TiO2 in anatase form is the most widely studied material for photocatalytic reactions. Utilization of oxide support materials such as silica with suitable transparency within band gap range of TiO2 is promising technique to obtain efficient photocatalysts for many applications. In the present study, simultaneous co-hydrolyzation of tetraethyl orthosilacate (TEOS) and titanium tetrabutaoxide (TBOT) precursors were carried out in the presence of hydrochloric acid. The effects of washing with low vapor pressure solvent(n-octane), drying conditions, hydrothermal ageing and TiO2/SiO2 ratio on the catalyst structure and photocatalytic activity were studied. The samples were characterized by XRD, BET, DRIFTS techniques and the activity was measured for liquid phase room temperature oxy/demineralization of phenol under artificial solar irradiation. The reaction intermediates were followed by UV/vis spectrophotometer and HPLC. It was found that the hydrothermal treatment contributes better degree of crystalinity, higher surface area and thus photocatalytic activity compared to the samples which were synthesized with conventional drying at 100oC overnight. The formation of Ti-O-Si interface indicating the degree of dispersion was evidenced by DRIFTS technique for all hydrothermally tretated samples. The highest surface area and photocatlytic activity was observed with hydrothermally treated catalyst with TiO2/SiO2:0.34 composition.

In this research, oxidative dehydrogenation of ethane to ethylene was studied over Cr-O and Cr-V-O mixed oxide catalysts through steady-state and dynamic experiments. The catalysts were prepared by the complexation method. By XRD, presence of Cr2O3 phase in Cr-O / and the small Cr2O3 and V2O4 phases of Cr-V-O were revealed. In H2-TPR, both catalysts showed reduction behaviour. From XPS the likely presence of Cr+6 on fresh Cr-O was found. On Cr-V-O, the possible reduction of V+5 and Cr+6 forms of the fresh sample to V+4, V+3 and Cr+3 states by TPR was discovered through XPS. With an O2/C2H6 feed ratio of 0.17, Cr-O exhibited the highest total conversion value of about 0.20 at 447&deg / C with an ethylene selectivity of 0.82. Maximum ethylene selectivity with Cr-O was obtained as 0.91 at 250&deg / C. An ethylene selectivity of 0.93 was reached with the Cr-V-O at 400&deg / C. In the experiments performed by using CO2 as the mild oxidant, a yield value of 0.15 was achieved at 449&deg / C on Cr-O catalyst. In dynamic experiments performed over Cr-O, with C2H6 pulses injected into O2-He flow, the possible occurrence of two reaction sites for the formation of CO2 and H2O was detected. By Gaussian fits to H2O curves, the presence of at least three production ways was thought to be probable. Different from Cr-O, no CO2 formation was observed on Cr-V-O during pulsing C2H6 to O2-He flow. In the runs performed by O2 pulses into C2H6-He flow over Cr-V-O, formation of CO rather than C2H4 was favored.

Made available in DSpace on 2014-10-09T12:44:35Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:39Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Les oxydes mixtes d'uranium et de plutonium sont envisagés en tant que combustible nucléaire pour les réacteurs de future génération du type Réacteurs à Neutrons Rapides à caloporteur Sodium (RNR-Na). En raison des choix technologiques et des contraintes de sûreté de ces futurs réacteurs, les combustibles oxydes présenteront une sous-stœchiométrie en oxygène, i.e. que leur rapport Oxygène/Métal (noté O/M) sera inférieur à 2,00. Le contrôle de l'écart à la stœchiométrie est indispensable car le rapport O/M dicte un certain nombre de propriétés du combustible sous irradiation (conductivité thermique, température de fusion, dilatation, etc.). Dans un premier temps, une attention toute particulière a été portée à l'élaboration, par métallurgie des poudres, de pastilles d'oxydes mixtes U1-yPuyO2-x à différentes teneurs en plutonium (y = 0,15 ; 0,28 et 0,45). Deux caractéristiques principales ont été recherchées : o une homogénéité de répartition U-Pu poussée afin de disposer de matériaux adéquats pour une étude thermodynamique. o une densité élevée pour déterminer, d'une part, des coefficients de diffusion chimique de l'oxygène au sein des trois composés d'intérêt par thermogravimétrie et, d'autre part, des coefficients d'autodiffusion de l'oxygène par spectrométrie de masse d'ions secondaires (SIMS). La deuxième partie de cette étude a été axée sur la mesure du rapport O/M associée à la caractérisation microstructurale et cristallographique des échantillons. Au préalable, la qualification des équipements de gravimétrie et thermogravimétrie dédiés à la mesure du rapport O/M a été réalisée. Ce travail a permis de proposer une méthode expérimentale robuste pour la détermination de la stœchiométrie en oxygène des oxydes mixtes d'uranium et de plutonium en tenant compte de la présence d'américium de décroissance au sein des échantillons. D'autre part, dans un objectif de contribution à la maîtrise du rapport O/M lors de l'élaboration d'oxydes mixtes (U,Pu)O2-x, l'influence de la vitesse de refroidissement lors du frittage a été investiguée. En particulier, le rapport O/M a été abordé via ses conséquences cristallographiques et microstructurales sur les composés d'intérêt lors de la descente en température et à température ambiante. Ces essais ont permis en outre l'acquisition de nouvelles données sur la cinétique et les mécanismes du phénomène de séparation de phases se produisant dans les oxydes mixtes sous-stœchiométriques à forte teneur Pu. Enfin, la stabilité des composés U1-yPuyO2-x à température ambiante a fait l'objet d'investigations thermogravimétriques, de spectroscopie d'absorption des rayons X et de diffraction des rayons X. Dans un troisième temps, les propriétés sensibles au type et à la concentration du défaut d'oxygène majoritaire ont été étudiées en fonction de la température et de la pression partielle d'oxygène. Les expériences de DRX-HT se sont révélées prometteuses mais l'interprétation des résultats en termes d'écart à la stœchiométrie pour toute teneur Pu nécessite la poursuite du développement de la méthode utilisée. Par ailleurs, les phénomènes d'autodiffusion de l'oxygène ont été étudiés en fonction de la pression partielle d'oxygène conduisant, pour la première fois, à la détermination de coefficients d'autodiffusion de l'oxygène dans un oxyde mixte d'uranium et de plutonium. Enfin, les essais préliminaires de détermination de coefficients de diffusion chimique de l'oxygène ont mis en évidence l'existence d'une réaction de surface limitante par rapport à la diffusion volumique lorsque les expériences sont menées en oxydant U1-yPuyO2-x. / Uranium-plutonium mixed oxides are considered within the scope of the development of nuclear fuel for the next generation of nuclear reactors (Sodium-cooled fast reactors). Because of some technological choices and safety constraints, the mixed oxide fuel will exhibit an oxygen hypostoichiometry, i.e. its Oxygen/Metal ratio (noted O/M) will be lower than 2.00. The control of this deviation from stoichiometry is essential as the O/M ratio influences numerous of the fuel properties irradiation (thermal conductivity, melting temperature, dilatation, etc.) which in turn strongly affect the behavior under. First, a special attention was paid to the fabrication of mixed oxide pellets U1-yPuyO2-x with different plutonium contents (y = 0.15 ; 0.28 and 0.45) by powder metallurgy. The two main goals were to obtain: o A homogeneous U-Pu distribution in order to have suitable materials for a thermodynamic study. o A high density of the resulting pellets in order to determine oxygen chemical diffusion coefficients within the three compounds by thermogravimetric analysis and oxygen self-diffusion coefficients by secondary ion mass spectrometry (SIMS). The second part of this study was focused on associating the O/M ratio values to the micro- and crystallographic structures of the fabricated samples. Beforehand, the qualification of the used gravimetric and thermogravimetric experimental devices dedicated to the O/M ratio measurements was performed. A reliable experimental method was then proposed for the determination of the oxygen stoichiometry of uranium-plutonium mixed oxides taking into account the presence of americium within the samples generated by natural decay of plutonium. With the aim of controlling the O/M ratio of U1-yPuyO2-x during fabrication, the influence of the cooling rate on the oxygen stoichiometry during sintering was investigated. Particularly, the crystallographic and microstructural effects of a variation in the O/M ratio during cooling were studied both at high and room-temperatures. Moreover, these effects made it possible to obtain new data on the kinetics and mechanisms of the phase separation occurring in the hypostoichiometric mixed oxides at high Pu content. Finally, the stability of U1-yPuyO2-x at room-temperature during standard storage conditions was investigated by thermogravimetry, X-ray absorption spectroscopy and X-ray diffraction. Finally, an experimental thermodynamic study of U1-yPuyO2-x was performed by thermogravimetric analysis and high-temperature X-ray diffraction as a function of temperature and oxygen partial pressure. The main factor allowing the establishment of the thermodynamic equilibrium being the oxygen diffusion, the associated chemical and self-diffusion coefficients were determined by thermogravimetry and SIMS after 16O – 18O isotopic exchange. These innovative results will allow a better understanding of the U-Pu mixed oxide properties on the basis of the point defect chemistry.

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.

Made available in DSpace on 2016-06-02T19:56:44Z (GMT). No. of bitstreams: 1 3658.pdf: 1636009 bytes, checksum: 903d87f9f9c4e621ffe250fed6d2e40b (MD5) Previous issue date: 2011-03-31 / Universidade Federal de Sao Carlos / Among biofuels of the 1st generation, biodiesel stands out for its equivalent features to those of mineral diesel, however less polluting. It can be obtained by transesterification of triglyceride fats or vegetable oils by (m)ethanolysis. Aiming at improving the chemical process, different types of catalysis have been studied: i) homogeneous (acid e.g. H2SO4 and basic e.g. KOH), ii) heterogeneous (acid e.g. Montmorillonite, basic e.g. Hydrotalcite and enzymatic e.g. immobilized Lipases). However, the basic solid catalysts show themselves attractive because they are easily separated from the reaction media by filtration, avoiding both the formation of by-products and the need for biodiesel neutralization. In this group of catalysts there are some that stand out from the others, such as hydrotalcites, which, when thermically treated, result in mixed oxides with high superficial area and basicity. In this study, the efficiency of these heterogeneous catalysts containing K-Mg-Al was investigated in the transesterification of the molecule-model (CH3COOCH3) via ethanolysis in mild reaction conditions: 323K, 30 min, EtOH:AcMe=6:1 and 4 wt % of catalyst. Two methods to synthesize the hydrotalcite were used: sol-gel and impregnation. In the sol-gel, the variables fixed were: mass of carbonate (2 wt %), synthesis time (18hrs) and temperature (363K). The ratio of Mg:Al and the aging time varied in the range of 2:1-3:1 and 1-3 days, respectively. For the evaluation of this method, the incipient-wetness impregnation was used through addition of different percentage of potassium cations (2, 5 and 10%) in mixed oxide originated from the free sol-gel alkali metals hydrotalcite. Through the results of X-ray diffraction and thermal analysis it was found that the compounds produced were different in crystallinity, structural order and quantity of water molecules present in the structure. The pores of the obtained materials presented, on average, large diameters, between 14-21 nm to sol-gel samples, and 12 nm for the impregnated ones. The basicity of these were determinate by test of CO2 desorption at a programmed temperature. Among the studied parameters in the reaction of transesterification, the temperature showed the biggest influence. Thus, the most active catalysts for this condition (343K, 30 min and ratio of 6:1) were tested in regards to their reuse. The most stable catalyst in catalytic activity was the oxide (2KHTTa3-1) synthesized through precursor via sol-gel with highest quantity of magnesium in its composition and aged for one day. / Entre os biocombustiveis da 1a geracao, destaca-se o biodiesel com caracteristicas equivalentes as do diesel mineral, porem menos poluentes. Ele pode ser obtido pela transesterificacao de triglicerideos de gorduras ou oleos vegetais por (m)etanolise. Visando a melhoria do processo quimico, tem sido realizados estudos com diferentes tipos de catalise: i) homogenea (acida p.ex.: H2SO4 e basica p.ex.: KOH), ii) heterogenea (acida p.ex.: montmorilonita, basica p.ex.: hidrotalcita e enzimatica p.ex.: lipase imobilizada). No entanto, os catalisadores basicos solidos mostram-se atrativos por serem mais faceis de separar do meio reacional por filtracao, evitando tanto a formacao de subprodutos, quanto a necessidade de neutralizacao do biodiesel. Nesse grupo, alguns catalisadores destacam-se dos demais, tais como as hidrotalcitas. Estas, tratadas termicamente, resultam em oxidos mistos com elevada area superficial e basicidade. A avaliacao da eficiencia desses catalisadores heterogeneos contendo K-Mg-Al foi estudada neste trabalho utilizando a reacao de transesterificacao de molecula-modelo (CH3COOCH3) por etanolise sob condicoes reacionais amenas: 50°C, 30 min, EtOH:AcMe= 6:1 e 4% de massa de catalisador. As hidrotalcitas foram preparadas pelos metodos de sol-gel e impregnacao. No sol-gel, fixaram-se as seguintes variaveis: teor de carbonato (2% m/m), tempo (18h) e temperatura (90°C) de sintese. O teor de Mg:Al e o tempo de envelhecimento foram variados em 2:1-3:1 e 1-3 dias, respectivamente. Realizou-se impregnacao, por via umida incipiente, de diferentes percentuais de cations potassio (2, 5 e 10%) em oxido misto obtido da hidrotalcita sintetizada por sol-gel. Atraves dos resultados de difracao de raios X e analise termica verificou-se que os compostos produzidos eram diferentes quanto a cristalinidade, ordenacao estrutural e quantidade de moleculas de agua presentes na estrutura. Os poros dos materiais obtidos apresentaram, em media, diametros grandes, entre 14-21 nm para as amostras sol-gel, e 12 nm para as impregnadas. A basicidade destes materiais foi determinada pelo teste de dessorcao de CO2 a temperatura programada. Pela analise dos efeitos das variaveis estudadas na reacao de transesterificacao observou-se maior influencia da temperatura e os catalisadores mais ativos para essa condicao (70°C, 30 min e razao de 6:1) foram testados quanto ao seu reuso. O catalisador mais estavel na atividade catalitica foi o oxido (2KHTTa3-1) sintetizado por precursor via sol-gel com maior teor de magnesio na composicao, envelhecido por um dia.

Made available in DSpace on 2014-10-09T12:53:26Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:38Z (GMT). No. of bitstreams: 0 / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Orientador: Yoshitaka Gushikem / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-04T23:27:35Z (GMT). No. of bitstreams: 1 Cardoso_WilliamdaSilva_D.pdf: 740346 bytes, checksum: bbae1435b7392cf211b02cc55af7333d (MD5) Previous issue date: 2005 / Doutorado / Quimica Inorganica / Doutor em Ciências

Made available in DSpace on 2014-10-09T12:44:35Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:57:39Z (GMT). No. of bitstreams: 0 / A incorporação do gadolínio diretamente no combustível de reatores nucleares para geração de eletricidade é importante para compensação da reatividade e para o ajuste da distribuição da densidade de potência, permitindo ciclos de queima mais longos, com intervalo de recarga de 18 meses, otimizando-se a utilização do combustível. A incorporação do Gd2O3 sob a forma de pó homogeneizado a seco diretamente com o pó de UO2 é o método comercialmente mais atraente devido à sua simplicidade . Contudo, este método de incorporação conduz a dificuldades na obtenção de corpos sinterizados com a densidade niínima especificada, devido a um bloqueio no processo de sinterização. Pouca informação existe na literatura específica sobre o possível mecanismo deste bloqueio, restrita principalmente à hipótese da formação de uma fase (U,Gd)O2 rica em gadolínio com baixa difusividade. Este trabalho tem como objetivo a investigação do mecanismo de bloqueio da sinterização neste sistema, contribuindo para o esclarecimento da causa deste bloqueio e na elaboração de possíveis soluções tecnológicas. Foi comprovado experimentalmente que o mecanismo responsável pelo bloqueio é baseado na formação de poros estáveis devido ao efeito Kirkendall, originados por ocasião da formação da solução sólida durante a etapa intermediária da sinterização, sendo difícil a sua eliminação posterior, nas etapas finais do processo de sinterização. Com base no conhecimento deste mecanismo, possíveis propostas são apresentadas na direção da solução tecnológica do problema de densificação característico do sistema UO2-Gd203. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Made available in DSpace on 2014-10-09T12:53:26Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:58:38Z (GMT). No. of bitstreams: 0 / Este trabalho apresenta a síntese, caracterização e estudos de adssorção de trocadores iônicos inorgânicos a base de óxidos mistos estanho-titânio para recuperação dos metais cádmio e níquel de efluentes aquosos, descartados no meio ambiente principalmente através de baterias de Ni-Cd. Os trocadores foram sintetizados via método sol-gel modificado da mistura de cloreto de estanho(IV) e cloreto de titânio(III) com hidróxido de amônio. Os materiais obtidos: SnO2/TiO2 e SnO2/TiO2:Eu3+ foram caracterizados via espectroscopia de infravermelho, análise térmica, microscopia eletrônica de varredura (MEV), difração de raios-X (DRX) (método do pó) e espectroscopia eletrônica (excitação e emissão) para o trocador dopado com európio. Os mesmo materiais também foram sintetizados em matriz polimérica para a sua utilização em coluna, devido os materiais sintetizados apresentarem tamanho de cristalito na escala nanométrica. Determinaram-se as razões de distribuição dos metais, tomando-se como parâmetros a influência do pH, da concentração dos metais (determinando-se as isotermas de adsorção) e do tempo de contato (determinando-se a cinética de adsorção). Os trocadores apresentaram alta capacidade de troca, com porcentagens de adsorção acima de 90%, cinética rápida, superfícies de troca energeticamente heterogenias, adsorção física e processo de troca espontâneo. Para o trocador dopado foram estudadas as propriedades espectroscópicas e calculado os parâmetros de intensidade também se obteve um rendimento quântico satisfatório. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP