Devido a crescente preocupação com relação ao efeito estufa e com o objetivo de obter produtos de maior valor agregado a partir dos gases CH4 e CO2, este trabalho estudou catalisadores de níquel suportados em diferentes óxidos (Al2O3, CeO2, MgO e ZrO2) promovidos com ZnO aplicados na reação de reforma seca de metano para obter gás de síntese (H2 + CO). Primeiramente foram estudados catalisadores de níquel suportados em ZrO2 dopados com diferentes teores de zinco: 0%, 5%, 12,5% e 25% a fim de selecionar o catalisador mais promissor para estudos posteriores. Também foram utilizados dois métodos de preparo: impregnação e co-precipitação. Os resultados de DRX mostraram que a adição de zinco estabilizou a fase tetragonal da zircônia em todos os teores de zinco e em ambos os métodos de preparo. As análises de RTP mostraram que os catalisadores impregnados sofreram maior redução do que os co-precipitados e para maiores teores de zinco foram necessárias maiores temperaturas de redução. Os testes catalíticos mostraram que o aditivo zinco não exerceu efeito sobre os catalisadores impregnados, porém para as amostras co-precipitadas notou-se um teor ótimo com relação à conversão de reagentes na reação e o catalisador 5Ni12ZZc apresentou os melhores resultados. A deposição de carbono também foi menor nos catalisadores co-precipitados. No estudo dos diferentes suportes, as análises de DRX sugerem a dopagem de todos os óxidos com zinco, pois houve mudanças no parâmetro de rede em todas as amostras. As análises de RTP mostraram que a adição de zinco diminui a temperatura de redução do catalisador suportado em alumina e, no suporte CeO2 o efeito é o contrário. Nos testes catalíticos observaram-se efeitos distintos: nos catalisadores Ni-ZnO-CeO2 e Ni-ZnO-MgO o efeito da adição de zinco causou diminuição na conversão dos reagentes, por outro lado, causou diminuição na deposição de carbono e inibição da formação do carbono grafite; nos catalisadores Ni-ZnO-Al2O3 a conversão de reagentes não se alterou com a adição de zinco porém houve uma diminuição na deposição de carbono. Os melhores resultados, portanto, foram apresentados pelo catalisador 5NiZnAl que converteu acima de 80% dos reagentes e não sofreu desativação pela deposição de carbono. / Due to the increasing concern related to the greenhouse effect and aiming to obtain products with higher added-value from CH4 and CO2 gases, nickel catalysts supported on different oxides (Al2O3, CeO2, MgO and ZrO2) promoted with ZnO were studied and applied to the dry reforming of methane reaction to obtain syngas (H2+CO). Firstly, ZrO2 supported Nickel catalysts doped with different zinc content: 0, 5, 12,5 and 25% molar ratio were used to identify and select the best amount of zinc to further studies. Two preparation methods were investigated: impregnation and co-precipitation. The XRD results showed that the zinc addition stabilized the zircon tetrahedral phase of all catalysts from both preparation methods. The TPR analyses showed that the impregnated catalysts reduced more than the co-precipitated ones and higher reduction temperature was needed for the catalysts with higher zinc content. The catalytic tests indicated that the zinc content did not have any effect over the impregnated catalysts, whilst for the co-precipitated samples, a great content was noted and the 5Ni12ZZc catalyst showed the best results. The co-precipitated catalysts also had lower carbon deposition. In the study of different supports, the XRD analyses showed that the zinc interacts with all the used oxides, because there were changes of the cell parameter of all samples. The TPR analyses indicated that the zinc addition lowers the reduction temperature of the alumina supported catalyst and the effect is opposite for the CeO2 support. Different effects were observed during the catalytic tests: for the CeO2 and MgO supported catalysts the effect of zinc addition caused a decrease in the conversion of reactants, but it lowered the deposition of carbon and inhibited the formation of graffiti carbon; for the Al2O3 supported catalysts, the reactant conversion was the same with the addition of zinc, however there was a reduction on the carbon deposition. Therefore, the best results were obtained for the 5NiZnAl catalyst, which converted over 80% of the reactants and wasn\'t deactivated by carbon deposition.

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.

Made available in DSpace on 2016-06-02T19:57:00Z (GMT). No. of bitstreams: 1 6808.pdf: 4907992 bytes, checksum: 8dda1b97e1ed03238369951b622517f4 (MD5) Previous issue date: 2015-03-18 / In this work, catalysts derived from hydrotalcites were employed in Direct Reforming of Biogas, once they feature the necessary basicity to allow and improve carbon removal during reforming. As a differential study, the effect of the step ageing elimination during hydrotalcites syntheses, which were prepared by means of coprecipitation technique, was also evaluated. The results obtained from temperature effect evaluation tests ranging from 800 to 500oC suggested there was no need of precursors ageing, which represents an energy saving during catalysts syntheses, once this step represents the most energy expensive. To improve the process and reduce carbon deposition, oxygen was added as synthetic air into the gaseous reactants feed, in a reaction known as Oxidative Reforming of Biogas. In this case, the ratio H2/CO was close to 1, along the temperature range from 800 to 500oC considered during the catalytic tests, which was assigned to the occurrence of methane partial oxidation, specially in lower temperatures. As an attempt to improve carbon gasification during reforming reactions, element cerium was also added during the syntheses of hydrotalcites, also by coprecipitation, fixing the amount of this element and ranging nickel amount, eliminating the step ageing. At this point, cerium promoted and unpromoted catalysts were compared through biogas direct reforming 6 hours stability tests at 650oC. The spent catalysts were characterized by thermogravimetric analysis in order to evaluate the amount of carbon deposited over the catalyst surface. It was found for the catalysts derived from oxides corresponding to 5 and 15% of nickel (% nominal, in weight) a higher carbon deposition at the presence of cerium promoted catalysts, although for the first one, the carbon temperature peak removal was lower than unpromoted catalyst. On the contrary, for the catalysts corresponding to 10 and 25% of nickel (% nominal, in weight), similar and lower carbon deposition was found in presence of cerium. It was also possible to confirm the reduction of carbon deposition after stability tests for oxidative reforming of biogas, compared to the direct reforming. / Neste trabalho, catalisadores derivados de hidrotalcitas foram empregados na reforma do biogás, uma vez que apresentam a basicidade que permite aprimoramento na remoção deste carbono durante a reação. O efeito da eliminação da etapa de envelhecimento das hidrotalcitas durante a síntese das mesmas, as quais foram preparadas pela técnica da coprecipitação, foi avaliado como um estudo diferencial. Os resultados obtidos a partir dos ensaios a patamares de temperatura na faixa de 800 a 500oC sugeriram que não há necessidade de envelhecimento da hidrotalcita, o que representa uma economia de energia durante as sínteses dos catalisadores, uma vez que esta etapa é a mais dispendiosa, em termos energéticos. Para melhorar o processo e reduzir a formação de coque, oxigênio foi adicionado como ar sintético à corrente dos reagentes, numa reação conhecida como Reforma Oxidativa do Biogás. Aqui, a proporção H2/CO foi próxima a 1, ao longo da faixa de temperatura considerada durante os testes catalíticos, associada à ocorrência da reação de oxidação parcial do metano, especialmente a temperaturas mais baixas. Como tentativa de aprimorar a gasificação do coque durante as reações de reforma, o elemento cério também foi adicionado durante a síntese das hidrotalcitas, também por coprecipitação, fixando a quantidade de cério e variando o teor de níquel, eliminando a etapa de envelhecimento. Neste ponto, os catalisadores não promovidos e promovidos com cério foram comparados através da reforma direta do biogás, em testes de estabilidade com duração de 6 horas, a 650oC. Após o uso, os catalisadores foram caracterizados por análise termogravimétrica a fim de avaliar a quantidade de carbono formado. Para os catalisadores derivados dos óxidos correspondentes a 5 e 15% de níquel (% nominal, em massa), foi encontrada maior deposição de carbono na presença dos catalisadores promovidos, embora para o primeiro, o pico de temperatura referente à remoção de carbono tenha sido menor comparado ao do catalisador não promovido. Ao contrário, para os catalisadores correspondentes a 10 e 25% de níquel (% nominal, em massa), similar e menor formação de carbono foram encontrados na presença de cério, respectivamente. Durante os ensaios de estabilidade de reforma oxidativa, foi possível constatar a redução da quantidade de carbono formado após os ensaios catalíticos.

Devido a crescente preocupação com relação ao efeito estufa e com o objetivo de obter produtos de maior valor agregado a partir dos gases CH4 e CO2, este trabalho estudou catalisadores de níquel suportados em diferentes óxidos (Al2O3, CeO2, MgO e ZrO2) promovidos com ZnO aplicados na reação de reforma seca de metano para obter gás de síntese (H2 + CO). Primeiramente foram estudados catalisadores de níquel suportados em ZrO2 dopados com diferentes teores de zinco: 0%, 5%, 12,5% e 25% a fim de selecionar o catalisador mais promissor para estudos posteriores. Também foram utilizados dois métodos de preparo: impregnação e co-precipitação. Os resultados de DRX mostraram que a adição de zinco estabilizou a fase tetragonal da zircônia em todos os teores de zinco e em ambos os métodos de preparo. As análises de RTP mostraram que os catalisadores impregnados sofreram maior redução do que os co-precipitados e para maiores teores de zinco foram necessárias maiores temperaturas de redução. Os testes catalíticos mostraram que o aditivo zinco não exerceu efeito sobre os catalisadores impregnados, porém para as amostras co-precipitadas notou-se um teor ótimo com relação à conversão de reagentes na reação e o catalisador 5Ni12ZZc apresentou os melhores resultados. A deposição de carbono também foi menor nos catalisadores co-precipitados. No estudo dos diferentes suportes, as análises de DRX sugerem a dopagem de todos os óxidos com zinco, pois houve mudanças no parâmetro de rede em todas as amostras. As análises de RTP mostraram que a adição de zinco diminui a temperatura de redução do catalisador suportado em alumina e, no suporte CeO2 o efeito é o contrário. Nos testes catalíticos observaram-se efeitos distintos: nos catalisadores Ni-ZnO-CeO2 e Ni-ZnO-MgO o efeito da adição de zinco causou diminuição na conversão dos reagentes, por outro lado, causou diminuição na deposição de carbono e inibição da formação do carbono grafite; nos catalisadores Ni-ZnO-Al2O3 a conversão de reagentes não se alterou com a adição de zinco porém houve uma diminuição na deposição de carbono. Os melhores resultados, portanto, foram apresentados pelo catalisador 5NiZnAl que converteu acima de 80% dos reagentes e não sofreu desativação pela deposição de carbono. / Due to the increasing concern related to the greenhouse effect and aiming to obtain products with higher added-value from CH4 and CO2 gases, nickel catalysts supported on different oxides (Al2O3, CeO2, MgO and ZrO2) promoted with ZnO were studied and applied to the dry reforming of methane reaction to obtain syngas (H2+CO). Firstly, ZrO2 supported Nickel catalysts doped with different zinc content: 0, 5, 12,5 and 25% molar ratio were used to identify and select the best amount of zinc to further studies. Two preparation methods were investigated: impregnation and co-precipitation. The XRD results showed that the zinc addition stabilized the zircon tetrahedral phase of all catalysts from both preparation methods. The TPR analyses showed that the impregnated catalysts reduced more than the co-precipitated ones and higher reduction temperature was needed for the catalysts with higher zinc content. The catalytic tests indicated that the zinc content did not have any effect over the impregnated catalysts, whilst for the co-precipitated samples, a great content was noted and the 5Ni12ZZc catalyst showed the best results. The co-precipitated catalysts also had lower carbon deposition. In the study of different supports, the XRD analyses showed that the zinc interacts with all the used oxides, because there were changes of the cell parameter of all samples. The TPR analyses indicated that the zinc addition lowers the reduction temperature of the alumina supported catalyst and the effect is opposite for the CeO2 support. Different effects were observed during the catalytic tests: for the CeO2 and MgO supported catalysts the effect of zinc addition caused a decrease in the conversion of reactants, but it lowered the deposition of carbon and inhibited the formation of graffiti carbon; for the Al2O3 supported catalysts, the reactant conversion was the same with the addition of zinc, however there was a reduction on the carbon deposition. Therefore, the best results were obtained for the 5NiZnAl catalyst, which converted over 80% of the reactants and wasn\'t deactivated by carbon deposition.

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.

京都大学 / 新制・課程博士 / 博士(人間・環境学) / 甲第24711号 / 人博第1084号 / 新制||人||254(附属図書館) / 2022||人博||1084(吉田南総合図書館) / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 吉田 寿雄, 教授 田部 勢津久, 教授 中村 敏浩, 教授 田中 庸裕 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DFAM

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.

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Made available in DSpace on 2014-12-17T14:08:54Z (GMT). No. of bitstreams: 1 DanielleLM_DISSERT.pdf: 1223674 bytes, checksum: 2d564bea614284da929e26c705739bfb (MD5) Previous issue date: 2013-06-24 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / The production of synthesis gas has received renewed attention due to demand for renewable energies to reduce the emissions of gases responsible for enhanced greenhouse effect. This work was carried out in order to synthesize, characterize and evaluate the implementation of nickel catalysts on MCM-41 in dry reforming reactions of methane. The mesoporous molecular sieves were synthesized using as silica sources the tetraethyl orthosilicate (TEOS) and residual glass powder (PV). The sieves were impregnated with 10% nickel to obtain the metallic catalysts (Ni/MCM-41). These materials were calcined and characterized by Thermogravimetric Analysis (TG), Infrared spectroscopy (FTIR), X-ray Diffraction (XRD), Temperature-Programmed Reduction (TPR) and N2 Adsorption/Desorption isotherms (BET/BJH). The catalytic properties of the samples were evaluated in methane dry reforming with CO2 in order to produce synthesis gas to be used in the petrochemical industry. The materials characterized showed hexagonal structure characteristic of mesoporous material MCM-41 type, being maintained after impregnation with nickel. The samples presented variations in the specific surface area, average volume and diameter of pores based on the type of interaction between the nickel and the mesoporous support. The result of the the catalytic tests showed conversions about 91% CO2, 86% CH4, yelds about 85% CO and 81% H2 to Ni/MCM-41_TEOS_C, and conversions about 87% CO2, 82% CH4, yelds about 70% CO and 59% H2 to Ni/MCM-41_PV_C. The similar performance confirms that the TEOS can be replaced by a less noble materials / A produ??o de g?s de s?ntese tem recebido muita import?ncia devido a procura por fontes de energias renov?veis para reduzir as emiss?es dos gases respons?veis pelo aumento do efeito estufa. Este trabalho foi realizado com o objetivo de sintetizar, caracterizar e avaliar a aplica??o dos catalisadores de n?quel sobre MCM-41, em rea?oes de reforma a seco de metano. As peneiras moleculares mesoporosas foram sintetizadas utilizando como fontes de s?lica o Tetraetil Ortosilicato (TEOS) e o res?duo de p? de vidro (PV). As peneiras foram impregnadas com 10% de n?quel para forma??o dos catalisadores met?licos (Ni/MCM-41). Esses materiais foram calcinados e caracterizados por Termogravimetria (TG), Espectroscopia na Regi?o do Infravermelho (FTIR), Difratometria de raios X (DRX), Redu??o de Temperatura Programada (TPR) e Adsor??o e Dessor??o de N2 (BET/BJH). As propriedades catal?ticas das amostras foram avaliadas na reforma a seco de metano com CO2, tendo como objetivo a produ??o de g?s de s?ntese para utiliza??o na ind?stria petroqu?mica. Os materiais caracterizados apresentaram estrutura hexagonal caracter?stica do material mesoporoso tipo MCM-41, sendo mantida ap?s a impregna??o com n?quel. As amostras apresentaram varia??es quanto ? ?rea superficial espec?fica e volume m?dio de poros, em fun??o do tipo de intera??o existente entre o n?quel e o suporte mesoporoso. Os resultados dos testes catal?ticos mostraram convers?es de 86% de CH4 e 91% de CO2 e rendimento de 85% de CO e 81% de H2 para o material Ni/MCM-41_TEOS_C, e convers?es de 82% de CH4 e 87% de CO2 e rendimentos na produ??o do g?s de s?ntese de 70% de CO e 59% de H2 para o material Ni/MCM-41_PV. Esse comportamento semelhante comprova que o TEOS pode ser substitu?do por um material menos nobre

Κατά τις τελευταίες δεκαετίες παρατηρείται συνεχής αύξηση της έντασης του φαινομένου του θερμοκηπίου γεγονός που προκαλεί σημαντικές συνέπειες στο περιβάλλον και στη ζωή μας γενικότερα. Συνεπώς, είναι απαραίτητη η μείωση της ανθρωπογενούς εκπομπής των αερίων που συμβάλλουν στην αύξηση του φαινομένου αυτού. Η εκμετάλλευση και χρήση των δύο πιο σημαντικών θερμοκηπικών αερίων, του μεθανίου και του διοξειδίου του άνθρακα, μπορεί να επιτευχθεί με την αναμόρφωση του CH4 με CO2 ή αλλιώς ξηρή αναμόρφωση του μεθανίου (Dry Reforming of Methane-DRM). Με τη διεργασία DRM τα δύο συγκεκριμένα αέρια μετατρέπονται σε αέριο σύνθεσης (synthesis gas), το οποίο χρησιμοποιείται είτε για τη σύνθεση πληθώρας οργανικών ενώσεων, είτε για την παραγωγή Η2 για ενεργειακούς σκοπούς. Η DRM παρουσιάζει σημαντικά πλεονεκτήματα: δεν απαιτείται η χρήση ύδατος, φθηνό σχετικά κόστος εγκαταστάσεων, χρησιμοποιείται σε χημικά συστήματα μεταφοράς ενέργειας, ενώ και το αέριο σύνθεσης που παράγεται έχει ακόμα κατάλληλη αναλογία για συνθέσεις Fischer–Tropsch. Παρόλα αυτά η DRM δεν έχει εκτεταμένη βιομηχανική εφαρμογή επειδή αντιμετωπίζει ένα σημαντικό μειονέκτημα: ο καταλύτης μετά από κάποιο χρόνο λειτουργίας απενεργοποιείται λόγω του άνθρακα που αποτίθεται πάνω του. Στην παρούσα εργασία μελετήθηκε ο state of the art καταλύτης Ni/Al2O3, τον οποίο τροποποιήσαμε με βόριο σε διάφορους λόγους [Β/(B+Νi)] με κύριο στόχο τη μείωση των ανθρακούχων αποθέσεων. Οι τροποποιημένοι καταλύτες συντέθηκαν με τη μέθοδο του υγρού συνεμποτισμού και χαρακτηρίστηκαν φυσικοχημικά με διάφορες τεχνικές, ώστε να μελετήσουμε την επίδραση του βορίου στην υφή τους (ΒΕΤ, porosimetry, SEM, TEM), στη δομή τους (XRD, UV-Vis DRS) και στην αναγωγιμότητά τους (H2-TPR). Η καταλυτική συμπεριφορά τους για την αντίδραση της ξηρής αναμόρφωσης του μεθανίου αξιολογήθηκε σε αντιδραστήρα σταθερής κλίνης, για 24h, σε συνθήκες: 973Κ, 1 atm, τροφοδοσία 50%CH4-50%CO2. Ο άνθρακας που αποτέθηκε στους χρησιμοποιημένους καταλύτες μετρήθηκε με τη μέθοδο της θερμοπρογραμματισμένης υδρογόνωσης (TPH). Τα ανηγμένα και χρησιμοποιημένα στην DRM καταλυτικά δείγματα μελετήθηκαν επίσης με ηλεκτρονικό μικροσκόπιο σάρωσης (SEM με αναλυτή EDS) και ηλεκτρονικό μικροσκόπιο διαπερατότητας (ΤΕΜ). Βρέθηκε ότι η παρουσία του Β μειώνει σημαντικά την ποσότητα του αποτιθέμενου άνθρακα στους καταλύτες Ni/Al2O3, σε ποσοστό έως και 86%, χωρίς να επηρεάζει ιδιαίτερα τη δραστικότητα και την εκλεκτικότητα των καταλυτών. Σημαντικό ρόλο παίζει το ποσοστό του Β στον καταλύτη, με τον καταλύτη με λόγο Β/(B+Νi) = 0,5 να εμφανίζει τη βέλτιστη συμπεριφορά. Τα αποτελέσματα μας έδειξαν ότι η ιδιαίτερη θετική επίδραση του βορίου οφείλεται κυρίως στο γεγονός ότι ευνοεί τη διασπορά του μεταλλικού νικελίου. Τροποποίηση με βόριο, σε κατάλληλη περιοχή φορτίσεων, του καταλύτη Ni/Al2O3 μεγιστοποιεί το πλήθος των νανοσωματιδίων νικελίου με μέση διάσταση < 6.0 nm, τα οποία, ως γνωστόν, ελαχιστοποιούν την απόθεση άνθρακα. / The intensity of the greenhouse effect is constantly increasing in the last few decades with an adverse effect both on the environment and the humanity. In order to decrease the effect, human-caused emissions should be minimized. The two most important greenhouse gases, methane and carbon dioxide, can be used in the DRM (Dry Reforming of Methane) process. With this process the above mentioned gases are converted to synthesis gas, which is then used for the synthesis of a great number of organic compounds and synthetic fuels (through the Fisher-Tropsch syntheses) or for the production hydrogen to be used as a fuel (energy purposes). The DRM process presents a number of advantages, namely: no water is required, relatively low cost of process plants,it can be used as a Chemical Energy Transfer System and, finally, the produced synthesis gas has adequate CO/H2 ratio for Fisher-Tropsch syntheses. Although DRM is a promising process, its industrial application is hindered by a major drawback: the catalysts are rapidly deactivating due to coking. In the current study, the state of the art catalyst Ni/Al2O3 was studied and modified with boron, using different ratios of Β/(B+Νi). Our primary objective was to reduce coking. The modified catalysts were synthesized by wet co-impregnation and physicochemically characterized in their oxidic, reduced and used forms, using various techniques, in order to investigate the influence of boron on the texture (BET, Porosimetry, SEM, TEM), structure (XRD, UV-Vis DRS) and reducibility (H2-TPR) of the catalysts. The catalytic performance for the DRM process was studied under stable conditions (973Κ, 1 atm and 50%CH4-50%CO2 undiluted feed), for 24h, using a fixed bed reactor. Carbonaceous deposits on the used catalysts were determined by Temperature Programmed Hydrogenation (TPH). Scanning Electron Microscopy (SEM) with EDS analyser and Transmission Electron Microscopy (TEM) were also used in the study of reduced and used catalytic samples. Modifying Ni/Al2O3 catalysts with boron results in a great decrease of the deposited coke (up to 86%), without any significantly influence on the activity and selectivity of the catalysts. A major factor influencing the catalyst is the B loading, with the ratio Β/(B+Νi)=0,5 giving the best results. Boron’s positive effect was mainly attributed to its ability to increase Ni dispersion. Modification of Ni/Al2O3 catalysts, by using the appropriate boron loading, resulted to an increase of the amount of nickel nanoparticles with an average dimension under 6.0 nm, which are known to minimize coke deposition.