Rozprawy doktorskie na temat „Platinum Dioxide”

Proton exchange membrane fuel cells are one of the most promising hydrogen energy conversion devices for portable, mobile and stationary applications. For wide spread usage to produce electricity platinum loading has to be decreased by using highly active electrocatalysts. Even 10 ppm carbon monoxide or higher than 30% carbon dioxide cause performance losses via deactivation which can be diminished by using binary catalysts. The aim of this thesis is to develop new platinum based electrocatalysts with high catalytic activity and to overcome the problems due to the deactivation. platinum and platinum-ruthenium based catalysts on different carbon supports have been prepared by supercritical carbon dioxide deposition and microwave irradiation methods. By using supercritical carbon dioxide deposition platinum on Vulcan XC72R (VXR), multi wall carbon nanotube (MWCNT) and Black Pearl 2000 (BP2000) catalysts were prepared and characterized by XRD, TEM and cyclic voltammetry (CV). XRD results showed that in catalysts prepared by using supercritical carbon dioxide deposition method, the particle sizes as low as 1-2 nm can be obtained. From the CV results the electrochemical surface areas obtained were Platinum/VXR>
Platinum/MWCNT>
PlatinumBP2000. By means of the oxygen reduction reaction (ORR), the number of electrons transferred per oxygen molecule was calculated as 3.5, 3.6 and 3.7 for Platinum/BP2000, Platinum/VXR and Platinum/MWCNT, respectively. The microwave irradiation was used to prepare platinum on VX, Regal and BP2000 and platinum-ruthenium on VX. The effects of microwave duration, base concentration, carbon support used and surfactant/precursor ratios were investigated. The particle sizes of the catalysts were ranging between 2-6 nm. The prepared catalysts were characterized by XRD, XPS, and then PEMFC tests were performed. The performance was ordered as Platinum/VX>
Platinum/Regal>
Platinum/BP2000. The power losses arising from carbon dioxide in hydrogen feed were decreased by using prepared platinum-ruthenium based catalysts.

The aim of this study is to test the limits of photocatalytic reduction of CO2 over Pt and light harvesting dye promoted TiO2 films under UV and visible light. Thick and thin TiO2 film catalysts are coated onto 1 cm long glass beads via a common sol-gel procedure and dip coating technique. TiO2 thin films were promoted by Pt and three different light harvesting molecules: RuBpy (Tris (2,2&rsquo
&ndash
bipyridyl) ruthenium (II) chloride hexahydrate) , BrGly (1,7-dibromo-N,N&rsquo
-(t-butoxycarbonyl-methyl)-3,4:9,10-perylene-diimide) and BrAsp (1,7-dibromo-N,N&rsquo
-(S-(1-t-butoxy-carbonyl-2-t-butoxycarbonyl-methyl)-ethyl)- 3,4:9,10-perylenediimide). Their SEM, XRD, UV-Vis spectroscopy and hydrogen chemisorption characterizations are performed. Reaction tests are performed for the catalysts under UV and visible light. The only quantifiable reaction product was methane. With RuBpy containing catalysts hydrogen production was observed under UV light, but not quantified. The results indicated that Pt addition resulted in higher yields in UV experiments. The presence of light harvesting molecules resulted in increase in photocatalytic activity for thin films, whereas it resulted in no change or decrease for the thick films. The latter case may occur due to the UV filtering effect of these dyes. Use of dyes (with visible range absorption bands) as promoters made visible light excitation possible. This resulted in photocatalytic activity under visible light, which was not observed with unpromoted and Pt promoted TiO2 thin film catalysts. Under visible light methane was the only quantified photoreduction product. CO evolution was also observed, but not quantified. The photocatalytic activities of the dye promoted TiO2 were in the order of RuBpy~BrAsp>
BrGly. The methane yields of visible light experiments were one order of magnitude lower than the ones under UV light.

Incorporation of magnetic microparticles (~ 1 um) at electrode structures increases electron transfer e¢ ciency, observed as increased current, for multiple electrochemical systems. Current increases occur with magnetic field. Inclusion of magnetic materials into the cathode matrix of alkaline MnO2 batteries requires the materials to be stable in the strong base electrolyte, typically 6 to 9 M KOH. Samarium cobalt magnetic particles sustain strong permanent magnetic fields and are stable in base without surface modification. Studies were undertaken at fast (C/2), moderate (C/3), and slow (C/5) constant current discharges. Here, alkaline MnO2 batteries generated increased power and energy when magnetic microparticles are incorporated into the cathode of the battery. Because of anode limitations in the battery, total coulombic output is not increased for the first electron discharge, but the available power and energy is significantly higher compared to nonmagnetic batteries at voltages above 0.9V. Constant current discharge curves of magnetic batteries demonstrate higher voltages than nonmagnetic batteries at a given time, which translates to greater power output. This effect is also observed by electrochemical impedance spectroscopy, where charge transfer resistance is less for magnetically modified cells. This work also developed voltammetric measurement protocols for acetone concentration collected in the liquid and vapor phase and measured in solution. Acetone on the breath is an indicator for physiological dysregulation. Measurements are demonstrated for acetone concentrations across the human physiological range, 1 uM to 10 mM at platinum electrodes in 0.5 M H2SO4. Effects arise through adsorption of acetone from the gas phase onto a platinum surface and hydrogen in acidic solution within the voltammetric butterfly region. The protocol is demonstrated to yield breath acetone concentration on a human subject within the physiological range and consistent with ketone urine test strip.

The photocatalytic production of H2 from water as well as from a 1:1 methanol:water solution employing pre–treated TiO2 and various Pt–TiO2 photocatalysts was studied by using an Nd:YAG laser as irradiation source. The photocatalysts (0.5–, 1–, 1.5– and 2 wt% Pt–TiO2) were prepared by utilizing a photocatalytic reduction method after which characterisation by various analytical techniques, i.e. XRD, TEM, ICP, SEM, and EDX, were conducted. XRD clearly indicated that platinum was not present in the crystal structure of TiO2, but was rather loaded onto the surface of TiO2. TEM analysis confirmed the presence of Pt on the surface with a particle/cluster size between 11 nm and 22 nm. SEM showed that repeatable results in respect of surface appearance were obtained. ICP and EDX indicated that the loading method was successful with only a slight deviation between the actual amount loaded and the calculated amount loaded. The impact of the loaded Pt on the band gaps of the different photocatalysts was investigated by diffuse reflectance spectroscopy (DRS) and calculated by employing the Kubelka–Munk method. The band gap values shifted sequentially from 3.236eV to 3.100 eV as the loading increased, moving closer to the absorbance region for visible light. The amount of hydrogen produced from the individual photocatalysts dispersed in both pure water and aqueous methanol solutions, was measured manually with a gas chromatograph. As soon as irradiation was initiated, a distinct colour change from shades of grey to dark blue–grey was observed for all the photocatalysts. XRD confirmed that it was due to the anatase phase transforming to produce more rutile phase. No H2 was detected for the various photocatalysts suspended in water, i.e. in the absence of methanol. The amount of hydrogen produced from the various Pt photocatalysts suspended in the aqueous methanol solution was found to be the highest for the 0.5wt%– and 1.5wt% Pt–TiO2 photocatalysts and the lowest for the 2wt% Pt–TiO2. This could be due to loading Pt above the optimum amount to such an extent, preventing sufficient light from reaching the TiO2 surface. Pt particles can also touch and overlap which will decrease Pt contact with TiO2 thus decreasing effective charge transfer.
Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2012.

Orientador: Edson Tomaz
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química
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Resumo: Compostos orgânicos voláteis, ou COV, são uma importante classe de poluentes do ar comumente encontrados na atmosfera ao nível do solo, nos centros urbanos e industriais. O tratamento de COV provenientes de fontes industriais através da fotocatálise heterogênea é uma técnica eficiente para a degradação de baixas concentrações de uma grande gama de compostos orgânicos diferentes (hidrocarbonetos, aromáticos, alcóois, cetonas, etc) operando em condições ambientes. Um dos problemas que ainda impede sua aplicação industrial é a desativação do catalisador e por isso muitos grupos de pesquisa têm se dedicado ao estudo desta técnica na tentativa de melhorá-la e solucionar estes entraves. A atividade fotocatalítica do TiO2 pode ser melhorada pela adição de metais na sua superfície. Neste trabalho, preparou-se catalisadores de TiO2 por impregnação de Pt (1% m/m). A platina foi reduzida com NaBH4, fazendo-se posteriormente caracterização por DRX, XPS, UV ¿Vis, BET, Quimissorção de H2 e MEV/EDS para a validação do método de síntese. Todas as técnicas confirmaram que o método de redução com NaBH4 não modifica estruturalmente o TiO2, mantendo a sua cristalinidade e a razão de anatase/rutilo. A técnica de XPS indicou a presença de metal em estado de oxidação reduzido. Para o estudo da influência da impregnação de Pt no óxido titânio, foram realizados experimentos de fotocatálise em um reator recoberto com TiO2puro, e em um reator recoberto com TiO2/Pt variando-se a concentração de entrada (de 50 à 500 ppmv) ou o tempo de residência (de 10 à 50 s) para os COV n-octano, iso-octano, n-hexano e ciclohexano. Utilizou-se reatores tubulares com volume interno de 1160 ml com os catalisadores, dióxido de titânio puro ou modificado, imobilizados na parede interna dos reatores. A fonte de radiação UV foi uma lâmpada do tipo germicida de 100W de potência, caracterizada por comprimentos de onda de 254 nm (banda de emissão UV-C). As concentrações na entrada e na saída do reator foram analisadas através de um monitor contínuo de hidrocarbonetos do tipo FID. A adição de platina ao TiO2 gera uma melhoria na eficiência fotocatalítica nas reações de oxidação de COV; a conversão dos COV utilizando o catalisador impregnado com platina atingiu 99 % de conversão, enquanto que TiO2 puro atingiu, no máximo 93%
Abstract: Volatile organic compounds, or VOC, are an important class of air pollutants commonly found in the atmosphere at ground level in urban and industrial centers. The treatment of VOC from industrial sources by oxidative photodegradation is presented as a good alternative. These systems are promising as pollution control technology, since they can decompose low concentrations of VOC efficiently and in ambient conditions. The recombination of electrons and holes formed on the surface of TiO2 is a factor that limits the photocatalytic efficiency. For this reason, many efforts have been made to maximize the separation of charges, in order to improve the photocatalytic efficiency. A proposed alternative is to add noble metals to TiO2 structure. This work aims to study the degradation of volatile organic compounds by heterogeneous photocatalytic oxidation using ultraviolet light, bare TiO2 and TiO2 impregnated with 1% w/w platinum as catalysts. TiO2 catalysts were prepared by impregnating Pt on TiO2 structure by reduction method with NaBH4. The photocatalysts were characterized using analytical techniques like XRD, XPS, UV-Vis Diffuse Reflectance, BET, H2 Chemisorption and SEM/EDS to validate the method of synthesis. All analysis confirmed that the reduction method with NaBH4 do not structurally modify TiO2, keeping its crystallinity and the ratio of anatase/rutile. XPS indicates the presence of metal in reduced oxidation state. To study the influence of the impregnation of platinum on titania, after synthesis and characterization, the study of gas-solid heterogeneous photocatalytic oxidation of some VOC was carried out at room temperature with annular plug flow reactors (1160 ml), one coated with pure TiO2 and another coated with TiO2/Pt, the catalysts were immobilized on reactor¿s internal walls. The photocatalystic tests were performed for n-octane , iso-octane, n-hexane and ciclohexane varying the inlet concentration (from 50 to 500 ppm) or residence time (from 10 to 50 s). The light source was an UV lamp (100 W, wavelengths with a maximum intensity at 254 nm. Reactants and products concentrations were analyzed using a continuous monitoring with a total hydrocarbon analyzer with flame ionization detector (FID). The addition of platinum to TiO2 improves photocatalytic efficiency of oxidation of VOC; conversion of the VOC using impregnated catalyst reached 99%, whereas pure TiO2 was at most 93%. No título do trabalho, a fórmula TiO2 deve vir com o "2" em subscrito, pois trata-se da fómula química da substância
Mestrado
Processos em Tecnologia Química
Mestra em Engenharia Química

The gradual depletion of and dependence on fossil fuels, air pollution and global warming have all accelerated the development of alternative energy systems which use hydrogen as an energy carrier. The hybrid sulphur cycle (HyS) is the foremost electrothermochemical process that can produce hydrogen as the energy carrier. The HyS cycle consists of two units, namely the sulphuric acid decomposition reactor and the sulphur dioxide electrolyser (SDE). The SDE is responsible for the SO2 electrooxidation to sulphuric acid and protons at the anode and the electro–reduction of protons to hydrogen at the cathode. This research study focuses on the kinetic data collected from the prepared catalysts for SO2 electro–oxidation at the anode. Platinum dispersed on carbon, niobium pentoxide, tantalum pentoxide and zirconium dioxide as electrocatalysts were prepared using sodium borohydride as a reducing agent. These electrocatalysts were characterized using transmission electron microscopy and x–ray diffraction. Cyclic voltammetry was used to study the electrochemical active surface area (EAS) and the results showed that Pt/ZrO2–C had a higher EAS area than Pt/Ta2O5–C, Pt/Nb2O5–C and Pt/C. The high EAS of Pt/ZrO2–C can be explained by the low crystal size however after a series of linear polarisation scans Pt/ZrO2–C experiences a much greater area loss than all the other catalysts. Linear polarisation scans for each of the catalysts revealed that the influence of increased temperature and sulphuric acid concentration were showed improved results. Levich and Koutecky–Levich plots revealed that the SO2 oxidation is a multistep reaction on all the prepared catalysts and that there are regions which are kinetic and diffusion controlled and diffusion–only controlled. Pt/Ta2O5–C catalysts exhibited superior catalytic activity and stability compared Pt/Nb2O5–C, Pt/ZrO2–C and Pt/C. The Pt/ZrO2–C exhibited the most inferior catalytic activity and stability.
Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2011.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Le travail de thèse propose d’éclaircir les dynamiques qui régissent les réactions d’hydrogénation du dioxyde d’azote (NO2) se déroulant à la surface de catalyseurs modèles de platine, de rhodium et de leur alliage Pt-Rh. Une meilleure compréhension de la réaction catalytique en conditions réactionnelles permettrait, à terme, un meilleur contrôle de la réaction. De manière similaire, le comportement du catalyseur permettrait d’orienter la synthèse de catalyseurs afin d’en augmenter la sélectivité et/ou activité. La structure de ces catalyseurs ainsi que l’analyse des processus sont effectuées à l’échelle nanométrique grâce à l’utilisation de microscopies à effet de champ :la microscopie ionique à effet de champ (FIM) et la microscopie d’émission d’électrons par effet de champ (FEM). La réaction NO2+H2 étudiée à 390 K sur le platine permet de mettre en évidence la présence de différents domaines réactionnels :dynamique monostable, oscillations périodiques auto-entretenues, oscillations périodiques bimodales, ainsi que des oscillations bruitées. Malgré la présence importante de fluctuations à l’échelle du nanomètre, les traitements de signaux mettent en évidence une importante robustesse qui se traduit par un temps de corrélation qui s’étend sur plusieurs centaines de périodes. Les données donnent matière à la reconstruction de l’attracteur dynamique consistant en un cycle limite. La pression d’hydrogène est le paramètre de contrôle qui est varié de sorte à provoquer l’apparition d’oscillations selon une bifurcation de type homocline dans ce cas-ci. Des mesures à haute-vitesse d’acquisition démontrent que l’ignition des différentes faces réactives s’effectue de manière désynchronisée, et la vitesse de propagation est de l’ordre de ~2 μm/s. Au sein d’une seule face, à l’échelle du nanomètre, des propagations de fronts d’ondes chimiques peuvent également être observées à une vitesse de ~2 μm/s, en accord avec les vitesses analysées lors d’expériences menées à l’échelle du micromètre et du millimètre. Sur base des observations, un mécanisme réactionnel de production d’H2O a été proposé. La réaction sur le rhodium à 450 K engendre également des oscillations périodiques qui diffèrent par une robustesse plus faible et par l’apparition d’un cycle limite selon une bifurcation de Hopf. Des mesures exploratoires à 500 K font ressortir la présence de chaos dans le système. Finalement, l’alliage Pt-Rh utilisé comme catalyseur permet d’obtenir des oscillations à 425 K de période comprise entre celles observées sur les deux métaux purs. L’ensemble des expériences et des résultats obtenus à l’échelle du nanomètre permet pour la première fois de valider la théorie des systèmes dynamiques à une telle échelle.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

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Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Le combustible usé contient de nombreux produits de fission dont les éléments platinoïdes (Ru, Rh et Pd) et le molybdène. Ces produits de fission se retrouvent essentiellement dans le combustible usé sous forme de précipités métalliques. La première étape du retraitement est la dissolution du combustible en milieu acide nitrique concentré. Ce travail de thèse vise à déterminer l’impact de ces éléments, incorporés sous forme de particules métalliques au sein de la matrice UO2, sur la cinétique et les mécanismes de la dissolution. Dans ce cadre, plusieurs systèmes modèles à base de UO2 incorporant chaque élément platinoïde et le molybdène à hauteur de 3 % molaires ont été synthétisés par voie humide. Pour chaque système, des pastilles denses et de microstructure proche de celle du combustible usé ont été préparées par frittage à haute température sous atmosphère réductrice, puis caractérisées. L’étude de la dissolution des composés modèles a été menée dans les conditions de retraitement des combustibles usés afin de quantifier l’effet de la présence des éléments platinoïdes et du molybdène sur la vitesse de dissolution de UO2. Des expériences de dissolution à l’échelle macroscopique ont été réalisées ainsi que le suivi operando de l’évolution de l’interface solide/liquide par MEBE. Des expériences de dissolution des composés modèles ont également été réalisées dans des conditions plus douces et adaptées à la mise en évidence des mécanismes impliquant ces éléments. L’ensemble des résultats obtenus a permis de comparer l’influence des éléments d’intérêt et de mettre en évidence leur différents modes d’action au cours de la dissolution de la matrice UO2 en milieu acide nitrique
Although a spent nuclear fuel is composed of about 96 wt. % of UO2, its composition and microstructure display an extreme complexity due to the presence of more than 30 fission products. Fission products found as metallic precipitates are mainly composed of the noble metals Ru, Rh, Pd, Mo (platinium group metals = PGM's). The first step of the spent nuclear fuel reprocessing is the dissolution in a concentrated nitric acid solution. In this context, this Ph. D. work focuses on the impact of these elements on the kinetics of dissolution of the UO2 matrix. Model samples of UO2 incorporating 3 mol. % of Ru, Rh, Pd or Mo were prepared using a wet chemistry route, then were sintered at high temperature under reducing atmosphere. The speciation, morphology as well as the spatial distribution of the elements in the sintered samples were determined. The pellets exhibited similar microstructure. Then, the synthesized samples were submitted to dissolution tests in order to quantify the impact of the presence of the metallic particles on the dissolution rate of UO2. Dissolution experiments were carried out under conditions representative of the reprocessing of SNF. The dissolution rate of each model compound was determined at macroscopic scale and compared to that of UO2. At microscopic scale, the evolution of the solid/liquid interface was monitored by MEBE. Additionally, specific dissolution experiments were designed to identify the mechanisms involving these elements. The obtained results allows to compare the influence of each element of interest and to improve our understanding of their specific role during the dissolution of UO2 in nitric acid. dissolution in a hydrochloric medium will also be carried out to erase the impact of nitrate ions on the dissolution

La production de l'hydrogène à partir de biomasse est actuellement à l'étude mais la méthode de valorisation du biogaz (mélange H2/CO2) par réactions catalytiques, autres que la simple combustion, n'a pas encore été retenue. Par conséquent, le principal objectif de ce travail est d'explorer les autres voies. L'effet du CO2 sur le système catalytique est mal connu et seulement un effet négatif sur la dissociation de l'hydrogène a été mentionné. L'hydrogénation du toluène sur un catalyseur Pt a d'abord été étudiée sans CO2 pour suivre son comportement et éventuellement sa perte d'activité. En présence de CO2, l'inactivité complète du catalyseur pour l'hydrogénation du toluène a été mis en évidence. La modification de la surface du catalyseur par le CO2 est quantifiée par DRIFT et un mécanisme à deux sites a été montré. La réaction de Reverse Water Gas Shift produisant du CO se trouve être la principale cause de la désactivation de la surface de catalyseur avec le CO2. Donc la compétition d'adsorption entre le CO et des acides carboxyliques a été mise à profit pour favoriser sélectivement la conversion des acides. Pour l'alumine, elle est polluée par des carbonates complexes venant du CO2. La silice étant aussi connue pour promouvoir la décomposition, ces supports ont été rejetés. L'oxyde de titane a été utilisé pour catalyser une autre gamme de produits. Sur ce catalyseur, le changement de sélectivité entre le RWGS et la conversion de l'acide a été observé. Quant à l'oxyde de fer (catalyseur moins actif), il n’est pas capable de produire du CO à partir du CO2. La chimie de surface de l'oxyde de fer joue un rôle important sur la sélectivité du produit parmi les cétones et les aldéhydes. Un mécanisme à deux sites peut réutiliser pour l'oxyde de fer, montrant qu'un fonctionnement stable peut être trouvé si la réduction par l'hydrogène est continue. Si l'oxyde de fer est totalement oxydé par le CO2, produit de réaction, la production des cétones cesse. Énergiquement, le procédé de production d'acétone peut être autosuffisant et l'acétone peut être utilisée comme une molécule de stockage d'énergie. Le procédé va aussi compenser le nouveau procédé de production de phénol qui ne produit pas l'acétone
Hydrogen potential from biomass is currently being studied but ways of valorization of such biogas (H2/CO2 mix) via catalytic reaction, other than simply burning has not yet been considered. Thus the main objective of this work is the exploration of such methods. Effect of CO2 over catalytic system was not well known and only hydrogen dissociation inhibition is reported. Toluene hydrogenation over Pt catalyst is studied and activity loss transition behavior is observed with no CO2 where as complete catalyst inactivity for toluene hydrogenation is found in presence of CO2. Catalyst surface change by CO2 is quantified by DRIFT analysis and two-site mechanism is found to prevail. Reverse water gas shift reaction producing CO is found to be the main cause behind such catalyst surface response to CO2. Adsorption competition between CO and carboxylic acids is exploited for selectivity shift in favor of acids conversion. Alumina support is fouled by carbonates complexes with CO2 while silica is reported to promote decomposition, thus both were rejected and titanium oxide is used instead with a range of products produced. The required selectivity shift between reverse water gas shift and acid conversion is thus observed. Less active iron oxide catalyst further suppresses CO2 conversion. Iron oxide surface chemistry plays an important role over product selectivity among ketones and aldehydes. Two sites mechanism still prevails over iron and stable continuous operation requires simultaneous iron reduction via hydrogen, if totally oxidized by CO2–a reaction product, will cease to produce ketones. Energetically the process devised for acetone production is self sufficient and acetone not only act as an energy storage molecule but can also compensate new phenol production process producing no acetone

2011/2012
The present work pertains to the surface science approach to heterogeneous catalysis. In particular model systems for CO2 hydrogenation to methanol, and NO selective catalytic reduction, are investigated by means of a combined approach, where the molecular-level insight provided by a low-temperature scanning tunneling microscope is complemented by density functional theory (DFT) calculations of their electronic structure. To this end, the Inelastic Electron Tunneling Spectroscopy (STM-IETS) technique was introduced for the first time in our laboratory, a recent development which allows to measure the vibrational spectrum of individual molecules adsorbed on a surface. Regarding CO2, we provide single molecule imaging and characterization of CO2/Ni(110), chemisorbed with high charge transfer from the substrate, in an activated state that plays a crucial role in the hydrogenation process. We obtain a detailed characterization of the adsorption geometries and an estimate of the energies corresponding to the different adsorbed states. A consistent picture of CO2 chemisorption on Ni(110) is provided on the basis of the newly available information, yielding a deeper insight into the previously existing spectroscopic and theoretical data. In the Selective Catalytic Reduction (SCR) process, nitrogen oxide is selectively transformed to N2 by reductants such as ammonia. The specificity of this reaction was tentatively attributed to the formation of NH3-NO coadsorption complexes, as indicated by several surface science techniques. Here we characterize the NH3-NO complex at the atomic scale on the (111) surface of platinum, investigating the intermolecular interactions that tune the selectivity. The structures that arise upon coadsorption of NH3 and NO are analyzed in terms of adsorption sites, geometry, energetics and charge rearrangement. An ordered 2 × 2 adlayer forms, where the two molecules are arranged in a configuration that maximizes mutual interactions. In this structure, NH3 adsorbs on top and NO on fcc-hollow sites, leading to a cohesional stabilization of the extended layer by 0.29 eV/unit cell. The calculated vibrational energies of the individually-adsorbed species and of the coadsorption structure fit the experimental values found in literature within less than 6%. The characterizations and optimizations that had to be tackled in order to successfully perform STM-IETS measurement are eventually presented, focusing in particular on an original method which allows to increase the achieved resolution. Namely, the modulation broadening associated to phase-sensitive detection is reduced by employing a tailored modulation function, different from the commonly-used sinusoid. This method is not limited to STM-IETS, but can be easily applied whenever a lock-in amplifier is used to measure a second derivative.
XXV Ciclo
1984

South Africa ratified the Stockholm Convention (SC), which became legally binding on 17 May 2004. This Convention targets 12 particularly toxic persistent organic pollutants (POPs) for virtual elimination. The Convention also requires parties to reduce the release of organochlorine pesticides and the intentionally- and unintentionally-produced POPs such as dioxins, furans and polychlorinated biphenyls (PCBs) (referred to as dioxin-like chemicals). Dioxins are a heterogeneous mixture of chlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) congeners. These substances were never intentionally produced but are produced as by-products of industrial processes (such as metallurgical processes and bleaching of paper pulp). They can also be formed during natural processes such as volcanic eruptions and forest fires. The largest contributor to releases of PCDD/Fs in the environment is incomplete combustion from waste incinerators leading to the unintentional production of these compounds. Polychlorinated biphenyls (PCBs) are used in transformers and capacitors, but can also be formed unintentionally during industrial and thermal processes. Dioxin-like chemicals (PCDD/Fs and/or PCBs) are classified as persistent because of the following characteristics: lipophilicity and hydrophobicity; resistance to photolytic, chemical and biological degradation and they are able to travel long distances. As South Africa is a semiarid region, POPs will be less prone to travel here because these substances favour colder regions with high soil organic matter. Fish, predatory birds, mammals (including humans) absorb high concentrations of POPs through the process of bio-concentration, leading to bio-accumulation of these substances in the fatty tissue. PCDD/Fs occur as unwanted trace contaminants in air, water, land, in residues and products (such as consumer goods e.g. paper and textiles). The distribution of these chemicals into various matrices is problematic since they cause damage to the environment and human health. These chemicals pose a threat to human health when found in high concentrations that may lead to acute hepatoxicity and dermal toxicity (chloracne). Long-term exposure to low concentrations of these substances might lead to chronic effects such as reproductive problems and carcinogenicity. Since ferrous and non-ferrous metal production is a source of dioxin-like chemicals, a platinum mine in the Limpopo Province, South Africa, was selected for this investigation. The aim of the study was to determine if there are dioxin-like chemicals associated with platinum mining and processing, and if the H4IIE reporter gene bio-assay could be used to semi-quantify and assess the potencies of the complex environmental and process samples by determining their Toxic Equivalency Quotients (TEQ). The implications of the sources to the formation of dioxin-like chemicals regarding the SC were investigated and recommendations were made to improve this study. Samples were collected from tailings dams, woodchips, a dumpsite and slag from the smelter at Union Section. Samples were extracted with the Soxhlet apparatus using hexane as solvent. The percentage total organic carbon (%TOC) was determined for each sample to normalise the data. The method used was the Walkley-Black method. In determining the TEQ of each sample, the H4IIE luc cell line was used. The cells of the H4IIE luc line are genetically modified rat hepatoma cells stably transfected with a luciferase firefly gene. The luciferase gene is activated by the presence of dioxin-like compounds and the concentration of the enzyme is measured as relative light units (RLUs). The amount of RLUs is directly proportional to the dioxin load in the extract. This method is rapid, cost and time-effective in determining the TEQ when compared to chemical analysis. The TEQ2o-valuesin the various samples, as determined with the H4IIE luc cell line, ranged from 0.007 ngTEQ/kg to 54.06 ngTEQ/kg. Thermal processes at the smelter, sorption of hydrophobic organic compounds (HOCs) to soil and tailings, and external sources such as anthropogenic activities contributed to high TEQ2o-values. Climatic conditions, wind, precipitation, and solubility of HOCs into surfactants lead to low TEQ20. The smelter at Union Section had a very high TEQ20of 44.62 ngTEQ/kg compared to Impala Platinum mine (5.15 ngTEQ/kg). This implies that workers at Union Section are possibly exposed to low and high concentrations of dioxin-like chemicals. Long-term exposure to these compounds could lead to bio-accumulation in the fatty tissue of the mine workers, leading to chronic effects such as reproductive problems and cancer. The air emission of the furnace at the smelter was 0.03 gTEQ/annum and the release of the PCDD/Fs into the slag was 0.60 gTEQ/annum. By effectively managing the smelter it is possible to reduce the TEQ. The TEQ of each sample increased due to normalising the data. The normalised TEQ20 ranged from 0.94 ng TEQ/kg to 42497.48 ngTEQ/kg. Dioxin-like chemicals are present on a platinum mine, but at varying quantities and the effects of these compounds might be detrimental to the environment and the workers at the platinum mine. Further analyses of the health impacts associated with the platinum mine are needed. The H4IIE reporter gene bio-assay could be used to effectively determine the TEQ of each sample. Although this investigation has identified the formation and presence of dioxin-like chemicals at certain stages of mining and processing, not all of the processes were investigated. Some of these processes have the potential to add, and even destroy, these chemicals, affecting potential human exposure and amounts released to the environment. This, however, requires further investigation. The financial assistance of the National Research Foundation (NRF) towards this research is hereby acknowledged. Opinions expressed and conclusions arrived at, are those of the author and are not necessarily to be attributed to the NRF.
Thesis (M. Environmental Science)--North-West University, Potchefstroom Campus, 2006.

Ce travail est consacre a l'etude de l'elimination par voie catalytique des oxydes d'azote emis lors du fonctionnement des moteurs diesel et essence melange pauvre. Differents catalyseurs ont ete etudies. Il s'agit d'oxydes simples (al#2o#3, sno#2, fe#2o#3) seuls ou en melange, d'oxydes mixtes (perovskites) et de metaux supportes (pt / support). Seuls certains oxydes (nd#2cuo#4, sno#2-al#2o#3) ont une activite significative en reduction (presence de propene dans le melange reactionnel) et en decomposition (absence de reducteur) des no#x. Pour ces catalyseurs, le domaine d'activite se situe entre 300 et 500c avec un maximum de conversion a 350-400c. L'augmentation d'activite due a l'ajout de platine se traduit d'une part par un deplacement des courbes de conversion vers les basses temperatures et d'autre part par la formation d'une espece nouvelle n#2o. L'etude a donc consiste a modifier les methodes de preparation des catalyseurs et les conditions operatoires de la reaction afin de minimiser la formation de protoxyde d'azote. Dans ce but, une methode de depot du platine en interaction avec le fer a ete mise au point. Elle a permis d'obtenir des catalyseurs plus actifs et plus selectifs en n#2. Pour l'autre volet, la modulation de l'alimentation en reducteur dans le reacteur modifie la repartition des produits de la reaction, en particulier par une augmentation de la selectivite en n#2 sans variation de l'activite moyenne globale. Ceci a permis de mettre en evidence, a la surface des catalyseurs a base de fer (pas sur pt / al#2o#3), la formation et l'accumulation d'un intermediaire carbone et azote dont la reaction avec les oxydes d'azote conduit a la formation de n#2.

Cette étude concerne l'oxydation totale du méthane à basse température sur des catalyseurs à base de Pd et/ou de Pt. L'application visée est l'épuration des échappements des moteurs fonctionnant au gaz naturel et en mélange pauvre. La problématique est que l'eau et les composés soufrés présents dans les effluents, sont susceptibles de limiter l'activité des catalyseurs utilisés. Les catalyseurs Pd/Al2O3 et Pt/Al2O3 ont été retenus comme systèmes de référence dans la réaction considérée. En absence et en présence d'eau dans le mélange réactionnel, le catalyseur Pd/Al2O3 est le plus actif. Il est, en revanche, très sensible à H2S et ne se régénère que partiellement sous oxygène à des températures de 650ʿC. Le catalyseur Pt/Al2O3 est moins sensible au soufre et se régénère quasi totalement sous O2 à 500ʿC. Afin d'obtenir des catalyseurs plus actifs en oxydation du méthane et offrant une meilleure résistance à l'eau et au soufre que les solides de référence, des systèmes à base de Pt et Pd déposés sur des supports à propriétés redox (SnO2 et Ce0,67Zr0,33O2) ont été préparés. Ces supports ne permettent une amélioration des performances catalytiques en absence et en présence d'eau que dans le cas du platine. Les catalyseurs Pt/SnO2 et Pt/Ce0,67Zr0,33O2 perdent, cependant, la majeure partie de leur activité en présence de H2S. Enfin, une étude a débuté sur des catalyseurs bimétalliques PdxPt1-x/Al2O3. Ils sont, en l'absence d'eau et de poison soufré, plus actifs que le solide Pd/Al2O3 pour x 0,65.

Ce travail est relatif au développement de microcapteurs de gaz sélectifs. De façon générale, ces dispositifs sont composés d'un oxyde semi-conducteur, le dioxyde d'étain, associé à deux électrodes métalliques. L'objectif de l'étude est double, d'une part, améliorer la sélectivité par dépôt de filtre catalytique métallique, et d'autre part mieux appréhender les interactions entre l'oxygène, les métaux qu'ils soient utilisés sous forme d'électrode ou de membrane et le dioxyde d'étain.

Le dépôt d'un film mince de platine sur une couche épaisse de 20 μm de dioxyde d'étain a permis d'améliorer la sélectivité du dispositif au CH4 en présence de C2H5OH et de CO. En revanche, lorsqu'il a été déposé à la surface d'une couche mince de 70 nm de dioxyde d'étain, le film mince de platine n'a pas rendu possible l'amélioration de la sélectivité du matériau sensible.

Par la suite, notre démarche a consisté à évaluer les propriétés physico-chimiques de chaque constituant du dispositif à savoir le dioxyde d'étain, le métal ou l'association des deux. Pour cela, nous avons fait appel à différentes techniques couramment utilisées pour la caractérisation des interactions gaz – solide telles que la catalyse, la calorimétrie ou la mesure électrique. Des effets de synergie entre le métal et l'oxyde vis-à-vis de l'adsorption et des effets électriques de l'oxygène gazeux ont pu être mis en évidence. Ces résultats ont été exploités pour proposer un mécanisme permettant d'expliciter les phénomènes électriques qui interviennent lors de la chimisorption d'oxygène à la surface d'un système regroupant le dioxyde d'étain et un métal. Ce modèle a été confronté aux résultats expérimentaux relatifs à l'influence de l'épaisseur du dioxyde d'étain sur les réponses électriques sous gaz réducteur des capteurs de gaz.

La production de l'hydrogène à partir de biomasse est actuellement à l'étude mais la méthode de valorisation du biogaz (mélange H2/CO2) par réactions catalytiques, autres que la simple combustion, n'a pas encore été retenue. Par conséquent, le principal objectif de ce travail est d'explorer les autres voies. L'effet du CO2 sur le système catalytique est mal connu et seulement un effet négatif sur la dissociation de l'hydrogène a été mentionné. L'hydrogénation du toluène sur un catalyseur Pt a d'abord été étudiée sans CO2 pour suivre son comportement et éventuellement sa perte d'activité. En présence de CO2, l'inactivité complète du catalyseur pour l'hydrogénation du toluène a été mis en évidence. La modification de la surface du catalyseur par le CO2 est quantifiée par DRIFT et un mécanisme à deux sites a été montré. La réaction de Reverse Water Gas Shift produisant du CO se trouve être la principale cause de la désactivation de la surface de catalyseur avec le CO2. Donc la compétition d'adsorption entre le CO et des acides carboxyliques a été mise à profit pour favoriser sélectivement la conversion des acides. Pour l'alumine, elle est polluée par des carbonates complexes venant du CO2. La silice étant aussi connue pour promouvoir la décomposition, ces supports ont été rejetés. L'oxyde de titane a été utilisé pour catalyser une autre gamme de produits. Sur ce catalyseur, le changement de sélectivité entre le RWGS et la conversion de l'acide a été observé. Quant à l'oxyde de fer (catalyseur moins actif), il n'est pas capable de produire du CO à partir du CO2. La chimie de surface de l'oxyde de fer joue un rôle important sur la sélectivité du produit parmi les cétones et les aldéhydes. Un mécanisme à deux sites peut réutiliser pour l'oxyde de fer, montrant qu'un fonctionnement stable peut être trouvé si la réduction par l'hydrogène est continue. Si l'oxyde de fer est totalement oxydé par le CO2, produit de réaction, la production des cétones cesse. Énergiquement, le procédé de production d'acétone peut être autosuffisant et l'acétone peut être utilisée comme une molécule de stockage d'énergie. Le procédé va aussi compenser le nouveau procédé de production de phénol qui ne produit pas l'acétone.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
This is work treat of the acetaldehyde and labeled ethanol oxidations, both kinds in percloric acidic medium, 0,1 Mol L-1 HClO4 on the Pt polycrystalline surface with used conventional electrochemical and spectroscopy techniques (FTIRS in situ). From acetaldehyde, wanted to find the mean concentration that better favor the reaction to evolve for CO2 in the potential smaller from production of the kind. The concentration 0,01 Mol L-1 was better suitable, but the increase of the concentration in solution, this is pathway was whole inhibited. However, in the high potential the form to acetic acidic is favorable. For main cronoamperometry, acetaldehyde in the concentration 0,02 Mol L-1, were able proof results in situ FTIRS. According to potential, this is results was interpreted second pattern to consider: the pear adsorbed kinds (Langmuir-Hinshelwood) and other where consider only one adsorbed kinds between adsorbed (pattern Eley-Rideal mechanism). In the case of ethanol labeled oxidation (H3 13CO 12CH2OH), it is search to look into the path delineated from way severous of the reaction from to form CO2. The results showed that is product would to be results of the intermediates oxidations contained carbon from alcohol group and intermediates contained carbon from group methyl; however, the intermediates contained carbon alcohol group is mores able reactive in the zone potential searched in the work, is this mores, confronted with able reactive metil group. The path double that yield CO2 in the zone potential below 1,0 V, are yielded coupling bands 12COL and 13COL which coexist in below potential. In the presence kind 13COL in 0,4 V potential proof that of the efficiency of the platinum electrode for the oxygenation group metil in the zone below potential. In the potential largest that 1,0 V, where exist the formation continuous of carbon dioxide, the difference in the greatness bands associated from 12CO2 e 13CO2 (double path product contained carbon), was interpreted in the sense of the electrochemical conditions infortunable for remover hydrogen group metil; additional this is kind was to promote for yield from molecules, which not is able identify for whole technique.
Este trabalho trata das reações de eletrooxidações de acetaldeído comum e etanol isotopicamente marcado, ambas reações em superfície de platina policristalina em meio de ácido perclórico, HClO4, 0,1 Mol L-1, com a utilização de técnicas eletroquímicas convencionais e espectroscopia (FTIRS in situ). Para o acetaldeído, essa reação foi estuda com a dependência do potencial aplicado e a concentração do aldeído em solução, que melhor resultaram na transformação desta molécula a CO2. Assim, para o potencial 0,6 V, a concentração de aldeído 0,01 Mol L-1 foi a mais apropriada deduzida a partir de FTIRS in situ e, a concentração 0,02 Mol L-1 permitiu a geração de maior densidade de corrente e foi inferida a partir de cronoamperometria. Essa discrepância foi discutida em termos das reações específicas que resultam no sinal analítico para cada técnica. Dependendo da concentração do acetaldeído, a via de formação de CO2 foi completamente inibida e, em altos potenciais, prevalecia sempre a formação de ácido acético. Paralelamente, dependendo do potencial, estes resultados foram interpretados com base em modelos de mecanismos de reações que considera: um par de reagentes adsorvidos (mecanismo Langmuir-Hinshelwood) e apenas uma espécie adsorvida do par fundamental de reagentes (mecanismo Eley-Rideal). Para o etanol isotopicamente marcado (H3 13C 12CH2OH), foram investigados passos delineados pelas diferentes vias de reação de formação de CO2. Os resultados mostraram que este produto pode ser resultante da eletrooxidação de intermediários contendo o carbono do grupo álcool e do grupo metil, sendo que o intermediário contendo o carbono do grupo álcool, para toda a faixa de potenciais investigados, é bem mais reativo que o intermediário contendo o carbono do grupo metil. As vias duplas que geram CO2 em potenciais abaixo de 1,0 V são resultantes de bandas acopladas de 12COL e 13COL que coexistem em baixos potenciais. A presença de 13COL em 0,35 V foi encarada como uma evidência da eficiência da Pt para oxigenação do grupo metil em baixos potenciais. Em potenciais acima de 1,0 V, onde há produção contínua de dióxido de carbono, a diferença na magnitude das intensidades de bandas relativa ao 13CO2 e 12CO2 (das vias de origem de carbono), foi interpretada como sendo as referidas condições eletroquímicas desfavoráveis para desprotonação do metil.

Cette thèse s'inscrit dans le contexte général des efforts de recherche pour développer des supports de catalyseur résistant à la corrosion qui peuvent potentiellement remplacer le carbone dans les piles à combustible à électrolyte polymère. Des nanofibres et des nanotubes à base de TiO2 et SnO2 dopés par Nb ont été préparés par filage électrostatique et caractérisés par diffraction des rayons X, spectroscopie des photoélectrons de rayons X, spectroscopie Raman, mesures de surface spécifique et de conductivité électronique. Les nanofibres de TiO2 et SnO2 dopées par Nb présentent une conductivité et une surface spécifique supérieure à celle des oxydes non dopés. Des nanoparticules de platine ont été préparées en utilisant une méthode polyol modifié par micro-ondes, et déposées sur les supports fibreux. La caractérisation électrochimique des électrocatalyseurs ainsi obtenus a été réalisée ex situ par voltamètre en utilisant une électrode à disque tournant. Le catalyseur supporté, Pt sur SnO2 dopé par Nb présenté une stabilité électrochimique supérieure à celle d'un catalyseur Pt sur carbone commercial (Vulcan XC-72R). Une cathode Pt/Nb-SnO2 préparée par pulvérisation a pu être intégrée dans un assemblage membrane-électrode (AME) et caractérisée in situ dans une cellule de pile à combustible à électrolyte polymère. L'AME a présenté une durée de vie plus élevée mais une densité de puissance plus faible qu'un AME contenant Pt/C. Les nanotubes de SnO2 dopés par Sb ont une conductivité plus élevée que celle des matériaux dopés par Nb et lorsqu'ils sont intégrés dans une cathode, fournissent une densité de puissance accrue par rapport à une cathode à base de Nb- SnO2
The objective of this thesis is to develop corrosion resistant catalyst support materials that can potentially replace carbon in Polymer electrolyte fuel cells. Therefore, Nb doped TiO2 and SnO2 nanofibres and nanotubes were prepared by electrospinning and characterised by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, N2 adsorption/desorption analysis and electronic conductivity measurements. The obtained Nb doped TiO2 and SnO2 one dimensional structures demonstrated higher conductivity and surface area than non-doped oxides. Pt nanoparticles were prepared using a modified microwave-assisted polyol method and deposited on the electrospun supports. Electrochemical characterisation of the obtained electrocatalysts was performed ex situ using a rotating disc electrode, and compared with a commercial carbon support (Vulcan XC-72R). Pt supported on Nb doped SnO2 provided higher electrochemical stability in comparison to Pt on carbon. Thus, a cathode of Pt/Nb-SnO2 prepared by spray-coating was integrated into Membrane Electrode Assembly (MEA) and characterised in situ in single Polymer electrolyte fuel cell. The MEA exhibited higher durability though lower power density compared to MEA with Pt/C based cathode. Sb doped SnO2 nanotubes have higher conductivity than Nb doped material and when integrated into a cathode, provided enhanced power density in comparison to Nb-SnO2 based cathode

碩士
國立中興大學
化學系所
101
The thesis is divided into two major parts. The first part focuses on the development of composite platinum nanoparticles -titanium dioxide (PtNP/TiO2) and the second part deals with its application as an electrochemical sensor. We use hexachloroplatinic acid solution (H2PtCl6) as a precursor in photo- reduction of platinum nanoparticles on TiO2. In order to understand the best condition for the fabrication of PtNP/TiO2, the influences of pH values, Pt and titanium dioxide concentration were investigated. Both Transmission Electron Microscopy (TEM) and Energy Dispersive Spectrometer (EDS) studies were used to analyze the morphology as well as the size of Pt nanoparticles deposited on TiO2. Well-defined Pt nanoparticles with the size of ~5 nm were distributed on the surface of TiO2 as confirmed from the TEM images. Previous works addressed about the preparation of platinum nanoparticles on TiO2, with the addition of reducing reagents (like NaBH4 and sodium citrate) or organic solvents in the process, some methods even need heating to accelerate the reduction rate of metal nanoparticles, and also use complicated process of annealing or calcination at high temperature for making platinum nanoparticles on the surface of TiO2. Compared to these works, the advantages of our proposed method are no complicated process involved or heating while in the preparation step without the addition of any reducing agents. The second part of this study aimed at the electrochemical applications of the PtNP/TiO2. The PtNP/TiO2 modified screen-printed carbon electrode (PtNP/TiO2-SPCE) displayed good electrocatalytic ability for dissolved oxygen (DO) measurement and the direct electrochemical oxidation of glucose. The DO measurement by the PtNP/TiO2-SPCE displayed good linearity with that of a commercial DO meter indicating that the proposed system can be used as a promising O2 sensor. Besides, combination of the PtNP/TiO2-SPCE and amperometry was used for the determination of glucose. The calibration plot was obtained in the range of 10 μM－3 mM glucose (r2 = 0.998) with a sensitivity of 20.084 μA mM–1 cm–2 and the lowest detection limit of 0.46 μM (S/N = 3). And this detection method could avoid the interference of the interferant such as Uric acid, L(+)-Ascorbic acid, and Acetaminophen. Overall, we present a simple method for the preparation of titanium dioxide supported platinum catalyst for use as a sensor with good sensitivity, wide linear range, and good stability, showing excellent electrocatalytic activity and practicability towards detection of both O2 and glucose.

碩士
國立臺北科技大學
製造科技研究所
96
This study puts CO2 in the system which affiliation two piece of flake graphite limit. To change 5 kind of surface energy (ε*=1、1.58、2.24、3.16、4.47),3 kind of temperature(240K、260K、280K) and 3 kind of density(ρ*=0.293、0.39、0.44). The results show that more CO2 change liquid from gas in surface energy is 4.47,the lowest temperature is 240K, and the highest density is 0.44. In this system, the adsorption is controlled by adsorptive energy at boundary, escaptive energy of temperature, and variation of density. We also puts CO2 in two piece of Pt limit to compare different between graphite and Pt. The results show that kinetic energy was increased with Τ*.

碩士
國立雲林科技大學
電子工程系
106
In this study, phosphorene was mixed with titanium dioxide (TiO2) colloid and deposited on fluorine-doped tin oxide (FTO) conductive substrate by doctor blade method as the photoelectrode of dye-sensitized solar cell (DSSC). The reason is because phosphorene has high electron mobility and high absorption, which could enhance the electron transfer ability and increase the recombination resistance, thus improve the current density. The surface morphology of phosphorene film was characterized by field-emission scanning electronic microscopy (FE-SEM). The optical absorption of phosphorene-TiO2 composited film was measured by UV–visible spectrometer. The interface resistance of DSSC was measured by electrochemical impedance spectroscopy. Compared with the photovoltaic conversion efficiency of 3.50% based on pure TiO2 photoelectrode, it is found that the optimal photovoltaic conversion efficiency of 4.35% is achieved when the phosphorene is introduced to TiO2 photoelectrode, and the efficiency increases by 24%. More than that, silver (Ag) was deposited by radio frequency sputtering to modify the conventional platinum (Pt) counter electrode to enhance the redox reaction between electrolyte and dye molecule. The reason is because Ag has the highest electrical conductivity in metal, and the lattice strain effect will increase the surface absorption ability of film. The silver modified Pt counter electrode with different Ag thicknesses was investigated for electrical conductivity and catalytic activity. The surface morphology of Pt/Ag counter electrode was characterized by FE-SEM. The sheet resistance of Pt/Ag counter electrode was measured by 4-point probing system. The interface resistance of DSSC was measured by electrochemical impedance spectroscopy. Compared with the pure Pt counter electrode, the silver modified Pt counter electrode can provide a higher electrical conductivity and a superior catalytic activity. Moreover, the photovoltaic conversion efficiency of DSSC can be enhanced from 3.82% with the Pt counter electrode to 4.46% with the Pt/Ag counter electrode, and the efficiency increases by 16%. Finally, the DSSC of optimal composited films with phosphorene-TiO2 photoelectrode and Pt/Ag counter electrode was investigated under low illumination. The photovoltaic conversion efficiency of the DSSC can be enhanced from 4.76% under illumination of 100 mW/cm2 to 7.21% under illumination of 1.75 mW/cm2 and the efficiency increases by 52%.

D.Phil. (Chemistry)
Elimination of toxic organic compounds from wastewater is currently one of the most important subjects in water-pollution control. Among the many organic pollutants are dyes and emerging pollutants such as natural organic matter (NOM). Dyes such as Eosin Yellow (EY), an anionic xanthene fluorescent dye, can originate from many sources such as textile industrial processes, paper pulp industries and agricultural processes. Most dyes are problematic because they are resistant to conventional chemical or biological water-treatment methods and therefore persist in the environment. NOM consists of a highly variable mixture of products found in water and soils. NOM is formed as a result of the decomposition of plant and animal material and is a precursor to the formation of disinfection by-products (DBP) during water disinfection. These organic compounds cause undesirable colour, taste and odour in water. NOM affects the capacity of other treatment processes to effectively remove organic micro-pollutants or inorganic species that may be present in the water. Its removal also uses up chemicals and energy and so it is expensive to treat. Titanium dioxide (TiO2) has emerged as one of the most fascinating materials in the modern era due to its semiconducting and catalytic properties. TiO2 is a large band-gap semiconductor that exists mainly in the anatase (band gap 3.2 eV) and rutile (band gap 3.0 eV) phases. Its response to UV light has led to increased interest in its application in the photocatalysis research field. It has been investigated extensively for its super hydrophilicity and use in environmental remediation and solar fuel production. In spite of extensive efforts to apply TiO2 for environmental remediation, photocatalytic activity in the visible region has remained quite low hence the ultimate goal of this research was to fabricate highly photoactive catalysts composed of non-metal, platinum-group metal (PGM) co-doped TiO2 and carbon nanotubes (CNTs) and to apply them for water purification using solar radiation...

D. Tech. Chemical, Metallurgical and Materials Engineering
This study provides experimental data and new perspectives on selective precipitation of platinum group metals (PGMs) in the presence of base metals while at the same time reviewing the mass transfer characteristics and models associated with metal sulphides precipitation in liquid-liquid and gas-liquid systems. In this study, the objective was to investigate and validate the concept of selective precipitation of platinum from chloride media using sulphur-bearing liquids or gases.

The aim of the studies presented in this thesis was to explore various materials and platforms for the detection of DNA in order to develop a cost-effective, repeatable and reproducible electrical/electrochemical DNA sensor. Chapter 1 is a review chapter consisting of a comparative study of the fundamental working principle, fabrication process, characteristics and performance of different types of DNA biosensors and a detailed discussion on the progress in the development of DNA biosensors. The studies described in Chapter 2 focuses on the development of a flexible, label-Free DNA Sensor using Platinum oxide (PtO) as the sensing element. PtO (100nm) deposited using an optimized reactive ion sputtering process revealed p-type semiconducting behaviour with a band-gap of 1.5 eV, resistivity of 0.16 Ω-m and activation energy of 0.22 eV. XPS spectra indicated the presence of PtO phase (32%) along with PtO2 phase (68%). The XRD spectra indicated the formation of α-PtO2 phase. Arrays of simple, two terminal sensors were fabricated on transparent, flexible, acetate substrates with platinum oxide thin film forming the active layer (8.0 mm X 60 μm) for DNA detection. The sensor operated on the principle of conductance change resulting from the change in charge carrier density due to attachment of DNA to the platinum oxide surface. The DNA attachment onto platinum oxide was experimentally verified by performing Fourier Transform Infrared Spectroscopy (FTIR) and optical fluorescence measurements. The binding constant of DNA to platinum oxide was found to be 7.35 p.m. for every percentage increase in fluorescence intensity. The sensor arrays showed a DNA concentration-dependent current change that was linear over a large dynamic range and sensitivity down to 0.5 nM. The label-free platinum oxide DNA sensors showed reproducibility with a coefficient of variation (CoV) of less than 10%. In chapter 2 reactively sputtered Platinum oxide thin film was used as a DNA sensing element. In chapter 3, we subject the reactively sputtered Platinum oxide thin films to an additional RIE step for 3, 6 and 9 minutes and carry out a detailed comparative study of the material and electrical properties of these films. XRD and XPS analysis revealed that when the reactively sputtered Platinum oxide film was subjected to RIE step for longer periods of time, it became progressively α-PtO2 in nature. Activation energies of 0.24 eV, 0.26 eV, 0.29 eV and 0.31 eV were obtained for the as deposited film and the films subjected to RIE step for 3, 6 and 9 minutes respectively. The Hall mobility of the as deposited Platinum oxide film was found to be 32.15 cm2V-1s-1 at room temperature. However, when the as deposited film was subjected to RIE step for 9 minutes the mobility value rises to as high as 136.13 cm2V-1s-1 at room temperature. In chapter 4, the development of an electrochemical, sequence specific DNA hybridization sensor using platinum microelectrodes is discussed. A new transduction hybridization pathway obtained by coupling electrochemical adsorption and long-range electron transfer through double-stranded DNA is presented. This property was used to investigate long-range electron transfer properties of synthetic oligonucleotides and plasmids layers. A check complementarity assay of two non-labelled short DNA, without heating or DNA labelling, in a 10 minutes protocol, was in fine established. In chapter 5, the possibility of DNA sensing using impedance spectroscopy of layer-by-layer self-assembly of weak polyelectrolytes is explored. Interdigitated capacitors (IDCs) with active area of 1X1 mm2 and electrode spacing of 5 μm are fabricated on acetate sheets for this purpose. Measurement results indicate that there is differential binding of DNA to differently charged polyelectrolyte terminating layer on the IDC surface. The differential binding of DNA to Poly (Allylamine Hydrochloride) (PAH) and Poly (Acrylic acid) was also confirmed using Fluorescence microscopy and FTIR spectroscopy.

After introducing fundamentals of catalysis with noble metal surfaces especially Pt metal for CO oxidation and subsequent developments on nano-crystalline Pt metals supported on oxide supports, an idea of Pt ion in reducible oxide supports acting as adsorption sites is proposed in chapter 1. Idea of red-ox cycling of an ion in an oxide matrix is presented taking Cu ion in YBa2Cu3O7 as an example. Noble metal ions in reducible oxides such as CeO2 or TiO2 acting as adsorption sites and hence a red-ox catalyst was arrived at from chemical considerations. Among several reducible oxide supports, TiO2 was chosen from crystal structure and electronic structure considerations. A good redox catalyst for auto exhaust and related applications should have high oxygen storage capacity (OSC). Any new material that can work as a redox catalyst should be tested for its OSC. Therefore we designed and fabricated a temperature programmed reduction by hydrogen (H2¬TPR) system to measure OSC. This is presented in chapter 2. We have synthesized a number of oxides by solution combustion method. Structures were determined by powder XRD and Rietveld refinement methods. Fe2O3, Fe2-xPdxO3-δ, Cu1-xMnAl1+xO4, LaCoO3, LaCo1-xPdxO3-δ, CeO2, Ce1¬xPdxO2-δ, TiO2, Ti1-xPdxO2-δ and many other oxide systems were synthesized and their structures were determined. OSC of these systems were determined employing the H2/TPR system. TPR studies were carried out for several redox cycles in each case. Except Pd ion substituted CeO2 and TiO2 other oxide systems decomposed during redox cycling. Pd ion substituted TiO2 gave highest OSC and also it was stable paving way to choose this system for further study. In chapter 3, we have described lattice oxygen of TiO2 activation by the substitution of Pd ion in its lattice. Ti1-xPdxO2-x (x = 0.01 to 0.03) have been synthesized by solution combustion method crystallizing in anatase TiO2 structure. Pd is in +2 oxidation state and Ti is in +4 oxidation state in the catalyst as seen by XPS. Pd is more ionic in TiO2 lattice compared to Pd in PdO. Oxygen storage capacity defined by ‘amount of oxygen that is used reversibly to oxidize CO’ is as high as 5100 μmol/g of Ti0.97Pd0.03O1.97. Oxygen is extracted by CO to CO2 in absence of feed oxygen even at room temperature. Rate of CO oxidation is 2.75 μmol.g-1.s-1 at 60 0C over Ti0.97Pd0.03O1.97 and C2H2 gets oxidized to CO2 and H2O at room temperature. Catalyst is not poisoned on long time operation of the reactor. Such high catalytic activity is due to activated lattice oxygen created by the substitution of Pd ion as seen from first-principles density functional theory (DFT) calculations with 96 atom supercells of Ti32O64, Ti31Pd1O63, Ti30Pd2O62 and Ti29Pd3O61. The compounds crystallize in anatase TiO2 structure with Pd2+ ion in nearly square planar geometry and TiO6 octahedra are distorted by the creation of weakly bound oxygens. Structural analysis of Ti31Pd1O63 which is close to 3% Pd ion substituted TiO2 shows that bond valence of oxygens associated with both Ti and Pd ions in the lattice is 1.87. A low bond valence of oxygen is characteristic of weak oxygen in the lattice compared to oxygens with bond valence 2 and above in the same lattice. Thus, the exact positions of activated oxygens have been identified in the lattice from DFT calculations. Pt has two stable valencies: +2 and +4. Ti ion in TiO2 is in +4 state. Is it possible to substitute Pt exclusively in +2 or +4 state in TiO2? Implications are that Pt in +2 will have oxide ion vacancies and Pt in +4 states will not have oxide ion vacancies. Indeed we could synthesize Pt ion substituted TiO2 with Pt in +2 and +4 states by solution combustion method. In chapter 4, we have shown the positive role of an oxide ion vacancy in the catalytic reaction. Ti0.97Pt2+0.03O1.97 and Ti0.97Pt4+0.03O2 have been synthesized by solution combustion method using alanine and glycine as the fuels respectively. Both are crystallizing in anatase TiO2 structure with 15 nm average crystallite size. X-ray photoelectron spectroscopy (XPS) confirmed Pt ions are only +2 state in Ti0.97Pt0.03O1.97 (alanine) and only in +4 state in Ti0.97Pt0.03O2 (glycine). CO oxidation rate with Ti0.97Pt2+0.03O1.97 is over 10 times higher compared to Ti0.97Pt4+0.03O2. The large shift in 100 % hydrocarbon oxidation to lower temperature was observed by Pt2+ ion substituted TiO2 from that by Pt4+ ion substituted TiO2. After reoxidation of the reduced compound by H2 as well as CO, Pt ions are stabilized in mixed valences, +2 and +4 states. The role of oxide ion vacancy in enhancing catalytic activity has been demonstrated by carrying out the CO oxidation and H2 + O2 recombination reaction in presence and in absence of O2. There is no deactivation of the catalyst by long time CO to CO2 catalytic reaction. We analyzed the activated lattice oxygens upon substitution of Pt2+ ion and Pt4+ ion in TiO2, using first-principles density functional theory (DFT) calculations with supercells Ti31Pt1O63, Ti30Pt2O62, Ti29Pt3O61 for Pt2+ ion substitution in TiO2 and Ti31Pt1O64, Ti30Pt2O62, Ti29Pt3O61 for Pt4+ ion substitution in TiO2. We find that the local structure of Pt2+ ion has a distorted square planar geometry and that of Pt4+ ion has an octahedral geometry similar to Ti4+ ion in pure TiO2. The change in coordination of Pt2+ ion gives rise to weakly bonded oxygens and these oxygens are responsible in high rates of catalytic reaction. Thus, the high catalytic activity results from synergistic roles of oxide ion vacancy and weakly bonded lattice oxygen. In chapter 5, we have shown high rates of H2 + O2 recombination reaction by Ti0.97Pd0.03O1.97 catalyst coated on honeycomb monolith made up of cordierite material. This catalyst was coated on γ¬Al2O3 coated monolith by solution combustion method using dip-dry-burn process. This is a modified conventional method to coat catalysts on honeycombs. Formation of Ti0.97Pd0.03O1.97 catalyst on monolith was confirmed by XRD. Form the XPS spectra of Pd(3d) core level in Ti1-xPdxO2-δ, Pd ion is the formed to be +2 state. Ti0.97Pd0.03O1.97 showed high rates of H2 + O2 recombination compared to 2 at % Pd(metal)/γ-Al2O3, Ce0.98Pd0.02O2-δ, Ce0.98Pt0.02O2-δ, Ce0.73Zr0.25Pd0.02O2-δ and Ti0.98Pd0.02O1.98. Activation energy of H2 + O2 recombination reaction over Ti0.97Pd0.03O1.97 is 7.8 kcal/mole. Rates of reaction over Ti0.97Pd0.03O1.97 are in the range of 10 – 20 μmol/g/s at 60 0C and 4174 h-1 space velocity. Rate is orders of magnitude higher compared to noble metal catalysts. From the industrial point of view, solvent-free hydrogenation of aromatic nitro compounds to amines at nearly 1 bar pressure is an important process. In chapter 6, we showed that Ti0.97Pd0.03O1.97 is a good –nitro to –amine conversion catalyst under solvent-free condition at 1.2 – 1.3 bar H2 pressure. Nitrobenzene, p-nitrotoluene and 2-chloro-4-nitrotoluene are taken for the catalytic reduction reaction. The amine products were analyzed by gas chromatography and mass spectrometry (GCMS). Further, confirmation of compounds was done by FTIR, 1H NMR and 13C NMR. In presence of alcohol as solvent, 100% conversion of aromatic nitro compounds to amines took place at higher temperature and it required more times. In n-butanol solvent, 100% conversion of nitrobenzene and p-nitrotoluene occurred within 10 h and 12 h at 105 °C respectively. We have compared solvent-free reduction of p-nitrotoluene over different catalysts at 90 °C. Catalytic activity for reduction of p¬nitrotoluene over Ti0.97Pd0.03O1.97 is much higher than that reaction over 3 atom % Pd on TiO2 and Pd metal. Turnover frequencies (TOF) for nitrobenzene and 2-chloro-4-nitrotoluene conversion are 217 and 20 over Ti0.97Pd0.03O1.97 respectively. With increase of temperature, TOF of aromatic nitro compound reduction is also increased. We have compared the solvent-free reduction of aromatic nitro compound over Ti0.97Pd0.03O1.97 with others in the literature. Upto 3 cycles of reduction reaction, there was no degradation of Ti0.97Pd0.03O1.97 catalyst and stability of catalyst structure was analyzed by XRD, XPS and TEM images. Catalyst is stable under reaction condition and the structure is retained with Pd in +2 state. Finally, we have proposed the mechanism of -nitro group reduction reaction based on the structure of Ti0.97Pd0.03O1.97. Instead of handling nano-crystalline materials we proceeded with coating our catalysts on cordierite honeycombs. In chapter 7, we have shown high catalytic activity towards Heck reaction over Ce0.98Pd0.02O2-δ and Ti0.97Pd0.03O1.97 coated on cordierite monolith. XRD patterns of Ce0.98Pd0.02O2¬δ coated on cordierite monolith were indexed to fluorite structure. Heck reaction of aryl halide with olefins over Ce0.98Pd0.02O2-δ and Ti0.97Pd0.03O1.97 coated on cordierite monolith were carried out at 120 °C. The products were first analyzed by GCMS and for the confirmation of compounds, we have recorded 1H NMR and 13C NMR. Heck reaction was carried out with different solvents and different bases for choosing the good base and a solvent. Hence, we have chosen K2CO3 as base and N,N¬dimethylformamide (DMF) as solvent. We have compared the rates of Heck reactions over these two catalysts and Ti0.97Pd0.03O1.97 catalyst showed much higher catalytic activity than Ce0.98Pd0.02O2-δ. With increase of temperature from 65 °C to 120 °C, the catalytic activity of Ti0.97Pd0.03O1.97 on Heck reaction is also increased. The catalyst was reused for next Heck reaction without significant loss of activity. A mechanism for Heck reaction of aryl halide with alkyl acrylate has been proposed based on the structure of Ti0.97Pd0.03O1.97. In chapter 8, we have provided a critical review of the work presented in the thesis. Critical issues such as noble metal ion doping in TiO2 vs noble metal ion substitution, difficulty of proving the substitution of low % noble metal ion in TiO2, need for better experimental methods to study noble metal ion in oxide matrix have been discussed. Finally, conclusions of the thesis are presented.

After introducing fundamentals of catalysis with noble metal surfaces especially Pt metal for CO oxidation and subsequent developments on nano-crystalline Pt metals supported on oxide supports, an idea of Pt ion in reducible oxide supports acting as adsorption sites is proposed in chapter 1. Idea of red-ox cycling of an ion in an oxide matrix is presented taking Cu ion in YBa2Cu3O7 as an example. Noble metal ions in reducible oxides such as CeO2 or TiO2 acting as adsorption sites and hence a red-ox catalyst was arrived at from chemical considerations. Among several reducible oxide supports, TiO2 was chosen from crystal structure and electronic structure considerations. A good redox catalyst for auto exhaust and related applications should have high oxygen storage capacity (OSC). Any new material that can work as a redox catalyst should be tested for its OSC. Therefore we designed and fabricated a temperature programmed reduction by hydrogen (H2¬TPR) system to measure OSC. This is presented in chapter 2. We have synthesized a number of oxides by solution combustion method. Structures were determined by powder XRD and Rietveld refinement methods. Fe2O3, Fe2-xPdxO3-δ, Cu1-xMnAl1+xO4, LaCoO3, LaCo1-xPdxO3-δ, CeO2, Ce1¬xPdxO2-δ, TiO2, Ti1-xPdxO2-δ and many other oxide systems were synthesized and their structures were determined. OSC of these systems were determined employing the H2/TPR system. TPR studies were carried out for several redox cycles in each case. Except Pd ion substituted CeO2 and TiO2 other oxide systems decomposed during redox cycling. Pd ion substituted TiO2 gave highest OSC and also it was stable paving way to choose this system for further study. In chapter 3, we have described lattice oxygen of TiO2 activation by the substitution of Pd ion in its lattice. Ti1-xPdxO2-x (x = 0.01 to 0.03) have been synthesized by solution combustion method crystallizing in anatase TiO2 structure. Pd is in +2 oxidation state and Ti is in +4 oxidation state in the catalyst as seen by XPS. Pd is more ionic in TiO2 lattice compared to Pd in PdO. Oxygen storage capacity defined by ‘amount of oxygen that is used reversibly to oxidize CO’ is as high as 5100 μmol/g of Ti0.97Pd0.03O1.97. Oxygen is extracted by CO to CO2 in absence of feed oxygen even at room temperature. Rate of CO oxidation is 2.75 μmol.g-1.s-1 at 60 0C over Ti0.97Pd0.03O1.97 and C2H2 gets oxidized to CO2 and H2O at room temperature. Catalyst is not poisoned on long time operation of the reactor. Such high catalytic activity is due to activated lattice oxygen created by the substitution of Pd ion as seen from first-principles density functional theory (DFT) calculations with 96 atom supercells of Ti32O64, Ti31Pd1O63, Ti30Pd2O62 and Ti29Pd3O61. The compounds crystallize in anatase TiO2 structure with Pd2+ ion in nearly square planar geometry and TiO6 octahedra are distorted by the creation of weakly bound oxygens. Structural analysis of Ti31Pd1O63 which is close to 3% Pd ion substituted TiO2 shows that bond valence of oxygens associated with both Ti and Pd ions in the lattice is 1.87. A low bond valence of oxygen is characteristic of weak oxygen in the lattice compared to oxygens with bond valence 2 and above in the same lattice. Thus, the exact positions of activated oxygens have been identified in the lattice from DFT calculations. Pt has two stable valencies: +2 and +4. Ti ion in TiO2 is in +4 state. Is it possible to substitute Pt exclusively in +2 or +4 state in TiO2? Implications are that Pt in +2 will have oxide ion vacancies and Pt in +4 states will not have oxide ion vacancies. Indeed we could synthesize Pt ion substituted TiO2 with Pt in +2 and +4 states by solution combustion method. In chapter 4, we have shown the positive role of an oxide ion vacancy in the catalytic reaction. Ti0.97Pt2+0.03O1.97 and Ti0.97Pt4+0.03O2 have been synthesized by solution combustion method using alanine and glycine as the fuels respectively. Both are crystallizing in anatase TiO2 structure with 15 nm average crystallite size. X-ray photoelectron spectroscopy (XPS) confirmed Pt ions are only +2 state in Ti0.97Pt0.03O1.97 (alanine) and only in +4 state in Ti0.97Pt0.03O2 (glycine). CO oxidation rate with Ti0.97Pt2+0.03O1.97 is over 10 times higher compared to Ti0.97Pt4+0.03O2. The large shift in 100 % hydrocarbon oxidation to lower temperature was observed by Pt2+ ion substituted TiO2 from that by Pt4+ ion substituted TiO2. After reoxidation of the reduced compound by H2 as well as CO, Pt ions are stabilized in mixed valences, +2 and +4 states. The role of oxide ion vacancy in enhancing catalytic activity has been demonstrated by carrying out the CO oxidation and H2 + O2 recombination reaction in presence and in absence of O2. There is no deactivation of the catalyst by long time CO to CO2 catalytic reaction. We analyzed the activated lattice oxygens upon substitution of Pt2+ ion and Pt4+ ion in TiO2, using first-principles density functional theory (DFT) calculations with supercells Ti31Pt1O63, Ti30Pt2O62, Ti29Pt3O61 for Pt2+ ion substitution in TiO2 and Ti31Pt1O64, Ti30Pt2O62, Ti29Pt3O61 for Pt4+ ion substitution in TiO2. We find that the local structure of Pt2+ ion has a distorted square planar geometry and that of Pt4+ ion has an octahedral geometry similar to Ti4+ ion in pure TiO2. The change in coordination of Pt2+ ion gives rise to weakly bonded oxygens and these oxygens are responsible in high rates of catalytic reaction. Thus, the high catalytic activity results from synergistic roles of oxide ion vacancy and weakly bonded lattice oxygen. In chapter 5, we have shown high rates of H2 + O2 recombination reaction by Ti0.97Pd0.03O1.97 catalyst coated on honeycomb monolith made up of cordierite material. This catalyst was coated on γ¬Al2O3 coated monolith by solution combustion method using dip-dry-burn process. This is a modified conventional method to coat catalysts on honeycombs. Formation of Ti0.97Pd0.03O1.97 catalyst on monolith was confirmed by XRD. Form the XPS spectra of Pd(3d) core level in Ti1-xPdxO2-δ, Pd ion is the formed to be +2 state. Ti0.97Pd0.03O1.97 showed high rates of H2 + O2 recombination compared to 2 at % Pd(metal)/γ-Al2O3, Ce0.98Pd0.02O2-δ, Ce0.98Pt0.02O2-δ, Ce0.73Zr0.25Pd0.02O2-δ and Ti0.98Pd0.02O1.98. Activation energy of H2 + O2 recombination reaction over Ti0.97Pd0.03O1.97 is 7.8 kcal/mole. Rates of reaction over Ti0.97Pd0.03O1.97 are in the range of 10 – 20 μmol/g/s at 60 0C and 4174 h-1 space velocity. Rate is orders of magnitude higher compared to noble metal catalysts. From the industrial point of view, solvent-free hydrogenation of aromatic nitro compounds to amines at nearly 1 bar pressure is an important process. In chapter 6, we showed that Ti0.97Pd0.03O1.97 is a good –nitro to –amine conversion catalyst under solvent-free condition at 1.2 – 1.3 bar H2 pressure. Nitrobenzene, p-nitrotoluene and 2-chloro-4-nitrotoluene are taken for the catalytic reduction reaction. The amine products were analyzed by gas chromatography and mass spectrometry (GCMS). Further, confirmation of compounds was done by FTIR, 1H NMR and 13C NMR. In presence of alcohol as solvent, 100% conversion of aromatic nitro compounds to amines took place at higher temperature and it required more times. In n-butanol solvent, 100% conversion of nitrobenzene and p-nitrotoluene occurred within 10 h and 12 h at 105 °C respectively. We have compared solvent-free reduction of p-nitrotoluene over different catalysts at 90 °C. Catalytic activity for reduction of p¬nitrotoluene over Ti0.97Pd0.03O1.97 is much higher than that reaction over 3 atom % Pd on TiO2 and Pd metal. Turnover frequencies (TOF) for nitrobenzene and 2-chloro-4-nitrotoluene conversion are 217 and 20 over Ti0.97Pd0.03O1.97 respectively. With increase of temperature, TOF of aromatic nitro compound reduction is also increased. We have compared the solvent-free reduction of aromatic nitro compound over Ti0.97Pd0.03O1.97 with others in the literature. Upto 3 cycles of reduction reaction, there was no degradation of Ti0.97Pd0.03O1.97 catalyst and stability of catalyst structure was analyzed by XRD, XPS and TEM images. Catalyst is stable under reaction condition and the structure is retained with Pd in +2 state. Finally, we have proposed the mechanism of -nitro group reduction reaction based on the structure of Ti0.97Pd0.03O1.97. Instead of handling nano-crystalline materials we proceeded with coating our catalysts on cordierite honeycombs. In chapter 7, we have shown high catalytic activity towards Heck reaction over Ce0.98Pd0.02O2-δ and Ti0.97Pd0.03O1.97 coated on cordierite monolith. XRD patterns of Ce0.98Pd0.02O2¬δ coated on cordierite monolith were indexed to fluorite structure. Heck reaction of aryl halide with olefins over Ce0.98Pd0.02O2-δ and Ti0.97Pd0.03O1.97 coated on cordierite monolith were carried out at 120 °C. The products were first analyzed by GCMS and for the confirmation of compounds, we have recorded 1H NMR and 13C NMR. Heck reaction was carried out with different solvents and different bases for choosing the good base and a solvent. Hence, we have chosen K2CO3 as base and N,N¬dimethylformamide (DMF) as solvent. We have compared the rates of Heck reactions over these two catalysts and Ti0.97Pd0.03O1.97 catalyst showed much higher catalytic activity than Ce0.98Pd0.02O2-δ. With increase of temperature from 65 °C to 120 °C, the catalytic activity of Ti0.97Pd0.03O1.97 on Heck reaction is also increased. The catalyst was reused for next Heck reaction without significant loss of activity. A mechanism for Heck reaction of aryl halide with alkyl acrylate has been proposed based on the structure of Ti0.97Pd0.03O1.97. In chapter 8, we have provided a critical review of the work presented in the thesis. Critical issues such as noble metal ion doping in TiO2 vs noble metal ion substitution, difficulty of proving the substitution of low % noble metal ion in TiO2, need for better experimental methods to study noble metal ion in oxide matrix have been discussed. Finally, conclusions of the thesis are presented.

In this study the focus was on the electrochemical techniques and aspects behind the establishment of the better catalyst (platinum or gold) for the sulphur dioxide oxidation reaction (SDOR). One of the primary issues regarding the SDOR is the catalyst material, thus the comparative investigation of the performance of platinum and gold in the SDOR, as found in this study. Ultimately, the SDOR could lead to an effective way of producing hydrogen gas, which is an excellent energy carrier. The electrochemical application of the oxygen reduction reaction (ORR) and ethanol oxidation reaction (EOR) is an integral part of the catalytic process of water electrolysis, and by using fuel cell technology, it becomes even more relevant to this study and can therefore be used as a control, guide and introduction to the techniques required for electrochemical investigation of catalyst effectiveness. Subsequently, the EOR as well as the ORR was used as introduction into the different electrochemical quantification and qualification techniques used in the electrochemical analyses of the SDOR. Considering the ORR, gold showed no viable activity in acidic medium, contrarily in alkaline medium, it showed good competition to platinum. Gold also lacked activity towards the EOR in acidic medium compared to platinum, with platinum the best catalyst in both acidic and alkaline media. Ultimately, platinum was established to be the material with better activity for the ORR with gold a good competitor in alkaline medium, and platinum the better catalyst for the EOR in both acidic and alkaline media. With the main focus of this study being the SDOR, gold proved to be the best catalyst in salt and gaseous forms of SO2 administration compared to platinum when the onset potential, maximum current density, Tafel slope and number of electrons transferred are taken into consideration. The onset potential was determined as 0.52 V vs. NHE for both platinum and gold using SO2 gas and 0.54 V and 0.5 V for gold and platinum respectively, using Na2SO3 salt. The maximum current density using gaseous SO2 for platinum at 0 RPM was 400 mA/cm2 with a Tafel slope of 891 mV/decade whereas gold had a maximum current density of 300 mA/cm2 and a Tafel slope of 378 mV/decade. Using Na2SO3 salt, the maximum current density of gold was 25 mA/cm2 with a Tafel slope of 59 mV/decade whereas platinum only achieved 18 mA/cm2 with a Tafel slope of 172 mV/decade. Concerning the number of electrons transferred, gold achieves a transfer of 2 while platinum only 1 for both SO2 gas and Na2SO3 salt. Taking all these summarised determinations into account, gold was established to be a very competitive catalyst material for the SDOR, compared to platinum.
MSc (Chemistry), North-West University, Potchefstroom Campus, 2015

Στα πλαίσια της παρούσας διδακτορικής διατριβής μελετήθηκαν και αναπτύχθηκαν νανοδομημένα λεπτά υμένια διοξειδίου του τιτανίου (TiO2) και λευκόχρυσου (Pt) για χρήση σε ευαισθητοποιημένες φωτοβολταϊκές κυψελίδες. Αφού πραγματοποιήθηκε η μελέτη των υμενίων, παρασκευάστηκαν υμένια TiO2 και Pt και βελτιστοποιήθηκαν, ώστε να έχουν τις επιθυμητές ιδιότητες. Για το χαρακτηρισμό των υμενίων TiO2 χρησιμοποιήθηκε ηλεκτρονικό μικροσκόπιο σάρωσης (SEM) και περίθλαση ακτίνων X (XRD). Μάλιστα προτάθηκε η χρήση νιτρικού οξέος, ανάμεσα σε 4 διαφορετικά οξέα, για την αποτελεσματική διασπορά των σωματιδίων του TiO2 και την παρασκευή ομοιόμορφων υμενίων, χωρίς την παρουσία ρωγμών και με πάχος πάνω από 10 μm. Τα υμένια που παρασκευάστηκαν χρησιμοποιήθηκαν σε ευαισθητοποιημένες φ/β κυψελίδες και μελετήθηκε η επίδραση της δομής τους στην απόδοση των κυψελίδων. Για τα υμένια Pt αναπτύχθηκαν δυο διαφορετικοί τρόποι παρασκευής (θερμική διάσπαση αλάτων Pt, ηλεκτροαπόθεση). Τα υμένια που προέκυψαν αξιολογήθηκαν με βάση τη μορφολογία και τις καταλυτικές τους ιδιότητες ως προς την αναγωγή των ιόντων τριωδίου και προτάθηκαν τρόποι για τη βελτιστοποίησή τους. Ιδιαίτερη βαρύτητα δόθηκε στη σταθερότητα των υμενίων Pt κατά την παραμονή τους σε διάλυμα ηλεκτρολύτη, ίδιο με αυτό που χρησιμοποιείται στις ευαισθητοποιημένες κυψελίδες. Τέλος τα υμένια TiO2 και Pt ενσωματώθηκαν σε πρότυπες φωτοηλεκτροχρωμικές διατάξεις, στις οποίες η ενέργεια που απαιτείται για τη μεταβολή της διαπερατότητάς τους παρέχεται από την ενσωματωμένη φ/β κυψελίδα. Μάλιστα προτάθηκε και μελετήθηκε ένας νέος τύπος διάταξης.
In this PhD thesis we have studied and prepared nanostructured titanium dioxide (TiO2) and platinum (Pt) thin films, in order to use them for dye sensitized solar cells. The morphology and the structure of the TiO2 films were examined with scanning electron microscopy (SEM) and x-ray diffraction (XRD). We have proposed the use of nitric acid, among four other acids, in order to achieve a more efficient dispersion of TiO2 nanoparticles and to prepare uniform and crack free films, with thickness above 10 μm. The TiO2 films were used in dye sensitized solar cells and was examined the relation between the structure of the films and the efficiency of the cells. For the deposition of Pt films we have used two different methods (thermal decomposition of Pt salts and electrodeposition). The films were characterized according to their morphology and their catalytic activity towards triiodide ions reduction. Moreover we have proposed methods for improving the properties of Pt films and we have studied their stability, especially when the films were stored in the same electrolyte solution as that in dye sensitized solar cells. Finally the TiO2 and Pt films were used in photoelectrochromic devices, where the energy produced by the photovoltaic cell is used for the modulation of device’s transmittance. Also a new type of a photoelectrochromic device was introduced and studied.

碩士
輔仁大學
物理學系
99
The purposes of this studyis to reduce the energy gap of TiO2 films by doping nitrogen, so that the films can still have phtocatalytic effect in visible light. This experiment consists of two parts. At the first part, we deposit TiO2 film by arc ion plating to understand its general characteristic. At the same time ,we observe the films surface structure by Electron Microscope(SEM) and Atomic Force Microscope(AFM) and find the best ellipsometry model to fit Optical constant. And then we use different nitrogen pressure to deposit the N-doped TiO2 films and fitting by the best ellipsometry model. Research the relationship between nitrogen pressure and optic characteristic. The results show that index of refraction and deposition rate increase as the flux of nitrogen increases, but index of refraction turn down when the nitrogen pressure is 4.4×10-3 torr. At the second part, we research the energy gap of film, phtocatalytic effect and binding . Because all the film in this research are amorphous, we use the ellipsometry TL-model fitting band gap. The results show that when the flux of nitrogen increases, the energy gap is gradually narrowing, but it will turn up when nitrogen pressure up to3.0x10-3torr. Besides, we proved the accordingly by photocatalyst Methylene Blue test, and when the above-mentioned happened, the N-doped TiO2 films binding had been changed. We can also evidence the change with XPS. In conclusion, we have been narrowed the original TiO2 film energy gap effectively, and confirmed the phtocatalytic effect through Methylene Blue test in this research.

碩士
逢甲大學
材料科學所
93
The great demand for petrochemical energy has led to the development of alternative power sources, such as solar cells, recent years and is expected to be clean energy source of the future. Development of solar cells from silicon-based devices to the new dye-sensitized type, referred to as dye-sensitized solar cells (DSSC), is a great step forward in this area, such as simpler fabrication techniques and reduced costs. The most common DSSC under current development is the titanium dioxide based type. Various production methods have been developed to fabricate TiO2 films for DSSC. The wet processes used are extensively investigated, but have disadvantages in terms of chemical by-products and the requirement for a post heat treatment, of over 400°C, in order to encourage anatase crystal growth. To overcome these short falls, vacuum deposition processes have been developed for the deposition of TiO2 layers. In this study, an arc ion plating (AIP) system shall be used to prepare the TiO2 layer, as this process is environmentally friendly, clean, relatively uncomplicated and may reduce solar cell production costs. Deposition parameters including oxygen partial pressure, substrate bias, deposition pressure and deposition time are varied to examine their effects on the microstructure and photovoltaic efficiency of the TiO2 deposits in form of the device ITO glass/〔TiO2(N3 dye)〕/ I + LiI electrolyte/Pt/ITO glass. Experimental results show that the increased oxygen partial pressure over 0.35 Pa favors the growth of stiochiometric TiO2 films, which are visually transparent and present anatase crystal structure. The substrate bias induces a denser film growth and hence higher transparency. When increasing deposition pressure, anatase phase become dominate and a loose film structure can be obtained due to thermalization effect. An excessive deposition pressure leads to the fine-grain growth of the deposit. In contrast to the thinner film deposited at shorter time, the thicker film presents less amount of rutile phase and high specific surface area. A dual-target AIP enhances the film growth rate. In summary the microstructure mentioned above, short current as an indication of photovoltaic efficiency of the solar cell device composed of AIP-TiO2 can be increased by the increasing oxygen partial pressure due to the increased amount of high crystallinity stiochiometric TiO2 film. A negative effect to the short current can be found by applying substrate bias owing to the reduced specific surface area of the denser film. The increased deposition pressure although is beneficial to the growth of loose films which exhibit higher short current, an excessive deposition pressure would then cause the fine-grain growth of the deposit and eventually decrease short current. A longer deposition time facilitate a thicker film with lager specific surface area there by larger short current. Under a pure oxygen deposition condition without substrate bias, a TiO2 film deposited for 60 min posses a short current of 0.052 mA/cm2 in corresponding to a photovoltaic efficiency of 0.08%. The dual-target AIP system minimizes the deposition time into 30 min while results similarly. Accordingly, the photovoltaic efficiency of AIP-TiO2 film is necessitated by the amount of anatase phase in the deposit. It is then determined by the specific surface area of the deposited film. It is recommended that an optimized TiO2 film can be obtained in a deposition condition with pure oxygen, under moderate deposition pressure whilst keeping no substrate bias for a satisfactory deposition time. Also noticeable is the substrate temperature can be below 350℃.

碩士
逢甲大學
材料科學所
91
Titanium dioxide photocatalyst is well developed and wildly used due to its safety, highly catalytic activity, and self-cleaning properties. However, recycling of TiO2 powder is difficult. This motivates the development of TiO2 thin-films processes to extend its application. In this study, arc ion plating technique was used to deposit TiO2 films on glass substrate. The influence of three most effective deposition parameters - deposition time, oxygen partial pressure, and substrate bias were discussed respectively. The cross sectional morphology, surface morphology, and microstructure was observed by SEM and XRD respectively. The photocatalysis-induced decolorization of methylene blue aqueous solution was measured by UV-visible spectrometer as an indication of photocatalytic activity of TiO2 thins to reveal the relationship between deposition parameters, film structure, and photocatalytic property. Experimental results show that the deposited films with anatase structure exhibit the higher photocatalytic efficiency. Photocatalytic efficiency increases with the fraction of anatase phase in TiO2 films. Crystallinity of TiO2 films is not only affected by substrate temperature but also by oxygen partial pressure. In high oxygen atmosphere, the probability of titanium ions reacting with oxygen to form the saturated TiO2 stoichiometry is increased, so that higher photocatalysis efficiency is obtained. Surface hardness of TiO2-coated glass specimen was found to be dependent on film thickness. The scratch test results show that the TiO2 films remain fully adherent. It is demonstrated that using arc ion plating can deposit photocatalytic TiO2 films onto glass substrate successfully. The high mechanical strength of films also promotes their potential in future environmental application.

碩士
國立臺北科技大學
製造科技研究所
107
Deep eutectic solvent (DES) is a new generation of ionic liquids. It has the advantages of cheap raw materials, simple synthesis, non-toxic, biodegradable, non-flammable, non-volatile, high viscosity, easy to store and good solubility. DES has the potential to replace traditional aqueous solutions as a new generation of organic and inorganic solvents. Supercritical CO2 has low viscosity, low surface tension and high diffusivity. The coating prepared in supercritical CO2 environment has good coverage and uniformity. The supercritical CO2 process can increase the hardness of the coating when used in electroplating solution. In this study, DES from the mixture of choline chloride and urea in 1:2 molar ratio and supercritical carbon dioxide was used as the electrolyte for electroplating nickel. Our study has found that the Ni coating prepared in the DES has a higher hardness than conventional aqueous solutions. Moreover, with the introduction of supercritical carbon dioxide further increased the coating’s hardness than its conventionally electroplated counterpart. Due to the low surface tension properties of supercritical carbon dioxide, the electroplated Ni coating has better surface roughness than conventional plating. The raise in the DES electrolyte temperature increased the current efficiency in plating because of the higher ion transfer efficiency. Adding saccharin in supercritical plating can improve current efficiency, lower grain size, surface roughness, internal stress and raise corrosion resistance.

Nous avons analysé le rôle joué dans les processus de détection, par des agrégats métalliques de Pt et de Pd dispersés dans des films minces de SnO2 destinés à la détection des gaz polluants réducteurs comme le CO, H2S ou NOx. L'évolution de l'état d'oxydation des agrégats de platine a été suivie par Spectroscopie d'Absorption X (XAS) in situ. Lorsqu'elles sont incorporées en quantité très faible, les particules de platine changent, d'une façon réversible, leur état d'oxydation, selon la nature de l'atmosphère environnante. L'état d'oxydation des particules dépend fortement de leur taille, (entre 0,5 et 4,5 nm) les plus petites passant d'un état complètement oxydé à un état fortement réduit -les liaisons Pt - O laissant place à des Pt - C lorsque les films sont en présence de CO. L'évolution de la conductance électrique lorsque les films sont mis en présence de CO a été corrélée à la rapidité de la réaction du réduction de platine. Une interaction électronique métal-SnO2 est à l'origine du pic de conductance observé à basse température. Une étude comparative des réponses électriques des couches platinées et dopées palladium, en présence de CO, H2 et H2S, a permis de proposer différents mécanismes de détection relatifs à chacun des gaz étudiés.