Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-09-19T19:40:40Z No. of bitstreams: 1 ElaniaMariaFernandesSilva_TESE.pdf: 3393670 bytes, checksum: 8755f5c2f474b6b328f5f50e212e7e18 (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-09-19T23:05:55Z (GMT) No. of bitstreams: 1 ElaniaMariaFernandesSilva_TESE.pdf: 3393670 bytes, checksum: 8755f5c2f474b6b328f5f50e212e7e18 (MD5) / Made available in DSpace on 2017-09-19T23:05:55Z (GMT). No. of bitstreams: 1 ElaniaMariaFernandesSilva_TESE.pdf: 3393670 bytes, checksum: 8755f5c2f474b6b328f5f50e212e7e18 (MD5) Previous issue date: 2017-07-25 / Catalisadores de alto desempenho v?m sendo bastante investigados com o objetivo de aumentar o rendimento dos processos de reforma a seco do metano (RSM). Alguns metais de transi??o, em especial o n?quel, s?o amplamente estudados para essa aplica??o. Por possu?rem propriedades catal?ticas, estabilidade t?rmica e qu?mica, os ?xidos com estrutura do tipo perovsquita s?o materiais promissores como precursores catal?ticos em processos de RSM. O objetivo deste estudo ? avaliar a efici?ncia de ?xidos do tipo perovsquita como catalisadores m?ssicos e como suportes catal?ticos na reforma a seco de metano (RSM). Assim, ?xidos tipo perovsquita ABO3 foram sintetizados pelo m?todo de combust?o assistida por micro-ondas usando ureia como combust?vel. Os materiais foram calcinados a 900 ?C por 2h. Ap?s a calcina??o todos os ?xidos preparados foram impregnados com 20 % (m/m) de n?quel e calcinados novamente a 600 ?C por 2h. As amostras foram caracterizadas por: difra??o de raios X (DRX), redu??o ? temperatura programada (RTP) e microscopia eletr?nica de varredura com espectroscopia de energia dispersiva (MEV-EDS). Testes de reforma de metano com CO2 foram realizados para avalia??o desses materiais como catalisadores na produ??o de g?s de s?ntese. Ap?s os testes de reforma, os catalisadores foram submetidos novamente a caracteriza??es para investiga??o da exist?ncia de carbono nas superf?cies dos ?xidos. De acordo com os difratogramas de raios X, fases secund?rias de ?xidos de n?quel foram formadas ap?s a impregna??o do n?quel nos p?s. Os mapeamentos obtidos atrav?s de EDS mostraram que a metodologia de impregna??o resultou numa dispers?o homog?nea das part?culas de ?xido de n?quel na superf?cie das perovsquitas. Os testes catal?ticos foram realizados a 750 ?C durante 10 horas. Os catalisadores avaliados apresentaram melhores desempenhos, tanto de convers?es como de estabilidade, ap?s a impregna??o de n?quel, mostrando que as perovsquitas podem ser potenciais suportes catal?ticos para reforma a seco do metano. / High-performance catalysts have been widely researched in order to increase the yield in methane dry reforming processes (DRM). Some transition metals, especially nickel, are largely studied for this purpose. Due to its catalysts? properties, thermal and chemical stability, perovskite-type oxides ABO3 are promising materials as catalytic precursors in DRM processes. The objective of this study is to evaluate the efficiency of perovskite type oxides as catalysts and as supports in dry reforming of methane (DRM). Perovskite-type oxides ABO3 were synthesized by microwave assisted combustion using urea as fuel and calcinated at 900 ?C for 2h. After the calcination, all the prepared oxides were impregnated with 20% (w/w) of nickel and calcinated again at 600?C for 2h. The samples were characterized by the following techniques: x-ray diffraction (XRD), temperature programmed reduction (TPR), and dispersive energy scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS). Methane reforming tests with CO2 were performed for evaluation of these materials as catalysts in the production of syngas. After the reforming tests, the catalysts were submitted once again to characterizations for the evaluation of the existence of carbon in the oxides? surface. According to the X-ray diffractograms, secondary phases of nickel oxides were formed after the nickel impregnation in the powders. The mapping by EDS showed that the impregnation methodology resulted in a homogeneous dispersion of the nickel oxide particles on the perovskite?s surface. The catalytic tests were performed at 750 ? C for 10 hours. The catalysts showed better performances, conversions and stability, after nickel impregnation, showing that the perovskites may be potential catalytic supports for dry reforming methane.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2016-08-26T23:16:09Z No. of bitstreams: 1 MonickarlaTeixeiraPegadoDaSilva_DISSERT.pdf: 2972749 bytes, checksum: 333ef217ee5461818b38fff8de7cfdeb (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2016-08-31T00:12:48Z (GMT) No. of bitstreams: 1 MonickarlaTeixeiraPegadoDaSilva_DISSERT.pdf: 2972749 bytes, checksum: 333ef217ee5461818b38fff8de7cfdeb (MD5) / Made available in DSpace on 2016-08-31T00:12:48Z (GMT). No. of bitstreams: 1 MonickarlaTeixeiraPegadoDaSilva_DISSERT.pdf: 2972749 bytes, checksum: 333ef217ee5461818b38fff8de7cfdeb (MD5) Previous issue date: 2016-02-23 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / Suportes catal?ticos ? base de ?xido de alum?nio foram sintetizados pelo m?todo e esferas h?bridas utilizando carboximetilcelulose (CMC) como precursor org?nico (template) e nitrato de alum?nio como precursor inorg?nico. As caracteriza??es foram realizadas por an?lises de termogravimetria (TG), difra??o de raios-X (DRX), espectroscopia no infravermelho por transformada de fourier (FTIR), microscopia eletr?nica de varredura (MEV) e fisissor??o N2. Os materiais sintetizados foram testados na rea??o de convers?o do glicerol em fase g?s. Os estudos da s?ntese indicaram que as caracter?sticas do biopol?mero (grau de substitui??o e de polimeriza??o) influenciam diretamente no valor m?ximo da rela??o entre o precursor org?nico e inorg?nico para a forma??o das esferas h?bridas. As propriedades f?sico-qu?micas do material final (cristalinidade, porosidade, ?rea espec?fica e morfologia) mostraram uma depend?ncia direta com as propriedades do biopol?mero (grau de substitui??o e de polimeriza??o), indicando a versatilidade desta rota s?ntese. Os espectros de FTIR confirmaram a forma??o de um material h?brido quando se compara o espectro da CMC pura com os s?lidos obtidos ap?s a secagem. Os resultados de DRX mostraram um perfil de material amorfo para algumas amostras. Para alguns s?lidos foi poss?vel identificar a forma??o de uma fase cristalina relacionada com a alumina hidratada, ?xido de alum?nio e ?xido de cobre. As imagens obtidas por MEV indicaram a forma??o de um material com morfologia semelhante a uma esponja ap?s a calcina??o, caracter?stico de um s?lido altamente poroso. O perfil de adsor??o/dessor??o de N2 confirma a forma??o de materiais contendo micro-mesoporos com uma ?rea espec?fica entre 50-162 m2.g-1 para os suportes e 112-303 m2.g-1 para os catalisadores com cobre, indicando um aumento ?rea ap?s a adi??o do Cu por impregna??o devido a redissolu??o e recristaliza??o da fase alumina. Testes catal?ticos indicaram que os ?xidos s?o ativos e seletivos para a convers?o do glicerol (92-15%) a bioprodutos de alto maior valor agregado, confirmando a viabilidade do m?todo de s?ntese. / Catalytic supports based on aluminum oxide were synthesized by the method of hybrid spheres using carboxymethylcellulose (CMC) as organic precursor (template) and aluminum nitrate as inorganic precursor. The characterizations were performed by thermal chemical analysis (TGA), X-Ray diffraction (XRD), fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and N2 physisorption. The study of synthesis indicated that the characteristics of the biopolymer (degree of substitution and polymerization) directly influence on the maximum value of the ratio between the organic and inorganic precursor for the formation of hybrid spheres. The physicochemical properties of the final material (crystallinity, porosity, surface area and morphology) showed a direct dependence on the biopolymer properties (degree of substitution and polymerization), indicating the versatility of this synthesis route. The FTIR spectra confirm the formation of a hybrid material when comparing the pure CMC spectrum with the obtained solids after drying. The XRD results show a profile of amorphous and crystalline material for the different samples. For some solids were possible to identify the formation of a crystalline phase related to the hydrated alumina, aluminium oxide and copper oxide. The images obtained by SEM analysis showed the formation of a material with sponge-like morphology after calcination, characteristic of highly porous solid. The N2 adsorption/desorption isotherm profile confirms the formation of micro-mesoporous materials with a specific surface area between 50-162 m2.g-1 for the supports and 112-303 m2.g-1 for the copper-based catalysts, indicating an increase in the area after the addition of Cu by impregnation due to redissolution and recrystallization of alumina phase. Catalytic tests were tested in the glycerol conversion reaction (92-15%) to added value products in order to confirm their real viability.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-12-12T18:02:43Z No. of bitstreams: 1 GilvanPereiraDeFigueredo_TESE.pdf: 4395902 bytes, checksum: dcc65d04331c39ac75781ca0d55044db (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-12-13T18:29:41Z (GMT) No. of bitstreams: 1 GilvanPereiraDeFigueredo_TESE.pdf: 4395902 bytes, checksum: dcc65d04331c39ac75781ca0d55044db (MD5) / Made available in DSpace on 2017-12-13T18:29:41Z (GMT). No. of bitstreams: 1 GilvanPereiraDeFigueredo_TESE.pdf: 4395902 bytes, checksum: dcc65d04331c39ac75781ca0d55044db (MD5) Previous issue date: 2017-08-11 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico (CNPq) / Os materiais cer?micos apresentam diversas aplica??es, principalmente por sua versatilidade e propriedades. V?rias metodologias foram consolidadas para a s?ntese destes materiais, mas algumas desvantagens limitam sua aplicabilidade em cat?lise. Assim, h? muitas pesquisas concentradas no estudo de m?todos de s?ntese de catalisadores e suportes catal?ticos que sejam simples, r?pidos, de baixo custo, ecol?gicos e que produzam materiais adequados. Nos ?ltimos anos algumas rotas alternativas de s?ntese t?m atra?do bastante aten??o, mas a obten??o do espin?lio MgAl2O4 pelo m?todo da gelatina e da perovskita LaAlO3 via rea??o de combust?o assistida por microondas tem sido pouco explorada. O MgAl2O4 ? bastante utilizado na reforma a seco do metano (RSM), mas estudos de RSM usando LaAlO3 como suporte s?o muito limitados. Neste contexto, os objetivos deste trabalho foram: sintetizar MgAl2O4 usando gelatina como precursor org?nico; preparar a perovskita LaAlO3 via rea??o de combust?o assistida por microondas; e, comparar o desempenho em reforma a seco do metano de dois catalisadores preparados com n?quel suportado no LaAlO3 e na ?-Al2O3 comercial. Pelo m?todo da gelatina foi poss?vel obter MgAl2O4 puro, nanom?trico e com cristalinidade de at? 90,40%. Um aumento brusco no tamanho dos cristalitos foi observado para temperatura de calcina??o acima de 900 ?C. Na s?ntese por microondas, a perovskita LaAlO3 monof?sica e nanom?trica foi obtida. Os perfis de RTP-H2 mostram que as vac?ncias de oxig?nio presentes na superf?cie da perovskita exerceram um forte efeito sobre a temperatura de redu??o e a redutibilidade das nanopart?culas de NiO, resultando em fraca intera??o Ni0/LaAlO3. Os resultados dos testes de 10 h com GHSV de 18 L g-1 h-1 mostram que o catalisador Ni/LaAlO3 ? 7,8 e 11,5 % mais est?vel do que o Ni/?-Al2O3 nas convers?es de CH4 e CO2, respectivamente. A maior estabilidade e atividade do Ni/LaAlO3 est? diretamente relacionada ? presen?a de NiO (3,38 %p) ap?s a ativa??o, que promoveu a forma??o de nanotubos de carbono (NTC), aumentando a dispers?o da fase met?lica. Mesmo em condi??es severas de ativa??o e rea??o (alta GHSV), como no teste a longo prazo (20 h), o catalisador Ni/LaAlO3 revelou um rendimento em H2 de 37,2% a mais que o Ni/?-Al2O3. As an?lises por Microscopia Eletr?nica de Transmiss?o (MET) revelam que o catalisador Ni/?-Al2O3 desativou por sinteriza??o. Assim, a presen?a de defeitos estruturais e de superf?cies ricas em vac?ncias de oxig?nio tornam a perovskita LaAlO3 um potencial suporte para aplica??o em processos de reforma catal?tica do metano. / Ceramic materials have several applications, mainly due to their versatility and properties. Several methodologies have been consolidated for the synthesis of these materials, but some disadvantages limit their applicability in catalysis. Thus, much research is concentrated on the study of catalyst synthesis methods that are simple, fast, low cost, ecofriendly and produce suitable materials. In recent years, some alternative synthesis routes have attracted great attention, however the obtainment of MgAl2O4 spinel by the gelatin method and perovskite LaAlO3 via microwave assisted combustion method has been little explored. MgAl2O4 is widely used in the dry reforming of methane (DRM), but DRM studies using LaAlO3 as support are very limited. In this context, the aims of this work were: to synthesize MgAl2O4 using gelatin as an organic precursor; to prepare LaAlO3 perovskite via microwave assisted combustion reaction; and to compare the methane dry reforming performance of two nickel catalysts supported on LaAlO3 and commercial ?-Al2O3. By the gelatin method it was possible to obtain pure and nano-sized MgAl2O4 with crystallinity of up to 90.40%. An abrupt increase in crystallite size was observed for calcination temperatures above 900 ?C. In the microwave synthesis, a monophasic and nano-sized LaAlO3 perovskite was obtained. The TPR-H2 profiles show that the oxygen vacancies present on the perovskite surface exerted a strong effect on the reduction temperature and the reducibility of NiO nanoparticles, resulting in poor Ni0/LaAlO3 interaction. The results of the 10 h catalytic tests with GHSV of 18 L g-1 h-1 show that the Ni/LaAlO3 catalyst is 7.8 and 11.5% more stable than Ni/?-Al2O3 for CH4 and CO2 conversions, respectively. The higher stability and activity of Ni/LaAlO3 is directly related to the presence of NiO (3.38% p) after activation, which promoted the formation of carbon nanotubes (CNT), increasing the dispersion of the metal phase. Even under severe activation and reaction conditions (high GHSV) as in the long-term test (20 h), Ni/LaAlO3 catalyst showed a H2 yield of 37.2% higher than Ni/?-Al2O3. Transmission Electron Microscopy (MET) analyzes revealed that the Ni/?-Al2O3 catalyst deactivated by sintering. Thus, the presence of structural defects and surfaces rich in oxygen vacancies makes the LaAlO3 perovskite a potential support for application in processes of catalytic reforming of methane.