Katalytisk förbränning är en lovande teknik för användning vid kraftgenerering, särskilt för gasturbiner. Genom att använda katalytisk förbränning kan man nå mycket låga emissioner av kväveoxider (NOX), kolmonoxid (CO) och oförbrända kolväten (UHC) samtidigt, vilket är svårt vid konventionell förbränning. Förutom att man erhåller låga emissioner, kan katalytisk förbränning stabilisera förbränningen och kan därmed användas för att uppnå stabil förbränning för gaser med låga värmevärden. Denna avhandling behandlar huvudsakligen högtemperaturdelen av den katalytiska förbränningskammaren. Kraven på denna del har visat sig svåra att nå. För att den katalytiska förbränningskammaren ska kunna göras till ett alternativ till den konventionella, måste katalysatorer med bättre stabilitet och aktivitet utvecklas. Målet med denna avhandling har varit att utveckla katalysatorer med högre aktivitet och stabilitet, lämpliga för högtemperaturdelen av en katalytisk förbränningskammare för förbränning av naturgas. En mikroemulsionsbaserad framställningsmetod utvecklades för att undersöka om den kunde ge katalysatorer med bättre stabilitet och aktivitet. Bärarmaterial som är kända för sin stabilitet, magnesia och hexaaluminat, framställdes med den nya metoden. Mikroemulsionsmetoden användes också för att impregnera de framställda materialen med de mer aktiva materialen perovskit (LaMnO3) och ceriumdioxid (CeO2). Det visade sig att mikroemulsionsmetoden kan användas för att framställa katalysatorer med bättre aktivitet jämfört med de konventionella framställningsmetoderna. Genom att använda mikroemulsionen för att lägga på aktiva material på bäraren erhölls också en högre aktivitet jämfört med konventionella beläggningsstekniker. Eftersom katalysatorerna ska användas under lång tid i förbräningskammaren utfördes också en åldringsstudie. Som jämförelse användes en av de mest stabila materialen som rapporterats i litteraturen: LMHA (mangan-substituerad lantan-hexaaluminat). Resultaten visade att LMHA deaktiverade mycket mer jämfört med flera av katalysatorerna innehållande ceriumdioxid på hexaaluminat som framställts med den utvecklade mikroemulsionstekniken. / Catalytic combustion is a promising technology for power applications, especially gas turbines. By using catalytic combustion ultra low emissions of nitrogen oxides (NOX), carbon monoxide (CO) and unburned hydrocarbons (UHC) can be reached simultaneously, which is very difficult with conventional combustion technologies. Besides achieving low emission levels, catalytic combustion can stabilize the combustion and thereby be used to obtain stable combustion with low heating-value gases. This thesis is focused on the high temperature part of the catalytic combustor. The level of performance demanded on this part has been proven hard to achieve. In order to make the catalytic combustor an alternative to the conventional flame combustor, more stable catalysts with higher activity have to be developed. The objective of this work was to develop catalysts with higher activity and stability, suitable for the high-temperature part of a catalytic combustor fueled by natural gas. A microemulsion-based preparation method was developed for this purpose in an attempt to increase the stability and activity of the catalysts. Supports known for their stability, magnesia and hexaaluminate, were prepared using the new method. The microemulsion method was also used to impregnate the prepared material with the more active materials perovskite (LaMnO3) and ceria (CeO2). It was shown that the microemulsion method could be used to prepare catalysts with better activity compared to the conventional methods. Furthermore, by using the microemulsion to apply active materials onto the support a significantly higher activity was obtained than when using conventional impregnation techniques. Since the catalysts will operate in the catalytic combustor for extended periods of time under harsh conditions, an aging study was performed. One of the most stable catalysts reported in the literature, LMHA (manganese-substituted lanthanum hexaaluminate), was included in the study for comparison purposes. The results show that LMHA deactivated much more strongly compared to several of the catalysts consisting of ceria supported on lanthanum hexaaluminate prepared by the developed microemulsion method. / QC 20101104

Research on the cure and early detection of diseases such as diabetes, Alzheimer's, and Parkinson's is becoming of great interest due to the increasing number of people affected by them every year. An accurate and quick detection of various damaging species is highly critical in treatments of such diseases not only for exploring possible cures but also for early detection. If these diseases are detected during the initial stages than the possibility of curing them is much higher. Motivated by this, many researchers today have developed numerous types of sensing devices that can detect various physiological and biological compounds. However, most of these sensors are enzyme based. They have several setbacks such as the lack of sensitivity, restricted selectivity, short shelf life, and biological fouling. To overcome these obstacles, we examine the use of nanoceria modified Pt and Au electrodes for the detection of glucose and reactive oxygen species such as hydrogen peroxide. Amperometric detection of glucose and hydrogen peroxide is critical for biological applications for diabetes and possible Alzheimer's and Parkinson's patients. This dissertation focuses on the exploration of non-enzymatic detection of glucose and reactive oxygen species which has the prospective to be used for biological applications, in addition to an investigation of an odor control technology that uses these reactive oxygen species for the treatment of wastewater plants. The combination of bi-metallic composites with nanoceria showed increased oxidation ability towards glucose and hydrogen peroxide. The following dissertation expands on the relationship between bi-metallic nanoceria composite materials and its electro-oxidation of glucose and hydrogen peroxide towards biological sensing along with an investigation of an odor control technology that utilizes generates hydroxyl radical fine particle mist for the degradation of hydrogen sulfide odor in wastewater treatment plants.

Cerium oxide (ceria)-based materials in the nanoscale regime are of significant fundamental and technological interest. Nanoceria in pure and doped forms has current and potential use in solid oxide fuel cells, catalysis, UV- screening, chemical mechanical planarization, oxygen sensors, and bio-medical applications. The characteristic feature of Ce to switch between the +3 and + 4 oxidation states renders oxygen buffering capability to ceria. The ease of this transformation was expected to be enhanced in the nanoceria. In most the practical scenarios, it is necessary to have a stable suspension of ceria nanoparticles (CNPs) over longer periods of time. However, the existing literature is confined to short term studies pertaining to synthesis and property evaluation. Having understood the need for a comprehensive understanding of the CNP suspensions, this dissertation is primarily aimed at understanding the behavior of CNPs in various chemical and physical environments. We have synthesized CNPs in the absence of any surfactants at room temperature and studied the aging characteristics. After gaining some understanding about the behavior of this functional oxide, the synthesis environment and aging temperature were varied, and their affects were carefully analyzed using various materials analysis techniques such as high resolution transmission electron microscopy (HRTEM), UV-Visible spectroscopy (UV-Vis), and X-ray photoelectron spectroscopy (XPS). When the CNPs were aged at room temperature in as-synthesized condition, they were observed to spontaneously assemble and evolve as fractal superoctahedral structures. The reasons for this unique polycrystalline morphology were attributed to the symmetry driven assembly of the individual truncated octahedral and octahedral seed of the ceria. HRTEM and Fast Fourier Transform (FFT) analyses were used to explain the agglomeration behavior and evolution of the octahedral morphology. Some of the observations were supported by molecular dynamic simulations. Poly (ethylene glycol) (PEG) and ethylene glycol (EG) were used to control the kinetics of this morphology evolution. The ability to control the agglomeration of CNPs in these media stems from the lower dielectric constant and an increased viscosity of the EG and PEG based solvents. CNPs when synthesized and aged in frozen conditions, i.e. in ice, were found to form one dimensional, high aspect ratio structures. A careful analysis has provided some evidence that the CNPs use the porous channels in ice as a template and undergo oriented attachment to form nanorods. When the aging treatment was done near freezing temperature in solution, the nanorods were not observed, confirming the role of channels in ice. When synthesized in aqueous media such as DI water, PEG and EG; CNPs were observed to exhibit a reversible oxidation state switching between +3 and +4. Band gap values were computed from the optical absorption data. The changes in the band gap values observed were attributed to the changes in the oxidation state of CNPs as opposed to the quantum confinement effects, as expected in other nanoparticle systems. The work presented in this dissertation demonstrates, with evidence, that in order to obtain a comprehensive understanding of the properties of nanoscale materials it is of paramount importance to monitor their behavior over relatively longer periods of time under various ambient environments. While the solution based techniques offer a versatility and low cost route to study the fundamental properties of nanomaterials, they suffer some inherent problems such as precursor contamination and uncontrolled chemical reactions. Especially when analyzing the behavior of ceria-based materials for applications like solid oxide fuel cells, a great control in the density and crystalline quality are desired. In order to achieve this, as a first step pure ceria thin films were synthesized using oxygen plasma assisted molecular beam epitaxy (OPA-MBE). The ceria films were analyzed using various in situ and ex situ techniques to study the crystal structure, growth mode and epitaxial quality of the films. It was observed that the epitaxial orientation of the ceria films could be tuned by varying the deposition rate. When the films were grown at low deposition rate (< 8 Å/min) ceria films with epitaxial (200) orientation were observed where as the films grown at high deposition rates (up to 30 Å/min) showed (111) orientation. Theoretical simulations were used to confirm some of the experimental facts observed in both nanoparticles and thin films.

No description available.

No description available.

This study mainly explores the development of alternative cathode materials for the electrochemical reduction of CO₂ by high temperature solid oxide electrolysis cells (HTSOECs), which operate in the reverse manner of solid oxide fuel cells (SOFCs). The conventional Ni-yttria stabilized zirconia (YSZ) cermets cathode suffered from coke formation, whereas the perovskite-type (La, Sr)(Cr, Mn)O₃ (LSCM) oxide material displayed excellent carbon resistance. Initial CO₂ electrolysis performance tests from different cathode materials prepared by screen-printing showed that LSCM based cathode performed poorer than Ni-YSZ cermets, due to non-optimized microstructure. Efforts were made on microstructure modification of LSCM based cathodes by means of various fabrication methods. Among the LSCM/YSZ graded cathode, extra catalyst (including Pd, Ni, CeO₂, and Pt) aided LSCM/GDC (Gd₀.₁Ce₀.₉O₁.₉₅) cathode, LSCM impregnated YSZ cathode, and GDC impregnated LSCM cathode, the GDC impregnated LSCM cathode, with porous LSCM as backbone for finely dispersed GDC nanoparticles, was found to possess the desired microstructure for CO₂ splitting reaction via SOEC. Incorporating of 0.5wt% Pd into GDC impregnated LSCM cathode gave rise to an Rp of 0.24 Ω cm² at open circuit voltage (OCV) at 900°C in CO₂-CO 70-30 mixture, comparable with the Ni/YSZ cermet cathode operated in the identical conditions. Meanwhile, the cathode kinetics and possible mechanisms of the electrochemical reduction of CO₂ were studied, and factors including CO₂/CO composition, operation temperature and potential were taken into account. The current-to-chemical efficiency of CO₂ electrolysis was evaluated with gas chromatography (GC). The high performance Pd and GDC co-impregnated LSCM cathode was also applied for CO₂ electrolysis without protective CO gas in feed. This cathode also displayed superb performance towards CO₂ electrochemical reduction under SOEC operation condition in CO₂/N₂ mixtures, though it had OCV as low as 0.12V at 900°C. The LSCM/GDC set of SOEC cathode materials were investigated in the application of steam electrolysis and H₂O-CO₂ co-electrolysis as well. For the former, adequate supply of steam was essential to avoid the appearance of S-shaped I-V curves and limited steam transport. The 0.5wt% Pd and GDC co-infiltrated LSCM material has been found to be a versatile cathode with high performance and good durability in SOEC operations.

Corrosion of metallic materials is a natural process, and our study shows that even in an alkaline environment severe corrosion may occur on a carbon steel surface. While corrosion cannot be stopped it can be retarded. Many of the traditional anti-corrosion approaches such as the chromate process are effective but hazardous to the environment and human health. Mefp-1, a protein derived from blue mussel byssus, is well known for its extraordinary adhesion and film forming properties. Moreover, it has been reported that Mefp-1 confers a certain corrosion protection for stainless steel. All these facts indicate that this protein may be developed into corrosion inhibitors with ‘green’, ‘effective’ and ‘smart’ properties. In this study, a range of surface-sensitive techniques have been used to investigate adsorption kinetics, film forming and film compaction mechanisms of Mefp-1. In situ atomic force microscopy (AFM) enables the protein adsorption on substrates to be visualized, whereas the ex situ AFM facilitates the characterization of micro- and nano-structures of the protein films. In situ Peak Force AFM can be used to determine nano-mechanical properties of the surface layers. The quartz crystal microbalance with dissipation monitoring (QCM-D) was used to reveal the build-up of the Mefp-1 film on substrates and measure the viscoelastic properties of the adsorbed film. Analytical techniques and theoretical calculations were applied to gain insights into the formation and compaction processes such as oxidation and complexation of pre-formed Mefp-1 films. The electron probe micro analyzer (EPMA) and X-ray photoelectron spectroscopy (XPS) were utilized to obtain the chemical composition of the surface layer. Electrochemical impedance spectroscopy (EIS) measurements were performed to evaluate the corrosion inhibition efficiency of different forms of Mefp-1 on carbon steel substrates. The results demonstrate that Mefp-1 adsorbs on carbon steel surfaces across a broad pH interval, and it forms a continuous film covering the substrate providing a certain extent of corrosion protection. At a higher pH, the adsorption is faster and the formed film is more compact. At neutral pH, results on the iron substrate suggest an initially fast adsorption, with the molecules oriented preferentially parallel to the surface, followed by a structural change within the film leading to molecules extending towards solution. Both oxidation and complexation of the Mefp-1 can lead to the compaction of the protein films. Addition of Fe3+ induces a transition from an extended and soft protein layer to a denser and stiffer one by enhancing the formation of tri-Fe3+/catechol complexes in the surface film, leading to water removal and film compaction. Exposure to a NaIO4 solution results in the cross-linking of Mefp-1, which also results in a significant compaction of the pre-formed protein film. Mefp-1 is an effective corrosion inhibitor for carbon steel when added to an acidic solution, and the inhibition efficiency increases with time. As a film-forming corrosion inhibitor, the pre-formed Mefp-1 film provides a certain level of corrosion protection for short term applications, and the protection efficiency can be significantly enhanced by the film compaction processes. For the long term applications, a thin film composed of Mefp-1 and ceria nanoparticles was developed. The deposited Mefp-1/ceria composite film contains micro-sized aggregates of Mefp-1/Fe3+ complexes and CeO2 particles. The Mefp-1/ceria film may promote the further oxidation of ferrous oxides, and the corrosion resistance increases with time. Moreover, phosphate ions react with Fe ions released from the surface and form deposits preferentially at the surface defect sites. The deposits incorporate into the Mefp-1/ceria composite film and heal the surface defects, which result in a significantly improved corrosion inhibition effect for the Mefp-1/ceria composite film in both initial and prolonged exposure situations / <p>QC 20130610</p>

Unter Verwendung von Dichtefunktionaltheorie werden die katalytischen Eigenschaften von Cerdioxidoberflächen mit verschiedenen Terminierungen untersucht. Cerdioxid wird auch als Trägermaterial in der heterogenen Katalyse eingesetzt, um Aktivität, Selektivität und Stabilität der aktiven Komponente zu erhöhen. In dieser Arbeit werden geträgerte Vanadiumoxidcluster diskutiert. Dabei wird die oxidative Dehydrierung von Methanol als Modellreaktion zur Aktivierung von C-H-Bindungen genutzt. Ceroxidpartikel werden oft in wässriger Lösung synthetisiert. Damit hängt die Form der Nanokristallite direkt von der relativen Stabilität der unterschiedlichen Terminierungen in der Gegenwart von Wasser ab. Außerdem ist Wasser an zahlreichen Reaktionen entweder als Produkt, Edukt oder Lösungsmittel beteiligt. Aus diesem Grund werden auch die Wasser-Oberflächenwechselwirkungen untersucht. Des Weiteren wird die Genauigkeit von drei verschiedenen Funktionalen (B3LYP, HSE und PBE+U) durch den Vergleich mit experimentellen Daten evaluiert. Diese beinhalten Barrieren, die mittels Temperatur-programmierter Desorptionsspektroskopie erhalten wurden, und Schwingungsspektren. / Density functional theory is applied to study the catalytic properties of ceria surfaces with different terminations. Ceria is also used as a support material in heterogeneous catalysis to improve activity, selectivity, and stability of the active component. In this work, supported vanadia clusters are discussed. The oxidative dehydrogenation of methanol is used as a model reaction for C–H bond activation. Ceria catalysts are often prepared in aqueous solution. As a result, the shape of ceria nanocrystallites depends on the relative stability of the different surface terminations in the presence of water. Furthermore, many reactions involve water either as a product, as a reagent, or as a solvent. Hence, water–surface interactions are studied as well. Furthermore, the accuracy of three different functionals (B3LYP, HSE, and PBE+U) is assessed by comparison to experimental data such as barriers obtained via temperature-programmed desorption and infrared spectra.

Estudos recentes demonstram que o sistema cerâmico zircônia-escândia-céria (ScCeSZ) apresenta-se promissor para aplicações como eletrólito sólido em células a combustível de óxido sólido de temperaturas intermediárias de operação (600 a 800 °C). Neste trabalho, foi realizada a sinterização convencional, de duas etapas e assistida por campo elétrico do ZrO2 contendo 10% em mol de Sc2O3 e 1% em mol de CeO2 comercializado pela Fuel Cell Materials visando melhorar a densificação com reduzido tamanho médio de grãos. A condutividade elétrica de amostras densas de ScCeSZ sinterizadas pelos diferentes métodos foi investigada por espectroscopia de impedância. Diferentes condições de sinterização foram analisadas. A taxa de retração dos compactos é máxima a 1180 °C, determinada pela análise de dilatometria. Foi confirmado por difração de raios X que a adição de céria à zircônia-escândia promove a estabilização da fase cúbica à temperatura ambiente. No entanto, dependendo das condições de sinterização pode haver a formação de fases secundárias, as quais foram detectadas por difração de raios X e espectroscopia Raman. A sinterização assistida por campo elétrico promoveu a formação das fases cúbica e tetragonal. Considerando os métodos convencional e de duas etapas, para a obtenção do material cúbico monofásico é necessária uma seleção cuidadosa das condições de sinterização. Os valores de condutividade elétrica estão de acordo com as condutividades do ScCeSZ reportadas na literatura. / Recent reports show that scandia-and ceria-doped zirconia (ScCeSZ) is a promising material for application as solid electrolyte in solid oxide fuel cells operating at intermediate temperatures (600 - 800 °C). In this work, ZrO2 containing 10 mol% Sc2O3 and 1 mol% CeO2 commercial powder (Fuel Cell Materials) was used to investigate the densification along with the mean grain size in specimens sintered by different methods: conventional, two-step sintering and electric field assisted sintering. The electrical conductivity of dense sintered specimens was studied by impedance spectroscopy. The linear shrinkage was followed by dilatometry. The maximum shrinkage rate of powder compacts was obtained at 1180 ºC. X-ray diffraction experiments revealed that ceria stabilizes the cubic phase of scandia-doped zirconia at room temperature. However, secondary phases (rhombohedric and tetragonal) were detected by both X-ray diffraction and Raman spectroscopy depending on the sintering conditions. The field assisted sintering method resulted in specimens with cubic and tetragonal phases. In the case of conventional and two-step sintering methods, a careful selection of the temperatures and sintering times is essential to obtain a cubic single-phase material. Values of the electrical conductivity of ScCeSZ are in general agreement with those reported in the literature.

Estudos recentes demonstram que o sistema cerâmico zircônia-escândia-céria (ScCeSZ) apresenta-se promissor para aplicações como eletrólito sólido em células a combustível de óxido sólido de temperaturas intermediárias de operação (600 a 800 °C). Neste trabalho, foi realizada a sinterização convencional, de duas etapas e assistida por campo elétrico do ZrO2 contendo 10% em mol de Sc2O3 e 1% em mol de CeO2 comercializado pela Fuel Cell Materials visando melhorar a densificação com reduzido tamanho médio de grãos. A condutividade elétrica de amostras densas de ScCeSZ sinterizadas pelos diferentes métodos foi investigada por espectroscopia de impedância. Diferentes condições de sinterização foram analisadas. A taxa de retração dos compactos é máxima a 1180 °C, determinada pela análise de dilatometria. Foi confirmado por difração de raios X que a adição de céria à zircônia-escândia promove a estabilização da fase cúbica à temperatura ambiente. No entanto, dependendo das condições de sinterização pode haver a formação de fases secundárias, as quais foram detectadas por difração de raios X e espectroscopia Raman. A sinterização assistida por campo elétrico promoveu a formação das fases cúbica e tetragonal. Considerando os métodos convencional e de duas etapas, para a obtenção do material cúbico monofásico é necessária uma seleção cuidadosa das condições de sinterização. Os valores de condutividade elétrica estão de acordo com as condutividades do ScCeSZ reportadas na literatura. / Recent reports show that scandia-and ceria-doped zirconia (ScCeSZ) is a promising material for application as solid electrolyte in solid oxide fuel cells operating at intermediate temperatures (600 - 800 °C). In this work, ZrO2 containing 10 mol% Sc2O3 and 1 mol% CeO2 commercial powder (Fuel Cell Materials) was used to investigate the densification along with the mean grain size in specimens sintered by different methods: conventional, two-step sintering and electric field assisted sintering. The electrical conductivity of dense sintered specimens was studied by impedance spectroscopy. The linear shrinkage was followed by dilatometry. The maximum shrinkage rate of powder compacts was obtained at 1180 ºC. X-ray diffraction experiments revealed that ceria stabilizes the cubic phase of scandia-doped zirconia at room temperature. However, secondary phases (rhombohedric and tetragonal) were detected by both X-ray diffraction and Raman spectroscopy depending on the sintering conditions. The field assisted sintering method resulted in specimens with cubic and tetragonal phases. In the case of conventional and two-step sintering methods, a careful selection of the temperatures and sintering times is essential to obtain a cubic single-phase material. Values of the electrical conductivity of ScCeSZ are in general agreement with those reported in the literature.