Made available in DSpace on 2016-06-02T20:35:00Z (GMT). No. of bitstreams: 1 6529.pdf: 5035748 bytes, checksum: 4afc5839aca3dce1e8643fcdf8100d4c (MD5) Previous issue date: 2014-07-18 / Financiadora de Estudos e Projetos / In both industry and academia the interest in biomass conversions into manufactured products has grown rapidly in recent years. Various products can be obtained from alcohol chemistry such as acetaldehyde, ethyl acetate, hydrogen, and others. Although copper-based catalysts are commonly used in the dehydrogenation of ethanol to acetaldehyde, recently Cu/ZrO2 catalysts have also revealed themselves to be highly active in the onepot transformation of ethanol into ethyl acetate. In this work, we studied the one-pot synthesis of ethyl acetate from ethanol by using two separate series of catalysts, Cu-Ag/ZrO2 and Cu/ZrO2/Al2O3. The characterization of the supports and catalysts were performed by N2 physisorption, X-ray diffraction, thermogravimetry, temperature programmed reduction, Fourier transformed infrared spectroscopy of the adsorbed CO (DRIFTS-CO), X-ray photoelectrons spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS). In the first part of this work, the study of the series of Cu-Ag/ZrO2 catalysts suggested that the Ag-Cu surface alloying alter the electronic properties in the catalysts surface, as verified by DRIFTS-CO. XPS measurements showed that increasing the Ag content in Cu-Ag/ZrO2 catalysts lead to a higher ratio Cu+/Cu0 on the surface. The predominance of Cu+ species on the surface led to catalysts with higher selectivity to acetaldehyde over ethyl acetate. The second part of this work studied the influences of Cu active phase dispersion on the ZrO2/Al2O3 support. Different Cu+/Cu0 species ratio, as verified by XPS, were obtained by varying the Cu content on ZrO2/Al2O3. Furthermore, the EXAFS results revealed that for the reduced catalyst increasing the Cu loading led to an enlargement in the size of the Cu0 particle. DRIFTS-CO showed that CO adsorption into these catalysts may be occurring on the surface of the copper xvi particles deposited on Al2O3 and/or ZrO2, since ZrO2 may not to be covering the whole Al2O3. Catalytic tests show that the products distribution in the one-pot ethanol conversion is affected by Cu0/Cu+ species ratio on the surface of the catalyst as well as the acid/base properties of the support. The increase of the Cu loading up to 30 wt. % favored the selectivity to ethyl acetate (67 % at 250 oC), due to an optimized Cu0/Cu+ species ratio on the surface of ZrO2/Al2O3 support. Theoretically, by increasing the relative Cu0 concentration, the formation of acyl species increases, which condenses with ethoxy species formed on Zrδ+ and Cu+ Lewis acid sites for the formation of ethyl acetate. Additionally, the Cu content of 30 wt. % provides greater surface coverage of the support ZrO2/Al2O3 suppressing the formation of acetaldehyde condensation products on the ZrO2 surface, such as crotonaldehyde; and further methyl ethyl ketone and diethyl ether formed in the alumina acid sites. / O interesse pela conversão de biomassa em produtos manufaturados tem crescido rapidamente nos últimos anos na indústria e na academia. Diversos produtos podem ser obtidos através da alcoolquímica, tais como acetaldeído, acetato de etila, hidrogênio, entre outros. Catalisadores à base de cobre são comumente utilizados na desidrogenação do etanol em acetaldeído, mas recentemente, catalisadores de Cu/ZrO2 mostraram-se altamente ativos na transformação direta do etanol em acetato de etila. Neste trabalho, a síntese direta de acetato de etila a partir do etanol foi estudada em duas séries distintas de catalisadores, Cu-Ag/ZrO2 e Cu/ZrO2/Al2O3. As caracterizações dos suportes e catalisadores foram efetuadas por fisissorção de N2, difração de raios X, termogravimetria, redução à temperatura programada, espectroscopia de refletância difusa na região do infravermelho com transformada de Fourier do CO adsorvido (DRIFTS-CO), espectroscopia de fotoelétrons excitados por raios X (XPS) e espectroscopia de estrutura fina estendida de absorção de raios X (EXAFS). Na primeira parte do trabalho, o estudo da série de catalisadores Cu- Ag/ZrO2 sugere que a formação da liga de superfície Cu-Ag modificou as propriedades eletrônicas da superfície dos catalisadores, como observado por DRIFTS-CO. Medidas de XPS mostraram que o aumento do teor de Ag nos catalisadores Cu-Ag/ZrO2 promoveu a formação de catalisadores com uma maior razão Cu+/Cu0 na superfície. A predominância da espécie Cu+ na superfície levou a catalisadores mais seletivos a acetaldeído em relação ao acetato de etila. A segunda parte do trabalho consistiu no estudo da influência da dispersão da fase ativa Cu sobre o suporte ZrO2/Al2O3. Diferentes razões das espécies Cu+/Cu0, identificadas por XPS, foram obtidas através da variação do teor de Cu sobre ZrO2/Al2O3. Os resultados de EXAFS para os catalisadores xiv reduzidos mostraram que o aumento do teor de Cu levou ao aumento do tamanho das partículas de Cu0. DRIFTS-CO sugere que a adsorção de CO sobre estes catalisadores pode estar ocorrendo na superfície de partículas de cobre. depositadas sobre a Al2O3 e/ou sobre a ZrO2, já que possivelmente a ZrO2 não está recobrindo toda a Al2O3. Testes catalíticos indicaram que a distribuição dos produtos na transformação direta de etanol é afetada pela composição de espécies Cu0/Cu+ na superfície do catalisador, bem como pelas propriedades ácido/base do suporte. O aumento do teor de Cu até 30 % favoreceu a seletividade ao acetato de etila (67 % a 250 oC), sendo atribuído à otimização da razão das espécies Cu0/Cu+ na superfície do suporte ZrO2/Al2O3. Possivelmente, com o aumento da concentração do Cu0 tem-se o aumento de espécies acila adsorvidas, as quais condensam com as espécies etóxido formadas em sítios ácidos Lewis de Cu+ e Zrδ+, para a formação do acetato de etila. O teor de 30 % de Cu proporcionou um maior recobrimento da superfície do suporte ZrO2/Al2O3 suprimindo a formação de produtos de condensação do acetaldeído na superfície da ZrO2, como o crotonaldeído; e ainda metil-etil-cetona e éter dietílico formados nos sítios ácidos da alumina.

Made available in DSpace on 2016-06-02T19:55:40Z (GMT). No. of bitstreams: 1 TeseACSFS.pdf: 1345541 bytes, checksum: 739bf6a345f45db1143fd6e560bf7977 (MD5) Previous issue date: 2005-03-10 / Universidade Federal de Sao Carlos / The effect of CeO2 loading in Pt/CeO2-Al2O3 catalysts was investigated. Pt catalysts supported on mixed CeO2-Al2O3 carriers with different CeO2 loading 1, 3, 6, 12, 20 wt.% were prepared by incipient wetness impregnation method. For all samples, the Pt content was about 1 wt.%. The catalysts were characterized by SBET, X-ray diffraction (XRD), temperature-programmed reduction (TPR), UVVis diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), reaction of dehydrogenation of cyclohexane and oxygen storage capacity (OSC) measurements. SBET results showed that the ceria promoted the stabilization of the superficial area of the alumina in samples of CeO2-Al2O3 with low CeO2 content (≤ 6%). XRD showed the formation of nanocrystallites of ceria on alumina surface when the amount of CeO2 was higher than 6 wt.%. TPR patterns indicated that the presence of Pt promoted the reduction of CeO2 in lower temperature than what was observed for the CeO2-Al2O3 supports. The increase of CeO2 loading lead to an increment in the OSC. The results for the reactions of partial oxidation, steam reforming and autothermal reforming of methane revealed that the activity of Pt/CeO2-Al2O3 catalysts was dependent of the CeO2 loading. Pt catalyst with CeO2 loading higher than 12 wt.% exhibited the highest specific activity and stability for partial oxidation of methane. This high stability was attributed to a combination of the properties as the presence of the CeO2 fluorite structure and different OSC values. Although the superficial structure of Pt did not show a decisive role for the high stability of Pt/CeO2-Al2O3 catalysts with CeO2 loading higher than 12 wt.%, the different Pt morphologies can show different rates for methane activation resulting in a better performance of surface carbon removal and therefore making more Pt sites available to the reaction. / O efeito do teor de CeO2 em catalisadores de Pt/CeO2-Al2O3 foi investigado. Os catalisadores de Pt suportados no óxido misto CeO2-Al2O3 contendo 1, 3, 6, 12 e 20 % de CeO2 foram preparados pelo método de impregnação. As amostras foram preparadas contendo 1% em peso de Pt. Os catalisadores foram caracterizados por medida da área superficial (BET), difração de raios X (DRX), redução à temperatura programada (TPR), espectroscopia de reflectância difusa no UVVisível (DRS), espectroscopia fotoeletrônica de raios X (XPS), reação de desidrogenação do cicloexano e medida da capacidade de armazenamento de oxigênio (OSC). Os resultados de BET mostraram que a céria promoveu a estabilização da área superficial da alumina nas amostras de CeO2-Al2O3 para teores de CeO2 ≤ 6%. Os resultados de DRX revelaram que nas amostras contendo mais de 6% de CeO2, a estrutura fluorita da céria é detectável. Os dados de TPR indicaram que a presença de Pt promoveu a redução da céria em região de menor temperatura em relação ao suporte CeO2-Al2O3. Com o aumento do teor de CeO2 tem-se o aumento no valor de OSC. Os testes de atividade para as reações de oxidação parcial, reforma a vapor e reforma autotérmica do metano revelaram que a atividade dos catalisadores de Pt/CeO2-Al2O3 foi dependente do teor de CeO2. Os catalisadores com teores de CeO2 ≥ 12% apresentaram alta atividade e estabilidade para a reação de oxidação parcial do metano. Essa alta estabilidade foi atribuída a uma combinação das propriedades como a presença da estrutura fluorita do CeO2 e diferentes valores de OSC. Embora a estrutura superficial da Pt não tenha apresentado um papel determinante para a elevada estabilidade dos catalisadores Pt/CeO2-Al2O3 com teores de CeO2 ≥ 12%, as diferentes estruturas da Pt podem mostrar diferentes velocidades para a ativação do metano resultando em uma maior eficiência na remoção de carbono da superfície do metal tornando os sítios de Pt disponíveis para a reação.

Made available in DSpace on 2014-06-11T19:29:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-07-06Bitstream added on 2014-06-13T18:38:54Z : No. of bitstreams: 1 klein_is_me_araiq.pdf: 1781422 bytes, checksum: 6f5028c57d1a8baefe1e772753ae105c (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Vidros no sistema binário NaPO3-WO3 vem despertando intenso interesse acadêmico e tecnológico devido as suas propriedades ópticas promissoras tais como fotocromismo, termocromismo e eletrocromismo, bem como altos índices de refração não-lineares. Contudo, um estudo de inclusão de nanopartículas metálicas nestes vidros ainda não foi desenvolvido, o que poderia potencializar as suas aplicações já conhecidas. Neste trabalho, foram obtidos vidros no sistema NaPO3-WO3-Ag2O, em que a concentração de óxido de tungstênio foi mantida fixa a 50% em mol, e variou-se a concentração de prata. A presença das nanopartículas de Ag em vidros submetidos a tratamento térmico foi confirmada por Microscopia Eletrônica de Transmissão, em que foi obtido o tamanho médio das partículas em função da concentração de Ag. No sistema estudado, foi confirmada a presença das unidades estruturais constituintes do sistema binário NaPO3-WO3, utilizando-se diversas técnicas espectroscópicas. A coloração dos vidros depende da concentração de prata incluída no sistema, em que as concentrações mais baixas (5-10% em mol) apresentam coloração vermelha, e em vidros contendo 12,5 a 20% em mols do metal apresentam coloração amarela. A fim de elucidar as diferenças entre estes domínios de concentração e coloração, diversas espectroscopias foram utilizadas, incluido Espectroscopia de Fotoelétrons induzida por raios- X (XPS), a qual permitiu concluir que todas as amostras possuem apenas tungstênio no seu estado mais oxidado (W+6), estando apenas “parcialmente” reduzido pela influência da prata nas amostras. Sugere-se que as diferenças entre os vidros então se devam principalmente na influência das ressonâncias de plasmon apresentadas pelas nanopartículas metálicas, sendo estas confirmadas por Espectroscopia Eletrônica na região do UV-Vis. / Glasses in binary system NaPO3-WO3 are of great interest due to its promising optical properties, such as photochromism, thermochromism and electrochromism, as well as high non-linear refraction index. However, a study concerning metallic nanoparticle inclusion into these glasses has not been reported yet. In this work, glasses in the system NaPO3-WO3-Ag2O were prepared keeping tungsten oxide concentration constant at 50% mol concentration rate and varying silver concentration. Glass samples submitted to adequate thermal treatment shown the presence of Ag nanoparticles confirmed by Transmission Electron Microscopy, which allowed to determine nanoparticle average size versus Ag concentration. In this system, the constituting structural units of the binary system NaPO3-WO3 were confirmed by several spectroscopic techniques. The coloration of glasses is directly correlated to silver concentration, showing a red color at lower amount of silver (5-10% mol) and yellowish for silver concentration in the range from 12.5 to 20% mol. To understand this behavior, several spectroscopy techniques were used, including X-Ray Photoelectron Spectroscopy (XPS), indicating the presence of tungsten only in its most oxidized form (W+6) been only “partially” reduced by the influence of silver. We suggest that the difference between the glasses arise mostly on plasmon resonance of the metallic nanoparticles, confirmed by UV-Vis Electronic Spectroscopy.

abstract: In this dissertation, the interface chemistry and electronic structure of plasma-enhanced atomic layer deposited (PEALD) dielectrics on GaN are investigated with x-ray and ultraviolet photoemission spectroscopy (XPS and UPS). Three interrelated issues are discussed in this study: (1) PEALD dielectric growth process optimization, (2) interface electronic structure of comparative PEALD dielectrics on GaN, and (3) interface electronic structure of PEALD dielectrics on Ga- and N-face GaN. The first study involved an in-depth case study of PEALD Al2O3 growth using dimethylaluminum isopropoxide, with a special focus on oxygen plasma effects. Saturated and self-limiting growth of Al2O3 films were obtained with an enhanced growth rate within the PEALD temperature window (25-220 ºC). The properties of Al2O3 deposited at various temperatures were characterized to better understand the relation between the growth parameters and film properties. In the second study, the interface electronic structures of PEALD dielectrics on Ga-face GaN films were measured. Five promising dielectrics (Al2O3, HfO2, SiO2, La2O3, and ZnO) with a range of band gap energies were chosen. Prior to dielectric growth, a combined wet chemical and in-situ H2/N2 plasma clean process was employed to remove the carbon contamination and prepare the surface for dielectric deposition. The surface band bending and band offsets were measured by XPS and UPS for dielectrics on GaN. The trends of the experimental band offsets on GaN were related to the dielectric band gap energies. In addition, the experimental band offsets were near the calculated values based on the charge neutrality level model. The third study focused on the effect of the polarization bound charge of the Ga- and N-face GaN on interface electronic structures. A surface pretreatment process consisting of a NH4OH wet chemical and an in-situ NH3 plasma treatment was applied to remove carbon contamination, retain monolayer oxygen coverage, and potentially passivate N-vacancy related defects. The surface band bending and polarization charge compensation of Ga- and N-face GaN were investigated. The surface band bending and band offsets were determined for Al2O3, HfO2, and SiO2 on Ga- and N-face GaN. Different dielectric thicknesses and post deposition processing were investigated to understand process related defect formation and/or reduction. / Dissertation/Thesis / Ph.D. Physics 2014

The electric vehicle itself today outlives its battery, necessitating battery replacement. Lithium titanium oxide (LTO) has, in this context, been suggested as a new anode material in heavy electric vehicle applications due to intrinsic properties regarding safety, lifetime and availability. The work presented here is focused on the LTO electrode/electrolyte interface. Photoelectron spectroscopy (PES) has been applied to determine how and if the usage of LTO could prevent extensive anode-side electrolyte decomposition and build-up of a surface layer. The presence of a solid electrolyte interphase (SEI) comprising LiF, carbonates and ether compounds was found in half-cells utilizing a standard ethylene:diethylcarbonate electrolyte with 1 M LiPF6. Via testing of symmetrical LTO-LTO cells, the stability of the formed SEI was put in to question. Moreover, the traditional polyvinylidene difluoride (PVdF) binder was replaced by more environmentally benign carboxylmethyl cellulose (CMC) and polyacrilic acid (PAA) binders in LTO electrodes, and it was found that CMC helped to form a more stable surface-layer that proved beneficial for long term cycling. Following the half-cell studies, full-cells were investigated to observe how different cathodes influence the SEI of LTO. The SEI in full-cells displayed characteristics similar to the half-cells, however, when utilizing a high voltage LiNi0.5Mn1.5O4 cathode, more electrolyte decomposition could be observed. Increasing the operational temperature of this battery cell generated even more degradation products on the LTO electrodes. Mn was also found on the anode when using Mn-based cathodes, however, it was found in its ionic state and did not significantly affect the composition or behavior of the observed SEI layer. Furthermore, by exchanging the electrolyte solvent for propylene carbonate, the thickness of the SEI increased, and by replacing the LiPF6 salt for LiBF4 the stability of the SEI improved. Thus is it demonstrated that such a passivation can be beneficial for the long-term surface stability of the electrode. These findings can therefore help prolong the lifetime of LTO-based battery chemistries.

The research in this thesis aims to develop new mechanistic knowledge for coating processes at 2024-Al alloy surfaces, ultimately to aid the design of new protective coatings. Coatings formed by phosphating, chromating, and permanganating were characterized especially by scanning Auger microscopy (SAM), X-ray photoelectron spectroscopy, and scanning electron microscopy . The objective was to learn about growth (nm level) as a function of time for different coating baths, as well as a function of lateral position across the different surface microstructural regions, specifically on the μm-sized Al-Cu-Mg and Al-Cu-Fe-Mn particles which are embedded in the alloy matrix . The research characterizes coating thickness, composition, and morphology. The thesis emphasizes learning about the effect of different additives in zinc phosphating baths . It was found that the Ni²⁺ additive has two main roles : first, the rate of increase in local solution pH is limited by the slower kinetics of reactions involving Ni²⁺ compared to Zn²⁺, leading to thinner zinc phosphate (ZPO) coatings when Ni²⁺ is present. Second, most Ni²⁺ deposition occurs during the later stages of the coating process in the form of nickel phosphate and a Ni-Al oxide in the coating pores on the alloy surface, increasing the corrosion resistance. Aluminum fluoride precipitates first during the initial stages of the coating process, followed by aluminum phosphate, zinc oxide, and finally ZPO. When Ni²⁺ is present in the coating solution at 2000 ppm, ZnO predominates in the coating above the A-Cu-Fe-Mn particle while ZPO dominates on the rest of the surface. The Mn²⁺ additive gives a more even coating distribution (compared with Ni²⁺) across the whole surface. The Mn²⁺ -containing ZPO coating is similar to the chromate coating in terms of evenness, while there is more coating deposition at the second-phase particles for permanganate coatings. The oxides on the Al-Cu-Fe-Mn and matrix regions are similar before coating, thereby confirming that a variety of observed differences in ZPO coating characteristics at these regions arise from the different electrochemical characteristics of the underlying metals. Upon exposure to a corrosive solution, the ZPO coating provides more protection to the second-phase particles compared to the matrix. / Science, Faculty of / Chemistry, Department of / Graduate

Overhead conductors used in the transmission of power in grids around the world are generally subjected to ageing, which is the time-based change of their properties. Important properties such as corona discharge, audible noise, hydrophobicity and corrosion are usually considered and investigated. On some conductors such as the aluminium conductor steel reinforced (ACSR), a reduction in audible noise over exposure time to the service environment has been noted to occur. However, the converse has been observed for the gap-type thermal resistant aluminium conductor steel reinforced (GTACSR or “Matthew” conductor), although this conductor is preferred due to its high ampacity. The relationship between conductor hydrophobicity, audible noise, surface contamination and roughness, wettability and corrosion were investigated using All Aluminium Alloy Conductor (AAAC), Aluminium Conductor Composite Core (ACCC) and GTACSR samples. Findings from Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectric Spectroscopy (XPS) and contact angle measurements revealed that carbon, hydrocarbon and silicone contamination was responsible for the hydrophobic nature of the surface. Furthermore, electrochemical investigations and electron microscopy showed that pitting or/and crevice corrosion were the predominant corrosion mechanisms on these conductors. Exposure to simulated industrial and marine environments further confirmed this finding and also showed that general corrosion also occurs on relatively uncontaminated conductors, thereby changing their surface roughness, as seen from the White Light Interferometry results. Corrosion was observed to be accelerated by the presence of surface contaminants such as oils and carbon, as these facilitated water (droplet) retention by reducing the conductor’s surface energy. Reduction/elimination of surface contamination/hydrophobicity were the desired solutions to the problem, and this was achieved by grit blasting. Partial/complete oxidation of the silicones resulted in the reduction/elimination of sample hydrophobicity – this was seen from more contact angles measurements and XPS data. Grit blasting also restored conductor cleanliness and roughened the surface sufficiently to produce surface run-off.

Absorption of octadecanethiol and p-nitrobenzenethiol onto gold surfaces from ethanol solutions has been studied by means of contact angle, optical ellipsometry, angle-resolved XPS (ARXPS), and with grazing angle total reflection FTIR. Growth of the monolayers from dilute solutions has been monitored and Langmuir isotherm adsorption curves were fitted to experimental data. A saturated film is formed within approximately 5h after immersion in solutions of concentrations ranging from 0.0005mM to 0.01mM. We found, that the final density of monolayer depends on the concentration of the solution.

No description available.

Title: Electronics and adsorption properties of model catalytic systems contains cerium Author: Miloš Cabala Department: Department of Surface and Plasma Science, Supervisor: RNDr. Kateřina Veltruská, Department of Surface and Plasma Science, Abstract: The doctoral thesis contains the study of model catalyst systems based on cerium and ceria. The thesis deals with model systems of CeAg, CeO2/Cu(111), Ni- CeO2/Cu(111) a Ni-Sn-CeO2/Cu(111). We have studied these systems using photoelectron spectroscopy, ion scattering spectroscopy and low energy electron diffraction. Model systems were prepared under strictly defined conditions. The strong bimetallic interaction was observed on the CeAg layers. Molecular adsorption of carbon monoxide on CeAg was demonstrated. We also observed intensive reaction of these layers with oxygen. By measurements in different directions of surface Brillouin zone, we managed to reconstruct the band structure of the prepared CeO2/Cu(111) layer. We have shown that the Cu substrate interacts weakly with deposited CeO2 layer. This interaction results in a charge transfer from Cu into CeO2. Overall, in the valence spectrum we have identified three main electron bands corresponding to O 2p state bound in CeO2. It has been proven that the deposition of Ni on CeO2 layers leads to partial...