Made available in DSpace on 2016-06-02T19:55:39Z (GMT). No. of bitstreams: 1 5785.pdf: 4761732 bytes, checksum: 604d605ce379585335d48545e6063093 (MD5) Previous issue date: 2014-03-24 / Financiadora de Estudos e Projetos / The silica hybrid CTA-MCM-41 (where CTA is the cetyltrimethylammonium cation) was synthesized and used in the transesterification of ethyl acetate with methanol. This is a model reaction used to test basic catalysts for the production of biodiesel from vegetable oils and fats. The basic sites in the catalyst consist of siloxy anions associated with CTA cations. In earlier work, it was found that progressive deactivation of the catalyst occurred when it was reused, due to leaching of the CTA cations located within the pores and on the external surface, resulting in partial loss of the basicity required for this type of reaction. The challenge of the present work was to stabilize the catalytic activity of CTA-MCM-41 by restricting the loss of cations from its interior (since the basicity derives from the interaction between the CTA cation and the siloxy anion). To this end, novel modifications were made to the synthesis of CTA-MCM-41, involving the encapsulation of acrylate monomers in the hydrophobic interior of the micelles followed by their subsequent polymerization using the application of ultraviolet irradiation together with a photoinitiator. The polymers formed then interacted with the hydrophobic tails of the micelles, which restricted the exit of CTA from the interior of the pores, hence improving the stability of the catalyst. The combination of the traditional synthesis method with polymerization using a microemulsion is innovative, because there are no reports in the literature that describe a synthesis in which the initial step is performed using emulsified polymers. The emulsions and the synthesized solids were evaluated using small angle X-ray scattering (SAXS). The materials were also analyzed by Xray diffraction, elemental (CHN) analysis, infrared absorption spectroscopy, scanning electron microscopy, and thermogravimetry. All these techniques helped to identify the presence of the monomer, as well as the polymer, in the channels of the CTA-MCM-41. It was confirmed that the presence of the polymer increased the catalytic stability of these new silica hybrids applied in the transesterification reaction. / A sílica híbrida CTA-MCM-41 (onde CTA é o cátion cetiltrimetilamônio) foi empregada, tal como sintetizada, na transesterificação do acetato de etila com metanol. Esta é uma reação modelo para testar catalisadores básicos para a produção de biodiesel a partir de óleos vegetais e gorduras. Os sítios básicos desse catalisador são identificados como sendo os ânions silóxi (≡SiO-) associados aos cátions CTA. Em trabalhos anteriores foi verificado que ocorre a desativação catalítica em seus sucessivos usos, ocasionados pela lixiviação dos cátions CTA localizados no interior dos poros e também na sua superfície externa. Desta forma, tem-se a perda de parte da basicidade requerida pela formação de grupos silanóis (SiOH) para este tipo de reação. Este trabalho teve como objetivo o desafio de estabilizar cataliticamente a CTA-MCM-41 dificultando a saída dos cátions do seu interior, pois, como já mencionado, a basicidade é promovida pela interação do cátion CTA com o ânion silóxi. Para isso, foram realizadas modificações inéditas na síntese da CTA-MCM-41 como o encapsulamento de monômeros acrílicos (metila, butila, octila e dodecila) no interior hidrofóbico das micelas e sua posterior polimerização sob a ação da radiação ultravioleta e de um fotoiniciador. Desse modo, os polímeros formados interagiram com as caudas hidrofóbicas das micelas, dificultando a saída do CTA do interior dos poros, por conseguinte proporcionando uma melhora na estabilidade catalítica. O método tradicional de síntese realizado juntamente com a polimerização em emulsão é inovador, pois ainda não há relatos na literatura cuja etapa inicial da síntese seja por meio de polímeros emulsificados. Assim, as emulsões e os sólidos sintetizados foram avaliados por meio da técnica de espalhamento de raios X a ângulos pequenos (SAXS). Os materiais foram analisados pelas técnicas de difratometria de raios X, análise química elementar (CHN), espectroscopia de absorção na região do infravermelho, microscopia eletrônica de varredura (MEV) e termogravimetria. Todas as técnicas auxiliaram para comprovar a presença do monômero e também do polímero nos canais da CTA-MCM-41. Desse modo, verificou-se que a presença do polímero melhorou a estabilidade catalítica destas novas sílicas híbridas sintetizadas e aplicadas na transesterificação.

Parmi les produits issus de la biomasse ou de la transformation des déchets organiques, le CO2 et le CH4 sont des intermédiaires chimiques importants qui ont de forts impacts environnementaux. En effet, ils sont les principaux gaz responsables de l'effet de serre et leur atténuation est un enjeu majeur. Une voie intéressante pour la valorisation de ces gaz est le reformage à sec du méthane (DRM), qui convertit le CO2 et le CH4 en gaz de synthèse (mélange d'hydrogène et de monoxyde de carbone). Ce mélange peut être utilisé pour plusieurs applications telles que la production de méthanol, d'éther diméthylique, d'hydrogène et des hydrocarbures liquides. Malgré cet intérêt, l'exploitation du DRM à l'échelle industrielle n'a pas encore vu le jour. La raison principale est la désactivation rapide des catalyseurs en raison des conditions sévères de fonctionnement du procédé (température élevée, dépôt de carbone). Cette thèse porte sur le développement de nouveaux catalyseurs à base de phosphate de calcium (CaP) dopés avec des métaux de transition pour la valorisation du CO2 et du CH4 en gaz de synthèse par DRM. Les CaP sont utilisés car ils possèdent des propriétés avantageuses en catalyse hétérogène comme la présence simultanée de sites acides et basiques, bonne stabilité thermique, large gamme de surface spécifique ... Dans un premier temps, des études sur les méthodes de synthèse de catalyseurs et sur la performance de différents métaux de transition (Zn, Fe, Co, Cu, Ni) ont été effectuées dans le but de sélectionner le catalyseur et sa méthode de préparation. Un réacteur à lit fixe capable de fonctionner à hautes température et pression a ensuite été testé pour un long temps de réaction afin d'évaluer correctement la performance des catalyseurs préparés. Ensuite, une étude paramétrique détaillée a été menée. L'influence des paramètres tels que le prétraitement des catalyseurs, la température (T = 400-700°C) et la pression (P = 1-25bar) de la réaction et les différents supports (hydroxyapatite, alumine) ont été étudiés. Enfin, la stabilité thermique et catalytique a été étudiée durant 300h de réaction. Les catalyseurs à base de CaP ont montré des rendements plus élevés en gaz de synthèse en comparaison aux catalyseurs commerciaux. Ces catalyseurs sont donc compétitifs dans les mêmes conditions opératoires (T = 700°C, P = 1bar, WHSV = 12272mLh-1gcat-1, t = 300h). Ce travail a montré l'intérêt des catalyseurs à base de CaP pour des processus à haute température, tel que le reformage à sec du méthane. / Among the products resulting from biomass or organic waste transformation, CO2 and CH4 are important chemical intermediates. They also have a strong environmental impact since they are primarily responsible for the greenhouse effect and their mitigation is a key issue. An attractive way of valorization of such gases is the dry reforming of methane (DRM), which converts CO2 and CH4 into syngas (mixture of hydrogen and carbon monoxide). This mixture can be used for several applications, such as the production of methanol, dimethyl ether, hydrogen and liquid hydrocarbons. Despite such interest, the exploitation of DRM on industrial scale has not emerged yet. The main reason is the rapid deactivation of the catalysts due to the severe operating conditions of the process (high temperature, carbon deposition). This thesis focuses on the development of new catalysts based on calcium phosphate (CaP) doped with transition metals for the valorization of CO2 and CH4 through DRM. Actually,CaP has advantageous properties in heterogeneous catalysis, as the simultaneous presence of acid and basic sites, good thermal stability, and wide range of surface area... Initially, a study on the catalyst synthesis methods and an investigation of the performance of different transition metals (Zn, Fe, Co, Cu, Ni) were carried out in order to select the catalyst system and the preparation method. Secondly, a fixed-bed reactor capable of operating at high temperature and pressure and for log time on stream was built and implemented during this work in order to properly evaluate the performance of the preparedcatalysts. Then, a detailed parametric study was conducted. The influence of parameters such as catalyst pre-treatment, temperature (T = 400-700°C) and pressure (P = 1-25bar) of the reaction and support (hydroxyapatite, alumina-based supports) were investigated. Finally, the catalytic stability was studied for 300h of time on stream (TOS). The CaP catalysts showing higher yields on syngas were compared to commercial catalysts. Our catalysts showed to be competitive in the same operating conditions (T = 700°C, P = 1bar, WHSV = 12272mLh-1gcat-1,TOS = 300h). This work shows the interest of CaP catalysts for high temperature process, such as dry reforming of methane.