Neste trabalho foram preparados materiais constituídos por Al2O3 e Nb2O5, na forma de grãos esferoidais para serem usados como suporte de catalisadores aplicados à propulsão. Os suportes foram preparados por quatro diferentes métodos: impregnação úmida do óxido de alumínio moldado por uma solução alcoólica de cloreto de nióbio (NbCl5); impregnação seca do óxido de alumínio por uma solução alcoólica de NbCl5; co-precipitação dos precursores de óxido de alumínio e óxido de nióbio; e mistura física dos precursores desses óxidos previamente autoclavados separadamente. Entre esses métodos, os suportes que apresentaram melhores características para aplicação em propulsão a monopropelente hidrazina (N2H4) foram aqueles preparados por mistura física, contendo 20% m/m de óxido de nióbio (Su20MF) e por impregnações secas sucessivas, contendo 10% m/m de óxido de nióbio (Su10IS). A adição do óxido de nióbio ao óxido de alumínio resultou em acentuado aumento da resistência mecânica à compressão, mas não causou variação significativa do número e força dos sítios ácidos de Lewis, em função dos tratamentos de calcinação efetuados a 873 K por 5 horas. Todos os suportes foram impregnados com solução de H2IrCl6 e após tratamentos de redução sob H2, obteve-se catalisadores de irídio suportados, com elevados teores metálicos, CAT-20Ir, contendo aproximadamente 20% m/m de Ir disperso na superfície do suporte Su10IS, e CAT-27Ir, contendo aproximadamente 27% m/m de Ir disperso na superfície do suporte Su20MF. Caracterizações por quimissorção de H2 e por MET/EDS mostraram que o irídio fixou-se quase que exclusivamente sobre o óxido de alumínio, gerando partículas metálicas com diâmetros médios tanto maiores quanto menores as áreas superficiais expostas desse óxido. Testes efetuados em bancada com as reações de decomposição de hidrazina e de amônia revelaram que a reação com hidrazina ocorre de forma completa em temperaturas acima de 393 K, gerando exclusivamente amônia e nitrogênio, enquanto que a decomposição da amônia inicia-se em temperaturas superiores e diferenciadas, dependendo do catalisador. Durante a reação da hidrazina, a reação de decomposição da amônia formada, produzindo hidrogênio foi acompanhada, sendo tanto menor quanto maior o diâmetro médio das partículas de irídio, sendo que a seletividade ao hidrogênio mostrou ser uma função linear do diâmetro médio, ao menos entre 24 Å e 40 Å. Esse comportamento se deve ao fato de que a decomposição da amônia é uma reação sensível à estrutura da fase ativa destes catalisadores. Já os testes efetuados em propulsores de 5 N de empuxo no Banco de Teste com Simulação de Altitude (BTSA), evidenciaram um aumento da temperatura, da pressão de câmara e também da força de empuxo, devido à menor decomposição da amônia e maiores tempos para o início da decomposição da hidrazina, efeito este relacionado ao número específico de sítios ativos presentes nas superfícies dos catalisadores. / In this work were prepared supports consisting of Al2O3 and Nb2O5, in the form of spheroidal grains by four different methods: wet impregnation of the aluminum oxide molded an alcoholic solution of niobium chloride (NbCl5); dry impregnation of aluminum oxide in an alcoholic solution of NbCl5; co-precipitation of the precursor of aluminum oxide and niobium oxide; and physical mixing of precursors of these oxides previously autoclaved separately. Among these methods, the supports that showed the best characteristics for application in propulsion monopropellant hydrazine were those prepared by physical mixture containing 20 wt % niobium oxide (Su20MF) and successive dry impregnations, containing 10 wt % niobium oxide (Su10IS).The addition of niobium oxide in aluminum oxide resulted in a significant increase in compressive strength of these selected supports, but caused no significant change in the number and strength of Lewis acid site, which was attributed to the calcination treatment carried out at 873 K by 5 hours. These supports were impregnated with H2IrCl6 solution and after reduction treatment under H2, were obtained supported iridium catalysts with high metal contents, named CAT-20Ir containing approximately 20 wt % of Ir dispersed on the support Su10IS and CAT-27Ir containing approximately 27 wt % of Ir Su20MF dispersed on the support. Characterization by chemisorption of H2 and by TEM/EDS showed that the iridium was anchored almost exclusively on aluminum oxide, generating metal particles with average diameters greater. Tests carried out in laboratory with decomposition of hydrazine and ammonia revealed that the reaction with hydrazine is completely in temperatures above 393 K, generating only ammonia and nitrogen, while the decomposition of ammonia, the reaction initiation above different temperatures depending on the catalyst. During decomposition hydrazine another accompanied reaction was the decomposition of ammonia generated, producing hydrogen. The selectivity to hydrogen showed to be a linear function of the mean diameter particle of iridium, least between 24 Å and 40 Å , these results were attributed to the fact that the decomposition of ammonia is a sensitive reaction to the structure of the active phase of these catalysts. Tests carried out at the Altitude Simulation Test Facility (BTSA/INPE) showed the following effects caused by Nb2O5 addition to iridium catalyst supports: increase of temperature, chamber pressure and thrust power, due to a smaller ammonia decomposition; and increase of time for hydrazine decomposition when there is an excessive reduction of the specific number of active sites.

Biocatalysis is becoming an increasingly attractive alternative to more traditional chemical transformations for use in pharmaceutical and industrial applications. This interest is primarily a consequence of the high regio-, stereo- and enantioselectivity that is associated with enzyme catalysed reactions. However, the proliferation of such techniques has been limited due to the dependence of enzyme activity upon the presence of redox cofactors, which are typically expensive and must be used in conjunction with efficient regeneration systems. Whilst numerous methods have been described, of particular potential are those that employ exogenous photosensitisers as a means of generating reducing equivalents to promote catalytic turnover. In this study the potential of transition metal complexes as photosensitisers towards the development of light-driven biocatalytic systems is evaluated. Use of such compounds gives great scope towards fine-tuning the spectral and redox properties of the sensitisers with the aim of optimising catalytic efficiency. Detailed herein is an extensive study towards the synthesis and characterisation of a range of ruthenium(II) and iridium(III) coordination compounds. Using NMR, UV-vis, and electrochemical techniques, all complexes were fully characterised and the origins of the photophysical properties further investigated using time-dependent density functional theory (TD-DFT) calculations. A series of ruthenium compounds were synthesised containing the bis(2,2′-bipyrazyl)ruthenium(II) moiety, investigating the impact of changes made to the functionality of the ancillary ligand upon the overall properties of the complex. New synthetic procedures have been developed towards the preparation of both 2,2′-bipyrazine and the related complexes, exhibiting significant benefits over previously established methods. Through manipulating the electron density of the ancillary ligand it is shown that the redox properties may be effectively tuned upon inducing changes in the energy of the metal-based HOMO. The utilisation of cyclometalated iridium(III) complexes in aqueous systems has been limited due to a poor water solubility that is typically associated with these compounds. Herein it is demonstrated that this issue may be effectively circumvented on inclusion of the positively charged pyridinium moiety. Upon incorporation of this functional group into either the cyclometalating or ancillary ligands, two distinct series of compounds were successfully prepared. Complexes of the substituted quaterpyridinium ligands possess complicated UV-vis spectra that exhibit low intensity absorbance up to 650 nm. A number of monoquaternised bipyridinium compounds were also utilised as pyridine derived N-heterocyclic carbene cyclometalating ligands, to afford a range of complexes with unique redox properties. The prepared photosensitisers were subsequently used to induce catalytic turnover in light-driven biocatalytic systems utilising the flavin dependent oxidoreductase enzymes, pentaerythritol tetranitrate reductase (PETNR) and the thermophilic old yellow enzyme (TOYE). Through an extensive investigation, optimal reaction conditions have been identified and a mechanism of electron transfer proposed. These systems were successfully implemented in the reduction of a broad range of substrates under both aqueous and biphasic conditions, delivering yields and enantiomeric excesses comparable to those obtained utilising an enzyme coupled regeneration system. This study clearly demonstrates that transition metal complexes are excellent candidates in developing practical light-driven biocatalytic systems. It is expected that, with further investigation, this approach can be readily expanded to incorporate a variety of applications and provide an effective alternative to the use of costly redox cofactors and a reliance upon complex regeneration techniques.

Copper under-potential deposition (UPD) on iridium was studied due to important implications it presents to the semiconductor industry. Copper UPD allows controlled superfilling on sub-micrometer trenches; iridium has characteristics to prevent copper interconnect penetration into the surrounding dielectric. Copper UPD is not favored on iridium oxides but data shows copper over-potential deposition when lower oxidation state Ir oxide is formed. Effect of anions in solution on silver UPD at platinum (Pt) electrodes was studied with the electrochemical quartz crystal microbalance. Silver UPD forms about one monolayer in the three different electrolytes employed. When phosphoric acid is used, silver oxide growth is identified due to presence of low coverage hydrous oxide species at potentials prior to the monolayer oxide region oxide region.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22455号 / 工博第4716号 / 新制||工||1737(附属図書館) / 京都大学大学院工学研究科材料化学専攻 / (主査)教授 中尾 佳亮, 教授 松原 誠二郎, 教授 杉野目 道紀 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Samouspořádání organických molekul je spontánní proces tvorby nanostruktur, při kterém je výsledná struktura určena mezimolekulárními and molekulárně-substrátovými interakcemi. Pochopení principů samouspořádávání je klíčem k přípravě funkčních nanostruktur s atomární přesností. Tato diplomová práce se zaměřuje na přípravu a studium samouspořádaných molekulárních struktur 4,4’-diphenyl dikarboxylové kyseliny na povrchu grafenu připraveného na Ir(111). Pro studium vlastností molekulárních struktur je využito rastrovací tunelovací mikroskopie a nízkoenergiové elektronové mikroskopie. Tato kombinace umožňuje získat informace z oblastí o velikosti v řádu nanometrů až milimetrů. V práci je popsána molekulární strukuktura stabilní při pokojové teplotě. Vazebný motiv této struktury je dán interakcí karboxylových skupin sousedních molekul.

This master’s thesis extends the teaching possibilities of the course “Building automation” in two areas. The first area is the visualization of KNX educational panel, which is made through iRidium software package in several variants. The second area is the design and manufacture of the educational switch panel with different types of switches, in which students can simply try wiring, which are commonly used mainly in civil engineering. Part of the second area is the creation of several teaching tasks.

Several applications require the detection of terrestrial UV-C signatures. Efficiency, compactness, environmentally friendly and cost-effective requirements for UV-C–detectors resulted in a research interest in wide-bandgap (WBG) semiconductor-based photovoltaic diodes with a 280 nm cut-off wavelength. Advances in producing group-III-nitride materials allowed the growth of high quality Al[x]Ga[1−x]N, a direct-WBG ternary semiconductor in which the Al mole fraction (x) could be varied, allowing for a tuneable bandgap that made the semiconductor intrinsically 'blind' to longer wavelengths and responsive to selected wavelengths shorter than 360 nm. This dissertation reports on the development and characterization of a tuneable AlGaN-based solar-blind UV-sensitive Schottky photodiode. A fabrication procedure was established using optimized metallization techniques derived from literature. This included metallization schemes, metal thicknesses and annealing methods for metallization of both the ohmic and Schottky contacts for a front-irradiated photodiode. Characterization was done with a newly constructed optoelectronic characterization system. Electrical characterization was performed inside a light-tight shielded enclosure and a software routine aided in applying current–voltage and capacitance–voltage measurements on a Schottky diode. Spectral characterization made use of either a UV source or a visible-to-near-infrared source that was coupled to a monochromator that allowed for wavelength selection. The monochromatic electromagnetic radiation was guided by an optical fibre from the monochromator into the enclosure where the photodiode was irradiated. An additional software routine was developed that allowed for the automation of the spectral characterization. The system was calibrated against standards traceable to the National Institute of Standards and Technology (NIST) by following the photodetector substitution method. The study concluded with the manufacturing of an epoxy wire-bonded front-irradiated four-quadrant detector that was mounted on a commercial microchip carrier. Metal depositions were done through physical contact masks. The quadrants were surrounded with optimized layered ohmic contacts and a quadrant consisted of a thin-film iridium(IV) oxide (IrO₂) as Schottky contact that is UV transmissive with a Au contact on top to which a wire was bonded. Optoelectronic characterization verified that the four-quadrant detector was intrinsically solar-blind and showed good uniformity across the quadrants. Electrical parameters obtained included an average ideality factor of 1.97 ± 0.09, a Schottky barrier height of (1.22 ± 0.08) eV, a reverse leakage current density of (2.1 ± 3.3) nA/cm² and a series resistance of (120 ± 30) Ω. Spectral parameters obtained included a (275 ± 5) nm cut-off wavelength, an average current responsivity at 250 nm of (28 ± 1.0) mA/W with a quantum efficiency of (14 ± 0.5) % and an UV-to-visible and near-infrared rejection ratio between 10³ and 10⁵ for 400 nm to 1100 nm wavelengths. These characteristics allowed for the detector to be used in demonstrating a working solar-blind UV-sensitive electro-optic device. / Dissertation (MSc)--University of Pretoria, 2015. / Physics / Unrestricted

The lack of catalytic efficiency towards the complete ethanol oxidation reaction (EOR) has hindered the development of direct ethanol fuel cells (DEFCs). Ir-based catalysts have recently been shown promise in the complete EOR. However, the reaction mechanism of the complete EOR remains unclear, which impedes the development of better Ir-based catalysts. Herein, we performed extensive density functional theory (DFT) calculations to develop a comprehensive reaction network of EOR on Ir(100). The EOR process consists of four dehydrogenation steps of ethanol leading to the generation of CH2CO species followed by two competitive reaction pathways, i.e., a C-O bond cleavage to poisoning species (e.g., CHC) and the surface diffusion of CH2CO leading to CO2. Furthermore, our studies show that for all CHxCOy (x = 1, 2, or 3 and y = 0 or 1) species, only when the C and O atoms (or two C atoms) bind to two different surface Ir atoms can the C-C/C-O bond cleavage occur. This work highlights the essential roles of adsorption structure and diffusion of CH2CO for the complete EOR and serves as a benchmark for the future investigation of the electronic and solvent effects.Pt-Ir-based alloy electrocatalysts have shown encouraging catalytic performance on the EOR in direct ethanol fuel cells. Nevertheless, designing a suitably qualified EOR electrocatalyst remains challenging because of several convoluted factors (e.g., C1 species poisoning, acetate acid formation, and C-C bond splitting). To understand the relationship between the EOR performance and the type of catalysts, we model three kinds of (100)-exposed Pt-Ir layered catalysts and perform density functional theory (DFT) calculations to explore 58 elementary reactions of the EOR over three catalyst surfaces. According to the calculated activation energies and reaction energies, we mapped out the reaction mechanisms for EOR on different catalysts, indicating corresponding rate-limiting steps (RLSs) of the complete EOR. We demonstrated that the C-O coupling/decoupling ability of the catalyst surface plays a leading role in the overall EOR performance because a perfect complete EOR not only has to avoid some C-O coupling reactions (e.g., CH¬3CO+OH→CH3COOH) but also needs to promote some C-O coupling reactions (e.g., CO+O→CO2). We further illustrated that Pt and Ir exhibit excellent C-O coupling and decoupling abilities, respectively, implying that modifying the compositions and structures of Pt-Ir catalysts is a promising way to achieve the complete EOR. Furthermore, the Ir@Pt(100) surface (Ir monolayer over Pt(100) surface) with a Pt-doped active site possesses the most significant potential on EOR, which could impede the acetate acid formation and facilitate the CO2 formation simultaneously. This work highlights the role of tuning the C-O coupling/decoupling ability of electrocatalyst in EOR activity, providing a new strategy for designing and selecting the EOR electrocatalyst. The solvent effect has always been a non-negligible factor for aqueous reactions. In computational chemistry, researchers have been looking for a compromise between computational efficiency and the rationality of solvent models to mimic the solvent environment. In this work, I investigated the ethanol dehydrogenation and C-C bond cleavages of EOR over Ir(100)using both implicit and explicit solvation models. The implicit model exhibited little impact on the adsorbates without the hydroxyl group, whereas the explicit model can reasonably describe the system’s hydrogen bonding and van der Waals interaction. This solvent effect study showed how different solvent models affected the elementary reactions geometrically and energetically.

Interference effects of co-generated hydrides of arsenic, antimony, bismuth and selenium on trapping behavior of selenium or antimony hydrides (analytes) within iridium modified, transversely heated graphite tube atomizer (THGA) was investigated. A twin-channel hydride generation system was used for independent separate generation and introduction of analyte and interferent hydrides, i.e. in simultaneous and/or sequential analyte-interferent and interferent-analyte mode of operation. Influence of the analyte and modifier mass, interferent amount, trapping temperature and composition of the gaseous phase was studied. A simple approach for elimination of mutual interference effects by modification of the gaseous phase with oxygen in substoichiometric ratio to chemically generated hydrogen is proposed and suppression of these interference effects is demonstrated. A hypothesis on mechanism of trapping and mutual interference effects is drawn.

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