Dissertations / Theses on the topic 'Catalyc performance'
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1
Rua, Gonzalez Diego. "Synthèse de matériaux catalytiques de type oxydes mixtes pour la production de méthanol par la précipitation en flux continu en système microfluidique." Electronic Thesis or Diss., Strasbourg, 2024. http://www.theses.fr/2024STRAF001.
Abstract:
Le réchauffement climatique est une préoccupation pour les générations actuelles et futures en raison de l'augmentation des émissions de gaz à effet de serre (GES) dans l'atmosphère, principalement dues à la dépendance aux combustibles fossiles. L'utilisation de carburants alternatifs tels que le méthanol durable produit à partir de H2 renouvelable et de CO2 contribuerait à réduire les émissions de GES et les effets du changement climatique. La synthèse du méthanol à partir de matières premières riches en CO2 se fait préférentiellement en utilisant un catalyseur solide composé de CuO, ZnO et ZrO2. Ce type de catalyseur peut être produit par coprécipitation des espèces métalliques à l'aide d'un dispositif microfluidique, avec des avantages qui ont été démontrés par rapport aux catalyseurs synthétisés par coprécipitation discontinue. Dans ce travail, différents catalyseurs pour l'hydrogénation du CO2 en méthanol ont été synthétisés en utilisant la technique microfluidique dans différentes conditions, afin d'explorer différents paramètres de synthèse pouvant conduire au développement de catalyseurs plus actifs. Les différences de propriétés et d'activité entre un catalyseur synthétisé par la méthode microfluidique et un autre synthétisé par la méthode batch ont été étudiées, suivies d'une exploration des effets du temps de vieillissement et de la température de coprécipitation sur les catalyseurs. Enfin, l'effet de différentes compositions de catalyseurs sur les propriétés et l'activité a été déterminé, en étudiant différentes teneurs en CuO, l'utilisation de CeO2 comme promoteur et l'utilisation de In2O3 comme promoteur et comme métal actifGlobal warming is a concern for the current and future generations due to the increasing greenhouse gases (GHG) emissions to the atmosphere, mainly due to the dependence on fossil fuels. The use of alternative fuels such as sustainable methanol produced from renewable H2 and from CO2 would contribute to reduce the GHG emissions and the effects of climate change. The synthesis of methanol using CO2 rich feedstock is preferentially done by using a solid catalyst composed of CuO, ZnO and ZrO2. This type of catalyst can be produced by coprecipitation of the metal species using a microfluidic device, with advantages that have been demonstrated over catalysts synthesized by batch coprecipitation. In this work, different catalysts for the hydrogenation of CO2 to methanol were synthesized using the microfluidic technique under different conditions, in order to explore different synthesis parameters that could lead to the development of more active catalysts. The differences in the properties and activity between a catalyst synthesized by the microfluidic method and another synthesized by the batch method were investigated, followed by an exploration of the effects of the aging time and the coprecipitation temperature on the catalysts. Lastly, the effect of different compositions of catalysts on the properties and activity were determined, by investigating different CuO contents, the use of CeO2 as a catalyst promoter, and the use of In2O3 as a catalyst promoter and as active metal
2
Deshpande, Nitish. "Catalytic Material Design: Design Factors Affecting Catalyst Performance for Biomass and FineChemical Applications." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu154273906480973.
3
Tangale, N. P. "Zeolite based micro-mesoporous composites: synthesis, characterization and catalytic performance as heterogeneous catalyst for valorization of sugar." Thesis(Ph.D.), CSIR- National Chemical Laboratory, Pune, 2018. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/4576.
4
Haimad, N. "A theoretical and experimental investigation of the flow performance of automotive catalytic converters." Thesis, Coventry University, 1997. http://curve.coventry.ac.uk/open/items/3f51aa95-571c-73d5-bee3-4b523cab0a1c/1.
Abstract:
Considerable research is being carried out into the parameters that affect catalyst performance in order to meet the latest emission regulations. The conversion efficiency and the durability of automotive catalytic converters are significantly dependent on catalyst flow performance. Related investigations are commonly conducted using CFD techniques which represent an inexpensive and fast alternative to experimental methods. This thesis focuses on the flow performance of automotive catalytic converters using both experimental and computational techniques. The work describes the effects of inlet flow conditions on catalyst performance, the application of radial vanes to catalyst systems and the refinement of the CFD flow model which increases the accuracy of the predicted catalyst flow performance. the effects of inlet flow conditions on the flow maldistribution across the catalyst face and the total pressure loss through the system were assessed using a steady air flow rig. Tests were conducted over a range of Reynolds numbers typically encountered in automotive catalytic converters using a uniform and a fully-developed inlet flow condition. The results showed that the flow maldistribution significantly increases with Reynolds number notably in wide-angled diffusers. The catalyst flow performance is considerably improved when the inlet flow is uniform rather than fully-developed, the non-dimensional total pressure loss is reduced by 8% at Re=60000 and the flow maldistribution across the catalyst face is decreased by 12.5% and 15% respective Reynolds numbers of 30000 and 60000 when using a 60 degree diffuser. The total pressure loss through the system was found to be mostly associated with the monolith brick resistance. When the flow maldistribution is approximately 2, the pressure loss across the monolith brick represents 80% of the system pressure loss. The flow maldistribution across the catalyst face was improved by locating a system of radial splitters in the diffuser. The optimum flow performance was found to be a complex function of the vane design. A maximum improvement in the flow maldistrution indices M and Mi of 25% and 50% respectively was achieved at the expense of an increase in total pressure loss of 13.5% at Re = 60000. Both CFD and flow visualisation techniques were used as an aid to interpreting the flow field in the diffuser. Although a qualitative agreement was obtained using CFD, the flow maldistribution across the catalyst face was underpredected by up to 20%. The accuracy of the flow predictions was significantly improved by investigating the flow field in the monolith channels. Flow recirculation occurs in the channel entry length when the flow approaches the monolith channels at an angle which induces an additional implemented into four models of the flow through axisymmetric catalyst assemblies using various diffuser geometries and inlet flow conditions. By including the flow entrance effects in the porous media approach, the flow maldistribution was predicted within 8% instead of 15% when these effects are neglected. Further investigation of the flow in the monolith channels will be required to accurately model three-dimentional flows (racetrack catalysts) and to include various channel geometries and system flow rates.
5
Inayat, Amer [Verfasser], and Wilhelm [Akademischer Betreuer] Schwieger. "Open-cell Foams as Catalyst Support: A Description of Morphology, Fluid Dynamics and Catalytic Performance / Amer Inayat. Gutachter: Wilhelm Schwieger." Erlangen : Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2014. http://d-nb.info/1054342253/34.
6
Lin, ChienShung. "Effect of wall thermal conductivity on the performance of Swiss roll combustors using ammonia pretreated Pt catalyst for catalytic reaction." Pullman, Wash. : Washington State University, 2009. http://www.dissertations.wsu.edu/Thesis/Spring2009/C_Lin_040609.pdf.
Abstract:
Thesis (M.S. in mechanical engineering)--Washington State University, May 2009.Title from PDF title page (viewed on May 27, 2009). "School of Mechanical and Material Engineering." Includes bibliographical references (p. 45-47).
7
Lakshmanan, Alagendran. "RFID : a catalyst for supply chain performance." Thesis, Jönköping University, JIBS, Centre of Logistics and Supply Chain Management, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:hj:diva-8068.
Abstract:
THE ADVANTAGE OF RFID TECHNOLOGY IMPLEMENTATION IN A MANUFACTURING FIRM. THE TECHNOLOGY IMPLEMENTATION STREAM LINES THE LOSS OF INFORMATION FLOW WHEN THE PRODUCT MOVES ALONG THE DIFFERENT CHAIN MEMBERS. THE COMMON SHARING OF THE ASSOCIATED BENEFIT BRINGS HIGHER PROCESS EFFICEINCY , WHEN THE PRODUCT MOVES ALONG THE UPSTREAM AND DOWNSTREAM SUPPLY CHAIN FOR THE SELECTED PRODUCT. THE IMPLEMENTATION IS A CUSTOMISED SOLUTION FOR THE MANUFACTURING UNIT FOR ITS PRODUCT, THIS THESIS WILL ENABLE THE IMPLEMENTATORS THE VALUABLE IMPLEMENTATION PROCEDURES THAT ONE HAS TO FOLLOW TO TAKE RIGHT BENEFIT FROM THIS TECHNOLOGY.
8
Todd, Heather Elizabeth. "Investigating catalyst performance in batch reactive distillation." Thesis, University of Newcastle Upon Tyne, 2011. http://hdl.handle.net/10443/1244.
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Reactive distillation (RD) combines chemical synthesis with separation by distillation, but this leads to a non-trivial system: the hardware selection, the system components, the mode of operation and the operating conditions all affect the performance of the RD process. A key process development issue is the identification of suitable catalysts that perform well under reactive distillation conditions, as catalysts are crucial for increasing reaction rate when operating temperature range is limited by evaporation. The main goal of this research is to develop a method, utilizing high throughput technology, which can be used to assess many candidate catalysts for batch RD systems. The identification of potentially suitable catalysts should be made as early as possible, but before experimental work begins the only information available is the catalyst composition and structure. The approach taken in this research is to correlate catalyst properties to the performance in RD tests and the outputs from the dynamic simulations. The case study used is a batch reactive distillation for the esterification of a long-chain fatty acid. Potential catalysts are studied at small scale in a high throughput platform, and further investigation if performaed in an experimental batch RD unit. The most active of the screened catalysts, sulfuric acid and MSA also have the highest initial activity under RD. Heteropoly acids appear to have a good activity level, while ferric sulfate gives intermediate but apparently increasing activity. Some outcomes of the RD experiments were unexpected: the strong homogeneous acid catalysts entail low distillate water yield, and some metal acetates had higher activity than anticipated in the RD tests. This demonstrates that pilot scale experiments currently remain necessary for the evaluation of catalyst performance for RD processes. The insights gained from this study lead to key recommendations for future studies: an increased scope of study with a larger number of candidates which preferable have similar structure; evaluation of additional catalyst performance indicators, performed over the full operating temperature range; use of the smallest suitable experimental column; and more focus on physical factors such as solubility. Use of a simulator with an established physical property calculation tool is essential for successful simulations of batch RD.
9
Zhan, Xiaotong. "Heterogeneous catalysis in microreactors : study of the performance of various supports." Thesis, Ecole centrale de Marseille, 2018. http://www.theses.fr/2018ECDM0007/document.
Abstract:
Cette étude présente la préparation et l’évaluation de l’activité d’un nouveau catalyseur monolithique en microréacteur. La réaction d’hydrogénation du p-nitrophénol par transfert d’hydrogène avec l’acide formique a été choisie comme réaction modèle pour comparer les performances du monolithe à celles d’un catalyseur commercial en lit fixe.Cette thèse comporte une partie expérimentale importante. D’un côté, un montage expérimental et des protocoles d’analyse en ligne ont été mis au point pour faire une étude quantitative précise de la réaction modèle. De l’autre côté, les conditions de préparation d’un monolithe de silice fonctionnalisée dans le tube-réacteur en acier chemisé de verre ont été optimisées. Il a été chargé en nanoparticules de Pd par une méthode en écoulement. Le monolithe comporte un réseau de macropores pour l’écoulement et une organisation hexagonale typique de mésopores et micropores, et cela presque sans retrait au séchage. L’activité des 2 types de catalyseurs dans la réaction modèle a été comparée par leur cinétique de réaction et leur comportement dynamique dans la phase de mise en régime du microréacteur. Une partie théorique présente la modélisation du microréacteur en régime stationnaire pour l’établissement des cinétiques et en régime transitoire pour rationaliser les observations expérimentales. Le monolithe Pd@silice et le catalyseur commercial Pd@alumine ont des comportements différents et obéissent à des lois cinétiques différentes. Un modèle réactionnel impliquant un changement de propriétés de la surface catalytique pourrait expliquer le profil de concentration inhabituel observé avec le catalyseur commercial. La comparaison démontre la supériorité du nouveau catalyseur monolithe, et lui ouvre de bonnes perspectives industriellesThis study presents the preparation and the evaluation of performance of a new monolithic catalyst in microreactor. The transfer hydrogenation of p-nitrophenol by formic acid is chosen as the model reaction for the comparison of the monolith with a traditional packed-bed microreactor containing commercial catalyst.This thesis includes an important experimental part. On the one hand, experimental set-up and protocols involving on-line analysis have been developed in order to study quantitatively the model reaction; On the other hand, the conditions of preparation of functionalized silica monolith in a stainless steel tube with the inner wall pre-coated by glass were optimized, and the palladium nanoparticles were immobilized by a continuous flow method. The monolith possesses the flow-through macropores, typical hexagonal organization of mesopores and micropores, and scarcely any shrinkage. The comparison of the two types of catalysts mainly focuses on the activity of catalysts in the model reaction, their kinetic model and their dynamic behavior in the start-up phase of the flow microreactor. In the theoretical part, the modelisation of reactor has been investigated both under stationary conditions for kinetics determination and under transient conditions for the rationalization of experimental observations. Pd@silica monolith and commercial Pd@alumina powder have different behavior and gives different kinetic laws. A reaction model with change in the catalytic surface properties could explain the unusual profile of concentrations observed with commercial catalyst. The superior performance of monolithic catalyst is demonstrated, which also exhibits particular industrial interests
10
Afshar, Farniya Ali. "Development and performance analysis of autonomous catalytic micropumps." Doctoral thesis, Universitat Autònoma de Barcelona, 2014. http://hdl.handle.net/10803/284892.
Abstract:
Uno de los principales retos de la ingeniería de nanomotores, además de las dificultades para fabricar objetos nanométricos complejos, es cómo proveerles de energía para que funcionen. La aplicación de campos externos es una forma común y fácil de impulsar motores relativamente grandes. Sin embargo, cuando el tamaño de los motores se hace más pequeño, la transferencia de energia desde la escala macroscópica a la nanoescala se vuelve más problemática. Por lo tanto, el desarrollo de sistemas a nivel de la nanoescala totalmente autónomos que puedan generar su propia energía para poder autopropulsarse es muy deseable. Los sistemas biológicos ofrecen numerosos ejemplos de micro/nano motores autónomos. El punto clave detrás de la eficiente maquinaria biológica es la conversión de energía química en movimiento direccional. Por lo tanto existe un alto interés en crear nuevos motores artificiales que puedan auto-impulsarse y realizar actividades autónomas de forma similar a la impresionante maquinaria molecular de los organismos vivos. Recientemente se ha comenzado una intensa actividad científica en el desarrollo de motores y sistemas de bombeo propulsados químicamente en base a la auto-generación local de gradientes.
El presente trabajo de investigación trata sobre el concepto de microsistemas de bombeo catalítico que fue reportado por primera vez en 2005. Un microsistema de bombeo catalítico es un sistema activo que tiene la capacidad de inducir fenómenos electrohidrodinámicos a partir de una reacción (electro)química sobre una micro/nano estructura bimetálica. Aunque los dispositivos catalíticos han sido objeto de investigaciones anteriores en el que sus aplicaciones nanotecnológicas han comenzado a demostrarse, el mecanismo de actuación quimio-mecánica ha sido menos estudiado. Esto es en parte debido a la compleja interrelación que existe entre las reacciones catalíticas y los fenómenos electro-hidrodinámicos. Como consecuencia de ello todavía hay una serie de preguntas sin resolver que requieren mayor investigación para establecer el rol desempeñado por los diferentes procesos y lograr una mejor comprensión del mecanismo detrás de ellos. Por lo tanto, en esta tesis doctoral se ha realizado una caracterización exhaustiva de la actuación quimio-mecánica para entender los principales factores fisicoquímicos que regulan el mecanismo de funcionamiento de microbombas bimetálicas de Au- Pt en presencia de peróxido de hidrógeno como combustible. Las investigaciones han sido solventadas no sólo con resultados experimentales sino también con simulaciones numéricas. Estos estudios fundamentales son relevantes no sólo para estos sistemas de bombeos catalíticos, sino también para micro/nanomotores o nanorobots suspendidos en fluidos o coloides activos autopropulsados. Los estudios se han extendido también a otras estructuras bimetálicas ( Au- Ag , Au- Ru , Au -Rh , Cu - Ag , Cu - Ni, Ni- Ru y Ni- Ag) y a dispositivos semiconductores/metálicos ( Si dopado p / Pt , Si dopado n / Pt) con la idea de evaluar sus potencialidades como sistemas de bombeo catalítico en presencia del mismo combustible químico. En el caso de los sistemas metal/semiconductor su funcionamiento se basa en la fotoactivación de reacciones catalíticas, lo que proporciona un valor añadido a estas bombas y permite el desarrollo de nuevos interruptores foto-electrohidrodinámicos. Estos logros pueden abrir nuevas y prometedoras líneas de investigación en el campo de los actuadores y nanomotores catalíticos. El trabajo de tesis describe también una de las posibles aplicaciones de estos dispositivos activos que está relacionada con el transporte y depósito de materia en lugares específicos de un sustrato guiado por los fenómenos electrohidrodinámicos locales. Eso permite fabricar superficies nanoestructuradas de forma autónoma con un gran impacto nanotecnológico en una amplia gama de campos.One of the main challenges in the engineering of nanomachines, besides the difficulties to fabricate complex nanometric objects, is how to power them. The application of external fields is a common and easy way to actuate relatively large machines. However, when the size of the machines becomes smaller, the transfer of power from the macroscopic scale to the nanoscale becomes problematic. Therefore, the development of fully autonomous nanoscale systems which can self-generate their required power is very desirable. Biological systems are the source of numerous examples of natural micro/nanoscale autonomous motors. The conversion of chemical energy into directional motion is the key point behind the high efficient nanofactory of biomolecular machines. Therefore there is a high interest to create novel artificial machines which can self-propel and perform autonomous activities in a similar way the impressive molecular machinery does in living organisms. Many research activities have recently focused on chemically powered motors and micropumps based on the local self-generation of gradients. The present research work deals with the catalytic micropump concept which was reported for the first time in 2005. A catalytic micropump is an active system which has the capability of triggering electrohydrodynamic phenomena due to an (electro)chemical reaction taken place on a micro/nano bimetallic structure. Although catalytic devices have been the subject of previous reports in which their nanotechnological applications have started to be demonstrated, the mechanism of the chemo-mechanical actuation has been less studied. That is in part due to the complex interrelation between the catalytic reactions and the electro-hydrodynamic phenomena. As a consequence there is still a number of intriguing questions that require further investigation for establishing the role played by the different processes and for achieving a better understanding of the mechanism behind them. Therefore, the research was focused on the full characterization of the chemomechanical actuation and the understanding of the main physicochemical factors governing the operating mechanism of Au-Pt bimetallic micropumps in presence of hydrogen peroxide fuel. The investigations were supported not only by experimental findings but also by numerical simulations. These fundamental studies are of high importance not only for catalytic micropumps but also for other autonomous micro/nano swimmers or active self-propelled colloids. The studies were also extended to other bimetallic structures (Au-Ag, Au-Ru, Au-Rh, Cu-Ag, Cu-Ni, Ni-Ru and Ni-Ag) and to semiconductor/metallic structures (p-doped Si/Pt, n-doped Si/Pt) to evaluate their potentialities as catalytic micropumps in presence of the same chemical fuel. In the last case photoactivation of the catalytic reactions can be accomplished which provides an added value to these pumps as novel photochemical-electrohydrodynamic switches. These achievements can open new and promising research activities in the field of catalytic actuators and nanomotors. The thesis work also describes one of the potential applications of these active devices which is related to the autonomous material guiding and self-assembly on particular locations of a sample. That allows fabricating nanostructured surfaces in an autonomous way with potential nanotechnological impact in a wide range of fields.
11
Chawla, Neha. "The Catalytic Performance of Lithium Oxygen Battery Cathodes." FIU Digital Commons, 2018. https://digitalcommons.fiu.edu/etd/3810.
Abstract:
High energy density batteries have garnered much attention in recent years due to their demand in electric vehicles. Lithium-oxygen (Li-O2) batteries are becoming some of the most promising energy storage and conversion technologies due to their ultra-high energy density. They are still in the infancy stage of development and there are many challenges needing to be overcome before their practical commercial application. Some of these challenges include low round-trip efficiency, lower than theoretical capacity, and poor rechargeability. Most of these issued stem from the poor catalytic performance of the cathode that leads to a high overpotential of the battery. In this doctoral work, Li-O2 cathodes containing nanoparticles of palladium were used to alleviate this problem. Cathodes composed of palladium-coated and palladium-filled carbon nanotubes (CNTs) were prepared and investigated for their battery performance. The full discharge of batteries showed 6-fold increase in the first discharge of the Pdfilled over the pristine CNTs and 35% increase over their Pd-coated counterparts. The Pd-filled CNTs also exhibited improved cyclability with 58 full cycles of 500 mAh·g-1 at current density of 250 mA·g-1 versus 35 and 43 cycles for pristine and Pd-coated CNTs, respectively. The effect of encapsulating the Pd catalysts inside the CNTs proved to increase the stability of the electrolyte during both discharging and charging. Voltammetry, Raman spectroscopy, XRD, UV/Vis spectroscopy, and visual inspection of the discharge products using scanning electron microscopy confirmed the increased stability of the electrolyte due catalyst shielding. The electrochemical oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) on carbon nanotubes (CNT) cathodes with palladium (Pd) catalyst, Pd-coated CNT and Pd-filled CNT, have been evaluated in an ether-based electrolyte solution to develop a lithium oxygen (Li−O2) battery with a high specific energy. The electrochemical properties of CNT cathodes were studied using electrochemical impedance spectroscopy (EIS). The infrared spectroscopy and SEM are employed to analyze the reaction products adsorbed on the electrode surface of the Li-O2 battery developed using Pd-coated and Pd-filled CNTs as cathode and an ether based electrolyte. vii Studies in this dissertation conclude that the use of nanocatalysts composed of palladium improved the overall performance of the Li-O2 batteries, while shielding these catalysts from direct contact with the electrolyte prolonged the life of the battery by stabilizing the electrolyte.
12
Keuler, Johan Nico. "Optimising catalyst and membrane performance and performing a fundamental analysis on the dehydrogenation of ethanol and 2-butanol in a catalytic membrane reactor." Thesis, Link to the online version, 2000. http://hdl.handle.net/10019.1/1277.
13
Jacobs, Clayton Jeffrey. "Influence of catalyst ink mixing procedures on catalyst layer properties and in-situ PEMFC performance." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/22932.
Abstract:
Despite the benefits of fuel cell technology its advancement to being commercially functional is hindered by a number of crucial factors. These factors are often associated with the lack of appropriate materials or manufacturing routes that would enable the cost of electricity per kWh to compete with existing technology. Whilst most research efforts have been directed towards developing more active catalysts, the amount of catalyst required in the fuel cell can be further reduced by improving the platinum utilisation in the membrane electrode assembly. The platinum utilisation is a strong function of the catalyst layer preparation step and there remains significant scope for optimisation of this step. Whereas significant work has been conducted into the different components of the catalyst ink there is limited work and understanding on the influence of the mixing method of the catalyst ink. This study will focus on the influence of the mixing technique on the catalyst ink properties and on the final fuel cell performance. Specifically, the study will investigate the effect of the three different mixing techniques on (i) catalyst ink quality (ii) the physical properties of the resultant catalyst layer and (iii) the in-situ electrochemical performance of the membrane electrode assembly. A large set of characterisation techniques were chosen to effectively study the step wise processing of the catalyst layer, and fuel cell performance. The results presented here include a comparison of the various mixing techniques and a comprehensive 2 x 2 factorial design into the individual techniques. The results suggest that high energy mixing is required for effective distribution of catalyst layer components, an even catalyst layer topography and a highly functional ionomer network which consequently, enhances performance. The mixing energy referred to involves prolonged mixing time, enhanced mixing intensity or a combination of the two. During bead milling of catalyst inks, high intensity mixing seems to be beneficial however, prolonged mixing time appears to be detrimental to the ionomer film structure. During high shear stirring and ultrasonic homogenisation of catalyst inks, the ink mixture significantly heats up. It has been observed that at higher temperatures, Nafion elongates and the contact with catalyst agglomerates is enhanced. High shear stirring of catalyst inks seems to be most effective at high agitation rates. High mixing energies result in high shear forces and in addition, high mixing temperatures which appear to be beneficial to establishing an effective catalyst/Nafion interface, enhancing the three phase boundary observed during in-situ testing. Ultrasonic homogenisation seems to be more effective at prolonged sonication times. Due to the erosive nature of ultrasonic dispersion, sufficient time is required to establish a well dispersed and distributed catalyst ink. However, the nature of particle size distribution resulting from ultrasonication shows that inks are unstable and is not recommended for high throughput processing. Overall, fuel cell performance is not significantly affected by the mixing step however; mixing does have an observable impact on catalyst layer formulation. Generally, when optimizing membrane electrode assembly fabrication, mixing parameters should be carefully chosen. This goes without saying that parameters need to be effectively studied before foregoing catalyst ink processing.
14
Gómez, Sanz Sara. "Exploiting carbon in enhancing the performance of catalytic materials." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708360.
15
Berger, Christine, Rainer A. Rakoczy, Roger Gläser, and Jens Weitkamp. "Synthesis and catalytic performance of large zeolite Y crystals." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-196408.
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Berger, Christine, Rainer A. Rakoczy, Roger Gläser, and Jens Weitkamp. "Synthesis and catalytic performance of large zeolite Y crystals." Diffusion fundamentals 2 (2005) 82, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14418.
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Gomes, Flores Camila. "Synthesis and catalytic performance of metal-zeolite composite catalysts." Thesis, Lille 1, 2019. http://www.theses.fr/2019LIL1R010/document.
Abstract:
Les zéolithes sont des solides cristallins microporeux avec un système de pores réguliers, qui ont trouvé de nombreuses applications dans les procédés industriels tels que le raffinage du pétrole, la synthèse organique, l'adsorption et la séparation. Une très petite taille des pores des zéolithes (~1 nm) impose des limitations diffusionelles pour des nombreuses réactions catalytiques. La performance catalytique des catalyseurs bifonctionnels à base de zéolites peut être améliorée en créant des zéolithes hiérarchisées et en contrôlant la localisation des espèces métalliques. L'imprégnation est une méthode efficace pour la préparation de catalyseurs bifonctionnels à base de cobalt-zéolite pour la production directe de carburants liquides à partir de gaz de synthèse. Dans les catalyseurs préparés par imprégnation, le cobalt occupe les sites cationiques dans les micropores de zéolite, ce qui diminue le nombre de sites acides disponibles pour l'isomérisation et le craquage des hydrocarbures. L'isolement des ions cobalt en sites cationiques réduit la réductibilité du catalyseur, rend difficile d’obtenir l’état métallique et diminue la quantité de sites actifs métalliques disponibles pour la synthèse Fischer Tropsch. Nous avons démontré que la présence des ions Na+ au lieu des ions H+ dans les sites cationiques de zéolite favorise le dépôt de cobalt à la surface externe, alors que les sites acides dans les micropores de la zéolite sont peu affectés. Une autre approche de cette thèse porte sur la synthèse de zéolithes hiérarchisées à plusieurs niveaux de méso- et microporosité en utilisant des agents structurants sacrificiels. Les zéolithes hiérarchisées synthétisées à l'aide de nanotubes de carbone contenant du cobalt présentaient une activité catalytique plus élevée, une sélectivité en méthane plus faible et une sélectivité plus importante en hydrocarbures isomérisés dans la synthèse Fischer-Tropsch. La stratégie de synthèse fondée sur les nanotubes de carbone comme agents structurants a été étendue à d'autres métaux comme le nickel et le magnésium. Cette nouvelle approche à la synthèse de composites métal-zéolite en utilisant des nanotubes de métal-carbone comme agents structurants sacrificiels augmente la mésoporosité et améliore la performance pour l’hydrogénation d’aromatiques et l’acylation d’anisoleZeolites are microporous crystalline solids with a regular pore system, which have found numerous applications in industrial processes such as oil refining, organic synthesis, adsorption and separation. Very small pore size of zeolites (~1 nm) imposes diffusional limitations for many catalytic reactions. The catalytic performance of metal zeolite bifunctional catalysts can be improved by creating hierarchical zeolites and by controlling localization of metal species within the zeolite crystals. Impregnation is an efficient method for the preparation of bi-functional cobalt-zeolite catalysts for the direct production of liquid fuels from syngas. In the catalysts prepared via impregnation, cobalt occupies the cation exchange positions in the zeolite micropores decreasing the number of acid sites available for hydrocarbon isomerization and cracking. Isolation of cobalt ions in cationic positions reduces catalyst reducibility, makes it difficult to achieve metallic state and decreases the amount available metal active sites for Fischer Tropsch synthesis. We found that the presence of Na+ instead of H+ ions in the exchange positions of the large pore Beta zeolite favored deposition of cobalt on the external surface of the zeolite, while the acid sites in the zeolite micropores were not much affected. The large pore cobalt Beta zeolite catalyst with cobalt species localized on the external surface and high concentration of acid sites in the zeolite crystals has showed enhanced catalytic performance in Fischer-Tropsch synthesis combined with hydrocarbon isomerization. Another approach of this thesis has addressed creating hierarchical zeolites with several levels of meso- and microporosity using sacrificial templates. Hierarchical zeolites synthesized using cobalt containing carbon nanotubes, as sacrificial hard templates exhibited higher catalytic activity, lower methane selectivity and higher selectivity to isomerized hydrocarbons in Fischer-Tropsch synthesis. The synthesis strategy based on metal carbon nanotubes as sacrificial templates has been extended to other metals such as nickel and magnesium. This new approach to the synthesis of metal-zeolite composite increases the mesoporosity and improves the catalytic performance in hydrogenation of aromatics and anisole acylation
18
Medina, Molano Natalia Stefania. "Contribution of radioactivity to catalytic performance in heterogeneous media." Electronic Thesis or Diss., Université de Lille (2022-....), 2023. http://www.theses.fr/2023ULILR025.
Abstract:
Afin d'établir des voies possibles d'utilisation de métaux nobles récupérées du combustible nucléaire tels que le 107Pd, la présente thèse vise à étudier l'effet du rayonnement dans trois applications différentes : la catalyse hétérogène, avec - comme réaction modèle - l'hydrogénation du cinnamaldéhyde (CNA) ; la photocatalyse, avec - comme réaction modèle - la décoloration de l'orange de méthyle (MO) et la régénération des catalyseurs, désactivés lors de la synthèse de l'hydroxyméthyl furfural. Des protocoles ont été élaborés pour répondre aux exigences de sécurité nucléaire : applicable en boîte à gant et sorbonne, selon le cas.Le rayonnement β émis par le 107Pd n'a montré aucun effet lors de l'hydrogénation du CNA, indépendamment des conditions de réaction. En revanche, la décoloration a été initié par la présence de la radiation β sur le catalyseur en substituant de la lumière visible. Une diminution de l'absorbance (au point isosbéstique) a été observée. Ce dernier corrélait avec la quantité de catalyseur radioactif, mettant en évidence l'activation par le rayonnement β. Enfin, la régénération du catalyseur à base de Pd a donné des résultats prometteurs après l'irradiation γ, montrant notamment une augmentation de la performance catalytique après irradiation du catalyseur désactivé. Par ailleurs, le catalyseur à base de Ru, bien que généralement peu performant, a montré une activité plus élevée que l'activité du catalyseur frais après irradiation par rayonnement This thesis aimed to identify applications of noble metals recovered from spent nuclear fuels such as 107Pd. To study the effect of the radiation three different applications were selected: heterogeneous catalysis, with the hydrogenation of cinnamaldehyde (CNA) as model reaction; photocatalysis, with the decolourisation of methyl orange (MO) as model reaction; and the regeneration of catalysts, deactivated with the synthesis of hydroxymethyl furfural. Protocols were developed for the synthesis of the catalysts and the performance testing in restricted nuclear environment, namely in glove box and for the implementation of the reactions in glove box and extractor column as appropriate.Regarding the results it was found that β-radiation did not show any effect on the hydrogenation of CNA independent of the applied reaction conditions. On the other hand, the decolourisation of MO was successfully activated by the β-radiation of the catalyst. A decrease in absorbance (at the isosbestic point) was observed and was correlated to the amount of the catalyst employed, evidencing the effect of the irradiation doses. Finally, the regeneration of the Pd-based catalyst showed promising results after γ-irradiation, notably with a partial recovery of the initial catalytic performance after -irradiation. Meanwhile, the Ru-based catalyst, although generally not performing well, showed increased activity compared to the fresh catalyst upon -irradiation
19
Gomes, Flores Camila. "Synthesis and catalytic performance of metal-zeolite composite catalysts." Electronic Thesis or Diss., Université de Lille (2018-2021), 2019. http://www.theses.fr/2019LILUR010.
Abstract:
Les zéolithes sont des solides cristallins microporeux avec un système de pores réguliers, qui ont trouvé de nombreuses applications dans les procédés industriels tels que le raffinage du pétrole, la synthèse organique, l'adsorption et la séparation. Une très petite taille des pores des zéolithes (~1 nm) impose des limitations diffusionelles pour des nombreuses réactions catalytiques. La performance catalytique des catalyseurs bifonctionnels à base de zéolites peut être améliorée en créant des zéolithes hiérarchisées et en contrôlant la localisation des espèces métalliques. L'imprégnation est une méthode efficace pour la préparation de catalyseurs bifonctionnels à base de cobalt-zéolite pour la production directe de carburants liquides à partir de gaz de synthèse. Dans les catalyseurs préparés par imprégnation, le cobalt occupe les sites cationiques dans les micropores de zéolite, ce qui diminue le nombre de sites acides disponibles pour l'isomérisation et le craquage des hydrocarbures. L'isolement des ions cobalt en sites cationiques réduit la réductibilité du catalyseur, rend difficile d’obtenir l’état métallique et diminue la quantité de sites actifs métalliques disponibles pour la synthèse Fischer Tropsch. Nous avons démontré que la présence des ions Na+ au lieu des ions H+ dans les sites cationiques de zéolite favorise le dépôt de cobalt à la surface externe, alors que les sites acides dans les micropores de la zéolite sont peu affectés. Une autre approche de cette thèse porte sur la synthèse de zéolithes hiérarchisées à plusieurs niveaux de méso- et microporosité en utilisant des agents structurants sacrificiels. Les zéolithes hiérarchisées synthétisées à l'aide de nanotubes de carbone contenant du cobalt présentaient une activité catalytique plus élevée, une sélectivité en méthane plus faible et une sélectivité plus importante en hydrocarbures isomérisés dans la synthèse Fischer-Tropsch. La stratégie de synthèse fondée sur les nanotubes de carbone comme agents structurants a été étendue à d'autres métaux comme le nickel et le magnésium. Cette nouvelle approche à la synthèse de composites métal-zéolite en utilisant des nanotubes de métal-carbone comme agents structurants sacrificiels augmente la mésoporosité et améliore la performance pour l’hydrogénation d’aromatiques et l’acylation d’anisoleZeolites are microporous crystalline solids with a regular pore system, which have found numerous applications in industrial processes such as oil refining, organic synthesis, adsorption and separation. Very small pore size of zeolites (~1 nm) imposes diffusional limitations for many catalytic reactions. The catalytic performance of metal zeolite bifunctional catalysts can be improved by creating hierarchical zeolites and by controlling localization of metal species within the zeolite crystals. Impregnation is an efficient method for the preparation of bi-functional cobalt-zeolite catalysts for the direct production of liquid fuels from syngas. In the catalysts prepared via impregnation, cobalt occupies the cation exchange positions in the zeolite micropores decreasing the number of acid sites available for hydrocarbon isomerization and cracking. Isolation of cobalt ions in cationic positions reduces catalyst reducibility, makes it difficult to achieve metallic state and decreases the amount available metal active sites for Fischer Tropsch synthesis. We found that the presence of Na+ instead of H+ ions in the exchange positions of the large pore Beta zeolite favored deposition of cobalt on the external surface of the zeolite, while the acid sites in the zeolite micropores were not much affected. The large pore cobalt Beta zeolite catalyst with cobalt species localized on the external surface and high concentration of acid sites in the zeolite crystals has showed enhanced catalytic performance in Fischer-Tropsch synthesis combined with hydrocarbon isomerization. Another approach of this thesis has addressed creating hierarchical zeolites with several levels of meso- and microporosity using sacrificial templates. Hierarchical zeolites synthesized using cobalt containing carbon nanotubes, as sacrificial hard templates exhibited higher catalytic activity, lower methane selectivity and higher selectivity to isomerized hydrocarbons in Fischer-Tropsch synthesis. The synthesis strategy based on metal carbon nanotubes as sacrificial templates has been extended to other metals such as nickel and magnesium. This new approach to the synthesis of metal-zeolite composite increases the mesoporosity and improves the catalytic performance in hydrogenation of aromatics and anisole acylation
20
Paula, Fernanda Lobato de. "Perfil empreendedor e performance no âmbito de microempreendedores individuais: um estudo em Catalão (GO)." Universidade Federal de Goiás, 2016. http://repositorio.bc.ufg.br/tede/handle/tede/6909.
Abstract:
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Over the years, research on entrepreneurship has grown significantly and has been the object of a multidisciplinary study of several areas with different interpretations. This dissertation approaches the theme in the context of individual microentrepreneurs and aims to establish the interconnections between the Catalão's individual micro entrepreneurs and the business' performance's characteristics, using as reference an evaluating proposed scale which was adapted and validated for this context. Such studying problem started from a gap of research identified in the literature which refers to topics linked to entrepreneurship and to the individual micro entrepreneurs (MEI).So it was developed an instrument adapted from the realization of the focal group's achievement with the opinions of specialists in entrepreneurship, MEI and the experience of a pre test done through a probable sample with the target public, instrument for this research. In order to indentify the effort of the MEI, it was based on the Sebrae´sdatas and also based on the websites Portal do Empreendedor, Tribunal Eleitoral de Goiás e Receita federal. It was done the Factorial Exploiter Analysis through the SPSS Statistics Program version 23.0 (Statistical Package for the Social Science in order to validate statistically the action proposed in this essay. Once the structured database was properly owned, describing analysis were made to characterization of the type of the sample and nonparametric tests (Mann Whitney and Kruskal-Wallis) to match the entrepreneurs characteristics profile with the variables of performance. IT was used the Correlation of Speaman to accomplish the main goal of this research. However, it can be conclude that the sample is composed mostly of women, with a mean age of 46,66 years with a high school diploma and a mean of 0.62 courses per year. The currentis the only activity they carry out and most are located in the commerce sector. In the Mann Whitney and Kruskal Wallis tests, it was found that men presented a higher score in FACTOR 3 (Need of realization) and higher average turnover in the analyzed period. In Spearman's correlation, it was found that there is a significant and positive interconnection between FACTOR 1(Planning) and average turnover, and that entrepreneurial characteristics and business performance are stronger in women.
Ao longo dos anos, as pesquisas sobre o tema empreendedorismo cresceram significativamente e tem sido objeto de estudo multidisciplinar de diversas áreas com diversas interpretações. Essa dissertação aborda o tema no contexto dos microempreendedores individuais e tem como objetivo estabelecer correlações entre as características empreendedoras dos microempreendedores individuais de Catalão (GO) e a performance dos negócios, tendo como referência uma escala avaliativa proposta e adaptada para este contexto. O problema de estudo surgiu a partir de uma lacuna na literatura que trata de temas vinculados ao empreendedorismo e aos microempreendedores individuais. Dessa forma, foi estruturado um instrumento de pesquisa adaptado a partir da realização do grupo focal com a opinião de especialistas em empreendedorismo e de microempreendedores individuais e a experiência de um pré-teste realizado através de amostra probabilística com o público alvo objeto desta pesquisa. Para identificar o desempenho dos negócios dos microempreendedores individuais, buscou-se a base de dados de atendimento do Sebrae/GO e dos sites do Portal do Empreendedor, Tribunal Eleitoral de Goiás e Receita federal. Para validar estatisticamente a medida proposta nessa dissertação, foi realizada uma Análise Fatorial Exploratória através do Programa SPSS Statistics versão 23.0 (Statistical Package for the Social Science). De posse da base de dados estruturada, foram realizadas análises descritivas para caracterização do perfil da amostra e testes não paramétricos (Mann Whitney e Kruskal- Wallis) para relacionar as variáveis de perfil com as características empreendedoras e as variáveis de performance. Para cumprir o objetivo principal da pesquisa, fezse uso da Correlação de Spearman. Contudo, pode-se concluir que a amostra é composta em sua maioria por mulheres, com idade média igual a 46,66 anos, com segundo grau completo e com a realização média de 0,62 cursos por ano. O negócio atual é a única atividade que exercem e a maioria se situa no setor de comércio.Nos testes Mann Whitney e Kruskal Wallis constatou-se que os homens apresentaram maior score no FATOR 3 (Necessidade de realização) e maior faturamento médio no período analisado. Na correlação de Spearman constatou-se que existe uma correlação significativa e positiva entre o FATOR 1(Planejamento) e faturamento médio e que as características empreendedoras e a performance do negócio são mais fortes nas mulheres.
21
Yilmaz, P. "Photoelectrochemical performance of catalyst systems based on Pd deposited TiO2 and Ag incorporated BiFeO3." Thesis, Queen Mary, University of London, 2016. http://qmro.qmul.ac.uk/xmlui/handle/123456789/18403.
Abstract:
Since the discovery of titanium dioxide's (TiO2) capability for water-splitting and photocatalytic degradation of organic compounds, semiconductor photocatalysis has received great attention and promises an environmentally clean and sustainable solution by solar hydrogen production and waste water treatment.1,2 In this thesis, the photocatalytic performance of two different photocatalyst systems based on Pd nanoparticle decorated n-type TiO2 nanorods and Ag incorporated ptype BiFeO3 thin films were investigated for solar hydrogen and oxygen production and photodecolourisation of a common textile dye, Rhodamine B. High surface area TiO2 nanorods were grown on glass fibre substrates by a hydrothermal method to produce a mechanically robust photocatalytic filter. Metallic Pd nanoparticles were deposited onto TiO2 nanorods via a photochemical method. It was found that the hybrid Pd/TiO2 catalyst system showed higher photoactivity with a doubled kinetic rate for the photodecolourisation of RhB. Full decolourisation has been achieved in 180 minutes with as-grown TiO2 nanorods whereas this time was reduced to only 90 minutes for the Pd/TiO2 hybrid catalyst. This enhancement was associated with the localised surface plasmon resonance (LSPR) effect due to the interaction of Pd with visible light and the electron scavenging role of Pd for efficient charge separation. The same hybrid Pd/TiO2 photocatalyst system was then developed on FTO coated glass substrates so that the photoelectrochemical experiments can be carried out using a potentiostat. Mott-Schottky curves demonstrated a positive shift in flat band potential and an increased charge carrier density after Pd deposition. The facilitated charge transfer at the interface of Pd and TiO2 was shown by EIS data with a smaller arc size for Pd/TiO2 in Nyquist plots. The photoelectrochemical performance of the bare TiO2 and hybrid Pd/TiO2 samples were compared through the photoelectrocatalysis of Rhodamine B (RhB) and solar hydrogen production in different electrolyte solutions at various applied voltage values. A higher amount of hydrogen by Pd/TiO2 was photogenerated in methanol solution whereas bare TiO2 produced a higher amount of hydrogen in 0.01M Na2SO4 and pure deionised water under the same conditions. The results were discussed by proposing possible reaction mechanisms with an emphasis on the charge trapping role of Pd nanoparticles. P-type BiFeO3 (BFO) thin films were deposited on large scale FTO coated glass substrates by a sol-gel method. A photocurrent density of -0.004mA/cm2 was achieved at 0V vs NHE under AM1.5 G illumination and 1.2μmol of O2 was produced in 2h at an external bias of -0.5V vs Ag/AgCl. These values were significantly increased upon the incorporation of Ag into the BFO matrix. Ag was incorporated into the BiFeO3 matrix at different concentrations as metallic Ag structures and Ag nanowires. The enhancement by Ag modification was attributed to enhanced light absorption due to light scattering effect and efficient charge separation by Ag as they act as electron sinks. These explanations were supported by shifts in flat band and onset potentials after Ag modification in detailed measurements of Mott-Schottky plots and j-v curves.
22
Peluso, Enzo. "Eggshell catalyst for hydrocarbon synthesis, kinetic modeling and reactor performance." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0033/MQ30754.pdf.
23
Mahali, Alude. "Piercing together a girlhood : (re)visiting memories of site using nostalgia as a catalyst for coping with atopia." Master's thesis, University of Cape Town, 2009. http://hdl.handle.net/11427/8256.
Abstract:
Includes abstract.Includes bibliographical references (leaves 60-63).
My research has been preoccupied with the playing of memory with reference to narratives of loss. This loss has been represented by a loss of language, place and family, resulting in the playing of unnerving memory fragments. The primary driving force of this loss has been the notion of a disrupted or uprooted childhood. The subject of this enquiry is black girlhood; in particular, the relationships between black girls/women. Consequently a large part of 'piecing together a girlhood' involves engaging with what Quashie (2004) calls the 'girlfriend aesthetic'. Quashie's 'girlfriend aesthetic' offers a methodology for re-membering by providing a reflective surface; you see in the experience of the girlfriend other something that triggers or incites your own memory that aids you in working towards completion of self. This explication traces my interest in this subject matter as a direct result of feeling that black girlhood as a topic is under-represented, explores my development of a viable creative methodology for this kind of work, interrogates the meaning of 'site' in this context, maps out the origin of nostalgia and how it affects the afficted in relation to lost 'site', unpacks the girlfriend aesthetic as a practice and reveals how the nostalgic searcher's obsession with the irrecoverability of the past manifests in corporeal ways. Whether or not completion of self is possible, what is discovered is theatre's ability to aid in coping with a feeling of placelessness or atopia. Although nostalgia may indicate a fixation with the past, it can be a valuable and restorative way of emancipating oneself from it.
24
Bayraktar, Oguz. "Effect of pretreatment on the performance of metal contaminated commercial FCC catalyst." Morgantown, W. Va. : [West Virginia University Libraries], 2001. http://etd.wvu.edu/templates/showETD.cfm?recnum=2071.
Abstract:
Thesis (Ph. D.)--West Virginia University, 2001.Title from document title page. Document formatted into pages; contains xvi, 214 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 199-208).
25
Navarro-Fernandez, Oscar. "Synthesis, Activation and Catalytic Activity of N-Heterocyclic Carbene Bearing Palladium Catalysts." ScholarWorks@UNO, 2006. http://scholarworks.uno.edu/td/330.
Abstract:
The syntheses and characterization of a series of (NHC)Pd(II) complexes (NHC = N-heterocyclic carbene) are described. A variety of architectures and precursors have been employed to lead to numerous air- and moisture-stable complexes. The use of those complexes as pre-catalysts in cross-coupling (Suzuki- Miyaura, Buchwald-Hartwig) and related (catalytic dehalogenation, £-ketone arylation) reactions is also discussed. A comparison of the activity of a variety of (NHC)Pd complexes as pre-catalysts for cross-coupling reactions was carried out. The results indicate that the activation of those pre-catalysts, leading to the catalytically active [(NHC)Pd(0)] species, was key in assuring high catalytic performance under mild reaction conditions. For the first series of complexes described, (NHC)Pd(allyl)Cl complexes, a better understanding of the process leading to the catalytically active species has permitted us to introduce simple modifications (alkyl or aryl groups at the allyl moiety) that dramatically alter the performance of the complexes by facilitating their activation, decreasing reaction times, catalyst loadings and even allowing reactions to be conducted at room temperature. Catalyst loadings as low as 0.05 mol% can be used for the Suzuki-Miyaura crosscoupling of aryl chlorides and aryl boronic acids at room temperature, leading to the synthesis of poly-ortho-substituted biaryls in excellent yields. This catalyst loading is the lowest ever used for this purpose. The system also allows for the first examples of coupling between aryl chlorides and alkenyl boronic acids at room temperature. When the temperature is raised to 80 ¢ XC for these reactions, a catalyst loading as low as 50 ppm can be used to effectively carry out Suzuki-Miyaura cross-couplings in remarkably short reaction times. As an added advantage, these complexes are air- and moisture-stable and can be prepared in a facile one-pot, multigram scale synthesis from commercially available starting materials in very high yields. The second series of complexes described revolves around the (NHC)Pd(acac)n framework. These complexes are also air- and moisture-stable and can be prepared in a one-step synthesis in high yields from commercially available materials. These complexes were tested forƒn £-ketone arylation and Buchwald-Hartwig amination reactions affording high yields of the desired products, in short reaction times and mild reaction conditions.
26
Garcia, Amaya Arias. "Investigation of the flow performance of automative close coupled catalyst on flow rigs and engines." Thesis, Coventry University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247185.
27
Zhang, Changlin. "RATIONAL DESIGN OF ELECTROCATALYSTS WITH ENHANCED CATALYTIC PERFORMANCE IN ENERGY CONVERSION." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1478274856161346.
28
Kruger, Dawid. "Gas phase heterogeneous catalyst performance testing in laboratory fixed-bed reactors." Master's thesis, Faculty of Engineering and the Built Environment, 2019. http://hdl.handle.net/11427/31115.
Abstract:
Activity, selectivity and stability are invariably among the key factors of the performance of a catalyst. In the development of catalysts these properties are often screened for a range of materials and formulations. Interpretation of these key performance indicators are prone to various confounding effects. Here, performance testing of solid, porous catalysts for gas phase reactions in tubular fixed bed reactors is considered. Transport limitations and particularly internal mass transfer limitations are often cited in this case. Many have given general discussions and guides for effective catalyst performance testing, reviewed or put forward theoretical descriptions for transport phenomena and have measured and correlated associated transport coefficients. Some quantitative requirements and the relative importance of different effects have been found to remain unclear. Here, some of these aspects are addressed by the development of 3 catalyst testing criteria. Specifically, an upper limit is derived for the chemical conversion in a firstorder reaction such that differential rate conditions are established, a lower limit on the chemical conversion is applied to limit the loss of precision in conversion measurements, and an expression is derived to limit the effect of pressure drop across a catalyst bed on the observed rate of a first-order reaction. The prevalence and sensitivity of these and other transport limitation criteria were investigated theoretically in the context of the low-temperature (LT) water-gas shift (WGS) reaction over a Cu/ZnO/Al2O3 catalyst in a laboratory scale performance test. Factorial combination of some commonly manipulated experimental parameters (reactant feed rate, temperature, catalyst particle size, catalyst loading, dilution fraction and reactor tube size) was employed in this regard. The upper conversion limit, the internal mass transfer criterion and the radial heat transfer criterion were found to be particularly severe. So too, to a lesser extent, were the axial dispersion and pressure drop criteria, and the lower conversion limit. The sensitivity analysis indicated optima in the varied experimental parameters and yielded insights into effective control of different effects by selection of process conditions. Application of the set of criteria in an experimental performance test was demonstrated using a proprietary medium-temperature (MT), WGS catalyst under reaction at temperatures of 275 °C, 300 °C and 375 °C, 1 atm total pressure, dry feed composition of 10% CO, 10% CO2, 70% H2, 10% N2, steam-to-dry gas ratio of 0.5 and 158 h-1 weight hourly space velocity (WHSV). The catalyst was found to have near total selectivity towards the WGS reaction with activities of 12.2 ± 1.1, 17.1 ± 0.5 and 24.9 ± 1.5 µmol/s.gcat at 275 °C, 300 °C and 375 °C respectively. This corresponds to an activation energy of 39 ± 2 kJ/mol; a value within range of what is reported in literature for similar catalysts. This experiment also served to compare experimental and predicted internal mass transfer limitations by testing catalyst particles of different mean sizes. This catalyst as well as a CuO/ZnO/Al2O3 catalyst precursor was characterised in respect of their pore size distributions (N2 physisorption and mercury intrusion porosimetry (MIP)), particle size distributions (by photo- and microscopic analysis), bulk and particle densities and product gas compositions (by gas chromatography) to enable evaluation of the various criteria employed. Evaluation of the various criteria indicated that, theoretically, the considered confounding effects had a negligible effect on the measured catalytic activities for the catalyst sample with the smallest mean particle size, while the larger particles experienced only internal mass transfer limitations. Different models considered for effective diffusivities all under-predicted values when compared to the effective diffusivities inferred from the reaction-diffusion experiments. Predictions ranged to within factors of 3 – 20 of the experimental values, depending on whether pore size distribution data were derived from MIP or physisorption data. Here, the lack of characterisation of the macro-porosity by N2 physisorption resulted in more severe under-estimations of the effective diffusivities than the equivalent estimations made with MIP data. The best prediction was made by the ‘parallel-path pore’ model by Johnson & Stewart (1965) using MIP data. Predictions of internal mass transfer limitations varied in a similar manner. It is noted that the simplifications of the highly complex porous catalyst by these model combinations introduce large sources of error in the prediction of internal mass transfer limitations.
29
Pathirathna, Kuruppulage Asela Buddhika. "Gas turbine thermodynamic and performance analysis methods using available catalog data." Thesis, Högskolan i Gävle, Avdelningen för bygg- energi- och miljöteknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:hig:diva-17482.
30
Hibino, Takashi, Mitsuru Sano, Masahiro Nagao, and Pilwon Heo. "A High-Performance Mo2C-ZrO2 Anode Catalyst for Intermediate-Temperature Fuel Cells." The Electrochemical Society, 2007. http://hdl.handle.net/2237/18429.
31
Rickett, Gavin Leon. "The performance of supported noble metal catalysts in conditions of catalytic combustion." Thesis, University of Leeds, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.441326.
32
Kaufman, Gabrielle. "Gaspar Cassado : a study of Catalan cello arrangements and cello performance style." Thesis, Birmingham City University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.631677.
Abstract:
This thesis explores the legacy of Catalan cellist and composer Gaspar Cassadó (1897–1966). It provides a summary of his life and legacy, an analysis of his performance style and transcription style, and explores the implications of the findings for the related fields of Catalan and Spanish twentieth-century music, musical transcription and twentieth-century cello performance. The text is complemented with a CD containing recordings of cello works by Cassadó performed by the author of this thesis, as well as the first attempt to list definitively Cassadó’s compositions, transcriptions and recordings, which are found in Appendices I–IV. Cassadó’s performance style is analysed mainly through recording comparisons between him and a number of cellists connected with his cultural and historical background. The comparisons conclude that Cassadó, although displaying certain similarities with other cellists in the comparison, cannot truly be said to have belonged to a tradition or generation based solely on performance characteristics; instead more general aspects of approach, philosophy and influence exerted on other performers need to be taken into account. The discussion of his transcriptions includes a study of music transcription history and the related area of language translation, to provide a context for a number of case studies, analysing genres and styles within Cassadó’s output. The study concludes that a definite attempt is perceptible on Cassadó’s part to widen the concept of cello transcription as creative practice, as well as to approach the great historical exponents in the field, such as Franz Liszt. It also emphasises the unusual breadth in styles and types of his output. An additional commentary relates the author’s own performance experience of Cassadó’s works, especially with regard to performing several unpublished works and first-hand study with one of Cassadó’s disciples. Some conclusions from this commentary include a number of interpretative details of possible use for the future performer of Cassadó’s works, with the intention not to be prescriptive but rather to open up new and stimulating possibilities for the performances of this repertoire, keeping in mind Cassadó’s own practice of using performances as a workshop to improve musical scores.
33
Wang, Yi. "Synthesis and catalytic performance of hierarchical Zeolites supported Nickel-Tungsten hydrodesulfurization catalysts." Thesis, Lille 1, 2015. http://www.theses.fr/2015LIL10124/document.
Abstract:
Des règles environnementales de plus en plus strictes imposent une concentration en soufre dans les carburants en-dessous de 10 à 15 ppm. Donc, des catalyseurs plus efficaces doivent être développés. Dans ce travail, des catalyseurs nickel-tungsten supportés sur zéolites Beta et Mordenite hiérarchisées ont été préparés et évaluées en hydrodésulfuration (HDS).Tout d'abord, des zéolites Beta hiérarchisées ont été obtenues par post-traitement et caractérisées par DRX, N2-sorption, SEM, TEM et RMN. En conséquence, la zéolite Beta hiérarchisée préparée par post-traitement base-acide présente une excellente activité dans les réactions en catalyse acide, en particulier pour la conversion de grosses molécules.Des catalyseurs NiW supportés sur Al2O3 (NiW/Al2O3), zéolite Beta commerciale et hierarchisée (NiW/HB et NiW/HB-M), zéolite Mordenite commerciale et hierarchisée (NiW/HM et NiW/HM-M) ont été préparés et caractérisés par XRD, N2-sorption, IR, TEM et XPS. L'activité en HDS du 4,6-DMDBT sur NiW/HM-M et NiW/HB-M est plus du double de celle du catalyseur à base d’alumine NiW/Al2O3. La désactivation de catalyseurs supportés sur zéolite Beta a été étudiée dans la réaction d’HDS du thiophène. Les résultats indiquent que le mélange des solides NiW/HB ou NiW/HB-M avec NiW/Al2O3 et l'utilisation de zéolite Beta après échange avec des ions Na+ comme support (NiW/NaB-M) améliorent remarquablement la capacité anti-désactivation des catalyseurs. En conséquence, les catalyseurs NiW/NaB-M et catalyseur mélangé conduisent à une activité catalytique supérieure à celle de NiW/HB-M et NiW/Al2O3More and more strict regulations were drawn up in many countries to limit the concentration of sulfur below 10 ppm or 15 ppm in transportation fuel oil. Therefore, more efficient catalysts have to be developed. In this work, hierarchical Beta and Mordenite zeolite supported nickel-tungsten catalysts were prepared and evaluated in hydrodesulfurization (HDS) reactions.Firstly, hierarchical Beta zeolite was prepared by post-treatment and characterized by XRD, N2-sorption, SEM/TEM and NMR techniques. As a result, hierarchical zeolite Beta prepared by base-acid treatment exhibited excellent catalytic activity in acid-catalytic reactions, especially towards large molecules. NiW catalysts supported on Al2O3, commercial Beta and Mordenite zeolites (HB and HM), and hierarchical Beta and Mordenite prepared by post treatment (HB-M and HM-M) were characterized by XRD, N2 sorption, IR, TEM and XPS. Zeolite supported catalysts exhibited higher catalytic performance in the HDS of 4,6-DMDBT, due to the strong acidity of the zeolitic support that supplied an additional isomerization reaction route. The use of hierarchical zeolite could further improve the isomerization ability of catalyst. As a result, the HDS activity of 4,6-DMDBT over NiW/HM-M and NiW/HB-M was more than twice as that of NiW/Al2O3. The deactivation of hierarchical Beta zeolite supported catalysts was studied in the HDS of thiophene. Interestingly, mixing NiW/HB or NiW/HB-M with NiW/Al2O3 and the utilization of Na+-exchanged Beta as support (NiW/NaB) improved remarkably the anti-deactivation ability of the catalysts. As a result, NiW/NaB-M and mixture catalyst gave superior catalytic activity than NiW/HB-M and NiW/Al2O3
34
Jaf, Zainab. "Catalytic performance, Thermo-elastic, surfaces and coating properties of transition metal nitrides." Thesis, Jaf, Zainab (2018) Catalytic performance, Thermo-elastic, surfaces and coating properties of transition metal nitrides. PhD thesis, Murdoch University, 2018. https://researchrepository.murdoch.edu.au/id/eprint/42920/.
Abstract:
Among transition metal nitrides (TMNs), refractory molybdenum nitrides have been deployed in a wide array of strategic industrial applications due to their remarkable mechanical electrical and catalytic properties. This dissertation has a two-fold aims; first to comprehensively report electronic, thermo-mechanical and electronic characteristics of the bulk and surfaces of molybdenum nitride, and secondly to construct robust mechanistic pathways for prominent catalysed reactions. Most parts of this thesis utilise the density functional theory (DFT) framework to acquire these two objectives. I have carefully benchmarked the accuracy of theoretically-obtained results against experimental quantities pertinent to investigated systems, most notably, lattice parameters of bulk phases, bulk modulus, surface relaxations, and chemical conversion values.
Atomic charge distributions and density of states enabled to illustrate the bonding nature of investigated phases of molybdenum nitrides. For instance, we found that the MoN phase largely exhibits a metallic character with strong Mo-N ionic bonds. Based on estimated Gibbs free energies, the cubic phase of molybdenum nitrides incurs higher thermodynamic stability than the hexagonal phase, with no detected phase transition in the selected T–P ranges, as experimentally observed. The elastic stiffness coefficients of MoN in the hexagonal structure indicated higher mechanical stability in reference to the cubic structure. The optical conductivity of both phases near zero-photon energy coincides well with their metallic character inferred by their corresponding density of states curves.
Motivated by the fact that, the hexagonal structure δ-MoN is a potential replacement for cubic boron nitride (c-BN) and diamond (ultra-incompressible materials), we elect to computationally study the electronic properties, thermodynamic stability phase diagram, and vacancy formation energies of all plausible atomic terminations of NiAs and WC-type configurations of δ3-MoN and δ-WN hexagonal phases, correspondingly. Various low Miller indices of surface terminations of δ3-MoN and δ-WN have been considered. Ab initio atomistic thermodynamic analysis predicts that N-terminated (111) and (100) slabs to be the most energetically favourable surface terminations amongst the explored surfaces of δ3-MoN and δ-WN, respectively. Evidenced by plotted density of states, bulk and surfaces of δ3-MoN and δ-WN display a metallic character. In terms of surface relaxation and reconstructions, most investigated surfaces experience mainly downward displacements of their topmost layers. Most notably, the relaxed Mo-termination in (111) and (100) surfaces of δ3-MoN, demonstrate significant reconstructions resulted in the first layer to be solely truncated with nitrogen atoms instead of molybdenum in the un-relaxed initial geometry. Nevertheless, no significant surface reconstruction has been noticed in most of considered δ-WN configurations. Calculated Bader’s electronic charges reveal charge transfer from Mo/W atoms to N atoms, largely retaining the ionic bond nature in their bulk phases. Moreover, computed vacancy formation energy calculations indicated that creation of surface nitrogen vacancies are a highly endothermic process.
After considering bulk and surface properties, mechanistic and kinetics aspects for several hydrogen-transfer involved reactions have been investigated. The selective hydrogenation of acetylene (ethyne), present in hydrocarbon feed into ethylene (ethene) plays a critical importance in petroleum unit operations. The dissociative adsorption of hydrogen over the γ-Mo2N surface preferentially occurs over the vacant nitrogen sites. Our calculated overall uptake rate of hydrogen molecules by the γ-Mo2N surface correlates very well with analogous experimental findings. Likewise, accessible energy barriers for hydrogen migration from a low energy site (N-vacant) to a higher energy site (atop N) accounts for the experimentally observed facile mobility of hydrogen atoms over surfaces of Mo2N. The constructed detailed mechanisms for the partial and full hydrogenation of C2H2 into C2H4 and C2H6; respectively, highlight several thermodynamic and kinetic factors that underline the selective occurrence of partial rather than full hydrogenation of alkynes over transitional metal nitrides in general. For instance, we demonstrate that a higher barrier for the initial hydrogenation step in the full hydrogenation route in comparison to the analogous step in partial hydrogenation pathway (17.4 kcal mol-1 versus 10.8 kcal mol-1) to contribute significantly in the selective occurrence of partial hydrogenation of alkynes cuts.
It is well-known that catalytic removal of the S-content from thiophenic compounds is an essential step in efforts aiming to diminish the environmental burdens of transportation fuels. We therefore investigate the hydrodesulfurization HDS mechanisms of thiophene C4H4S over γ-Mo2N catalyst via DFT calculations. We found that the thiophene molecule preferentially adsorbs in a flat mode over 3-fold fcc nitrogen hollow sites. The HDS mechanism may potentially proceed either unimolecularly (direct desulfurization) or via H-assisted reactions (hydrogenation). Due to a sizable activation barrier required for the first C−S bond scission, we predict that the direct desulfurization to contribute insignificantly in the HDS mechanism. Migration of adsorbed hydrogen atoms from the γ-Mo2N surface to the thiophene ring significantly reduces activation barrier required in the C−S bond scission. Estimated conversion values predict a 50-70% consumption of thiophene at temperature as low as 700 K and at low values of gas hourly space velocities. Our computed conversion values were in a qualitative agreement with analogous limited experimental estimates.
I also probed the reduction mechanism of p-chloronitrobenzene (p-CNB) to p-chloroaniline (p-CAN) over the γ-Mo2N (111) surface. Our findings display that, p-CNB prefers to be adsorbed over two distinct adsorption sites namely, hollow fcc and N-hollow hcp sites with relatively sizable adsorption energies. We establish that, the activation of nitro group proceeds through direct pathway along with forming several reaction intermediates. Most of these intermediaries reside in a significant well-depth in reference to the entrance channel. Central to the constructed mechanism is H-transfer steps from fcc and hcp hollow sites to the NO/-NH groups through modest reaction barriers. Our computed rate constant for the conversion of p-CNB correlates very well with the experimental finding at the temperature window of the catalytic tests. Plotted species profiles via a simplified kinetics model confirm the experimentally reported high selectivity toward the formation of p-CAN at relatively low temperatures.
In this dissertation, not only binary TMNs, but also ternary TMNs have been investigated in the form of Cr−Mo−N thin films. Closed field unbalanced magnetron sputtering ion plating (CFUMSIP) was deployed to fabricate the aforementioned films with different Mo contents. XRD results confirmed the face centered cubic (fcc) structure of pure CrN film. The incorporation of molybdenum (Mo) in the CrN matrix, however, was confirmed by both XRD and XPS analyses. The CrMoN coatings demonstrate various polycrystalline phases including CrN, γ-Mo2N, Cr with oxides layers of MoO3, CrO3, and Cr2O3. Microstructure results show that the grain size of Cr-Mo-N coatings increases with the increase of Mo content due to the formation of MoN phase, when Mo atoms interact with N atoms around the grain boundaries of CrN phase. The optical results revealed that, the synthesised coatings exhibit low reflection magnitudes in the visible region of the solar spectrum, introducing them as good antireflection surfaces. Mo-containing samples improved solar absorptance of about 76% was recorded in the wavelength range of 200 – 800 nm. However, low thermal emittance of about 20% was obtained at 2500 – 15000 nm. Measured experimental and DFT computed values exhibited absorption coefficients (α) with a matching trend, across the wavelength range of 200 to 800 nm.
35
Fong, Jenny L. "The study of the effect of an alkaline pulping catalyst derived from plicatic acid /." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=65541.
36
Lively, Treise. "Ethanol fuel cell electrocatalysis : novel catalyst preparation, characterization and performance towards ethanol electrooxidation." Thesis, Queen's University Belfast, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602560.
37
Gomes, Pedro Miguel Vidinha. "Strategies for the enhancement of the catalytic performance of cutinase in nonaqueous media." Doctoral thesis, Faculdade de Ciências e Tecnologia, 2007. http://hdl.handle.net/10362/9364.
38
sharafi, mona. "Bottom-Up Synthesis Of Macromolecules And Their Selective Catalytic Performance At The Nanoscale." ScholarWorks @ UVM, 2020. https://scholarworks.uvm.edu/graddis/1189.
Abstract:
Finding sustainable ways to create complex, sequence-defined polymers is
essential for future advances in the fields of medicine, electronics, and energy. Thus,
inspired by how nature builds functional macromolecules, this account aims to discover
catalysts, which will facilitate the accurate replication of synthetic nanoscale structures. In
this regard, the comprehensive sight of the work described within this dissertation is to
resolve the following fundamental questions: i) How to generate large, preorganized
macromolecules which can behave as supramolecular hosts to tune the properties of
molecules present in the vicinity of them? ii) What shapes do sequence-defined
oligomers/polymers adopt in solution under various conditions? In what ways can local
polymer conformations be manipulated by binding to supramolecular hosts? iii) Can we
exploit the folding behavior of these polymers as a powerful tool to provide selective
reactivity at the nanoscale and enhance the replication accuracy? Various synthetic
approaches leading to the successful precise manufacturing of synthetic macromolecules
including molecular strips, large macrocycles and porous cages are described. A significant
portion of my PhD research was also focused on the framework of selective catalysis for
polymers functionalization and replication; a unique concept which hasn’t been reported
previously.
Selective catalysis at the molecular scale represents a cornerstone of chemical
synthesis. However, it still remains an open question how to elevate tunable catalysis to
larger length-scales, where nanoscale structures (e.g. whole polymer chains) act as the
substrates and get functionalized in a selective manner. The efficient synthesis of a
hydrazone-linked tetrahedron with large opening, which acts as a catalyst to sizeselectively
functionalize polydisperse polymer-mixtures is described in details.
Experimental and computational evidence are provided to support a dual catalytic effect
exerted by the molecular tetrahedron, which (i) helps to unfold the polymer substrates and
(ii) exposes the amino groups on the polymeric side chains to the 12 triglyme units of the
tetrahedron to accelerate aminolysis. I was able to demonstrate complete reversal of the
intrinsic size-selectivity for polymer functionalization with our tetrahedral cage as the
catalyst. This finding enable the possibility to engineer hydrolytically stable molecular
polyhedra as organocatalysts for size- and future site-selective, post-synthetic polymer
modification (inspired by post-translational protein modification).
39
Mercier, Anne-Gaelle. "Etude et réalisation de couches actives de PEFMC architecturées." Thesis, Grenoble, 2012. http://www.theses.fr/2012GRENI050.
Abstract:
Les piles à combustible de type PEMFC constituent un maillon essentiel du cycle utilisant l'hydrogène comme vecteur d'énergie afin de permettre l'utilisation des énergies renouvelables. Cependant, leur développement connaît encore des limitations en termes de performances initiales, de coût et de durabilité. Cette thèse se concentre sur les couches actives des électrodes dont le catalyseur, souvent du platine, peut représenter jusqu'à 25% du coût global. Un des enjeux a ainsi été de mieux comprendre le fonctionnement de ces électrodes, qui peut être inhomogène, afin d'améliorer la distribution du platine dans la couche active et optimiser son utilisation. Pour cela, des électrodes « architecturées », c'est-à-dire avec des chargements en platine variables au sein de la couche active, ont été réalisées grâce à la flexibilité de deux procédés d'impression : le jet d'encre et la sérigraphie. Une adaptation de la formulation des encres catalytiques et des paramètres d'impression a permis la mise en œuvre de ces deux procédés et la réalisation de couches actives présentant une large gamme de chargements en catalyseur (0,05mgPt/cm² à 0,5mgPt/cm²). Différentes distributions de platine ont été étudiées et comparées à des couches actives uniformes: dans le plan d'une part, à l'échelle dent/canal de la plaque bipolaire et à l'échelle entrée/sortie, et dans l'épaisseur d'autre part. Les architectures ont permis de mettre en évidence différentes contributions de la couche active suivant sa localisation sous la plaque bipolaire et ainsi de proposer des modifications de sa structure qui peuvent être réalisées grâce aux procédés d'impression. Par ailleurs, la durabilité des structures les plus pertinentes a été évaluée par des essais de longue durée qui ont montré qu'il est possible de réduire la pente de dégradation par la modification de la distribution du platinePEM fuel cells stand for an essential link in the cycle using hydrogen as an energy carrier.However, their development is still limited by initial performance, costs and durability.This study focuses on the electrode catalyst layer which contains most of the time platinum, anexpensive catalyst that can represent 25% of the overall cost of a system. Thus, one of the issues hasbeen to provide a better understanding of electrode operating, which can be heterogeneous. The aim ofthis study is particularly to enhance platinum distribution in the catalyst layer to optimize itsutilization.Architectured electrodes, that is to say with variable platinum loading inside the catalyst layerhave been developed thanks to the flexibility of two printing processes : inkjet printing and screenprinting. The adjustment of catalyst ink formulation and printing parameters enabled to fabricatecatalyst layers with a wide range of platinum loading, from 0,05mgPt/cm² to 0,5mgPt/cm². Severalplatinum distributions were compared to uniform catalyst layers at different scales: the scale of ribsand channels and of gas inlet and oultet of bipolar plate, as well as through the catalyst layer thickness.Electrodes architecture enabled to point out different contribution of catalyst layers according to itslocalizing under the bipolar plate and to suggest modifications of its structure that provide an increaseof performance.Otherwise, the estimation of lifetime of several architectures thanks to ageing tests in loadcycling mode showed that these structures enabled to reduce their performance decay rate
40
Väliheikki, A. (Ari). "Resistance of catalytic materials towards chemical impurities:the effect of sulphur and biomaterial-based compounds on the performance of DOC and SCR catalysts." Doctoral thesis, Oulun yliopisto, 2016. http://urn.fi/urn:isbn:9789526212845.
Abstract:
Abstract Exhaust gas emissions, e.g. nitrogen oxides (NOx), hydrocarbons (HCs) and carbon monoxide (CO), are harmful to human health and the environment. Catalysis is an efficient method to decrease these emissions. Unfortunately, the fuels and lubricant oils may contain chemical impurities that are also present in exhaust gases. Thus, catalytic materials with high activity and chemical resistance towards impurities are needed in the abatement of exhaust gas emission. In this thesis, the aim was to gain new knowledge about the effects of chemical impurities on the behaviour and activity of the catalysts. To find out these effects, the impurities existing in the exhaust gas particulate matter after combustion of biofuels and fossil fuels were analysed. The studied zeolite (ZSM-5), cerium-zirconium mixed oxides (CeZr and ZrCe) and silicon-zirconium oxide (SiZr) based catalysts were also treated with impurities to simulate the poisoning of the catalysts by, e.g. potassium, sodium, phosphorus and sulphur, using gas or liquid phase treatments. Several characterization techniques were applied to find out the effects of impurities on catalysts’ properties. The activity of catalysts was tested in laboratory-scale measurements in CO and HC oxidation and NOx reduction using ammonia (NH3) and hydrogen (H2) as reductants. The results revealed that the CeZr based catalysts had a high activity in NOx reduction by NH3 and moderate activity by H2. Sulphur was proven to enhance the activity of CeZr catalysts in NOx reduction. This is due to an increase in chemisorbed oxygen after the sulphur treatment on the catalyst surface. Instead, in HC and CO oxidation reactions, sulphur had a negligible impact on the activity of the SiZr based diesel oxidation catalyst. Thus, both CeZr and SiZr based catalysts can be utilized in exhaust gas purification when sulphur is present. ZSM-5 based catalysts were proven to be resistant to potassium and sodium. Alternatively, the activity of SiZr based catalysts decreased due to phosphorus. Thus, the removal of biomaterial-based impurities from the exhaust gases is needed to retain high catalyst activity in the exhaust gas after-treatment systemTiivistelmä Pakokaasupäästöissä olevat typen oksidit (NOx), hiilivedyt (HCs) ja hiilimonoksidi (CO) ovat haitallisia ihmisten terveydelle ja ympäristölle. Katalyysi on tehokas menetelmä vähentää näitä päästökomponentteja. Polttoaineet ja voiteluöljyt sisältävät epäpuhtauksia, jotka siirtyvät myös pakokaasuihin. Tästä johtuen pakokaasupäästöjen hallinnassa tarvitaan katalyyttimateriaaleja, joilla on hyvä vastustuskyky myrkyttymistä vastaan. Tavoitteena oli saada uutta tietoa kemiallisten epäpuhtauksien vaikutuksesta katalyyttien toimintaan. Biopolttoaineiden sisältämät mahdolliset epäpuhtaudet selvitettiin analysoimalla fossiilisen ja biopolttoaineen palamisessa muodostuvia partikkeleita ja vertaamalla niitä polttoaineiden hivenaineanalyysiin. Tutkimuksessa käytetyt zeoliitti (ZSM-5), cerium-zirkonium-sekaoksidi (CeZr) ja pii-zirkonium-oksidipohjaiset (SiZr) katalyytit käsiteltiin epäpuhtauksilla (kalium, natrium, fosfori ja rikki) kaasu- ja nestefaasissa. Tutkimuksessa käytettiin useita karakterisointitekniikoita, joiden avulla selvitettiin epäpuhtauksien vaikutuksia katalyyttien ominaisuuksiin. Katalyyttien toimintaa testattiin laboratoriomittakaavan kokeissa CO:n ja HC-yhdisteiden hapetuksessa sekä NOx:ien pelkistyksessä käyttäen ammoniakkia (NH3) tai vetyä (H2) pelkistimenä. Tulokset osoittavat, että CeZr-pohjaisten katalyyttien aktiivisuus NOx:ien pelkistyksessä oli hyvä käytettäessä pelkistimenä NH3:a ja kohtalainen käytettäessä vetyä. Rikki paransi CeZr-katalyyttien aktiivisuutta NOx:ien pelkistyksessä, mikä johtui kemiallisesti sitoutuneen hapen osuudesta katalyyttien pinnoilla. Vastaavasti hiilivetyjen ja CO:n hapetusreaktioissa rikki ei vaikuttanut SiZr-pohjaisten dieselhapetuskatalyyttien aktiivisuuteen. Sekä CeZr- ja SiZr-pohjaisia katalyytteja voidaan siten käyttää rikkiä sisältävien pakokaasujen puhdistuksessa. SiZr-pohjaisten katalyyttien aktiivisuus laski fosforin vuoksi. ZSM-5-pohjaiset katalyytit olivat vastustuskykyisiä kaliumille ja natriumille. Kestäviä katalyyttejä on siten kehitettävä, mikäli biopolttoaineiden sisältämien epäpuhtauksien poistaminen polttoaineista ei ole mahdollista
41
Roso, Martina. "Multistructured membranes based on electro-dynamic technologies: process optimization and catalytic performances." Doctoral thesis, Università degli studi di Padova, 2009. http://hdl.handle.net/11577/3426399.
Abstract:
Electodynamic technologies represent a challenging task in the nanotechnology field for producing multistructured and multifunctional membranes, based on nanofibers and nanoparticles that have been shown to be a good candidate as photocatalytic membrane on VOCs degradation. Before going toward fabrication of multistructured membranes, it is necessary to optimize the process of fiber formation. At this regard Response Surface Methodology (RSM) represents a versatile tool for exploring the space of the process or independent variables, empirical statistical modeling to develop an appropriate approximating relationship between the yield and the process variables, and optimization methods for finding the values of the process variables that produce desirable values of the response. Subsequently, it has been implemented a method for multilayer membranes fabrication in order to deposit inorganic nanoparticles and optimize their distribution over polymeric nanofibers. The processed membranes have been adequately characterized and phocatalytic performance tested.le tecnologie elettroidro dinamiche costituiscono un valido strumento nell'ambito delle nanotecnologie per la produzione di membrane multistrutturate e multifunzionali costituite da nanofibre e nanoparticelle che trovano applicazione nel settore della fotocatalisi per la rimozione di VOCs. Prima di procedere alla produzione vera e propria è necessario ottimizare il processo di elettrofilatura. a tal riguardo la metodologia di risposta delle superfici è un valido strumento per esplorare il processo, valutare e stabilire un'adeguata relazione tra la variabile risposta e le variabili di processo e rilevare la configurazione più adeguata per l'ottenimento di una fissata risposta. Successivamente, è stato implementato un metodo per la produzione di membrane multistrato in cui particelle inorganice sono depositate su nanofibre polimeriche. Tali membrane sono state adeguatamente caratterizzate ed è stata studiata la loro attività catalitica nei confronti di agenti inquinanti.
42
Wang, Fagen. "Hydrogen production from steam reforming of ethanol over an Ir/ceria-based catalyst : catalyst ageing analysis and performance improvement upon ceria doping." Phd thesis, Université Claude Bernard - Lyon I, 2012. http://tel.archives-ouvertes.fr/tel-00967128.
Abstract:
The objective of the thesis was to analyze the ageing processes and the modifications of an Ir/CeO2catalyst for steam reforming of ethanol. Over a model Ir/CeO2 catalyst, the initial and fast deactivationwas ascribed to ceria surface restructuring and the build-up of intermediates monolayer (acetate,carbonate and hydroxyl groups). In parallel, a progressive and slow deactivation was found to come fromthe structural changes at the ceria/Ir interface linked to Ir sintering and ceria restructuring. Theencapsulating carbon, coming from C2 intermediates polymerization, did not seem too detrimental to theactivity in the investigated operating conditions. By doping ceria with PrOx, the oxygen storage capacityand thermal stability were greatly promoted, resulting in the enhanced activity and stability. The Ir/CeO2catalyst was then modified by changing the shape of ceria. It was found that the shape and therefore thestructure of ceria influenced the activity and stability significantly. A simplified modeling of theseprocesses has contributed to support the new proposals of this work.
43
Baik, Jungshik. "Experimental Investigation of the Effect of Composition on the Performance and Characteristics of PEM Fuel Cell Catalyst Layers." Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/34438.
Abstract:
The catalyst layer of a proton exchange membrane (PEM) fuel cell is a mixture of polymer, carbon, and platinum. The characteristics of the catalyst layer play a critical role in determining the performance of the PEM fuel cell. This research investigates the role of catalyst layer composition using a Central Composite Design (CCD) experiment with two factors which are Nafion content and carbon loading while the platinum catalyst surface area is held constant. For each catalyst layer composition, polarization curves are measured to evaluate cell performance at common operating conditions, Electrochemical Impedance Spectroscopy (EIS), and Cyclic Voltammetry (CV) are then applied to investigate the cause of the observed variations in performance. The results show that both Nafion and carbon content significantly affect MEA performance. The ohmic resistance and active catalyst area of the cell do not correlate with catalyst layer composition, and observed variations in the cell resistance and active catalyst area produced changes in performance that were not significant relative to compositions of catalyst layers.Master of Science
44
Pinabiau, Maryse. "Préparation, caractérisation et performances catalytiques de réservoirs d'hydrogène "intermétalliques terres rares - nickel oxydes"." Lille 1, 1987. http://www.theses.fr/1987LIL10116.
45
Fedock, John Andrew. "Low temperature polymer electrolyte fuel cell performance degradation." [Tampa, Fla] : University of South Florida, 2008. http://purl.fcla.edu/usf/dc/et/SFE0002565.
46
Cabiac, Amandine. "Influence des propriétés texturales et de la méthode de préparation sur les performances hydrogénantes de catalyseurs Pd/C." Montpellier 2, 2006. http://www.theses.fr/2006MON20167.
Abstract:
Nous nous sommes attachés à étudier l’influence des propriétés physicochimiques et texturales du charbon sur les caractéristiques et les performances catalytiques de catalyseurs 5% Pd/C dans des réactions d’hydrogénation (cinnamaldéhyde et cyclododécatriène). La première voie de préparation de catalyseurs est l’échange cationique H+<-> Pd2+. Cette technique requiert une fonctionnalisation oxydante (HNO3, NaOCl, H2O2) afin de créer des fonctions d’ancrage. Les matériaux ainsi préparés sont très dispersés (dPd = 1,5 nm). Cependant leur stabilité thermique est restreinte du fait de la décomposition des fonctions stabilisantes dès 200°C. Une technique alternative est la préparation par déposition-précipitation (DP) qui ne requiert aucun prétraitement oxydant mais un contrôle strict des conditions opératoires est nécessaire pour assurer une reproductibilité parfaite. La préparation de catalyseurs Pd/C à partir de deux lots commerciaux (L3S) selon les techniques précédentes conduit à des matériaux aux caractéristiques et aux performances hydrogénantes identiques
47
Lu, Yaxiang. "Advanced one-dimensional nanostructures for high performance catalyst electrodes in polymer electrolyte fuel cells." Thesis, University of Birmingham, 2016. http://etheses.bham.ac.uk//id/eprint/6469/.
Abstract:
In the past decades, the study of nanotechnology has brought in tremendous progress to the development of polymer electrolyte fuel cells (PEFC) and many advanced catalyst approaches have been developed. However, many of these still remain at ‘test-tube’ level and have not been implemented in practical fuel cells. The concerns about the gap between the pure material research and fuel cells are increasing, and a study focusing on the electrode structures is required to help address this issue. In this thesis, the in-situ growing process of one-dimensional (1D) Pt-based nanostructures on gas diffusion layers (GDLs) was systematically studied to help understand the structure-property relationship of the gas diffusion electrodes (GDEs). The crystal nucleation and growth, coupled with the distribution of the produced nanostructures were investigated based on the corresponding GDE performance in PEFCs. The influence of the in-situ growing temperature, the hybridizing Pd metal and the structures of the GDL itself were comprehensively investigated for a further understanding of the in-situ nanowire growing process. This work demonstrates that besides the intrinsic catalytic activities of the catalysts themselves, their optimal implementation in electrodes, i.e. the electrode structure, play an important role in the power performance of PEFCs than we initially expected.
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Hajar, Yasmine. "Effect of Electrochemical Promotion and Metal-Support Interaction on Catalytic Performance of Nano-catalysts." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39701.
Abstract:
In heterogeneous catalysis, promoting the activity of the catalytic metals is long known as an important method to make a process more efficient and viable. Noble metals have been promoted classically by a chemical coverage of an ionic solution on the surface of the catalyst or using inert support, e.g., silica or alumina, allowing an increase of the dispersion of the catalyst. Therefore, new methods of promotion needed to be better explored to improve the efficiency of metal and metal oxide catalysts. One way of enhancing the catalyst’s activity is to disperse the noble metal at the nanoscale using an active type of support that is ion-conducting. Not only lattice ions can be exchanged with the surface of the nanoparticles but it can also engage in the oxidation reaction on the surface, resulting in what is known as metal-support interaction (MSI). Another method of improving the catalytic activity is to polarize the catalyst, allowing ions to migrate from a solid electrolyte to the gas-exposed surface, in a phenomenon known as electrochemical promotion of catalysis (EPOC). The change in the ions concentration on the surface would change the adsorption energy of the gaseous reactants and enhance or supress the catalytic rate.
In this thesis, the effect of supporting nanoparticles of noble and non-noble metal (oxides) (Pt, Ru, Ir, Ni) was studied for the case of ionic and ionic-electronic conducting supports (CeO2, TiO2, YSZ). The enhancement in their catalytic rate was found and correlated to an electrochemical property, the exchange current density. Then, using isotopically-labeled oxygen, the oxygen exchange ability of the conductive oxides was evaluated when supporting Ir and Ru nanoparticles and correlated with the results from C3H8 isotopic oxidation reaction, which showed the extent of involvement of oxygen from the support as carried by the isotopically-labeled CO2 produced.
Following this, electrochemical promotion of catalysis experiments were performed for different reactant/catalyst systems (C2H4 - Pt, Ru; C3H8 - Pt; CH4 - Pd, Ni9Pd). In the first system, the main outcome was the functional equivalence found for the MSI and EPOC effect in promoting the catalysts as experiments were performed at different temperatures, reactants partial pressures and polarization values. In the case of C3H8/Pt, the novel dispersion of Pt on an intermediate supporting layer (LSM/GDC) was found as a feasible method to obtain long stability of the catalyst while electrochemically promoting the rate of reaction. For CH4 oxidation, the polarization of the Pd nanoparticles showed continuous oxidation of the bulk of the catalyst resulting in a continuous increase of the catalytic rate. The Ni9Pd synthesized in a way to form a core/double-shell layer of Ni/Pd resulted in an enhanced catalytic rate and enhanced stability compared to stand-alone Pd.
And lastly, to comprehend the ions’ effect in the electrochemical promotion and the non-Faradaic nature of the phenomena, density-functional theory (DFT) modeling was used to demonstrate the increase of the heat of adsorption of reactants depending on their electronegative/positive nature.
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Jiang, Lulu. "Catalytic Performance and Characterization of Zn-doped Cryptomelane-type Manganese Dioxide For Ethanol Oxidation." Miami University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=miami1352827354.
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Cheng, Feng. "Bio-compounds as reducing agents of reforming catalyst and their subsequent steam reforming performance." Thesis, University of Leeds, 2014. http://etheses.whiterose.ac.uk/7715/.
Abstract:
At present, H2 is mainly produced through catalytic steam reforming of natural gas. Sustainable H2 production from renewable resources is of great significance to achieve a ‘hydrogen economy’ in the future. Aiming at exploring the potential of bio-derived fuel (e.g. bio-oil) for H2 production via chemical looping reforming (CLR), this study investigated the direct reduction of a reforming catalyst (18 wt% NiO/Al2O3) with five bio-compounds (acetic acid, ethanol, acetone, furfural and glucose) and subsequent steam reforming (SR), which represented one half of a cycle in CLR. First, thermodynamic analysis was conducted. Results indicated that for a system consisting of bio-compound, steam and NiO above 200 °C, the bio-compounds would preferably reduce NiO rather than react with steam or decompose. The reduction was hardly affected by temperature, pressure, or the presence of steam. The formation of carbon during reduction depended on temperature and the availability of NiO. Moreover, the dependence of SR performance (equilibrium yields, and carbon formation) on temperature, molar steam to carbon ratio (S/C) and the type of bio-compound was studied. Equilibrium yields of H2, CO, CO2 and CH4 were successfully fitted into linear functions of the O/C and H/C ratios in bio-compound molecules. The wide suitability of these fitted equations made it possible to predict the potential of various feedstocks in H2 production without doing repeated simulation work. Moreover, the integrated catalyst reduction and SR process was experimentally investigated in a packed bed reactor over the temperature range of 500-750 °C and S/C range of 4.5-9 for glucose and 0-5 for the other bio-compounds at atmospheric pressure. The effects of temperature and S/C on reduction kinetics as well as the subsequent SR were systematically investigated. Kinetic modelling was performed within NiO conversion of 0-50% and two-dimensional nuclei growth model (A2) was found to fit very well except for glucose. For all the bio-compounds, the apparent activation energy of NiO reduction was between 30 and 40 kJ/mol. Their pre-exponential factors decreased in this order: CH4>ethanol≈acetone>acetic acid>furfural> glucose, probably due to the different activities of reducing species they produced. Optimal S/C values for reduction kinetics were found between 1 and 2. The main barrier for each bio-compound in SR process was summarised. In addition, temperature programmed reduction (TPR) of the NiO catalyst with solid bio-compounds (glucose and citric acid) under N2 was investigated by TGA-FTIR technique. It was found that the coke formed by bio-compound pyrolysis acted as the actual reductant for NiO reduction with CO2 as main reduction product. The reduction extent depended on the initial loading of bio-compounds and their charring characteristics. The reduction kinetics was studied by the Kissinger method. A two-step reduction mechanism (initially solid-solid reduction, and then gaseous reduction with CO) was proposed to explain the multiple reduction phases observed.