèse est de mieux comprendre les conditions environnementales permettant le développement de microbialites actuels provenant de 10 lacs volcaniques mexicains. Une grande diversité de compositions minéralogiques des microbialites a été observée, comprenant divers carbonates et la quasi omniprésence de silicates de magnésium authigènes. A partir de cette étude nous proposons une valeur minimale d'alcalinité permettant le développement des microbialites. De plus, une corrélation positive entre l'alcalinité et la teneur en sodium des lacs est apparue. Cette corrélation pourrait s'expliquer par des niveaux différents d'évaporation des lacs et/ou des degrés différents d'altération des silicates alentours. L'étude plus particulière des silicates de magnésium a révélé que ces phases sont faiblement cristallisées, semblables à la kérolite et ont un fort potentiel de fossilisation des microorganismes et de la matière organique. Ces silicates de magnésium sont parfois associés à du fer dont l'origine pose question dans ces environnements alcalins et oxygénés. Nous avons mis en évidence la présence de différents types de phases porteuses du fer : des hydroxydes doubles lamellaires (hydrotalcites), des oxy(hydroxy)des, des silicates de magnésium et des sulfures. Nous proposons plus spécifiquement que l'hydrotalcite pourrait être issue de l'altération des basaltes par la circulation de fluides souterrains et plus généralement que cette phase pourrait être un précurseur des silicates de magnésium abondamment observés dans les microbialites actuels. / The processes leading to the formation of microbialites, which are organo-sedimentary rocks, are not well understood. The main goal of this thesis is to better understand the environmental conditions allowing the development of modern microbialites. Here we performed geochemical analyses of water solutions and mineralogical analyses of microbialites in 10 Mexican volcanic lakes. We found a large diversity of microbialites in terms of mineralogical composition, with occurrence of diverse carbonate phases as well as the frequent presence of authigenic magnesium silicate phases. From this study, we infer a minimum alkalinity value for the formation of lacustrine microbialites. Moreover, we observe a positive correlation between the alkalinity and the sodium content of the lakes. This may relate to variations in evaporation intensity and/or various degrees of weathering of the surrounding silicates. The study of Mg-silicates revealed that this phase is similar to kerolite, a poorly crystalline hydrated talc phase, and has a strong potential for the fossilization of microorganisms and organic matter. These silicates are sometimes associated with iron, the origin of which remains uncertain in these alkaline and oxidized environments. By the mineralogical study of several microbialites, we found several phases bearing iron: layered double hydroxides (hydrotalcites), Mg-silicates, oxy(hydroxi)des and sulfides. We propose more specifically that hydrotalcite could be the by-product of basalts weathering by groundwater. We propose more generally that hydrotalcite could be a precursor phase of Mg-silicates abundantly observed in modern microbialites.

L'augmentation des émissions de dioxyde de carbone force l'implémentation de différentes stratégies de réduction des émissions de CO2 qui peuvent être divisées en deux groupes principaux: (i) Le captage du carbone et stockage (CCS) and (ii) le captage du carbone et utilisation (CCU). Un des procédés convertissant le CO2 en un produit à valeur ajoutée est le reformage à sec du méthane (DRM). Cependant le procédé de DRM n'a pas été commercialisé en raison de la forte endothermicité de la réaction et par manque de catalyseur actif, stable et bon marché à ce jour. Les matériaux possédant des propriétés bénéfiques pour la réaction de DRM et pouvant inclure les composants catalyseurs désirés à savoir Ni, MgO et Al2O3 sont les hydrotalcites. L'objectif principal de cette thèse est d'évaluer la performance catalytique de différents systèmes catalytiques à base d'hydrotalcite contenant du nickel lors de DRM. Cette thèse a été divisée en trois parties: (i) l'influence de l'introduction de nickel dans un système catalytique à base d'hydrotalcite, (ii) l'évaluation de la teneur en nickel des couches de brucite de l'hydrotalcite sur les propriétés catalytiques du matériau et (iii) l'évaluation de l'effet des promoteurs Ce et/ou Zr. Afin de répondre à ces problématiques, plusieurs catalyseurs à base d'hydrotalcite ont été synthétisés par la méthode de co-précipitation. Les propriétés physico-chimiques des matériaux préparés ont été évalués au moyen d'analyse élémentaire (XRF ou ICP-MS), XRD, FTIR, N2-sorption à basse température, H2-TPR, CO2-DPT, TEM, expériences SEM et TG. Les matériaux ont ensuite été testés dans la réaction de DRM à 550, 650 et 750°C / The growing emissions of carbon dioxide forced implementation of different CO2 emissions reduction strategies, which may be divided into two main groups: (i) carbon capture and storage (CCS) and (ii) carbon capture and utilization (CCU) technologies. The latter approach allows to recycle CO2. One of the processes that converts CO2 into added-value products is dry reforming of methane (DRM). The DRM process has not yet been commercialized due to the high endothermicity of the reaction and lack of cheap, active and stable catalysts.The materials which have beneficial properties in DRM reaction and may include desired catalysts components i.e. Ni, MgO and Al2O3 are hydrotalcites. The main goal of this PhD thesis was to evaluate catalytic performance of different hydrotalcite-based catalytic systems containing nickel in methane dry reforming process. This PhD was divided into three parts: (i) the comparison of the influence of nickel introduction into HTs-based catalytic system, (ii) the evaluation of wide range of nickel content in hydrotalcite brucite-like layers on materials catalytic properties and (iii) the evaluation of the effect of Ce and/or Zr promoters. In order to address these issues a number of different hydrotalcite-based catalysts was synthesized by co-precipitation. The physico-chemical properties of the prepared materials were evaluated by means of elemental analysis (XRF or ICP-MS), XRD, FTIR, low temperature N2 sorption, H2-TPR, CO2-TPD, TEM, SEM and TG experiments. The materials were subsequently tested in the DRM reaction. Most of catalytic tests were carried out at 550°C, but higher temperatures (650 and 750°C) were also studied.

Fast ionic conductors, i.e. materials in which charge transport mainly occurs through the motion of ions, are an important class of materials with immense scope for industrial applications. There are different classes of fast ionic conductors e.g. polymer electrolytes, glasses, oxide ion conductors etc. and they find applications such as solid electrolytes in batteries, in fuel cells and in electro active sensors. There are mixed conducting materials as well which have both ions and electrons as conducting species that are used as electrode materials. Specifically, polymer electrolytes 1−3 have been in use in lithium polymer batteries, which have much more advantages compared to other secondary batteries. Polymer electrolyte membranes have been in use in direct methanol fuel cells (DMFC). The membranes act as proton conductors and allow the protons produced from the fuel (methanol) to pass through. Oxide ion conductors are used in high temperature solid oxide fuel cells (SOFC) and they conduct via oxygen ion vacancies. Fuel cells are rapidly replacing the internal combustion engines, because they are more energy efficient and environment friendly. The present thesis is concerned with the preparation, characterization and conductivity studies on the following fast ionic conductors: (MPEG)xLiClO4, (MPEG)xLiCF3SO3 where (MPEG) is methoxy poly(ethylene glycol), the hydrotalcite [Mg0.66Al0.33(OH)2][(CO3)0.17.mH2O] and the nanocomposite SPE, (PEG)46 LiClO4 with dispersed nanoparticles of hydrotalcite. We also present our investigations of spin probe electron spin resonance (SPESR) as a possible technique to determine the glass transition temperature (Tg) of polymer electrolytes where the conventional technique of Tg determination, namely, differential scanning calorimetry, (DSC), is not useful due to the high crystallinity of the polymers. In the following we summarize the main contents of the thesis. In Chapter 1 we provide a brief introduction to the phenomenon of fast ionic conduction. A description of the different experimental techniques used as well as the relevant theories is also given in this chapter. In most solid polymer electrolytes (SPE), the usability is limited by the low value of the ionic conductivity. A number of different routes to enhance the electrical, thermal and mechanical properties of these materials is presently under investigation. One such route to enhance the ionic conductivity in polymer electrolytes is by irradiating the polymer electrolyte with gamma rays, electron beam, ion beams etc. In Chapter 2, we describe our work on the effect of electron beam (e-beam) irradiation on the solid polymer electrolytes (MPEG)xLiClO4 and (MPEG)xLiCF3SO3. The polymer used is methoxy poly(ethylene glycol) or poly(ethylene glycol) methyl ether with a molecular weight 2000. Salts used are LiClO4 and LiCF3SO3. ’x’ in the subscript is a measure of the salt concentration; it is the ratio of the number of ether oxygens in the polymer chain to that of the Li+ ion. ’x’ values chosen are 100, 46, 30 and 16. Nearly one order of magnitude increase in the conductivity is observed for samples (MPEG)100LiClO4 and (MPEG)16LiCF3SO3 on irradiation. It was found that the increase in the net ionic conductivity is a function of both the irradiation dose and the salt concentration. The enhanced ionic conductivity remains constant for ∼ 100 hrs, which signifies a possible near permanent change in the polymer electrolyte system due to irradiation. The samples were also characterized using DSC and Fourier transform infrared spectroscopy (FTIR). DSC results could be correlated with conductivity findings, giving low Tg values for samples having high conductivity. It was also found that there is a small increase in the crystalline fraction of the samples on irradiation, which agrees with earlier reports on samples irradiated with low dosage. FTIR results are suggestive of decreased cross linking as the reason for increased ionic conductivity. However, this aspect needs a further confirmatory look before the findings can be termed conclusive. In Chapter 3, we describe the studies we have carried out on Li -doped hydrotalcite. We report the details of preparation and characterization of hydrotalcite as well as NMR and ionic conductivity measurements on both doped (with Li+ ions) and undoped hydrotalcite. Hydrotalcite was prepared by co-precipitation method and the composition of hydrotalcite was chosen as [Mg0.66Al0.33(OH)2][(CO3)0.17.mH2O]. Samples were prepared with salt (LiClO4) concentration 5 %, 10 %, 15 %, 20 % and 25 %. It was found that the highest ionic conductivity occurs for the sample with 20 % doping. 7Li NMR plots for all the samples clearly show an overlap of a Gaussian and a Lorentzian lineshape. The Gaussian line is because of the presence of a less mobile fraction of the 7Li+ ions and the Lorentzian line is because of the presence of a more mobile fraction of 7Li+ ions. The highest ionic conductivity was found for the salt concentration 20 % and from the room temperature 7Li NMR studies we found that for this particular concentration, the mobile fraction of the 7Li ion is also maximum. Without the salt doping, the conductivity of the sample was too small to be measured. Temperature variation of both 1H and 7Li NMR was also done, to compare the ionic conductivities from NMR. Another method to obtain enhanced properties in polymer electrolytes is by forming ’nanocomposite’ polymer electrolytes. Nanocomposites are formed by dispersing nanoparticles of certain materials in the polymer electrolyte matrix. Till now, nanoparticles used are mostly oxides of metals, e.g. Al2O3, TiO2, MgO, SiO2 etc and clays like montmorillonite, liponite, hydrotalcite etc. Chapter 4 describes the preparation and characterization of the nanocomposite polymer electrolyte (PEG)46LiClO4 formed with hydrotalcite nanoparticles. The polymer used is PEG, poly(ethylene glycol) of molecular weight 2000, and salt used is LiClO4. The salt concentration is selected so as to give the highest ionic conductivity for the solid polymer electrolyte. Hydrotalcite belongs to a class of materials called LDH, layered double hydroxides. The composition selected is [Mg0.66Al0.33(OH)2][(CO3)0.17 .mH2O], since this is the most stable composition. These materials are easy to prepare in the nano size and are being used in a number of applications. These are characterized by the presence of layers of positively charged double hydroxides separated by layers of anions and water molecules. The water molecules give stability to the structure. Nanoparticles of hydrotalcite were prepared in the laboratory itself. XRD data of hydrotalcite confirm the crystal structure. TEM data show the particle size to be ∼ 50 nm. The polymer electrolyte (PEG)46LiClO4 was doped with these nanoparticles and the doping levels are 1.8 %, 2.1 %, 2.7 %, 3.6 % and 4.5 % by weight. Impedance spectroscopy was used to find the ionic conductivity. We have found that the sample with a doping of 3.6 % by weight gives the highest ionic conductivity and the increase in ionic conductivity is nearly one order of magnitude. DSC was used for thermal characterization of these nanocomposites. The glass transition temperatures, Tg , found from DSC measurements corroborates the ionic conductivity data, giving the lowest Tg for the sample with highest conductivity. Temperature variation of the ionic conductivity shows Arrhenius behavior. 7Li NMR was done on the pristine SPE (PEG)46LiClO4 and the nanocomposite of (PEG)46LiClO4 with 3.6 % filler. The ionic conductivity was also estimated from the temperature variation of 7Li NMR line widths. Studies on the DSC endotherms of the nanocomposites give the fractional crystallinity of the samples. From these studies it can be concluded that the variation in ionic conductivity can be attributed to the change in fractional crystallinity; the nanocomposite polymer electrolyte having highest ionic conductivity, i.e. the NCPE with filler concentration of 3.6 % also has the lowest fractional crystallinity. Additionally, a possible increase in the segmental motion inferred from a reduction in the glass transition temperature coupled with a lowering of the activation energy may also contribute to the increased ionic conductivity in the nanocomposite polymer electrolyte. Glass transition temperature Tg has a very important role in studying the dynamics of polymer electrolytes. In Chapter 5, we explore the possibility of using spin probe electron spin resonance (SPESR) as a tool to study the glass transition temperature of polymer electrolytes. When the temperature of the polymer is increased across the glass transition, the viscosity of the sample decreases. This corresponds to a transition from a slow tumbling regime with τc = 10−6 s to a fast tumbling regime with τc = 10−9 s where τc is the correlation time for the probe dynamics. Spin probe ESR can be used to probe this transition in polymers. We have used 4-hydroxy tempo (TEMPOL) as the spin probe which is dispersed in the nanocomposite polymer electrolyte based on (PEG)46LiClO4 and hydrotalcite. Below and across the glass transition, this nitroxide probe exhibits a powder pattern showing both Zeeman (g) and hyperfine (hf) interaction anisotropy. When the frequency of the dynamics increases such that the jump frequency f is of the same order of magnitude as the anisotropy of the hf interaction, i.e., ∼ 108 Hz, the anisotropy of the interactions averages out and a spectrum of reduced splitting and increased symmetry in the line shape is observed. This splitting corresponds to the nonvanishing isotropic value of the hyperfine tensor and is observed at a temperature higher than but correlated with Tg. The crossover from the anisotropic to isotropic spectrum is reflected in a sharp reduction in the separation between the two outermost components of the ESR spectrum, which corresponds to twice the value of the z-principal component of the nitrogen hyperfine tensor, 2Azz, from ∼75 G to ∼ 35 G. In our study, we have varied the concentration of the nano-fillers. The Tg for all the samples were estimated from the measurement of T50G and the known correlation between 4 T50G and Tg, where T50G is the temperature at which the extrema separation (2Azz) of the ESR spectra becomes 50 Gauss. The values obtained from this method are compared with the values found from DSC done on the same samples. Within experimental error, these two techniques give reasonably close values. Tg’s were also estimated by a cross over in the correlation time (τc) vs temperature plot. The τc values were calculated using a spectral simulation program. We conclude that spin probe ESR can be an alternative to the DSC technique for polymers with high fraction of crystallinity, for which DSC often does not give any glass transition signature. In Appendix I, ionic conductivity studies on quenched and gamma irradiated polymer electrolytes (PEG)46LiClO4 and (MPEG)16LiClO4 is done. It is observed that, (i) the samples quenched to 77 K after melting show enhancement of ionic conductivity by a factor of 3 & 4; (ii) on irradiation, the ionic conductivity decreases for a dose of 5 kGy and subsequently, keeps on increasing for higher doses of 10 kGy and 15 kGy. In Appendix II, the BASIC language program (eq-res.bas) used for impedance data analysis is given.

Catalisadores ativos e estáveis, preparados a partir dos hidróxidos duplos lamelares (HDLs) contendo os cátions Ni2+, Zn2+, Al3+ e Zr4+(NiZn-Al, NiZn-AlZr e NiZn-Zr), foram avaliados na reação de reforma seca do metano. Os precursores foram caracterizados por difração de raios X, confirmando a formação das fases para as amostras de NiZn-Al e NiZn-AlZr. As espectroscopias no infravermelho/Raman elucidaram a ocorrência dos ânions (CO32-) e das moléculas de água na intercamada. A Fisissorção de nitrogênio ( método de BET) determinou a presença de poros e a área superficial específica. As formas das isotermas foram do tipo IV, de acordo com a IUPAC, e representa uma estrutura mesoporosa. A análise termogravimétrica foi utilizada para determinar a temperatura de calcinação dos precursores para obtenção dos catalisadores e as temperaturas utilizadas foram 550 °C, 650 °C e 750 °C. Os resultados de difração de raios X dos catalisadores apresentaram uma mistura de óxidos binários (NiO, ZnO, ZrO2 e Al2O3) e óxidos ternários (NiAl2O4 e ZnAl2O4). As fases de espinélios foram observadas nos catalisadores obtidos a 650°C (Ni/ZnAl-6 e Ni/ZnAlZr-6) e 750°C (Ni/ZnAl-7 e Ni/ZnAlZr-7). A redução a temperatura programada de hidrogênio (TPR-H2) forneceu informações sobre a redução do catalisador. Os resultados exibiram interações entre a fase ativa com as outras fases presentes no intervalo entre 350 - 800 °C, enquanto que a dessorção àtemperatura programada de CO2 (DTP-CO2) mostrou que os catalisadores possuem sítios básicos fracos. Ademais, os catalisadores foram caracterizados por fisissorção de nitrogênio, microscopia eletrônica de varredura (MEV), espectroscopia Raman e basicidade usando um indicador de Hammett. O desempenho dos catalisadores foi avaliado na reação de reforma seca do metano utilizando uma razão molar de alimentação de CH4: CO2 = 1,5:1,0; a fim de simular a composição do biogás. Os resultados mostraram uma maior conversão para o CO2 em todos os catalisadores investigados, o que pode ser atribuído ao maior teor de CH4 alimentado. Além disso, é importante ressaltar a contribuição dos sítios básicos presentes nas amostras, o que pode também contribuir para a conversão do CO2. A maior conversão de CH4 foi observada para os catalisadores tratados a 750 °C. Após as reações, foi observada a formação de carbono grafite sobre todos os catalisadores, com menor percentual para a amostra Ni/ZnAl, calcinadas a 550 °C e 650 °C, e Ni/ZnZr-7, calcinada a 750 °C. Finalmente, os catalisadores calcinados a 650 °C e 750 °C também foram ativados na temperatura de 750°C e os resultados reacionais mostraram que essa temperatura favoreceu o processo de aglomeração e, portanto, promoveu baixas conversões para o CH4 e CO2. / Active and stable catalysts, prepared from the lamellar double hydroxides (HDLs) containing the cations Ni2 +, Zn2 +, Al3 + and Zr4 + (NiZn-Al, NiZn-AlZr and NiZn-Zr) were evaluated in the dry reforming reaction of methane. The precursors were characterized by X-ray diffraction method, confirming the formation of phases for NiZn-Al and NiZn-AlZr samples. Infrared / Raman spectroscopies elucidated the occurrence of anions (CO32-) and water molecules in the interlayer. Nitrogen physisorption (BET method) determined the presence of pores and the specific surface area. The shape of the isotherms were type IV, according to the IUPAC, representing a mesoporous structure. The thermogravimetric analysis was used to determine the calcination temperature of the precursors to obtain the catalysts and the temperatures used were 550 ° C, 650 ° C and 750 ° C. The X-ray diffraction results of the catalysts showed a mixture of binary oxides (NiO, ZnO, ZrO2 and Al2O3) and ternary oxides (NiAl2O4 and ZnAl2O4). The spinel phases were observed in the catalysts obtained at 650 °C (Ni/ZnAl-6 and Ni/ZnAlZr-6) and 750°C (Ni/ZnAl-7 and Ni/ZnAlZr-7) Temperature- programmed reduction with hydrogen (H2-TPR) provided information on catalyst reduction. The results showed interactions between the active phase and the other phases present in the range of 350 - 800 ° C, while temperature- programmed desorption of CO2 (CO2-TPD) showed that the catalysts have weak basic sites. In addition, the catalysts were characterized by Nitrogen physisorption, scanning electron microscopy (SEM), Raman spectroscopy and basicity using a Hammett indicator. The performance of the catalysts was evaluated in the dry reforming reaction of the methane using a CH4: CO2 molar feed ratio = 1.5: 1.0; In order to simulate the biogas composition. The results showed a higher conversion to CO2 in all the catalysts investigated, which can be attributed to the higher content of CH4 fed. In addition, it is important to restate the contribution of the basic sites present in the samples, which may also contribute to the conversion of CO2.The higher conversion of CH4 was observed for the catalysts treated at 750 ° C. After the reactions, the formation of graphite carbon was observed on all the catalysts, with a lower percentage for Ni / ZnAl samples, calcined at 550 ° C and 650 ° C, and Ni / ZnZr-7, calcined at 750 ° C. Finally, the catalysts calcined at 650 ° C and 750 ° C were also activated at the temperature of 750 ° C. and the reaction results showed that this temperature favored the agglomeration process and, therefore, promoted low conversions for CH4 and CO2.

A utilização de combustíveis fósseis é um problema a ser contornado visto que sua utilização gera problemas ambientais tais como o aumento do efeito estufa. Como combustível alternativo, ganha destaque o hidrogênio, o qual pode ser utilizado em células à combustível, gerando energia e apenas água como sub-produto. Uma forma de produção de hidrogênio é a partir da reforma a vapor do bio-óleo, proveniente da pirólise da biomassa. Devido à complexidade do bio-óleo, compostos modelo, como o ácido acético e acetol, vêm sendo estudados nos sistemas reacionais. Neste trabalho, estudou-se a reação de reforma a vapor do acetol para obtenção de H2 utilizando-se catalisadores baseados em Ni0 e Co0 derivados de hidróxidos duplos lamelares (HDLs), também chamados de compostos do tipo hidrotalcita. Os HDLs foram sintetizados pelo método de coprecipitação. Análise de difração de raios X (DRX) mostraram a formação dos HDLs e os diferentes teores de Al3+ nas lamelas foram observados através da técnica de espectroscopia na região do infravermelho. Espectroscopia por energia dispersiva de raios X (EDX) indicou que os catalisadores derivados de HDLs calcinados a 750°C possuem quantidades reais de metais ativos próximas aos valores nominais e que possuem diferentes teores de Mg2+. As análises de TPR-H2 mostraram a redução das fases óxidas presentes em altas temperaturas, devido a formação de solução sólida MgNiO2, MgCoO2 e fases espinélios. Nos ensaios catalíticos, catalisadores baseados em Ni0 se mostraram mais seletivos para H2 enquanto que os baseados em Co0 foram mais seletivos para o eteno e compostos líquidos. Ainda, observou-se a tendência de maior seletividade para H2 quanto maior o teor de Mg2+ no catalisador. Para os catalisadores derivados de HDL´s calcinados a 600°C, as caracterizações mostraram resultados semelhantes aos calcinados a 750°C, evidenciando a facilidade de formação das soluções sólida para estes compostos do tipo HDL´s. Para estas amostras também ficou evidenciado que maiores teores de Mg2+ nos catalisadores facilitam a conversão em H2 na reforma a vapor do acetol, o que pode estar associado a propriedade basicidade, que foi quantificada através de termo-dessorção programada de CO2 (TPD-CO2). / The use of fossil fuels is a problem to be circumvented, since its use generates environmental problems such as the increase of the greenhouse effect. As an alternative fuel, hydrogen is highlighted, which can be used in fuel cells, generating energy without the emission of polluting gases. One form of hydrogen production is from the steam reforming of the bio-oil, from the pyrolysis of the biomass. Due to the complexity of the bio-oil, model compounds, present in greater quantity, such as acetic acid and acetol have been studied individually. In this work, the reaction of steam reforming of the acetol to obtain H2 was carried out using catalysts based on Ni0 and Co0 derived from lamellar double hydroxides (HDLs), also called hydrotalcite like compounds. HDLs were synthesized by the coprecipitation method. X-ray diffraction (XRD) analysis showed the formation of HDLs and different Al3+ contents in the lamellae, as well as the Fourier transform infrared spectroscopy technique. X-ray dispersive energy spectroscopy (EDS) has indicated that the catalysts derived from HDLs calcined at 750°C have real amounts of active metals close to the nominal values and that have different levels of Mg2 + and Al3+. The TPR-H2 analysis showed that the reduction of Ni2+ and Co2+ occurs at high temperatures due to the formation of solid solutions MgNiO2, MgCoO2, and spinel phases. In the catalytic tests, Ni2+ based catalysts were more selective for H2, while Co0 based catalysts were more selective for liquid compounds such as acetone. Also, the tendency of greater selectivity for H2 was observed when the Mg2+ content in the catalyst was higher. For the catalysts derived from HDL\'s calcined at 600°C, the characterizations showed results similar to those calcined at 750°C, evidencing the difficult reducibility of oxides derived from HDL\'s. For these catalysts, it was also observed that higher Mg2+ contents facilitate the conversion to H2 in the steam reforming of the acetol, which may be associated with the basicity of the material, which was quantified by means of programmed thermodesorption of CO2 (TPD-CO2).