Métodos de síntese que viabilizam a obtenção de compósitos contendo xerogéis de óxido de tungstênio e de pentóxido de vanádio pelo método sol-gel foram investigados, bem como a caracterização e propriedades catalíticas nas reações de epoxidação destes materiais. Brometo de cetiltrimetilamina e hexadecilamina foram intercalados nos xerogéis de óxidos vanádio e de tungstênio formando compostos híbridos orgânico-inorgânico ternários. Estas moléculas foram usadas com o objetivo de aumentar a distância interlamelar e conferir caráter hidrofóbico nos compostos híbridos para que facilitasse o acesso dos substratos orgânicos quando utilizados como catalisadores nas reações de epoxidação. Os parâmetros de difração de raios X comprovam a intercalação, com aumento da distância interplanar. Observa-se uma variação na posição da banda M=O para maiores valores de energia devido à interação eletrostática entre as cargas positivas das espécies convidadas com densidade de carga negativa das ligações M=O. O xerogel de óxido de tungstênio e o compósito com xerogel de óxido de vanádio com óxido tungstênio foram dispersos em matrizes de óxido hidróxido de alumínio e de xerogel de óxido de silício. Foi observado que os modos vibracionais no infravermelho não sofreram variações significativas, indicando que pequenas distorções ocorrem quando os xerogéis dos óxidos estão dispersos, ou seja, há interações fracas entre os componentes, corroborando com os padrões de difração de raios X que mostram a manutenção da estrutura inicial dos óxidos. No caso dos compósitos contendo óxido de vanádio em sílica empregando metiltrietóxissilano, houve a formação de partículas esféricas de sílica recobertas por filmes de óxido de vanádio. No entanto, ao utilizar o tetraelilortossilicato como precursor, houve a manutenção da estrutura lamelar dos óxidos, mas não se observou a formação das partículas esféricas de sílica. As propriedades catalíticas destes materiais foram testadas em reações de oxidação do cis-cicloocteno, estireno e ciclo-hexano usando peróxido de hidrogênio (H2O2), terc-butil hidroperóxido (t-BOOH) e ácido meta-cloroperbenzóico (m-CPBA) como agentes oxidantes. De modo geral, os resultados obtidos são satisfatórios e estão de acordo com os resultados apresentados na literatura para sistemas similares, sugerindo uma aplicação potencial destes materiais como catalisadores em reações de epoxidação e oxidação. / Synthetic procedures based on sol-gel process were developed aiming produce xerogel composites of mixed oxides such as tungsten oxide and vanadium oxide, as well as their characterization and catalytic properties in epoxidation reactions. Cetyltrimetylamine bromide and hexadecylamine were intercalated into vanadium oxide and tungsten oxide xerogels resulting in ternary hybrid inorganic-organic compounds. These molecules were used in order to increase the interlamelar distance and confer hydrophobic character facilitating the substrate access in catalyzes epoxidation reactions. X ray diffraction patterns demonstrate the intercalation. It was verified the shift of the M=O vibrational mode towards higher energy region due to electrostatic interaction between positive charges of guest species with negative character of M-O bonding. Tungsten oxide and vanadium and tungsten mixed oxide xerogels were dispersed in oxohydroxiy aluminum and silicon oxide matrices. No significant changes in the infrared vibrational modes were observed, suggesting that few distortions occur when xerogel materials are dispersed, due to weak interactions corroborating previous results. In the case of composites containing vanadium oxide and silica (methyltriethoxysilane as precursor), the final material is formed by sphere particles of silica covered with vanadium oxide film. However, when tetraethylorthosilicate was used as silica precursor, the lamelar structure of metal oxide is retained instead of spherical morphology. The catalytic properties of these materials were verified in oxidation of cis-cyclooctene, styrene, and cyclohexane using hydrogen peroxide (H2O2), terc-butyl hydroperoxide (t-BOOH), and cloroperoxybenzoic acid (m-CPBA) as oxygen donors. From a general point of view, the results are satisfactory and close with those found for similar systems, enabling them as catalysts for epoxidation and oxidation.

O xerogel de pentóxido de vanádio possui estrutura bi-dimensional que viabiliza a intercalação de diferentes espécies como íons, compostos orgânicos e espécies poliméricas. E, quando associeado a outros óxidos de metais transição, tais como, WO3 e MoO3 apresenta uma importância em reações de catálise, pois estes óxidos atuam como promotores em reações como, por exemplo, a redução catalítica seletiva do NOx a NH3 e a oxidação de hidrocarbonetos. Além disso, estes óxidos melhoram as propriedades eletroquímicas e eletrocrômicas, favorecendo assim sua utilização em células fotoquímicas, células para conversão de energia solar e cátodos de baterias e lítio. Dentre estes óxidos, o óxido de tungstênio hidratado foi escolhido não somente por favorecer a dissociação ácida das moléculas, mas também por apresentar uma estrutura lamelar que favorece reações de intercalação sem afetar significativamente sua estrutura original. Neste contexto, o xerogel de óxido misto V2O5/WO3 foi sintetizado e suas propriedades eletroquímicas bem como sua capacidade de intercalação foi investigada. em relação ao comportamento eletroquímico, a melhor resposta foi obtida para o óxido misto com menor concentração de WO3, ao passo que para os óxidos com alta quantidade de óxido de tungstênio, a intercalação dos íons Li+ não foi eficiente. Estudos de voltametria cíclica revelaram que a resposta eletroquímica do óxido misto é similar à encontrada para o xerogel de pentóxido de vanádio. Em adição, outros resultados revelaram a dependência da resposta eletroquímica com a natureza do eletrólito suporte. Também foi verificado que é possível intercalar anilina e agentes tensoativos (Brometo de Cetiltrimetilamônio - CTAB), mantendo o caráter bi-dimensional. Neste trabalho, o compósito V2O5/WO3/SiO2 foi preparado pelo método sol-gel. A metodologia usada possibilitou a preparação de microesferas de sílica cobertas por xerogel de V2O5/WO3, conservando não somente a estrutura, mas também as propriedades eletroquímicas. A atividade catalítica avaliou a oxidação do estireno em fase líquida. / Vanadium pentoxide xerogel has a bi-dimensional structure which is suitable for intercalation of a variety of ions, organic compounds, and even polymeric species. In addition, when associated with other metal oxides such as WO3 and MoO3, it presents an important role in catalysis, since the resulting oxides act as promoters in catalytic reduction of the NOx to NH3 and hydrocarbons oxidation. Besides, these oxides improve electrochemical and electrochromic properties, leading to their use in photochemical cells, cathodes and in solar energy cells. Among several metal oxides, hydrated tungsten oxide was chosen not only because of favor the acid dissociation of molecles but also because of its lamellar structure that allows intercalation reactions without affect significantly the original structure. In this context, V2O5/WO3 xerogel mixed oxides were synthesized and electrochemical properties as well as intercalation capacity were investigated. Concerning the electrochemical behavior, the best response was obtained for the mixed oxides with low concentration of WO3, whereas for the oxides with high amount of tungsten oxide, the lithium ions intercalation was not efficient. Cyclic voltammetric studies revealed that the electrochemical response of mixed oxide is similar to that found for the vanadium pentoxide xerogel. In addition, our results reveal the dependence of the electrochemical response on the nature of the supporting electrolyte. It was also verified that it is possible to intercalate aniline and surfactant molecules (N-cetyl-N,N,N,-trimethyl-ammonium bromide - CTAB), maintaining the bi-dimensional character. In this work, V2O5/WO3/SiO2 composite was prepared by sol-gel method. The methodology used enables the preparation of silica microspheres covered by V2O5/WO3 xerogel mixed oxides, retaining not only its structure but also the electrochemical properties. the catalytic activity evaluated in the oxidation of the styrene in liquidphase.

Strongly correlated oxides are studied widely for the host of unique applications, such as hightemperature superconductivity, colossal magneto resistance, exotic magnetic, charge and orbital ordering, and insulator-to-metal transitions. Transitional metal oxides which form the majority of the correlated oxide systems and oxides of Vanadium, especially VO2 and V2O5 are the two most favourite systems among researchers for several applications. In this thesis, the growth and characterization of VO2 and V2O5 are discussed along with a special focus on the optical property, especially thermochromic properties. Traditionally SMT behaviour and Infrared reflectively was the focus area for VO2 research, and its only until recently that VO2 is being treated as a much more complex system and investigated as highly responsive naturally disordered metamaterial near the phase transition temperature where the material exhibits semiconducting and metallic phase co-existence. Since each phase of VO2 has a distinct optical and electrical properties, controlling the extent of phase transitions by accurate temperature modulation, enables exploitation of the material for new properties like emissivity modulation in the NIR region and for creating IR visible reversible and rewritable patterns. V2O5 is traditionally seen as a high TCR material and regarded as material of choice for application ranging from catalysis, gas sensors to lithium batteries. In this study, however we focus on the optical properties of the material, especially the visible range thermochromic nature of V2O5 coatings synthesised by oxidative annealing of MOCVD grown VOx coatings. The impact of doping and selective oxygen vacancy generation on the thermochromic property are discussed

Please read the abstract in the section 00front of this document / Dissertation (M Eng (Metallurgical Engineering))--University of Pretoria, 2007. / Materials Science and Metallurgical Engineering / unrestricted

[EN] The project of this Ph.D. thesis is based on a co-supervised collaboration between Università di Bologna, ALMA MATER STUDIORUM (Italy) and Instituto de Tecnología Química, Universitat Politècnica de València ITQ-UPV (Spain). This Ph.D. thesis is about the synthesis, characterization and catalytic testing of complex mixed-oxide catalysts mainly related to the family of Hexagonal Tungsten Bronzes (HTBs). These materials have been little explored as catalysts, although they have a great potential as multifunctional materials. Their peculiar acid properties can be coupled to other functionalities (e.g. redox sites) by isomorphous substitution of tungsten atoms with other transition metals such as vanadium, niobium and molybdenum. In this PhD thesis, it was demonstrated how it is possible to prepare substituted-HTBs by hydrothermal synthesis; these mixed-oxide were fully characterize by a number of physicochemical techniques such as XPS, HR-TEM, XAS etc. They were also used as catalysts for the one-pot glycerol oxidehydration to acrylic acid; this reaction might represent a viable chemical route to solve the important issue related to the co-production of glycerin along the biodiesel production chain. Acrylic acid yields as high as 51% were obtained and important structure-reactivity correlations were proved to govern the catalytic performance; only fine tuning of acid and redox properties as well as the in-framework presence of vanadium are fundamental to achieve noteworthy yields into the acid monomer. The overall results reported herein might represent an important contribution for future applications of HTBs in catalysis as well as a general guideline for a multifaceted approach for their physicochemical characterization. / [ES] El proyecto de esta tesis doctoral está basado en un convenio de cotutela firmado por la Università di Bologna, ALMA MATER STUDIORUM (Italia) y el Instituto de Tecnología Química, Universitat Politècnica de València ITQ-UPV (España). La presente tesis doctoral muestra el estudio sobre la síntesis, caracterización y ensayos catalíticos de materiales complejos a base de óxidos mixtos relacionados con la familia de los bronces de tungsteno hexagonales. Estos materiales han sido utilizados minoritariamente como catalizadores, aunque tienen un potencial importante come materiales multifuncionales. Sus peculiares propiedades acidas pueden ser acopladas con otras características (por ejemplo, sitios oxido-reductivos) a través de la substitución isomórfica de átomos de tungsteno con otros metales de transición como vanadio, niobio y molibdeno. En esta tesis doctoral se ha demostrado como sea posible preparar bronces de tungsteno hexagonales substituidos a través de síntesis hidrotermal; estos óxidos mixtos fueron caracterizados por completo empleando numerosas técnicas de caracterización quimico-fisicas como XPS, HR-TEM, XAS etc. Fueron también utilizados como catalizadores para la síntesis directa de acido acrílico de glicerol; esta es una reacción que puede representar una solución viable para el problema relacionado con la coproducción de glicerina a lo largo de la cadena productiva del biodiesel. Rendimientos en acido acrílico hasta el 51% fueron obtenidos y importantes relaciones entre las estructuras y la actividad catalítica fueron demostradas ser determinantes para el proceso catalítico; solo la afinación de las propiedades acidas y redox tanto como la presencia en-red de vanadio son esenciales para conseguir rendimientos relevantes en el monómero acido. En general, los resultados presentados en esta tesis doctoral pueden ser una contribución relevante para futuras aplicaciones de los bronces de tungsteno hexagonales en catálisis y también como una guía general para un completa caracterización quimico-fisica de estos oxidos. / [CAT] Esta tesi doctoral està basada en un conveni de cotutela signat per la Università di Bologna, ALMA MATER STUDIORUM (Italia) i el Institut de Tecnologia Química , Universitat Politècnica de València ITQ-UPV(Espanya). La present tesi doctoral estudia la síntesis, caracterització i assajos catalítics de òxids mixtes relacionats amb la família dels bronzes de tungstèn hexagonals. Aquestos materials presenten un gran potencial com materials multi funcionals, encara que no han sigut molt emprats com catalitzadors. Les propietats àcides particulars de aquestos materials poden ser potenciades amb altres característiques (per exemple, llocs redox) mitjançant la substitució isomòrfica d'àtoms de tungstèn amb altres metalls de transició com vanadi, niobi i molibdè. En aquesta tesi doctoral es demostra com es possible sintetitzar bronzes de tungstèn hexagonals substituïts a partir de síntesis hidrotermal. Aquestos òxids mixtes han segut caracteritzats emprant diverses tècniques de caracterització físico-químiques com XPS, HR-TEM, XAS, etc... Per altra part, s'han utilitzat com catalitzadors per a la síntesis directa de àcid acrílic a partir de glicerol, aquesta reacció pot representar una solució viable per al problema relacionat amb la coproducció de glicerina al llarg de la cadena productiva de biodiesel. S'han obtingut rendiments a àcid acrílic del 51%. A més, s'han observat importants relacions entre les estructures i la activitat catalítica, les quals han sigut determinants per al procés catalític. El ajust de les propietats àcides i redox i la presència en red de vanadi són essencials per a obtindre rendiments rellevants en el monòmer àcid. En general, el resultats presentats en aquesta tesi doctoral poden ser una contribució rellevant per a futures aplicacions del bronzes de tungstèn hexagonal en catàlisis i també com una guia general per a una completa caracterització físico-química d'aquestos òxids. / Chieregato, A. (2015). Glycerol oxidehydration to acrylic acid on complex mixed-metal oxides [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/49558 / TESIS

The high demand for copper is coinciding with a sharp decline in the grade of copper reserves, and as a result, copper scarcities are expected to arise in the coming decades. In this work, a transformative hydrometallurgical process is being developed to lower the costs of copper production and thereby sustain the use of copper throughout the global transition to renewable energy technologies. The focal point of the hydrometallurgical process is the reductive treatment of chalcopyrite, which is in contrast to the oxidative treatment more commonly pursued in the literature. Chalcopyrite may be reduced directly by the cathode of an electrochemical reactor, which is monitored by atomic absorption spectroscopy (AAS), x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS). The efficiency of the electrochemical reaction is optimized by adjusting the electrode materials, applied current density, and reactor design. Chalcopyrite may also be reduced by reaction with the vanadium (II) ion, which circumvents engineering challenges associated with slurry electrodes but requires the separation and electrochemical regeneration of the vanadium (II) ion. A preliminary technoeconomic analysis suggests that both reduction pathways may be competitive with the pyrometallurgical standard for copper production. The performance of vanadium redox flow batteries (VRFBs) is hindered by the diffusion and migration of the vanadium species across the separator, however the migration of vanadium species has not been accurately measured or characterized with values of the transference numbers. In this work, models based on dilute solution theory and concentrated solution theory are developed to introduce the dimensionless ratio of migration to diffusion (M/D) to the literature. It is shown that transference numbers may be measured with high accuracy and precision for experiments conducted in the migration-dominated regime. An experimental procedure is designed to measure vanadium crossover as a function of current density for vanadium-containing electrolytes of various state of charge (SOC), state of discharge (SOD), and sulfuric acid concentration. Model-guided design of experiment is used to estimate the transference number of the vanadium species in Nafion 117 with minimal uncertainty related to unknown or unmeasured physical properties. Markov Chain Monte Carlo simulations are used to quantify the relative uncertainties of the transference number estimates to be less than five percent, consistently. The transference number estimates are related to faradaic efficiency loss and capacity fade of working VRFBs operating in the migration-dominated regime. The technique used in this work may be generalized to measure salt transference numbers in novel electrochemical systems and membrane separators to inform their rational design.

>Magister Scientiae - MSc / When the spacecrafts orbit in space, it is subjected to significant thermal cycling variation. Thermal regulation of the spacecraft temperature is required to ensure a good operation of the small crafts such as CubeSats and the on-board equipment while minimizing the weight. Three methods employed for the Smart Radiator Devices (SRD) are (i) mechanical louvers, (ii) electrochromic coatings and (iii) thermochromic coatings (which is of interest in this study). Based on the characteristics of the thermochromic coatings, the passive smart radiator device is by far the most efficient option since there are no mechanical moving components and also no electric energy needed for the craft to operate.

In a wireless system, the frequency-reconfigurable RF components are highly desired because one such component can replace multiple RF components to reduce the size, cost, and weight. Typically, the reconfigurable RF components are realized using capacitive varactors, PIN diodes, or MEMS switches. Most of these RF switches are expensive, rigid, and need tedious soldering steps, which are not suitable for futuristic flexible and wearable applications. Therefore, there is a need to have a solution for low cost, flexible, and easy to integrate RF switches. All the above-mentioned issues can be alleviated if these switches can be simply printed at the place of interest. In this work, we have demonstrated vanadium dioxide (VO2) based RF switches that have been realized through additive manufacturing technologies (inkjet printing and screen printing), which dramatically brings the cost down to a few cents. Also, no soldering or additional attachment step is required as the switch can be simply printed on the RF component. The printed VO2 switches are configured in two types (shunt configuration and series configuration) where both types have been characterized with two activation mechanisms (thermal activation and electrical activation) up to 40 GHz. The measured insertion loss of 1-3 dB, isolation of 20-30 dB, and switching speed of 400 ns are comparable to other non-printed and expensive RF switches. As an application for the printed VO2 switches, a fully printed frequency reconfigurable filter has also been designed in this work. An open-ended dual-mode resonator with meandered loadings has been co-designed with the VO2 switches, resulting in a compact filter with decent insertion loss of 2.6 dB at both switchable frequency bands (4 GHz and 3.75 GHz). Moreover, the filter is flexible and highly immune to the bending effect, which is essential for wearable applications. Finally, a multi-parameter (switch thickness, width, length, temperature) model has been established using a customized artificial neural network (ANN) to achieve a faster simulation speed. The optimized model’s average error and correlation coefficient are only 0.0003 and 0.9905, respectively, which both indicate the model’s high accuracy.

Vanadium is a white bright metal that belongs to group 5 in the periodic table of elements. It can exist in different oxidation states from -2 to +5 although the forms can be found naturally in the environment are (III), (IV) and (V). As vanadium is toxic at high concentrations, and as vanadium is a common contaminant from e.g., steel slags, more detailed knowledge on the environmental behavior of this metal is required. One important property is its sorption to soils, as this will determine the bioavailability and the risk of leaching from soils. In surface soils vanadium(V) is commonly the predominating redox species. Therefore the purpose of this study was to determine vanadium(V) sorption in 7 different soils in order to investigate the factors determining vanadium(V) sorption and to estimate the capacity of the soils to bind vanadium. From laboratory adsorption experiments, vanadium sorption has been studied as a function of pH, vanadium(V) concentration, and phosphorus status. The adsorbed vanadium(V) of investigated soils was compared on the basis of the Freundlich parameters m and log Kf. The clay content of the soil and the content of oxalate soluble iron and aluminum were two important factors for the vanadium(V) sorption behavior. The higher the values of these soil properties, the stronger was vanadium(V) sorption. Among the soils investigated here the sorption strength was highest for the Kungängen A3 soil and then decreased in the following order Säby, Kungsängen D3, Pustnäs, Termunck, Guadalajara and Zwijnaarde. It is notable that the three soils with the strongest vanadium(V) sorption were clay soils, whereas the other four were sandy or silty soils. The pH dependence of vanadium sorption was also determined. The results show that the percentage sorbed vanadium(V) increases with decreasing pH. This is due probably to the anion properties of vanadium(V) (i.e. vanadate) in combination with increased positive surface charge on the soil colloids at lower pH. Moreover there is a competition between phosphate and vanadium(V) for sorption sites, which will cause less vanadium(V) sorption in soils. Therefore both the pH value and the phosphorus status are two additional factors that influence the vanadium sorption properties of soils.

京都大学 / 新制・論文博士 / 博士(工学) / 乙第13403号 / 論工博第4189号 / 新制||工||1761(附属図書館) / (主査)教授 田中 庸裕, 教授 江口 浩一, 教授 阿部 竜 / 学位規則第4条第2項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM