Luz e oxigênio induzem reações de degradação (foto-oxidação) que modificam as propriedades físicas e químicas da matéria, efeitos nocivos da radiação ultravioleta (UV) podem causar descoloração de corantes e pigmentos, amarelamento de plásticos, perda de brilho e da propriedade mecânica (cracking) de materiais, queimaduras, câncer de pele, entre outros problemas relacionados à luz UV. A fim de reduzir os efeitos nocivos da radiação UV e alcançar uma adequada conservação das propriedades dos materiais surgem os absorvedores ou filtros UV. Uma vez que materiais nanométricos a base de cério apresentam atividade fotocatalítica menor e elevada absorção na região do UV tornam-se filtros solares com aplicabilidade em diversas áreas quando comparados aos óxidos utilizados atualmente com função de filtros solares (ZnO e TiO2). Fosfatos de cério (III) (CePO4) foram preparados por Pechini (modificado), síntese hidrotermal e microemulsão reversa; as amostras foram submetidas a tratamento térmico em distintas temperaturas com o intuito de averiguar a estrutura do CePO4 e influência desta na capacidade da absorção UV. Sistemas de óxidos metálicos contendo cério também foram estudados, sendo sintetizados por sol-gel não-alcoóxido e aplicados na forma de pó e filme fino sobre substrato de vidro. A preocupação com a morfologia e o tamanho dos materiais motivou a escolha pelas metodologias de síntese empregadas. Neste trabalho foram exploradas e elucidadas as propriedades dos materiais a base de cério em absorver luz UV, devido às transições 4f-5d dos íons Ce3+ e/ou às transições entre banda de condução e banda de valência. As amostras foram analisadas por espectroscopia de absorção no UV-Vis e na região do infravermelho (FTIR), difração de raios X (XRD), difração de elétrons, susceptibilidade magnética (MS), microscopia eletrônica de varredura (SEM), microscopia eletrônica de transmissão (TEM), espectroscopia de reflectância difusa (DRS), atividade fotocatalítica (AF) e ressonância paramagnética de elétrons (EPR). As excelentes propriedades morfológicas, ópticas e fotocatalíticas indicam a possível aplicação dos materiais à base de cério, foco de investigação do presente trabalho, como filtros solares em proteção cosmetológica (cremes, shampoos, sprays etc) ou de materiais (tintas, vernizes, vidros e outros). / Light and oxygen induce degradation reactions (photo-oxidation) that modify the physical and chemical properties of the matter. The damaging UV radiation is responsible for the discoloration of dyes and pigments, weathering, yellowing of plastics, loss of gloss and mechanical properties (cracking), sunburnt skin and other problems associated to UV light. UV absorbers or UV filters have been used in order to reduce these damaging effects and achieve an adequate conservation of the properties of the materials. In front of this problem, cerium based nanomaterials are promising inorganic UV absorbers for the substitution of zinc and titanium oxide, once it presents high UV absorptivity, a lower refraction index than TiO2 and ZnO, and a higher chemical inertia (and thus a lower photocatalytic activity). Nanostructured cerium phosphates (CePO4) were prepared by Pechini, hydrothermal and reverse microemulsion synthesis, and some parameters (calcinations temperature and reactants rate) employed in each synthesis were investigated. Cerium metal oxide systems synthesized by sol-gel (non-alcooxide) and applied as powder and thin films materials were investigated too. The methodology of the synthesis were chosen aiming ideal morphology and particles size. In this work we explored and elucidated the properties of UV absorber cerium based nanomaterials , due to 4f-5d transitions of Ce3+ ions, charge transference of Ce4+ and, a little portion is due to the contribution of valence and conduction band. The samples were characterized by UV-Vis absorption spectroscopy , Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), electron diffraction, magnetic susceptibility (MS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), diffuse reflectance spectroscopy (DRS), photocatalytic activity (PA) and electron paramagnetic resonance (EPR). The excellent morphological, optical and photocatalytic properties indicate the possible application of cerium based materials in solar protection for cosmetics (creams, shampoos, sprays etc.) or materials (paints, varnishes, glass and others).

Neste trabalho, a investigação das propriedades de proteção proporcionadas por novos tratamentos de preparação da superfície do alumínio visando substituição de tratamentos prejudiciais ao meio ambiente e à saúde humana, foi realizada. Foram avaliados os seguintes tratamentos: passivação à base de cromo trivalente, tratamento com moléculas auto-organizáveis (Self Assembling Molecules-SAM), tratamento de imersão em água em ebulição para crescimento de óxido sobre o alumínio, imersão em água em ebulição com aditivos, especificamente, partículas de zircônia (ZrO2) e íons de cério. A combinação destes últimos tratamentos com o tratamento com moléculas autoorganizáveis também foi estudada. Foi também testado o efeito do tratamento da superfície do alumínio comercialmente puro (AA1050) com complexos de Flúor/Zircônio [ZrF6]-2. A resistência à corrosão do alumínio com os vários tratamentos foi avaliada por diversas técnicas, especificamente ensaios acelerados em câmara de névoa salina, segundo norma ASTM B-117, técnicas eletroquímicas e de microscopia eletrônica de varredura (MEV). As técnicas eletroquímicas adotadas foram medidas de potencial de circuito aberto (PCA) em função do tempo, espectroscopia de impedância eletroquímica (EIE) e curvas de polarização, anódica e catódica. Os resultados mostraram que os tratamentos à base de Zr, seja com partículas nanocerâmicas (ZrO2) ou complexos de Flúor/Zircônio [ZrF6]-2, não resultaram em aumento na resistência à corrosão do alumínio, o que ficou evidente pelos ensaios de névoa salina. O tratamento com moléculas auto-organizáveis da superfície desengraxada e desoxidada também não mostrou efeito favorável na proteção contra a corrosão do alumínio. O tratamento de imersão em água em ebulição causou a formação de um filme de óxi-hidróxido poroso que favoreceu o ataque localizado na forma de corrosão por pites nas regiões de defeitos/porosidades. O tratamento com moléculas auto-organizáveis após tratamento de imersão em água fervente, por sua vez, produziu melhoria nas propriedades de proteção da camada superficial mostrando a importância da camada de oxi-hidróxido na adsorção de moléculas auto-organizáveis. O tratamento de passivação à base de cromo trivalente adotado resultou em superfície com maior resistência à corrosão que a superfície do alumínio tratada com passivante à base de cromo hexavalente mostrando que a passivação com cromo trivalente é uma alternativa viável e equivalente àquela associada com substância tóxica e poluente, como é o caso do cromo hexavalente. O tratamento associado com as melhores características de proteção contra a corrosão do alumínio AA1050 foi o de imersão em água fervente contendo íons de cério, os quais foram incorporados ao filme de oxi-hidróxido. A presença destes íons na camada de oxi-hidróxido levou à formação de precipitados de hidróxido de cério nas regiões catódicas devido ao aumento localizado da alcalinidade. A combinação deste tratamento com o tratamento com moléculas auto-organizáveis causou a deterioração das propriedades da camada superficial ao diminuir a tendência à formação dos precipitados de cério que conferem proteção nas regiões de atividade de corrosão. A combinação de ensaios acelerados de névoa salina, técnicas eletroquímicas e avaliação por microscopia eletrônica de varredura permitiram a seleção de tratamentos de modificação da superfície do alumínio que resultam em maior resistência à corrosão. / In this study, the protective properties provided by new surface treatments for aluminum aiming the replacement of treatments that are harmful to the environment and human health, have been evaluated. The following treatments were investigated: passivation in solution with trivalent chromium ions, surface modification with self assembling molecules (SAM), immersion in boiling water for oxide growth, immersion in boiling water with additives, specifically zirconia (ZrO2) particles and cerium ions. The combination of these latter treatments along with the treatment with self assembling molecules was also investigated. The effect of surface treatment of commercially pure aluminum (AA1050) with fluor/zirconium complexes [ZrF6]-2 was also tested. The corrosion resistance of the various surface treatments was evaluated by various techniques, specifically, salt spray test according to ASTM B-117 standard, electrochemical techniques and scanning electron microscopy, (SEM). The electrochemical techniques used were open circuit potential measurements as a function of immersion time, electrochemical impedance spectroscopy (EIS) and polarization curves, both anodic and cathodic. The results showed that the treatment based on Zr, either with nanoceramic zirconia particles (ZrO2) or fluor/zirconium complexes [ZrF6]-2, did not increase the aluminum corrosion resistance, and this was evidenced by the salt spray tests. Immersion of degreased and deoxidized aluminum surface in solution with selfassembling molecules did not increase corrosion resistance. The treatment of immersion in boiling water for oxide growth resulted in the formation of a porous oxy-hydroxide film that assisted localized attack as pitting corrosion at the surface. The surface treatment with self-assembling molecules after immersion in boiling water for oxide growth, in turn, produced a surface layer with improved corrosion protection properties that showed the importance of an oxy-hydroxide surface layer for adsorption of self-assembling molecules. The passivation treatment based on trivalent chromium led to a surface with better corrosion resistance than that treated in a passivating solution based on hexavalent chromium. This result shows that the former is a viable alternative to replace hexavelent chromium process that is toxic and environmentally harmful. The surface treatment that produced the best corrosion performance of the aluminum AA1050 among the tested ones was the immersion in boiling water with cerium ions added which were incorporated in the oxy-hydroxide layer. The presence of the cerium ions in the surface layer led to the precipitation of cerium hydroxide at the cathodic areas due to the localized increase in alkalinity. The association of this treatment with self-assembling molecules caused deterioration of the properties of the surface layer due to the decreased susceptibility to form cerium precipitates that offer corrosion protection at the active corrosion sites. The use of salt spray tests associated with electrochemical methods and scanning electron microscopy permitted the selection of treatments for surface modification of aluminum that lead to increased corrosion resistance.

Ho Chun Man. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references. / Abstracts in English and Chinese. / ABSTRACT --- p.iv / DECLARATION --- p.vi / ACKNOWLEDGEMENT --- p.vii / TABLE OF CONTENTS --- p.viii / LIST OF TABLES --- p.xi / LIST OF FIGURES --- p.xii / Chapter Chapter One: --- Introduction --- p.1 / Chapter 1.1 --- Overview --- p.1 / Chapter 1.2 --- Fundamental of CeO2 --- p.2 / Chapter 1.3.1 --- Synthesis and Modification of Ceria-based Materials --- p.5 / Chapter 1.3.1 --- Synthetic Method --- p.5 / Chapter 1.3.2 --- "Mesoporous Structure of Ce02, CexZr1-x02" --- p.6 / Chapter 1.3.3 --- Doped Ce02 Materials --- p.6 / Chapter 1.3.4 --- Fabrication of Ceria and Cerium-based Nanoparticles --- p.7 / Chapter 1.4 --- Scope of work --- p.8 / Chapter 1.5 --- References --- p.11 / Chapter Chapter Two: --- Meso- and Macro-porous Pd/CexZr1-x02 as Carbon Monoxide Oxidation Catalysts --- p.16 / Chapter 2.1 --- Introduction --- p.16 / Chapter 2.2 --- Experimental Section --- p.18 / Chapter 2.2.1 --- Sample Preparation - Synthesis of the Catalyst Support --- p.18 / Chapter 2.2.2 --- Addition of Pd to the Catalyst Support --- p.19 / Chapter 2.2.3 --- Characterization --- p.20 / Chapter 2.2.4 --- Carbon monoxide oxidation measurement --- p.21 / Chapter 2.3 --- Results and Discussion --- p.22 / Chapter 2.3.1 --- XRD analysis --- p.22 / Chapter 2.3.2 --- SEM and TEM --- p.25 / Chapter 2.3.3 --- N2-Soprtion --- p.32 / Chapter 2.3.4 --- X-ray Photoelectron Spectroscopy --- p.40 / Chapter 2.3.5 --- Thermal Catalysis Study --- p.45 / Chapter 2.4 --- Conclusion --- p.52 / Chapter 2.5 --- References --- p.54 / Chapter Chapter Three: --- Morphology-Controllable Synthesis of Ce02 Nano and Meso-structures --- p.60 / Chapter 3.1 --- Introduction --- p.60 / Chapter 3.2 --- Experimental Section --- p.62 / Chapter 3.2.1 --- Materials and Experimental Conditions --- p.62 / Chapter 3.2.2 --- Characterization --- p.64 / Chapter 3.3 --- Results and Discussion --- p.67 / Chapter 3.3.1 --- SEM and TEM Analysis --- p.67 / Chapter 3.3.2 --- XRD Analysis --- p.75 / Chapter 3.3.3 --- N2-Soprtion --- p.78 / Chapter 3.3.4 --- X-ray Photoelectron Spectroscopy --- p.84 / Chapter 3.3.5 --- FT-IR Analysis --- p.87 / Chapter 3.3.6 --- GC-MS Analysis --- p.89 / Chapter 3.3.7 --- Proposed Formation of Ce02 nanospheres and their transformation to microrods --- p.95 / Chapter 3.3.8 --- UV absorption spectra and band gap energies --- p.97 / Chapter 3.3.9 --- Thermal Catalysis Study --- p.100 / Chapter 3.4 --- Conclusion --- p.103 / Chapter 3.5 --- References --- p.105 / Chapter Chapter Four: --- Conclusion --- p.110 / LIST OF PUBLICATIONS --- p.112

Future nuclear fission reactors (GEN IV) are designed to include fast breeder reactor technologies, which can accept transuranics (elements heavier than uranium) as fuel. This has the potential of being more fuel efficient but requires the closing of the nuclear fuel cycle: full recycling of existing and newly generated nuclear waste to extract uranium and transuranic elements which can be reused as fuel. In the UK a system being investigated is electrochemical pyroprocessing which uses molten LiCl-KCl eutectic (LKE), which aims to recover uranium by electrodeposition on an inert (steel) electrode and the transuranics by electrodeposition as alloys with an active metal electrode (bismuth, cadmium or aluminium). Of the three active metal candidates, aluminium has the best separation efficiency of actinides and lanthanides, which is important as lanthanides are neutron poisons and so are not to be extracted. The development of pyroprocessing requires fundamental understandings of electrochemical alloy formation, as well as on-line monitoring tools to ensure the reprocessing occurs safely and efficiently. To that end, this thesis investigates cerium-aluminium alloying (a non-radioactive model system for plutonium-aluminium) on macro- and microelectrodes to understand the limiting factors during the alloying reaction at each electrode scale and also the circumstances under which the Ce3+ concentration can be reliably determined for on-line monitoring. On a bulk aluminium macroelectrode one cerium-aluminium alloying reaction was observed. This reaction was kinetically limited by the phase change from cerium insertion into the aluminium, and resulted in lattice expansion and progressive roughening of the electrode surface. These factors made it difficult to reliably calculate the Ce3+ concentration. Li+ from the solution was also able to reduce and form alloys with aluminium, approximately 0.3 V more negative than the first cerium-aluminium alloying peak. Since lithium atoms are smaller than cerium, and there is an abundance of Li+ in the salt, lithium-aluminium alloy was found to form preferentially to cerium-aluminium alloy at these more negative potentials. By co-depositing Al3+ and Ce3+ together on a tungsten electrode which is inert under these conditions (it does not alloy), the kinetic barrier to alloy formation by cerium insertion was decreased, which is beneficial to studying the thermodynamics of alloying. Studies of pure aluminium plating and pure cerium plating showed each individual reaction was diffusion limited, with an increased contribution of convection to the mass transport at slow scan rates. Co-deposition on macroelectrodes with a low ratio of [CeCl3]:[AlCl3] showed only one cerium-aluminium alloying peak. The co-deposition currents, and ratio of oxidation peaks charges, showed that co-deposition was occurring with both species under diffusion control, resulting in an amorphous alloy with a Ce:Al ratio that smoothly varied with the [CeCl3]:[AlCl3] ratio. This was in contrast to the alloying behaviour of cerium with liquid bismuth, in which co-deposition occurred at specific ratios determined by the crystal phases that could be formed at the applied potentials, with higher co-deposition ratios being achieved at more negative potentials. Co-deposition on macroelectrodes with a high ratio of [CeCl 3]:[AlCl3] could result in up to five cerium-aluminium alloy peaks, corresponding to all five CexAly crystalline phases predicted by the phase diagram. This phase change from amorphous to crystalline was promoted by the high Ce:Al ratio in the amorphous alloy resulting from the high [CeCl3]:[AlCl3] ratio and by plating pure cerium on the surface, which could then insert into the alloy. Charge analysis of these peaks confirmed the expected stoichiometries of the crystal phase from these in-situ measurements which is important for rapid analysis, whereas all previous literature has relied on ex-situ techniques which cooled the alloy, possibly changing its composition and structure. In all circumstances of alloy formation on macroelectrodes, the rate of reduction of Ce3+ was time dependent and sensitive to convection. This significantly complicated analysis of the electrochemical signal, making it very difficult to reliably calculate the concentration of Ce3+, which is required for on-line monitoring. Co-deposition on in-house microfabricated tungsten microelectrodes resulted in steady state currents for both pure aluminium deposition and cerium-aluminium co-deposition (up to the beginning of lithium-aluminium alloying). Thus, unlike on macroelectrodes, the deposition rate occurred at the flux ratio of each species from solution and only one oxidation peak was observed corresponding to the amorphous cerium-aluminium phase, even at high [CeCl3]:[AlCl3] ratios. The steady state alloying current meant that calculating the Ce3+ concentration was relatively simple from co-deposition on microelectrodes. Co-deposition was highly beneficial for studying alloying, however to avoid the addition of Al3+ to the molten salt, in-house microfabricated thin film aluminium microelectrodes were also used to study alloying. Alloying on microfabricated thin film aluminium microelectrodes was hampered by the formation of a native aluminium oxide layer, which prevented cerium insertion into the aluminium. The oxide layer could be disrupted by reduction of lithium, which showed steady state currents (albeit with significant capacitance) could be achieved for alloying by cerium insertion. However, the full surface area of the microelectrode could not be attained and all microelectrodes lost their aluminium layer after multiple lithiation/de-lithiation cycles. These devices need further development to overcome the oxide layer, or prevent its formation, in order to study alloying in greater detail with aluminium microelectrodes to fully realise their advantages for sensing and monitoring in pyroprocessing.

The work within this thesis focuses on the study of alloy formation using an active liquid metal electrode for fundamental analysis and for the extraction and separation of the lanthanides and actinides in a pyroprocessing system. The electrochemical work herein is performed in a molten salt of lithium chloride and potassium chloride at its eutectic point (LKE). This salt is a likely candidate for pyroprocessing due to its relatively low melting point and resistance to degradation on exposure to high levels of radiation. The active electrode material under examination is bismuth due to its propensity to alloy with other elements, its relatively low melting point, high density and non-toxicity. The alloying processes studied are those of bismuth-lithium and bismuth-cerium. Lithium is the limiting reduction reaction defining the negative solvent limit in LKE. As a result, understanding the processes that would occur if the electrode were to be pushed to such negative potentials is of significant importance. Cerium is a commonly-used surrogate for plutonium, which is an element of relatively high concentration in waste nuclear fuel and is of significant interest to the nuclear international community in waste fuel recycling. This work examines the alloying processes in terms of which intermetallic compounds are formed and by what mechanisms. This is achieved through the use of co-deposition on a macro tungsten rod, employing a number of electrochemical techniques to extract pertinent information. Lithium electrodeposition and alloying with bismuth (at the negative solvent limit) was found to form BiLim alloy with increasing m at more reducing potentials, followed by the deposition of near pure lithium. Mixing of these two then gave rise to specific bismuth-lithium alloys and the apparent ejection of a lithium metal fog into the molten salt, which resulted in the chemical reduction of Bi3+ and the loss of the bismuth electrodeposition current. When electrodepositing cerium on, and alloying with, bismuth, the formation of intermetallic compounds is governed by potential with a maximum BiCem stoichiometry of m = 1 with equimolar Bi3+ and Ce3+. However, at concentrations of cerium greater than that of bismuth, alloys much richer in cerium were also deposited at more negative potentials. There is evidence that deposited cerium may also escape into solution and chemically react with Bi3+. In-house microelectrodes are also developed and used for this purpose, both through co-deposition and direct alloy formation on a liquid bismuth thin-film microelectrode. This work demonstrates that these devices provide a richness of information due to their highly beneficial microelectrode properties. A means of controllably depositing bismuth from an aqueous plating bath, without dendrite formation, on both platinum and tungsten microelectrodes was devised. This was followed by electrodeposition of bismuth films on these devices in LKE. Platinum was found to be an active electrode material, alloying with bismuth, while tungsten remained inert. Nonetheless, both electrode types produced characteristic microelectrode behaviour, which was successfully used to determine the diffusion coefficient of bismuth in LKE. A comparison of bismuth-cerium and cerium alloying on a thin film liquid bismuth microelectrode found that the latter indicated the formation of BiCe2 where only BiCe had been seen previously during co-deposition in an equivalent salt. This is thought to be due to the thin film liquid bismuth microelectrode configuration with enhanced Ce3+ mass transport. This response was also used to calculate the diffusion coefficient of cerium inside the bismuth film, which was found to be slightly slower than for Ce3+ in LKE.

Submitted by Erika Demachki (erikademachki@gmail.com) on 2015-02-12T19:58:19Z No. of bitstreams: 2 Dissertação - Marcelo Mendes Lourenço - 2012.pdf: 2641976 bytes, checksum: 881f9a3b035c8f36d76de655b3ee307b (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Approved for entry into archive by Erika Demachki (erikademachki@gmail.com) on 2015-02-12T19:58:49Z (GMT) No. of bitstreams: 2 Dissertação - Marcelo Mendes Lourenço - 2012.pdf: 2641976 bytes, checksum: 881f9a3b035c8f36d76de655b3ee307b (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) / Made available in DSpace on 2015-02-12T19:58:49Z (GMT). No. of bitstreams: 2 Dissertação - Marcelo Mendes Lourenço - 2012.pdf: 2641976 bytes, checksum: 881f9a3b035c8f36d76de655b3ee307b (MD5) license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Previous issue date: 2013-01-08 / Nanoparticles of zinc oxide doped cerium (Zn1 -xCexO) with 0.0 ≤ x ≤ 0,48% were synthesized by forced hydrolysis reaction. Structural analysis of samples was performed by X-Ray Diffraction (XRD) powder method. The chemical analysis was performed by EDS, Photo Electron Spectroscopy Excited X-ray (XPS) and Spectroscopy Infrared Fourier Transform (FTIR). Thermal analysis was obtained by Thermogravimetry (TG) analysis and magnetic analysis was performed by Magnetometry Vibrating Sample (VSM). The chemistry analysis by EDS show the samples presented amounts of the Ce with 0,0 ≤ x ≤ 0,48% . The samples presented phases corresponding the hexagonal wurtzite system compact and absence of secondary phases in the sample without heat treatment and with low amounts of dopant (2.5%). The average particle diameter was 29 nm calculated by the Scherrer equation. Chemical analysis by XPS showed peaks of greater intensity associated with the elements Zn, O and Ce being confirmed tetravalent oxidation state to the dopant (Ce4+). FTIR analysis revealed the presence of connections Zn-O type, presence of organic residues and displacement bands possibly related to the presence of dopant. Thermogravimetric analysis revealed the presence of organic residues present in the samples and a mass gain of ~ 0.2% probably associated with the formation of secondary phase of CeO2. The magnetic analyzes revealed that the samples show ferromagnetism at room temperature with coercive field (Hc) of between 60 and 90 Oe and remnant magnetization (Mr) on the order of 10-4 emu/g. The evaluation of the magnetic sample to 0,22% (Zn0,9978Ce0,0022O), heat treated, showed a reduction in the magnetic behavior of this sample with increasing heat treatment temperature. / Nanopartículas de óxido de zinco dopado com cério (Zn1 -xCexO), com 0,0 ≤ x ≤ 0,48% foram sintetizadas por reação de Hidrólise Forçada. A análise estrutural das amostras foi realizada por Difração de Raios X (XRD) método do pó. A análise química foi realizada por Espectrometria de Energia Dispersiva de Raios-x (EDS), Espectroscopia de Fotoelétrons Excitados por Raios-X (XPS) e Espectroscopia no Infravermelho com Transformada de Fourier (FTIR). A análise térmica foi obtida pela análise Termogravimétrica (TG) e a análise magnética foi realizada por Magnetometria de Amostra Vibrante (VSM). A análise química por EDS revelou que as amostras apresentaram porcentagens de Ce que variaram entre 0 e 0,48%. Os difratogramas das amostras apresentaram fases correspondentes à wurtzita no sistema hexagonal compacto e ausência de fases secundárias. O diâmetro médio das partículas foi de 29 nm, calculado pela equação de Scherrer. A análise por XPS apresentou picos de maior intensidade associados aos elementos Zn, O e Ce sendo confirmado o estado de oxidação tetravalente para o dopante (Ce4+). As análises de FTIR revelaram a presença de ligações do tipo Zn-O, presença de resíduos orgânicos e deslocamento nas bandas possivelmente relacionado à presença do dopante nas amostras. A análise termogravimétrica (TG) revelou a presença de resíduos orgânicos presentes nas amostras bem como um ganho de massa de ~0,2% provavelmente associado à formação da fase secundária de CeO2. As análises magnéticas revelaram que as amostras apresentam ferromagnetismo à temperatura ambiente com campo coercivo (Hc) entre 60 e 90 Oe e magnetização remanescente (Mr) na ordem de 10-4emu/g. A avaliação magnética da amostra a 0.22% (Zn0,9978Ce0,0022O), tratada termicamente, revelou uma redução no comportamento magnético com o aumento da temperatura do tratamento térmico.

Este trabalho investigou a técnica de solução coloidal(gelcasting) em meio polimérico para a obtenção de partículas de óxido de cério, visando seu emprego como catalisadores na combustão do metano. A formulação do sistema coloidal foi baseada na hidrólise de sais, como acetilacetonato de cério e nitrato de cério em presença de aditivos tais como polivinilbutiral (PVB), polivinilpirrolidona (PVP) e polivinilacetato (PVA), nas concentrações de 5, 10 e 15%, em meio alcoólico ou aquoso. Essas soluções, contendo os íons de interesse, foram submetidas a um tratamento térmico a 650°C, por 30 minutos, com taxa de aquecimento de 2°C/min. Após o tratamento térmico, os produtos obtidos foram caracterizados quanto a sua morfologia, área superficial, cristalinidade, perda de massa e atividade catalítica. As amostras obtidas a partir de acetilacetonato de cério mostraram-se mais reativas do que as obtidas a partir de nitrato de cério na catálise da combustão do metano, pois apresentaram maiores conversões e atingiram maiores temperaturas durante o processo, o que é de extrema importância uma vez que a combustão catalítica do metano é utilizada para a geração de energia térmica. Durante o processo de combustão, utilizando-se as partículas obtidas a partir de acetilacetonato de cério, observou-se a liberação de grandes quantidades de compostos nitrogenados quando comparado aos resultados dos ensaios com as partículas obtidas com nitrato de cério. Após a combustão do metano, as amostras sofreram significativa alteração na área superficial, provavelmente devido à intensidade do calor liberado, o que deu origem a maior aglomeração dos particulados. / This study investigatedto obtainparticles ofcerium oxide, for use as catalysts for thecombustion of methaneusing the techniqueofthroughpolymericcolloidal solution (gelcasting).Obtaining thecolloidal systemisbased onhydrolysis ofsalts such asceriumacetylacetonate,cerium nitratein the presence ofadditives such aspolyvinylbutyral(PVB),polyvinylpyrrolidone (PVP) and polyvinyl acetate(PVA),at concentrations of 5, 10 and 15% inaqueousoralcoholic medium. Thesesolutions containingionsof interestwere subjected to aheat treatment at 650°C for30 minutes, with heating rate of2°C/min.After heat treatment, the fibers were characterized accordingto their morphology, surface area, crystallinity, weight loss andcatalytic activity. Samplesobtained fromceriumacetylacetonatewere morereactivethan theceriumnitrateto thecombustion of methane, as showed greaterconversions andhigher temperaturesreachedduring the process, which is of utmost importancesince thecombustioncatalyticmethaneis usedfor generatingthermal energy.Duringthe combustion processusing theobtained fromparticlesof ceriumacetylacetonate, there was the release of largequantities ofnitrogencomparedto the results ofassays withthe particles obtainedwithcerium nitrate.Afterthe reactionwith methane, the samples underwentsignificantchange insurface area, probably dueto the intensity of heat of this reaction, which helps to agglomerate the particles.

Na atualidade, a reforma do metano é de grande interesse industrial para o aproveitamento deste gás na produção de hidrogênio e de gás de síntese. Entre as reações de reforma do metano, destacam-se as reações de reforma a vapor e a reação com dióxido de carbono.O catalisador comumente utilizado nos processos re reforma do metano é Ni/Al2O3. Porém durante este processo, ocorre uma indesejada formação de depósitos de espécies carbonáceas na superfície deste catalisador, os quais levam a sua destruição mecânica e conseqüentemente sua desativação. Por isso, uma das propriedades mais importantes de um bom catalisador para as reações de reforma do metano é a sua resistência à desativação. Entre as propostas para melhorar o desempenho do catalisador encontra-se a incorporação do óxido de céria junto ao suporte alumina.Catalisadores 5%Ni/xCeO2/Al2O3 (x = 0, 1, 5, 10, 20 e 100%) forma preparados, caracterizados e submetidos a ensaios catalíticos nas reações de reforma a vapor e com dióxido de carbono de metano com objetivo de avaliar o efeito da adição de céria ao suporte.Os suportes e os catalisadores forma obtidos pelo método de impregnação e calcinados a 500ºC. Estes compostos foram caracterizados por Fisissorção de Nitrogênio pelo método B. E. T., Espectroscopia dispersiva de raios-X (EDX), espectroscopia de na região do ultra violeta e do visível (UV-vis-NIR) e Redução à Temperatura Programada (RTP). Após todas as reações catalíticas verificou-se que a adição de céria é benéfica ao catalisador Ni/Al2O3 e entre todos os catalisadores avaliados, o melhor desempenho obtido foram dos catalisadores contendo 20% de céria em massa, seguido do catalisador contendo 10%. / Nowadays, the methane reforming is large interest industrial for the take advantage of these gas in production the hydrogen and synthesis gas (syngas). Among in the reactions of methane stand of the reactiosn steam reformig and carbon dioxide reforming of methane. The main catalysts uses in the methane reforming is Ni/Al2O3. However, the supported-nickel catalyst is susceptible to the deactivation or the destruction by coke deposition. The carbon dissolves in the nickel crystallite and its diffuses through the nickel, leading for formation of the carbon whiskers, which results in fragmentation of the catalyst. Modification of such catalysts, like incorporation of suitable promoters, is desirable to achieve reduction of the methane hydrogenolysis and/or promotion of the carbon gasification. Catalysts 5%Ni/xCeO2/Al2O3 (x = 0, 1, 5, 10, 20 e 100%) were prepared, characterized and evalueted in reactions steam and carbon dioxide refoming of methane with objetive the value effect loading oxide ceria in support. The suppots and catalysts were prepared by impregnation method and calcined at 500ºC. The supports and catalysts were characterized by X Nitrogen Adsorption by B.E.T., method -rays diffraction (XRD), , Xrays dispersive spectroscopy (XDS), to spectroscopy in the region of the ultraviolet and the visible (UV-vis NIR) to and temperature programmed reduction (TPR). After all the catalytic reactions check which the addition of cerium is beneficial for Ni/Al2O3 catalysts and the best catlysts is 5%Ni/20%CeO2/Al2O3 following 5%Ni/10%CeO2/Al2O3.

Os revestimentos eletrozincados empregados como proteção galvânica ativa sobre os aços são utilizados industrialmente há longo tempo. Entretanto, como o zinco é um elemento muito reativo, o tratamento da sua superfície é necessário para aumentar sua vida útil. O tratamento mais utilizado consiste em imersão em solução de conversão contendo cromo hexavalente, o qual vem sendo banido por gerar substâncias tóxicas e carcinogênicas, tendo sua utilização proibida pelas normas europeias. Neste trabalho, foram estudados tratamentos alternativos ao cromato para o aço eletrozincado que não geram resíduos tóxicos. O tratamento escolhido foi desenvolvido em etapas. A primeira etapa envolveu o uso de um composto orgânico, o 2 butino-1,4 diol propoxilato, em solução com sais oxidantes e com nitrato de cério como aditivo. A etapa seguinte consistiu em imersão da superfície tratada pela etapa anterior, em um agente oxidante, o peróxido de hidrogênio. A terceira etapa consistiu na imersão em solução com 2 butino-1,4 diol propoxilato e oxalato de nióbio amoniacal (ANO). As superfícies tratadas, após cada uma das etapas, foram caracterizadas por microscopia óptica e eletrônica de varredura (MEV), difração de raios X (DRX), espectroscopia por infravermelho (FTIR) e espectroscopia fotoeletrônica de raios X (XPS). A caracterização quanto à corrosão das superfícies tratadas foi feita por ensaios de névoa salina e espectroscopia de impedância eletroquímica (EIE). Os resultados mostraram que cada uma das etapas teve uma contribuição no aumento da resistência à corrosão e esta foi dependente do tempo de tratamento em cada uma das três etapas. A composição química das camadas obtidas foi caracterizada por FTIR e XPS. Esta última técnica permitiu analisar a distribuição dos elementos nas camadas formadas ao longo da espessura da mesma, usando a técnica de desbaste (sputtering), obtendo perfis de profundidade. A presença de ácido carboxílico ligado ao substrato metálico (zinco) foi observada. Os resultados mostraram que ocorreu formação de camada orgânica e a incorporação de cério e de nióbio a esta camada. Estes se apresentam distribuídos em toda a extensão da camada, na forma de óxidos em dois estados de oxidação, III e IV, no caso do cério, e IV e V, no caso do nióbio. As camadas formadas após as várias etapas adotadas contêm uma estrutura polimérica formada por filme orgânico e uma mistura de óxidos, particularmente óxido e hidróxido de zinco, os quais ficam retidos na estrutura da camada e conferem proteção à corrosão do substrato metálico por períodos prolongados de imersão. Os resultados quanto a proteção à corrosão mostraram que o tratamento com o melhor desempenho (T10_10_10) proporcionou proteção ao substrato por longos períodos de tempo e esta foi superior em comparação à promovida por camada de cromato, tanto pelo ensaio de névoa salina como o de EIE. Este tratamento mostrou-se, portanto, uma alternativa promissora para substituição de camada de cromato na proteção de aço eletrozincado, tanto do ponto de vista ambiental, por não gerar resíduos tóxicos, como de resistência à corrosão. / Electrogalvanized coatings are employed as active galvanic protection to steel and its applications have been used industrially for a long time. However, as zinc is a very reactive element, the treatment of the surface is necessary to increase its lifespan. The most common treatment consisted of a conversion treatment in solution containing hexavalent chromium, which has been banned by generating toxic and carcinogenic substances, and its use prohibited by European standards. In this work, surface treatments alternative to chromating for electrogalvanized steel that do not generate toxic waste were studied. The chosen treatment was developed in stages. The first stage involved the use of an organic compound, 2 butyne 1,4 diol propoxylate in solution with oxidizing salts and cerium nitrate as an additive. The next step involved immersing the treated surface by the previous step in an oxidizing agent, hydrogen peroxide. The third step consisted of immersion in solution with 2-butyne 1,4 diol propoxylate and ammonium niobium oxalate (ANO). Treated surfaces after each step were characterized by optical microscopy and scanning electron microscopy (SEM), X-ray diffraction (XRD), infrared spectroscopy (FTIR) and photoelectron spectroscopy X- ray (XPS). The characterization for corrosion of the treated surfaces was made by salt spray tests and electrochemical impedance spectroscopy (EIS). The results showed that each step has a contribution in increasing the corrosion resistance and this was dependent on the treatment time adopted in each of the three stages. The chemical composition of the layers obtained was characterized by FTIR and XPS. This last technique allowed to analyze the distribution of the elements in the layer formed along its thickness, by sputtering the surface to obtain depth profiling. The presence of carboxylic acid bonded to the metal substrate (zinc) was observed. The results showed that there was formation of organic layer and the incorporation of cerium and niobium this layer. These elements were distributed throughout the length of the layer in the form of oxides in two oxidation states; in the case of cerium, as III and IV, and IV and V, in the case of niobium. The layers formed after the various steps contain a polymeric structure and a mixture of oxides/hydroxide, particularly of zinc, which are retained in the structure of the layer and provide corrosion protection to the metal substrate for prolonged periods. The corrosion results showed that the best treatment (T10_10_10) provided protection to the substrate for long periods of time and that was higher compared to that promoted by the chromate layer, either by the salt spray test as the EIS test. Therefore, this treatment proved a promising replacement to chromate layer in the corrosion protection of electrogalvanised steel, either from its corrosion properties or from an environmental point of view.

The main objective of this Thesis is the synthesis, characterization and application in the PROX reaction of several series of catalysts synthesized using different methods, in order to find efficient materials with high catalytic activity. This work has been divided in six chapters. Chapter I presents an introduction about current energy problems and hydrogen (energy carrier) as a solution, with its limitations and advances on its use: storage, transport and security. Finally, its use as a fuel in PEMFC (Proton Exchange Membrane Fuel Cells) and the advantages comparing other existent fuel cells has been discussed. A brief summary was done about the catalytic systems studied in literature for PROX reaction and their characteristics. Following, Chapter 2 describes all the characterization techniques which were used to study the properties of the synthesized supports and catalysts, together with the experimental system employed for the catalytic tests. Most of these equipments belong to SSTTI of University of Alicante or are hand-made systems in the LMA group. DRIFTs and DTP were done at TUDelft, Catalysis Engineering Section. Next chapters contain the most important results obtained during the complete research work; they have been divided in two parts. On one hand, Chapter 3 describes the synthesis of pure TiO2 using five different methods, and its use as platinum support for PROX catalysts. On the other hand, taking into account the obtained results, three synthesis methods were chosen, and the study was centered in the addition of CeO2 to TiO2. Chapter 4 discusses the TixCe(1-x)O2 series synthesized using the sol-gel method. In Chapter 5 a solvothermal procedure was employed for the synthesis of supports with similar composition and, finally, impregnation of cerium over commercial P25 titania was compared in Chapter 6. Each chapter contains a complete study of characterization of both supports and catalysts. Synthesis parameters, pretreatment and reaction conditions were also modified for the best catalyst of the three series. Analyzing the catalysts’ behavior, a reaction mechanism was proposed. Finally, general conclusions summarize the most relevant results obtained in each chapter.