Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-05-04T13:40:00Z No. of bitstreams: 1 webertonreisdocarmo.pdf: 10785206 bytes, checksum: 2f8475c0ec8915c5f59c44191ffae7a0 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-05-17T13:31:07Z (GMT) No. of bitstreams: 1 webertonreisdocarmo.pdf: 10785206 bytes, checksum: 2f8475c0ec8915c5f59c44191ffae7a0 (MD5) / Made available in DSpace on 2017-05-17T13:31:07Z (GMT). No. of bitstreams: 1 webertonreisdocarmo.pdf: 10785206 bytes, checksum: 2f8475c0ec8915c5f59c44191ffae7a0 (MD5) Previous issue date: 2016-02-26 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A catálise heterogênea desempenha um importante papel no desenvolvimento de tecnologias ambientais sustentáveis, abrangendo vários setores industriais. Normas cada vez mais rigorosas em relação às emissões de gases poluentes impõem melhorias nos processos empregados pela indústria. Baseado neste fato, a melhoria na preparação de catalisadores de hidrotratamento tem ganhado atenção de vários grupos de pesquisa devido à necessidade de produzir combustíveis mais limpos contendo menos impurezas, como os compostos de enxofre. Dependendo da finalidade, o processo de desenvolvimento de um catalisador pode consistir na produção de um novo catalisador sem nenhum dado disponível a seu respeito, ou o processo pode ter como objetivo melhorar um catalisador já conhecido. Nesse trabalho, tentamos contribuir com a melhora na atividade de um catalisador já conhecido alterando os suportes no qual esse catalisador é disperso. Para isso foram sintetizados compostos de hidrotalcitas do tipo MgZnAl-carbonato que foram usados como precursores dos suportes. Após a calcinação a 500 °C os suportes foram obtidos, e impregnados com sais de cobalto e molibdênio. Esses materiais foram calcinados com o objetivo de se obter os óxidos de cobalto e molibdênio dispersos sobre a superfície dos suportes para posterior sulfetação e ativação. Essa etapa final aconteceu in situ, onde logo após procedeu-se à avaliação catalítica para HDS de tiofeno e HID de cicloexeno. Os precursores foram preparados a partir de diferentes rotas sintéticas tais como: coprecipitação, hidrólise de uréia e coprecipitação assistida por ultrassom. Para todas as sínteses a variação da razão molar de Mg2+ /Zn2+, y, ocorreu nas quantidades de 5, 10, 15, 20, 25, 50, 75 e 100 mol%. Esses materiais foram caracterizados a partir de diferentes técnicas analíticas, onde foi possível constatar a formação da fase cristalina característica de compostos do tipo hidrotalcita com carbonato na região interlamelar. As análises de ICP-AES e CHN sugeriram um maior controle estequiométrico para as amostras obtidas por ultrassom e coprecipitação. A decomposição térmica das amostras de hidrotalcitas das diferentes séries, Znys, foi avaliada por difração de raios X in situ variando-se a temperatura no intervalo de 100 a 1000 °C, onde observou-se um comportamento térmico muito parecido para as amostras obtidas por diferentes rotas sintéticas contendo a mesma quantidade de zinco. Adicionalmente, o estudo da termodecomposição mostrou que as amostras formam uma fase amorfa próximo de 400 °C e que essa fase associada ao tamanho do cristalito é responsável pelo alargamento dos picos na região de médio ângulo no difratograma. A influencia da substituição dos cátions de Mg2+ por Zn2+ e da metodologia de síntese nas propriedades texturais dos óxidos mistos derivados da termodecomposição das hidrotalcitas foi estudada pela adsorção e dessorção de N2, bem como por microscopia eletrônica de varredura, onde constatou-se que a forma de obtenção dos precursores influência nas propriedades físico-químicas dos suportes. A avaliação catalítica dos materiais mostrou que todos aqueles testados são ativos para a hidrodessulfurização de tiofeno e hidrogenação de cicloexeno e ainda, quando comparado com o catalisador convencional suportado em alumina as amostras Zn5uCoMoS, Zn15cCoMoS se mostraram mais seletivas nas reações de hidrogenação e hidrodessulfurização. Em relação ao catalisador comercial todos os catalisadores da série ZnysCoMoS obtidos neste trabalho se mostraram mais seletivos, com destaque para o catalisador Zn5cCoMoS que além de mais seletivo, apresentou-se mais eficiente para a hidrodessulfurização de tiofeno quando comparado ao catalisador comercial. Ainda, a partir dos resultados, o que se observa é que a atividade catalítica e a seletividade dos catalisadores são muito sensíveis a pequenas mudanças no procedimento de preparação empregado para a obtenção dos suportes, uma vez que catalisadores com composições químicas muito próximas apresentaram diferentes propriedades catalíticas. / The heterogeneous catalysis plays an important role in the development of environmentally sustainable technologies, including multiple industries sectors. An increasingly stringent standard for pollutant emissions imposes an enhancement in these processes. Based on this fact, improvement in the preparation of hydrotreating catalysts is gaining attention from several research groups because of the need to produce cleaner fuels, as lower amounts of impurities such as sulfur compounds. Depending on the purpose, the development process of a catalyst may consist in an extreme situation, as the development of a new catalyst where no data is available about it, or the process may consist in improving a catalyst already known. In this work, we try to contribute to the improvement of a known catalyst already, altering the support in which it is dispersed. To these purposes hydrotalcites like MgZnAl-CO32- compounds were synthesized. After calcination at 500 °C supports were obtained and impregnated as salts of cobalt and molybdenum. These materials were calcined to obtain oxides of cobalt and molybdenum dispersed on the surface of the supports for subsequent sulfidation and activation. This final stage was made in situ, where soon after occurred the catalytic evaluation for HDS of thiophene and HID of cyclohexene. The precursors were prepared from different synthetic routes such as coprecipitation, urea hydrolysis, and coprecipitation assisted by ultrasound. For all synthesis, the ratio between divalent metallic cations (Zn2+ and Mg2+), y, was tested at 5, 10, 15, 20, 25, 50, 75 and 100 mol%. These materials were studied with different analytical techniques, where the formation of the typical compounds of the phase hydrotalcite with carbonate in the interlayer region can be seen. The analysis of ICP-AES and CNH suggested greater control of stoichiometry in samples obtained by ultrasound and co-precipitation. Thermal decomposition of hydrotalcites samples from different series, Znys were investigated by X-ray diffraction in situ, where varying the temperature range of 100 to 1000 °C, we observed a very similar thermal response to the samples obtained by different synthetic routes but with the same zinc content. Furthermore, the study showed that thermodecomposition of the samples formed an amorphous phase around 400 °C and that the phase associated with the crystallite size is responsible by peak broadening in the region of the middle angle diffraction. The influence of the zinc content and synthesis methodology on the physicochemical properties of mixed oxide derivatives from the hydrotalcite precursor MgZnAl-HT was evaluated through the adsorption/desorption of N2 and scanning electron microscopy (SEM), where it was observed that precursors synthesis variables influence on the physicochemical properties of the supports. The catalytic evaluation of the materials showed that all of them were active for hydrodesulfurization of thiophene and hydrogenation of cyclohexene. Samples Zn5uCoMoS and Zn15cCoMoS were selectivity in the hydrogenation and hydrodesulfurization reactions than the conventional catalyst supported in alumina. Regarding the commercial catalyst, all catalysts of the ZnysCoMoS series obtained in this study were more selective, highlighting the Zn5cCoMoS catalyst which in addition to more selective presented itself more efficient for hydrodesulfurization of thiophene as compared to the commercial catalyst. Thus, from the results it was observed that the catalytic activity and selectivity of the catalysts are sensitive to small changes in preparation procedures used to obtain the supports, since catalysts with very similar chemical compositions showed different catalytic properties.

Les facteurs qui différencient les mécanismes de corrosion du revêtement ZnMgAl pour l'acier en environnement naturel de tests accélérés avec du NaCl ont été identifié. Un nouvel électrolyte (RW) qui contient NH4+, HCO3-, Cl- and SO42- a été développé pour des tests accélérés en respectant la vitesse de corrosion relative entre les revêtements à base de Zn et la formation tardive des hydroxydes à double couche (LDH), qui sont connus pour l'exposition naturelle. En considérant le mécanisme de corrosion type dissolution-précipitation, le rôle des ions présents dans l'électrolyte RW sur la cinétique de dissolution et sur l'accumulation de produits insolubles a été étudié. NH4+ et HCO3- ont été démontrés capables d'augmenter la réactivité anodique et la dissolution cathodique de l'Al. La formation des LDH a été retardée par NH4+, HCO3- et SO42-. La réactivité anodique plus élevée du ZnMgAl en comparaison avec le revêtement de zinc pur combinée avec sa meilleure résistance à la corrosion montrent l'importance de la réaction cathodique (réduction de l'oxygène). En comparant les courants dues à la réduction de l'oxygène sur les revêtements frais et sur la surface sous une couche de produits de corrosion, l'effet barrière des sels basiques de zinc (BZS) et LDH a été clairement démontré. Cet effet barrière est disparu sur le revêtement de zinc pur sous polarisation cathodique en raison de la transformation BZS -> ZnO/Zn(OH)2 mais est resté stable sur ZnMgAl dans les mêmes conditions - l'effet d'inhibition du Mg2+ sur le cinétique de cette transformation a été mis en évidence. Un " squelette " résiduel d'Al non-réagi a contribué à la compacité de produits de corrosion. / Factors differing corrosion mechanisms of ZnMgAl coatings on steel in natural environments and in accelerated tests with NaCl solution were identified. A new electrolyte (RW) containing NH4+, HCO3-, Cl- and SO42- was developed, for which the accelerated tests respected the relative corrosion rates of different Zn-based coatings and the delayed formation of layered double hydroxides (LDH) known for field exposure. Considering dissolution-precipitation mechanism of corrosion, the role of ions present in RW electrolyte on the leaching kinetics and on the accumulation of insoluble products was studied. NH4+ and HCO3- were demonstrated to increase the anodic reactivity and cathodic Al dissolution. LDH formation was delayed by NH4+, HCO3- and SO42-. Higher anodic reactivity of ZnMgAl than zinc coating combined with better resistance in corrosion tests indicated the importance of cathodic reaction (oxygen reduction). Comparing oxygen reduction currents on fresh coatings and on the surface under patinas, clear barrier effect of basic zinc salts (BZS) and LDH was demonstrated. The barrier effect was lost under cathodic polarization on Zn coating due to the transformation BZS ->ZnO/Zn(OH)2 but was stable on ZnMgAl in the same conditions – the inhibiting effect of Mg2+ on the kinetics of this transformation was evidenced. A residual “skeleton” of unreacted Al contributed to the increased compactness of the corrosion products.