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Haibo, E. "Quantitative analysis of core-shell nanoparticle catalysts by scanning transmission electron microscopy." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:19c3b989-0ffb-487f-8cb3-f6e9dea83e63.
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This thesis concerns the application of aberration corrected scanning transmission electron microscopy (STEM) to the quantitative analysis of industrial Pd-Pt core-shell catalyst nanoparticles. High angle annular dark field imaging (HAADF), an incoherent imaging mode, is used to determine particle size distribution and particle morphology of various particle designs with differing amounts of Pt coverage. The limitations to imaging, discrete tomography and spectral analysis imposed by the sample’s sensitivity to the beam are also explored. Since scattered intensity in HAADF is strongly dependent on both thickness and composition, determining the three dimensional structure of a particle and its bimetallic composition in each atomic column requires further analysis. A quantitative method was developed to interpret single images, obtained from commercially available microscopes, by analysis of the cross sections of HAADF scattering from individual atomic columns. This technique uses thorough detector calibrations and full dynamical simulations in order to allow comparison between experimentally measured cross section to simulated ones and is shown to be robust to many experimental parameters. Potential difficulties in its applications are discussed. The cross section approach is tested on model materials before applying it to the identification of column compositions of core-shell nanoparticles. Energy dispersive X-ray analysis is then used to provide compositional sensitivity. The potential sources of error are discussed and steps towards optimisation of experimental parameters presented. Finally, a combination of HAADF cross section analysis and EDX spectrum imaging is used to investigate the core-shell nanoparticles and the results are correlated to findings regarding structure and catalyst activity from other techniques. The results show that analysis by cross section combined with EDX spectrum mapping shows great promise in elucidating the atom-by-atom composition of individual columns in a core-shell nanoparticle. However, there is a clear need for further investigation to solve the thickness / composition dualism.
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Liu, Chen. "Structural Studies of Pt-Based Electrocatalysts for Polymer Electrolyte Fuel Cells." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263807.
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付記する学位プログラム名: 京都大学大学院思修館京都大学
新制・課程博士
博士(総合学術)
甲第23346号
総総博第19号
京都大学大学院総合生存学館総合生存学専攻
(主査)教授 寶 馨, 教授 内本 喜晴, 特定教授 橋本 道雄
学位規則第4条第1項該当
Doctor of Philosophy
Kyoto University
DFAM
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直也, 青木, and Naoya Aoki. "固体高分子形燃料電池用高活性・高耐久コアシェル触媒の新規合成法に関する研究." Thesis, https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB13158528/?lang=0, 2021. https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB13158528/?lang=0.
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Cho, Sung-Jin. "Synthesis and characterization of core/shell structured magnetic nanomaterials /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2005. http://uclibs.org/PID/11984.
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Ceylan, Abdullah. "Core/shell structured magnetic nanoparticles synthesized by inert gas condensation." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 139 p, 2007. http://proquest.umi.com/pqdweb?did=1397915001&sid=7&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Williams, Benjamin Parker. "Using Core-Shell Nanocatalysts to Unravel the Impact of Surface Structure on Catalytic Activity:." Thesis, Boston College, 2020. http://hdl.handle.net/2345/bc-ir:108918.
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Thesis advisor: Udayan MohantyThe high surface area and atomic-level tunability offered by nanoparticles has defined their promise as heterogeneous catalysts. While initial studies began with nanoparticles of a single metal assuming thermodynamic shapes, modern work has focused on using nanoparticle composition and geometry to optimize nanocatalysts for a wide variety of reactions. Further optimization of these refined nanocatalysts remains difficult, however, as the factors that determine catalytic activity are intertwined and a fundamental understanding of each remains elusive. In this work, precise synthetic methods are used to tune a number of factors, including composition, strain, metal-to-metal charge transfer, atomic order, and surface faceting, and understand their impact on catalysis. The first chapter focuses on current achievements and challenges in the synthesis of intermetallic nanocatalysts, which offer long-range order that allows for total control of surface structure. A particular focus is given to the impact of the synthetic approach on the activity of the resulting nanoparticles. In the second chapter, multilayered Pd-(Ni-Pt)x nanoparticles serve as a controlled arena for the study of metallic mixing and order formation on the nanoscale. The third chapter controls the shell thickness of Au@PdPt core-alloyed shell nanoparticles on a nanometer scale to isolate strain at the nanoparticle surface. In the fourth chapter, the synthetic approaches of chapters two and three are applied to catalysis. In totality, the work presented here represents a brick in the foundation of understanding and exploiting structure-function relationships on the nanoscale, with an eye toward the rational design of tailored nanocatalysts
Thesis (PhD) — Boston College, 2020
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
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De, Clercq Astrid. "In-situ study of the growth, structure and reactivity of Pt-Pd nanoalloys." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4077/document.
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Les propriétés catalytiques des nanoparticules métalliques peuvent être améliorées par effet d’alliages. La synthèse en solution par voie colloïdale permet de préparer des nanoalliages homogènes en taille, en forme et en composition chimique, de structure ordonnée, désordonnée ou cœur-coquille. La nucléation et la croissance des nanoalliages de Pt-Pd sont étudiées ici par microscopie électronique en transmission, en condition standard, puis in situ dans une cellule liquide formée par des feuilles d’oxyde de graphène. La cinétique de croissance des nanoalliages de Pt-Pd correspond à l’incorporation directe des monomères en solution, compatible avec un processus limité par la réaction de surface, sans phénomène de coalescence, contrairement à la croissance du Pt pur. La structure théorique à l’équilibre des nanoalliages de Pt-Pd est déterminée par des simulations Monte Carlo. La structure la plus probable correspond à une surface riche en Pd et à une sous couche atomique riche en Pt, stable à des températures élevées. L’effet de l’adsorption de gaz oxydants ou réducteurs sur la forme des nanoparticules, est étudié in situ par microscopie environnementale sous pression de quelques mbar, dans un porte objet environnemental. On observe des changements de formes sous oxygène, dus au développement de facettes d’indices plus élevés. La réactivité des nanocubes de Pd@Pt est étudiée pour l’oxydation du CO en fonction du recouvrement de Pt à la surface. La réactivité maximale pour un faible recouvrement est interprétée par une baisse de l’énergie d’adsorption du CO liée au désaccord paramétrique entre le Pt et le Pd et à la modification de la structure électronique du Pt lié au PdThe catalytic properties of metal nanoparticles can be improved by the alloying effect. Nanoalloys homogeneous in size, shape and chemical composition can be prepared with the colloidal synthesis method, with an ordered, random or core-shell chemical structure. Nucleation and growth of colloidal Pt-Pd nanoalloys were studied by transmission electron microscopy (TEM), in standard conditions and in situ with the aid of a graphene oxide liquid cell. The growth kinetics of homogeneous Pt-Pd nanoalloys corresponds to the direct incorporation of the monomers in solution. It was compatible with a process limited by the surface reaction, without coalescence (Lifshitz-Slyozov-Wagner mechanism). On the contrary, coalescence occurs during the growth of pure Pt nanoparticles. The theoretical structure of Pt-Pd nanoalloys is determined by Monte Carlo simulations. The most stable structure corresponds to a Pd surface and Pt subsurface layer, which is stable up to high temperatures. The effect of adsorption of oxidizing or reducing gasses on the shape of pure Pd nanocubes and core-shell Pd@Pt nanocubes is studied in situ by TEM with an environmental cell. The observed changes in a few mbar of oxygen are due to the development of higher index facets. The CO oxidation reaction is used to compare the reactivity of homogeneous Pt-Pd nanoalloys and core-shell Pd@Pt nanocubes with increasing coverage of Pt at the surface. A maximal reactivity is attained for a low coverage. The effect is interpreted by a decrease in adsorption energy of CO, due to electronic effects originating from the lattice mismatch between Pt and Pd and the mixed Pt-Pd bonds
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Hu, Pan. "Surfactant Directed Encapsulation of Metal Nanocrystals in Metal-Organic Frameworks." Thesis, Boston College, 2015. http://hdl.handle.net/2345/bc-ir:104132.
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Thesis advisor: Dunwei WangMetal nanocrystals with size and shape control have great potential in heterogeneous catalysis. Controllable encapsulation of well-defined metal nanoparticles into the novel porous materials results in new multifunctional nanomaterials. The core-shell nanostructure can enhance the selectivity, durability, or reactivity of the catalysts and even provide additional functionalities. Metal-organic frameworks (MOFs) are a class of novel crystalline nanoporous materials, with well-defined pore structures and distinctive chemical properties. Using MOFs as the encapsulating porous materials has drawn great interest recently due to their tunable structures and properties. However, it could be challenging to grow another porous material layer on metal surface due to the unfavorable interfacial energy. In this work we develop a new concept of colloidal synthesis to synthesize the metal@MOF core-shell nanostructures, in which a layer of self-assembled molecules directed the growth and alignment between two materials. Surfactant cetyltrimethylammonium bromide (CTAB) is designated to facilitate the overgrowth of MOF onto metal surface, and an alignment between the {100} planes of the metal and {110} planes of the MOF can be observed. By utilizing the same concept, a third layer of mesoporous silica could also be coated on the MOF shell with assistance of CTAB. And our method could be a general strategy to fabricate multiple-layer MOF materials
Thesis (MS) — Boston College, 2015
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
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Zhang, Furui. "Mechanism and Interface Study of One-to-one Metal NP/Metal Organic Framework Core-shell Structure." Thesis, Boston College, 2017. http://hdl.handle.net/2345/bc-ir:107565.
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Thesis advisor: Chia-Kuang (Frank) TsungThe core-shell hybrid structure is the simplest motif of two-component systems which consists of an inner core coated by an outer shell. Core-shell composite materials are attractive for their biomedical, electronic and catalytic applications in which interface between core and shell is critical for various functionalities. However, it is still challenging to study the exact role that interface plays during the formation of the core-shell structures and in the properties of the resulted materials. By studying the formation mechanism of a well interface controlled one-to-one metal nanoparticle (NP)@zeolite imidazolate framework-8 (ZIF-8) core-shell material, we found that the dissociation of capping agents on the NP surface results in direct contact between NP and ZIF-8, which is essential for the formation of core-shell structure. And the amount of capping agents on the NP surface has a significant effect to the crystallinity and stability of ZIF-8 coating shell. Guided by our understanding to the interface, one-to-one NP@UiO-66 core-shell structure has also been achieved for the first time. We believe that our research will help the development of rational design and synthesis of core-shell structures, particularly in those requiring good interface controls
Thesis (MS) — Boston College, 2017
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
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Otor, Hope O. "Catalyst Development and Control of Catalyst Deactivation for Carbon Dioxide Conversion." University of Toledo / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1596134702392137.
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Chen, Si. "New approach to aqueous biphasic catalysis through catalyst confinement in nanoscopic core-shell polymers." Thesis, Toulouse 3, 2015. http://www.theses.fr/2015TOU30163/document.
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Les catalyseurs sont indispensables à l'industrie chimique moderne. La récupération des catalyseurs est nécessaire d'un point de vue économique et environnemental lorsqu'elle fait appel à des métaux coûteux et/ou toxiques. L'utilisation de la catalyse micellaire est un bon choix d'un point de vue de l'activité, du transfert de masse, et de recyclage mais comporte les problèmes de la formation d'émulsions stables liée au gonflement excessif et la perte physique du tensioactif libre en équilibre avec les micelles. L'objectif de ma thèse est réticuler les micelles au cœur pour éliminer ces problèmes. Après avoir construit de telles nanoparticules fonctionnalisées du ligand phosphine par la synthèse " one-pot " via PRC de type RAFT en émulsion. La première application des nanoréacteurs catalytiques a été réalisée en hydroformylation de l'octène en biphasique, donnant lieu à une conversion complète avec de faibles charges catalytiques, une décantation rapide et la possibilité de recycler le milieu catalytique. De manière inattendue, le catalyseur reste actif après une longue exposition à l'air, montrant un effet protecteur du polymère contre la dégradation du catalyseur. L'absence de coagulation à la fin de réaction est une preuve que ces nouveaux objets franchissent les limitations de la catalyse micellaireThe catalytic processes are at the heart of chemical industry. Modern chemical industry, under pressure of stricter regulations and societal concern, is faced with the need to improve efficiency and cleaner production processes and catalysis is one the major keys to green chemical technology. Catalysts recovery is necessary from an economic and environmental point of view when it makes use of expensive and / or toxic metals. The aim of this thesis is based on an innovative approach related to micellar catalyst but in which the catalyst is covalent linked to the hydrophobic core of well-defined unimolecular, core-cross-linked micelles. The synthetic protocol is based on a convergent method via RAFT-mediated one-pot aqueous emulsion polymerization. The efficiency of these unimolecular micelles as catalytic nanoreactors has been shown using the industrially relevant hydroformylation of 1-octene, in order to provide a proof of principle, as a test reaction yielding turnover frequencies and l/b ratio comparable to those of related homogeneous systems. However, the catalyst phase could be easily separated from the organic product phase and recycled. A remarkable protecting effect of the active catalyst by the polymer scaffold has also been demonstrated. The absence of the coagulation at the end of reaction is evidence that these new objects function as micelles while eliminating the disadvantages of micellar catalysis such as the formation of stable emulsion
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Albrecht, Karl Oscar. "Development and testing of a combined catalyst/sorbent core-in-shell material for the production of high concentration hydrogen." [Ames, Iowa : Iowa State University], 2008.
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Chanda, Jagannath, Leonid Ionov, Alina Kirillovaab, and Alla Synytska. "New insight into icing and de-icing properties of hydrophobic and hydrophilic structured surfaces based on core–shell particles." Royal Society of Chemistry, 2015. https://tud.qucosa.de/id/qucosa%3A36410.
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Icing is an important problem, which often leads to emergency situations in northern countries. The reduction of icing requires a detailed understanding of this process. In this work, we report on a systematic investigation of the effects of geometry and chemical properties of surfaces on the formation of an ice layer, its properties, and thawing. We compare in detail icing and ice thawing on flat and rough hydrophilic and hydrophobic surfaces. We also show advantages and disadvantages of the surfaces of each kind. We demonstrate that water condenses in a liquid form, leading to the formation of a thin continuous water layer on a hydrophilic surface. Meanwhile, separated rounded water droplets are formed on hydrophobic surfaces. As a result of slower heat exchange, the freezing of rounded water droplets on a hydrophobic surface occurs later than the freezing of the continuous water layer on a hydrophilic one. Moreover, growth of ice on hydrophobic surfaces is slower than on the hydrophilic ones, because ice grows due to the condensation of water vapor on already formed ice crystals, and not due to the condensation on the polymer surface. Rough hydrophobic surfaces also demonstrate a very low ice adhesion value, which is because of the reduced contact area with ice. The main disadvantage of hydrophobic and superhydrophobic surfaces is the pinning of water droplets on them after thawing. Flat hydrophilic poly(ethylene glycol)-modified surfaces also exhibit very low ice adhesion, which is due to the very low freezing point of the water–poly(ethylene glycol) mixtures. Water easily leaves from flat hydrophilic poly(ethylene glycol)-modified surfaces, and they quickly become dry. However, the ice growth rate on poly(ethylene glycol)-modified hydrophilic surfaces is the highest. These results indicate that neither purely (super)hydrophobic polymeric surfaces, nor ‘‘antifreeze’’ hydrophilic ones provide an ideal solution to the problem of icing.
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Peng, Fang. "CORE-SHELL STRUCTURED FILAMENTS FOR FUSED FILAMENT FABRICATION THREE-DIMENSIONAL PRINTING & ROLL-TO-ROLL MANUFACTURING OF PIEZORESISTIVE ELASTOMERIC FILMS." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1542976477808743.
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Vettori, Marco. "Growth optimization and characterization of regular arrays of GaAs/AIGaAs core/shell nanowires for tandem solar cells on silicon." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEC010/document.
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L'objectif de cette thèse est de réaliser l'intégration monolithique de nanofils (NFs) à base de l’alliage Al0.2Ga0.8As sur des substrats de Si par épitaxie par jets moléculaires via la méthode vapeur-liquide-solide (VLS) auto-assistée et de développer une cellule solaire tandem (TSC) à base de ces NFs.Pour atteindre cet objectif, nous avons tout d'abord étudié la croissance de NFs GaAs, étape clé pour le développement des NFs p-GaAs/p.i.n-Al0.2Ga 0.8As coeur/coquille, qui devraient constituer la cellule supérieure de la TSC. Nous avons montré, en particulier, l'influence de l'angle d'incidence du flux de Ga sur la cinétique de croissance des NFs GaAs. Un modèle théorique et des simulations numériques ont été réalisées pour expliquer ces résultats expérimentaux.Nous avons ensuite utilisé le savoir-faire acquis pour faire croître des NFs p-GaAs/p.i.n-Al0,2Ga0,8As coeur/coquille sur des substrats de Si prêts pour l'emploi. Les caractérisations EBIC réalisées sur ces NFs ont montré qu'ils sont des candidats potentiels pour la réalisation d’une cellule photovoltaïque. Nous avons ensuite fait croître ces NFs sur des substrats de Si patternés afin d'obtenir des réseaux réguliers de ces NFs. Nous avons développé un protocole, basé sur un pré-traitement thermique, qui permet d'obtenir des rendements élevés de NFs verticaux (80-90 %) sur une surface patternée de 0,9 x 0,9 mm2.Enfin, nous avons consacré une partie de notre travail à définir le procédé de fabrication optimal pour la TSC, en concentrant notre attention sur le développement de la jonction tunnel de la TSC, l'encapsulation des NFs et le contact électrique supérieur du réseau de NFsThe objective of this thesis is to achieve monolithical integration of Al0.2Ga0.8As-based nanowires (NWs) on Si substrates by molecular beam epitaxy via the self-assisted vapour-liquid-solid (VLS) method and develop a NWs-based tandem solar cell (TSC).In order to fulfil this purpose, we firstly focused our attention on the growth of GaAs NWs this being a key-step for the development of p-GaAs/p.i.n-Al0.2Ga0.8As core/shell NWs, which are expected to constitute the top cell of the TSC. We have shown, in particular, the influence of the incidence angle of the Ga flux on the GaAs NW growth kinetic. A theoretical model and numerical simulations were performed to explain these experimental results.Subsequently, we employed the skills acquired to grow p-GaAs/p.i.n-Al0.2Ga0.8As core/shell NWs on epi-ready Si substrates. EBIC characterizations performed on these NWs have shown that they are potential building blocks for a photovoltaic cell. We then committed to growing them on patterned Si substrates so as to obtain regular arrays of NWs. We have developed a protocol, based on a thermal pre-treatment, which allows obtaining high vertical yields of such NWs (80-90 %) on patterned Si substrates (on a surface of 0.9 x 0.9 mm2).Finally, we dedicated part of our work to define the optimal fabrication process for the TSC, focusing our attention to the development of the TSC tunnel junction, the NW encapsulation and the top contacting of the NWs
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Jiang, Haowei. "Time-Salt Superposition In Polyelectrolyte Complexes And Enhanced Mechanical Properties of Three-Dimensional Printed Objects By Core-Shell Structured Thermoplastic Filaments." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1533054312671917.
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Alvarenga, Marinho Andre Luiz. "Development of catalytic process for biogas upgrading : study of structure and oxygen mobility on Ni and Pt nanoparticles encapsulated catalysts." Thesis, Poitiers, 2020. http://www.theses.fr/2020POIT2272.
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Le reformage à sec du méthane (DRM) est un procédé catalytique permettant de produire, à partir de biogaz issu de la dégradation de la biomasse, du gaz de synthèse (CO + H2) dont les applications industrielles sont nombreuses. La formation de coke et le frittage des sites actifs métalliques sont les principaux problèmes à résoudre pour amener cette technologie à l’échelle industrielle.Ce travail de thèse vise à étudier l’effet de l’encapsulation de Ni au sein de deux structures différentes : nanoparticules incluses dans une matrice ou distribuées dans un support mésoporeux. Les résultats montrent que les particules de Ni incluses dans CeO2 améliore la résistance au frittage lors de la réduction à haute température (800°C) et entraine une plus forte interaction métal-support. Le dopage de la cérine par Zr inhibe la croissance des particules de Ni et augmente la mobilité de l’oxygène comme révélé par les expériences d’échange isotopique. Le dopage par Gd ou Sm n’améliore ni la stabilité thermique du matériau ni le frittage des sites métallique. L’échange du Ni par le Pt préserve l’effet promoteur lié à l’inclusion du site actif dans la matrice oxyde ainsi que la mobilité de l’oxygène. Des oxydes mixtes mésoporeux CeO2-Al2O3 contenant du Ni ont été préparés par la méthode d’auto-assemblage induit par évaporation (EISA). Après réduction, des particules de Ni de petites tailles sont observées (<5 nm). Un comportement différent se produit lorsque le Ni est imprégné a posteriori sur le support CeO2-Al2O3 préparé par EISA à cause de la présence de particules de Ni plus larges et isolées qui promeuvent la réaction de décomposition de CH4.L’absence de dépôts carbonés après 24 h de réaction sur Ni@CeZrO2 ou après 72 h de réaction sur 10Ni-CeO2-Al2O3 confirme l’intérêt de ces catalyseurs pour la transformation du biogaz en gaz de synthèse par reformage à sec du méthaneDry reforming of methane (DRM) is a catalytic process able to convert the biogas generated from biomass degradation into syngas, which has many industrial applications. However, coke formation and metal sintering are the main drawbacks to upgrade this technology to an industrial scale. This work evaluates the effect of Ni encapsulation in two different structures: embedded nanoparticles and distributed nanoparticles over mesoporous support. Results showed that Ni embedded in ceria improved the resistance to sintering along the reduction at high temperature (800 °C) and led to a higher metal-support interaction compared to impregnated catalyst. Doping ceria with Zr inhibited the growth of CeO2 and Ni clusters in embedded catalysts and increased the oxygen mobility as revealed by oxygen isotopic exchange experiments. The doping with Gd and Sm did not enhance thermal stability on the material and the sintering is still observed. The nature of metal exchanging Ni by Pt did not affect the promotional effects of encapsulation in embedded structures. Ni-based mesoporous mixed CeO2-Al2O3 oxide catalysts prepared by one pot Evaporation Induced Self Assembly (EISA) presented small metallic Ni particles (< 5 nm). Different behavior occurs with CeO2-Al2O3 oxide prepared by EISA method when Ni is post-impregnated because of the presence of isolated larger Ni particles which promotes the decomposition of CH4. Finally carbon deposits were not detected over embedded Ni@CeZrO2 after 24 h of reaction and meosoporous 10Ni- CeO2-Al2O3 after 72 h of reaction and, therefore, these catalysts presented promising results in this work for biogas upgrading process by dry reforming of methane reaction
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Van, Zyl A. J. P. (Andries Jakobus Petrus). "Synthesis, characterization and testing of nano-structured particles for effective impact modification of glassy amorphous polymers." Thesis, Stellenbosch : Stellenbosch University, 2003. http://hdl.handle.net/10019.1/53609.
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Thesis (PhD)--Stellenbosch University, 2003.ENGLISH ABSTRACT: The synthesis of structured nanoparticles, in particular core/shells, IS of great technological and economical importance to modem materials science. One of the advantages of structured particles is that they can be synthesized with either a solid core (albeit soft or hard) or a liquid core (of varying viscosity). This adds to the versatility of structured particles and their relevance to a majority of industrial and commercial endapplications. The synthesis of core/shell particles with liquid cores was investigated for the effective impact modification of glassy amorphous polymers. Polybutyl acrylate was chosen as the shell due to its rubbery nature. Hexadecane functioned as the core oil and facilitated osmotic stability by being a suitable hydrophobe for the miniemulsion synthesis. Polymer synthesis was preceded by the prediction of particle morphology by using thermodynamic prediction models. Core/shell particles with liquid cores were synthesized via miniemulsion polymerization. This resulted in the direct introduction of core-oil and monomer into the miniemulsion droplets. Polymerization was achieved in situ, resulting in the formation of particles with the desired morphology. For additional strength, stability and matrix mixing capabilities, methyl methacrylate (MMA) was grafted onto the initial core/shell particles. The obtained morphology was in contradiction with the predicted morphology, thus pointing to strong kinetic influences during the polymerization process. These influences could be attributed to surface anchoring of polymer chains due to the initiator (KPS) used, the establishment of the polymerization locus as well as the increase in viscosity at the polymerization locus. To test these influences a surface-inactive initiating species (AIBN) and an interfacial redox initiating species (cumyl hydroperoxide/Fe/") were used. Use of the former resulted in the formation of solid polymer particles due to homogeneous polymerization throughout the droplet, thus leading to an inverse core/shell morphology as a result of thermodynamic considerations. The redox initiator promoted kinetic influences as a result of fast polymerization kinetics at the droplet/water interface. This, as well as the increase in viscosity, facilitated the production of core/shell particles. To obtain core/shell particles with the desired size, the influence of surfactant concentration was investigated. Capillary hydrodynamic fractionation (CHDF) was used to determine the particle size of the initial core/shell particles as well as the size of the MMA-grafted core/shell particles. The area stabilized per surfactant molecule was calculated stoichiometrically and compared to "classical" miniemulsion results, i.e. data generated from the synthesis of polymeric latexes in the presence of a hydrophobe, but at a much lower hydrophobe:monomer ratio than was used here. The influence of methanol as well as the possibility of scaling-up the process was also investigated. The study was further expanded to the investigation of living miniemulsion polymerization techniques to control the molecular architecture of synthesized core/shell latexes. The influence of different RAFT agents, initiators and monomers were investigated on the core/shell formation properties of the investigated systems. The combined effects of establishing the polymerization locus as well as increased polymerization kinetics, thus increasing the viscosity at the polymerization locus, lead to the successful formation of liquid- filled core/shell particles. To conclude, the ability of the synthesized core/shell particles to induce impact modification in glassy amorphous polymers was investigated. Results showed that incorporation of these particles could effectively modify the intrinsic properties of the investigated polymers, resulting in a brittle-to-ductile transition. Improved impact results of the investigated glassy matrix were obtained. Keywords: core/shell, liquid-filled, RAFT, miniemulsion, impact modification
AFRIKAANSE OPSOMMING: Die sintese van gestruktureerde nano-partikels, meer spesifiek kern/skil partikels, is van onskatbare tegnologiese en ekonomiese belang vir moderne materiaalkunde. Een van die voordele van hierdie tipe partikels is dat sintese kan geskied met 'n soliede kern (hard of sag) of vloeistofkern (met wisselende viskositeit). Dit dra by tot die veelsydigheid van gestruktureerde partikels en dus tot grootskaalse aanwending in industriële en kommersiële toepassings. Die sintese van kern/skiI partikels met vloeistofkerne is ondersoek met die oog op effektiewe slagsterkte modifikasie van glasagtige amorfe polimere. Polibutielakrilaat is gekies as skil-polimeer op grond van sy rubberige voorkoms. Heksadekaan moes funksioneer as die kern-olie, maar het ook bykomende osmotiese stabiliteit verleen tydens die miniemulsie-polimerisasie proses. Dit is as gevolg van die gepaste hidrofobiese eienskappe van heksadekaan. Polimeer sintese is voorafgegaan deur die voorspelling van partikel morfologie met behulp van termodinamies gebaseerde voorspellingsmodelle. Kern/skil partikels is gesintetiseer deur middel van 'n miniemulsie-polimerisasie reaksie wat die direkte inkorporering van kern-olie en monomeer in die miniemulsiedruppel teweeg bring. Polimerisasie vind in situ (lat. vir in die oorspronklike plek, m.a.w. binne-in die druppel) plaas en lei tot die vorming van partikels met die gewenste morfologie. Metielmetakrilaat is ge-ent op die oorspronklike kern/skil partikels om addisionele sterkte, stabiliteit en vermenging met die matriks polimeer te bewerkstellig. Die verkrygde morfologie is teenstrydig met die voorspelde morfologie, wat dus die teenwoordigheid van sterk kinetiese invloede aandui. Hierdie invloede kan toegeskryf word aan die oppervlak-aktiewe afsetter (KPS, kaliumpersulfaat) wat gebruik is, die daarstelling van die polimerisasie lokus asook die toename in viskositeit by die lokus van polimerisasie. Om hierdie invloede te toets is 'n oppervlak-onaktiewe afsetter (AIBN, asobisisobutironitriel) en intervlak redoks-afsetter (kumielhidroperoksied/Pe'") gebruik. Gebruik van eersgenoemde het die vorming van soliede partikels teweeg gebring. Dit is as gevolg van homogene polimerisasie in die druppel en dus die ontstaan van omgekeerde kern/skiI partikels weens termodinamiese oorwegings. Die redoks-afsetter het egter die kinetiese oorwegings bevoordeel as gevolg van vinnige polimerisasiekinetika by die druppel/water intervlak. Dit, tesame met die toename in viskositeit, maak die produksie van kern/skil partikels moontlik. Vir die verkryging van kern/skiI partikels met die gewenste partikelgrootte is die invloed van die seep konsentrasie ondersoek. CHDF (eng. capillary hydrodynamic fractionation) is gebruik om die partikelgrootte van die oorspronklike kern/skiI partikels, sowel as dié ge-ent met metielmetakrilaat, te bepaal. Die area gestabiliseer per seepmolekule is bereken d.m.v. stoichiometrie en vergelyk met "klassieke" miniemuisie data, d.i. data verkry deur die sintese van latekse in die teenwoordigheid van 'n hidrofoob, maar teen 'n baie laer hidrofoob:monomeer-verhouding as wat hier gebruik is. Die invloed van metanol, asook die moontlikheid om die reaksie op te skaal, is ondersoek. Die studie is verder uitgebrei om die invloed van lewende miniemulsie-polimerisasie tegnieke in te sluit, om sodoende beheer uit te oefen oor die molekulêre argitektuur van die gesintetiseerde latekse. Die invloed van verskeie RAFT (eng. reversible additionfragmentation chain transfer) agente, afsetters en monomere op die kern/skiI vormingsmoontlikhede van die bestudeerde stelsels, is ondersoek. Die gesamentlike effek van die daarstelling van die polimerisasie lokus en dus die verhoging van die viskositeit by die lokus, lei tot die suksesvolle vorming van vloeistof-gevulde kern/skiI partikels. Laastens is die invloed van die gesintetiseerde kern/skil partikels op die slagsterkte van glasagtige amorfe polimere ondersoek. Resultate dui daarop dat die insluiting van hierdie partikels kan lei tot die effektiewe verandering van die intrinsieke eienskappe van die bestudeerde polimere, en dus 'n oorgang van bros na rekbaar kan veroorsaak. 'n Verbetering in die slagsterkte resultate van die bestudeerde glasagtigte matriks is ook waargeneem.
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Bouharras, Fatima Ezzahra. "Développement de nanocomposites BaTiO3 @ polymères fluorés pour les matériaux diélectriques et comme liant de cathode dans les batteries lithium Core shell structured Poly(Vinylidene Fluoride) -grafted- BaTiO3 nanocomposites prepared via Reversible Addition-fragmentation chain transfer (RAFT) polymerization of VDF for high energy storage capacitors Recent Progress on Core-Shell Structured BaTiO3/Fluorinated Polymers Nanocomposites for High Energy Storage: Synthesis, Dielectric properties and Applications." Thesis, Montpellier, Ecole nationale supérieure de chimie, 2020. http://www.theses.fr/2020ENCM0002.
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Les matériaux nanocomposites présentent des propriétés physico-chimiques uniques qui ne peuvent être obtenues en utilisant un seul composant. Ainsi, l'amélioration des propriétés de ces matériaux a suscité un intérêt majeur dans différents domaines. Les matériaux nanocomposites diélectriques à haute densité d'énergie présentent des performances prometteuses pour les applications de stockage d'énergie. Des efforts importants ont été menés pour combiner la constante diélectrique élevée de la céramique avec la flexibilité et la facilité de mise en œuvre des polymères. Ainsi, cette thèse porte sur le développement et la caractérisation de nanocomposites à base de céramique BaTiO3 et de polymères fluorés. Dans un premier temps, la synthèse de PVDF-g-BaTiO3 a été réalisée en utilisant la polymérisation RAFT du VDF à partir de la surface des nanoparticules fonctionnalisées, en utilisant différentes concentrations en BaTiO3, et l'effet de ce pourcentage sur les propriétés finales a été étudié. Les résultats ont montré que le greffage du PVDF a été réalisé avec succès, conduisant à des nanocomposites avec une stabilité thermique améliorée. De plus, le succès du greffage du PVDF a été principalement prouvé par la spectroscopie RMN HRMAS, qui a été utilisée pour la première fois pour caractériser les nanocomposites préparés. Les propriétés diélectriques de ces matériaux ont été étudiés et révèlent l'existence de trois relaxations : la première a été attribué à la relaxation secondaire β dans le PVDF, la seconde a été liée à la fraction cristalline dans le polymère, tandis que la troisième relaxation a été attribué à la polarisation interfaciale résultant de la présence de charges et d'impuretés dans le système. Cependant, la relaxation liée à la température de transition vitreuse n'a pas pu être observé en raison de la cristallinité élevée du polymère. Le procédé de mélange en solution a été également utilisé pour préparer des matériaux nanocomposites constitués de PVDF-g-BaTiO3/P(VDF-co-HFP) et les films préparés ont été entièrement caractérisés. La dispersion uniforme des nanocomposites PVDF-g-BaTiO3 dans la matrice de copolymère a conduit à des performances mécaniques améliorées. Ensuite, pour fournir une application pour les nanocomposites PVDF-g-BaTiO3 préparés, ces derniers ont été utilisés comme liant pour préparer un matériau de cathode pour les batteries. La procédure de calandrage a été utilisée pour préparer les films d'électrode et a permis d'obtenir une structure uniforme et des performances de cyclage amélioréesNanocomposite materials present unique physic-chemical properties that cannot be obtained using one component. Thus, the improvement in the properties of such materials have resulted in major interest for versatile fields. Dielectric nanocomposite materials with high energy density exhibit promising performances for energy storage applications. Major efforts have been conducted to combine the efficient properties and high dielectric constant of ceramics with the flexibility and easy processing of polymers. Thus, this thesis focuses on the development and characterizations of nanocomposites based on BaTiO3 ceramic and fluoropolymers. First, the synthesis of PVDF-g-BaTiO3 was realized using RAFT polymerization of VDF from the surface of functionalized nanoparticles, using different BaTiO3 concentrations, and the effect of such percentage on the final properties was studied. Results showed the successful grafting of PVDF leading to nanocomposites with enhanced thermal stability. Furthermore, the successful grafting of PVDF onto the functionalized nanoparticles was mainly proved by HRMAS NMR spectroscopy, which was used for the first time to characterize the prepared nanocomposites. The dielectric properties of such materials were investigated, and reveals the existence of three relaxations: the first one was attributed to the well-known β secondary relaxation in PVDF, the second one was assigned to the crystalline fraction in the polymer, while the third relaxation was assigned to interfacial polarization arising from the presence of fillers and impurities in the system. However, the relaxation related to glass transition temperature could not be observed due to the high crystallinity of the polymer. Solution blending strategy was also used to prepare nanocomposite materials consisting of PVDF-g-BaTiO3/P(VDF-co-HFP) and the prepared films were fully characterized. The uniform distribution of PVDF-g-BaTiO3 nanocomposites in the copolymer matrix leads to enhanced mechanical performances resulting in increased Young’s modulus. Then, to supply an application for the prepared PVDF-g-BaTiO3 nanocomposites, those later were used as binder to prepare cathode material for batteries. Calendering procedure was used to prepare the electrode films and enabled to obtain uniform structure and enhanced cycling performances
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Tajra, Feras [Verfasser], Dietmar [Akademischer Betreuer] Stephan, Dietmar [Gutachter] Stephan, Frank U. [Gutachter] Vogdt, and Karl-Christian [Gutachter] Thienel. "Study on the production of core-shell structured lightweight aggregate by cold-bonding agglomeration process and its utilization in concrete / Feras Tajra ; Gutachter: Dietmar Stephan, Frank U. Vogdt, Karl-Christian Thienel ; Betreuer: Dietmar Stephan." Berlin : Technische Universität Berlin, 2020. http://d-nb.info/1206245581/34.
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Wery, Madeleine. "Synthèse de catalyseurs de type coeur@coquille pour le procédé d’hydrodésulfuration en phase gazeuse." Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAF036.
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Afin de réduire la teneur en soufre des essences, l’hydrodésulfuration transforme les molécules soufrées en hydrocarbures en présence d’un catalyseur supporté (métaux de transition sulfurés : MoS2) et dopé (Co, Ni). Cette phase active, déposée sur des nanoparticules, présente un nombre plus important de défauts, sites actifs essentiels à la catalyse. Les nanoparticules ont un ratio S/V élevé, une grande réactivité de surface avec une juste utilisation des quantités de métaux. L’objectif de ce projet de thèse est de synthétiser des catalyseurs nanométriques de type coeur@coquille possédant une meilleure activité catalytique qu’un simple mélange mécanique de deux métaux sulfurés. Le coeur est composé de Fe3O4 ou de nanodiamants et la coquille de MoS2, NiMoS, CoMoS ou NiCoMoS, supporté sur du TiO2 ou de la γ-Al2O3. Une réaction modèle (HDS du thiophène) a été utilisée afin d’évaluer l’activité catalytique et d’optimiser la structure du catalyseur. L’étude portera sur les paramètres de synthèse et l’effet de la taille du coeur, la synthèse utilisée, les interactions entre le coeur et la coquille, le support, la (co)– promotion (Ni/Co) et l’activation par la températureIn hydrodesulfurization of fossil fuels, the sulfur levels are reduced by sulfur extraction from hydrocarbons by using supported catalysts (MoS2), doped (Co, Ni). Ultra-deep hydrodesulfurization will be achieved by improving new catalysts. Nanoparticles are a promising candidate with their high S/V ratio and permit to use the precise amount of metallic sulphide. The aim of this thesis is the synthesis of core@shell nanometric catalyst with improved activities. Core composed of Fe3O4 or nanodiamonds will be surrounded by a shell formed of MoS2, NiMoS, CoMoS or NiCoMoS, supported on TiO2, γ-Al2O3. Model reaction (thiophene) has allowed to compare conversion rates between each catalyst. Additionally, characterizations have provided a better understanding of the HDS catalyst structure and performances. Some factors have been investigated such as the size of the core, theinteractions between the core and the shell, the type of synthesis, the support chosen, the synergetic effect with doping ions and also the activation of the catalyst at low temperature
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Beausoleil, Julien. "Synthèse de nanotubes de carbone multi-parois sur supports pulvérulents et étude des mécanismes de croissance catalytique." Thesis, Toulouse, INPT, 2010. http://www.theses.fr/2010INPT0007/document.
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Produire à grande échelle des nanotubes de carbone en maîtrisant les principaux paramètres de croissance et la morphologie de ces matériaux est un enjeu important en vue de leur exploitation industrielle dans de nombreux domaines tels que l’élaboration de composites ou le stockage de l’énergie. C’est dans ce contexte que s’inscrit ce travail, basé sur la technique de dépôt chimique à partir d’une phase vapeur (CVD) mise en oeuvre dans un procédé faisant appel à un lit fluidisé de particules catalytiques (FB-CCVD). Dans un premier temps, nous avons étudié le catalyseur mis au point par la société Arkema, de sa préparation à son utilisation en catalyse pour la croissance de nanotubes de carbone multi-parois. Nous avons ainsi mis en évidence que la phase active était principalement localisée à la surface du support sous la forme d’une gangue discontinue d’hématite. Lors de la synthèse, nous avons constaté deux régimes cinétiques différents que nous avons confrontés aux évolutions physico-chimiques du matériau au cours du dépôt. Par la suite, nous avons préparé à partir du procédé Arkema différents catalyseurs bimétalliques afin d’augmenter le rendement de la synthèse de nanotubes de carbone et de diminuer leur diamètre. Un système à base de fer et de molybdène a montré une activité trois fois supérieure au catalyseur initial sous réserve de travailler à une température particulière. Enfin, dans une dernière partie, nous avons tenté de proposer une explication sur le rôle joué par le molybdène lors de la croissance des nanotubes de carbone. Nos observations nous ont mené à la préparation de catalyseurs coeur-écorce à base de fer et de molybdène présentant des activités supérieures à un système homogèneThe large scale production of carbon nanotubes associated with control of the main growth parameters and of the morphology is a challenging aim for future industrial exploitation of these nanostructured materials in numerous fields like composite production and energy storage. This work based on the fluidized bed catalytic chemical vapour deposition technique (FB-CCVD) lies in this industrial framework. At first, we have studied the catalyst produced by Arkema, from its synthesis to its use for carbon nanotubes growth. We have shown that the active phase is mainly located at the support surface in the form of a discontinuous film of hematite. During the synthesis, we have noticed two kinetic regimes that we analysed through caracterisation of the material at different times of the reaction. Then, we have prepared bimetallic catalysts using the Arkema process in order to improve the reaction yield and to decrease carbon nanotubes diameter. We have discovered thaht an iron and molybdenum based catalyst shows three times higher activity than the classic one, if we work at a specific temperature. At last, we have tried to explain the role played by molybdenum in the growth of carbon nanotubes. Our findings have lead us to develop core shell iron and molybdenum based catalysts presenting higher activity than the homogeneous sytem
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Chen, Chun-Tse, and 陳俊擇. "Structure modification of TiO2@Pt core-shell catalyst for oxygen reduction reaction." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/f86yg4.
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碩士國立臺灣科技大學
化學工程系
106
Design and synthesis of new nano-structured Pt-based ORR catalysts is highly needed. In previous work, for the first time, we proposed that unsupported core-shell TiO2@Pt (TiO2cPts) particles as a model catalyst could generate efficient ORR catalysis. However, TiO2@Pt particles derived from the photo-deposition method did not have a completely covered Pt shell structure, and thus it did not achieve expected ORR catalytic activity. In this work, the photo-deposition method was improved by droplet controlled growth of Pt nanoparticles to synthesize TiO2@Pt. High-resolution transmission electron microscopy (TEM) and elemental mapping images showed that the complete Pt shell on TiO2 core was formed, and the thickness of Pt shell was 2-3 nm. X-ray diffraction (XRD) reveals that Pt shell is composed of numerous ultra-small Pt clusters. X-ray absorption spectroscopy (XAS) shows that TiO2@Pt indicate the presence of Strong Metal-Support Interaction (SMSI). Electrochemical tests demonstrate that TiO2@Pt exhibits over 5-fold specific activity and 8-fold mass activity than commercial Pt nanoparticles. This uniquely designed configuration with TiO2-core and Pt thin shell has made a significant progress in improving the stability. The durability test shows no degradation in both ECSA and mass activity after 5000 cycles. More efficient ORR catalysts can be expected by further fine tuning of the shell structure in TiO2@Pt.
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Heh, Ya-Shiuan, and 賀雅萱. "Structural evolution and modification of highly active and durable TiO2@Pt core-shell catalyst for oxygen reduction reaction." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/78tts8.
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碩士國立臺灣科技大學
化學工程系
107
Structural evolution and modification of new nanostructured platinum-based oxygen reduction reaction catalysts are the objectives of this study. In our previous work, unsupported core-shell TiO2@Pt particles were proposed as a model catalyst could generate efficient ORR catalyst. Although TiO2@Pt particles derived from the photo-deposition method could have a completely covered Pt shell structure, and achieved reasonable ORR catalytic activity. In this work, a well-controlled feeding method using a syringe pump for Pt precursor is introduced to achieve uniform and thin Pt photodeposition on TiO2 particle. High-resolution transmission electron microscopy (HRTEM) and elemental mapping images showed that the complete Pt shell on TiO2 core was formed, and the thickness of Pt shell was around 2 nm as a result of more precise control over Pt growth. The optimized TiO2@Pt exhibits mass activity of 0.107 mA/ μ gPt and specific activity of 0.070 mA/cm2, outperforming the commercial benchmark Pt/C. In addition, the unique structure of TiO2@Pt also possesses excellent stability during the accelerated durability test (ADT). The sample is able to retain 80% of its original mass activity after 50000 cycles. It is also interesting and important to study the structural evolution of TiO2@Pt, especially Pt NPs, after such long cycles. Through Cs-STEM we verify the sample TiO2@Pt after ADT still has thin platinum layer on titanium dioxide. It is suggested the low-coordination platinum atom is preferentially dissolved and then deposited on the side of the highly coordinated platinum atoms when TiO2@Pt undergoes electrochemical scanning. Nitrogen doped TiO2 (N-doped TiO2) has also been applied to prepare N-doped TiO2@Pt catalysts. The properties and the metal-support interaction N-doped TiO2@Pt catalysts have been explored. Similar coreshell structured nanocatalyst was prepared by the same photo-deposition method. From the electrochemical results, it found that N-doped TiO2@Pt has improved specific activity, but not mass activity.
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直也, 青木, and Naoya Aoki. "固体高分子形燃料電池用高活性・高耐久コアシェル触媒の新規合成法に関する研究." Thesis, 2003. http://id.nii.ac.jp/1707/00028194/.
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Chen, Yi-pei, and 陳謚霈. "Photosensing properties of Zn-ZnO core/shell structured nanowires." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/00673168413433865661.
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碩士國立臺灣科技大學
光電工程研究所
100
Single crystalline Zn-ZnO core-shell nanowires have been successfully prepared by thermal evaporation of metallic zinc in oxygen ambient. The diameter of the zinc core is ~ 50 nm, while the thickness of the outer ZnO shell is ~ 7.5 nm, both are grown along the direction. Post-growth annealing causes out-diffusion and oxidation of the Zn core that result in the formation of polycrystalline ZnO nanotubes. Photosensing property measurement shows that both the responsivity and rise/decay time depend on annealing time and ambient oxygen concentrations. The responsivity decreases as annealing time increases, while the decay time shortens as annealing time increases. The decay of the responsivity after annealing is due to the loss of excess zinc which acts as donors. The shortening of the decay time after annealing is likely due to improved grain size. An optimized UV responsivity of 1.1 A/W can be achieved with a normalized gain of 1.1?e10-7 m2V-1 after 10 minutes of post-growth annealing at 350?aC.
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Hung, Chia-Chun, and 洪嘉駿. "Study on TiO2@Pt core-shell catalyst synthesized by photodeposition." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/xb6f2c.
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碩士國立臺灣科技大學
應用科技研究所
105
The main objective of this study is to develop a novel M@Pt(M= metal oxide) core-shell catalyst for oxygen reduction reaction under acidic conditions. The photodeposition method was adopted to deposit platinum on titanium dioxide. Gas atmosphere, light intensity and reaction time were used as variables to systematically investigate the morphology of the prepared catalyst. Furthermore, the oxygen reactivity and stability of this novel core-shell catalyst were also examined in this study. First, photodeposition was conducted both in air or an atmosphere filled with carbon monoxide. It is interesting to note that Pt-complex ions were observed in carbon monoxide atmosphere by UV-vis spectroscopy.As seen by TEM, the samples prepared under exposure to carbon monoxide have obviously aggregated Pt formation on TiO2 particles. On the other hand, TiO2@Pt core-shell catalyst could be successfully prepared in air by photodeposition, and XAS spectroscopy confirms that Pt in the samples synthesized under these conditions had less unfilled d-state, indicating the presence of Strong Metal-Support Interaction(SMSI). For the electrochemical test, TiO2@Pt prepared in air exhibits a higher electrochemical surface area or oxygen reduction activity, which are significantly better than the counterpart synthesized under carbon monoxide ones. TiO2@Pt prepared in air under light intensity 0.1 sun for 3 hours (onset potential = 0.86 VRHE) has the mass activity and electrochemically surface area comparable to commercial Pt/C (onset potential = 0.85 VRHE).Finally, the designed configuration with TiO2-core and Pt thin shell has made a significant progress in improving the stability of electrocatalysts for Oxygen Reduction Reaction (ORR). TiO2@Pt prepared in air under light intensity 0.1 sun for 3 hours experienced only degradation of 55 % in mass activity, whereby commercial Pt/C suffered a loss of 79% after 5000 cycles.
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Wang, Chia-Han, and 王家漢. "The Influences of Hollow Core-shell Structure in Cu@hCeO2 Catalysts for Hydrogen Production." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/24386636054558023812.
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碩士東吳大學
化學系
102
The energy shortage is the most important issue nowadays, so find the alternative energy is the way to solve the problems of fossil fuel decrease. The development of hydrogen energy is chosen due to its high energy density by weight and environmental friendly. Especially, hydrogen can be produced easily by steam reformation of alcohol in low temperature. Therefore, develop high-performance, stable and reusable catalysts have been a significant research direction. The objective of this study is to explore hollow core-shell copper/ceria (Cu@hCeO2) catalysts for steam reforming of methanol (SRM) to produce hydrogen. In this work, we use traditional perception method to synthesis the copper/ceria catalysts. It surface area is closed to ceria support. In order to enhance the surface area to offer more activity sites, so the metal properties on the support surface are changed. Use reflux method to prepare the polyvinylpyrrolidone-capped (Cu-PVP) via copper-polyol process. The surface area is higher than previous sample and the copper particles changed to appropraite size. Finally, added carbon sphere to improve the aggregate problem after calcination. We expect that the carbon template will vanish in the calcination process and the copper dispersion could be improved. By integrating the above-mentioned, we use the facile hydrothermal process to obtain the Cu@hCeO2 catalysts as follow: Cu-PVP modified nanoparticles were doped onto carbon template first, then cerium chloride added and calcined at 500oC. Thus tiny Cu nanoparticle cores encapsulated within CeO2 hollow shells can be prepared. The core-shell structure efficiently prevents the aggregation of Cu nanoparticles and deactivation of catalytic ability in the calcination process and SRM reactions. By integrating the above-mentioned, Cu@hCeO2 can be used as a stable and reusable catalyst. Crystalline, structural characterization and morphology of the samples was investigated by XRD, BET and SEM. Redox behaviors between copper-ceria and catalytic performance over Cu@hCeO2 catalysts can be researched by the TPR and GCMS.
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Hirunsit, Pussana. "Oxygen Reduction Reaction on Dispersed and Core-Shell Metal Alloy Catalysts: Density Functional Theory Studies." Thesis, 2010. http://hdl.handle.net/1969.1/ETD-TAMU-2010-08-8371.
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Pt-based alloy surfaces are used to catalyze the electrochemical oxygen reduction
reaction (ORR), where molecular oxygen is converted into water on fuel cell electrodes.
In this work, we address challenges due to the cost of high Pt loadings in the cathode
electrocatalyst, as well as those arising from catalyst durability. We aim to develop an
increased understanding of the factors that determine ORR activity together with
stability against surface segregation and dissolution of Pt-based alloys. We firstly focus
on the problem of determining surface atomic distribution resulting from surface
segregation phenomena. We use first-principles density functional theory (DFT)
calculations on PtCo and Pt3Co overall compositions, as well as adsorption of water and
atomic oxygen on PtCo(111) and Pt-skin structures. The bonding between water and
surfaces of PtCo and Pt-skin monolayers are investigated in terms of orbital population.
Also, on both surfaces, the surface reconstruction effect due to high oxygen coverage
and water co-adsorption is investigated.
Although the PtCo structures show good activity, a large dissolution of Co atoms tends
to occur in acid medium. To tackle this problem, we examine core-shell structures which
showed improved stability and activity compared to Pt(111), in particular, one consisting
of a surface Pt-skin monolayer over an IrCo or Ir3Co core, with or without a Pd
interlayer between the Pt surface and the Ir-Co core. DFT analysis of surface
segregation, surface stability against dissolution, surface Pourbaix diagrams, and reaction mechanisms provide useful predictions on catalyst durability, onset potential for
water oxidation, surface atomic distribution, coverage of oxygenated species, and
activity. The roles of the Pd interlayer in the core-shell structures that influence higher
ORR activity are clarified. Furthermore, the stability and activity enhancement of new
shell-anchor-core structures of Pt/Fe-C/core, Pt/Co-C/core and Pt/Ni-C/core are
demonstrated with core materials of Ir, Pd3Co, Ir3Co, IrCo and IrNi. Based on the
analysis, Pt/Fe-C/Ir, Pt/Co-C/Ir, Pt/Ni-C/Ir, Pt/Co-C/Pd3Co, Pt/Fe-C/Pd3Co, Pt/Co-
C/Ir3Co, Pt/Fe-C/Ir3Co, Pt/Co-C/IrCo, Pt/Co-C/IrNi, and Pt/Fe-C/IrNi structures show
promise in terms of both improved durability and relatively high ORR activity.
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Li, Min Jhan, and 李旻展. "Development of Biodegradable Shell-core Structured Microspheres for Drug Delivery." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/4b2awg.
Full textAbstract:
碩士長庚大學
機械工程學系
105
In this study, electrospraying techniques were used to prepare biodegradable particle carriers. Poly (lactide-co-glycolide), hydrochloride, vancomycin hydrochloride, ceftazidime hydrate, green fluorescent protein, along with different kinds of solvents were used to manufacture the biodegradable drug-eluting microspheres. The diameter of the microspheres of the solid microspheres and the shell-core microspheres prepared by using the optimum processing parameters is about 5 ~ 10 μm. The microspheres of the shell and core structure were confirmed by transmission electron microscopy and laser scanning confocal microscopy, which proved that the shell - core structure and the fluorescent protein activity of the core layer existed. The confocal images also demonstrated the activity of the fluorescent protein from being damaged by the solvent. The experimental results showed that electrosprayed microspheres can release antibiotics in vitro for 21 days with concentrations well above the minimum inhibitory concentrations. In vivo experiments with animals also suggested that microsphere can release high drug concentrations (above the minimum inhibitory concentration) over 14 days in the rabbit knee joint. In addition, the experimental results in this study show that microspheres of different size and geometry can be prepared by electrospray technology by changing the processing parameters. This might find potential applications in medicine in the future.
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Ho, Bo-Chen, and 何柏諶. "Study on Core-shell Catalyst of Proton Exchange Membrane Fuel Cell." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/4p2b5w.
Full textAbstract:
碩士元智大學
機械工程學系
105
One of the most important materials of PEMFCs is the catalyst. At this stage, it is found that Pt is the best catalyst for PEMFCs, but the amount of Pt is very expensive. Therefore, the main purpose is hope can improve and reduce waste. This study attempts to develop a core-shell Co @ Pt catalyst to reduce of Pt. And the carbon nanotubes as catalysts were used to improve the dispersibility of the nanocatalyst particles and compared with the Pt/cCNT synthesized by the anti-microcapsule method and the commercial Pt/C. as well as electrochemical analysis to investigate the properties and electrochemical activity of the catalyst. The results can be obtained from HRTEM that the sample has a core-shell structure, from the color depth to judge, the color of the deep part of the Co metal particles, and the lighter part of the color is Pt, thus determined to form a core shell Co @ Pt catalyst can be known from the XPS data for the standard Pt / cCNT carbon material, and from the CV results that Pt/C ECSA is the best.
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YU, TSE-WEI, and 游哲瑋. "The study of core-shell PtSn catalyst for n-butane dehydrogenation." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/wje6xr.
Full textAbstract:
碩士東海大學
化學工程與材料工程學系
106
This study combined chemical reduction method and Stober method for preparing core-shell PtSn@SiO2 catalysts and used the catalysts to catalyze n-butane dehydrogenation to butenes. SiO2 shell can prevent metal sintering, and reduce side reactions (cracking and isomerization) in n-butane dehydrogenation. In catalyst preparation, different TEOS concentrations were used to change the shell thickness of SiO2. We also changed Pt/Sn metal mole ratio to find the best catalyst compositions. Experimental results showed that the catalyst with TEOS concentration of 0.0118M and Pt/Sn metal mole ratio of 1:1 had the best performances in butane dehydrogenation. The PtSn@SiO2(0.0118M TEOS) catalyst was tested in the temperature range of 525℃ ~620℃ for 4hr. When temperature was 600℃ and time of stream was 10min, n-butane conversion was 62.48%, butene selectivity and yield were 81.56% and 50.96%, respectively. N-butane dehydrogenation produce coke deposition on the catalyst surface, which cause catalyst deactivation. The catalyst deactivation rate constant at 600℃ was 0.0029min-1. Catalyst was regenerated in order to resume its catalytic activity. We regenerated the catalyst several times. Catalyst activity reduced for the first time reuse, but remained essential constant after that, which implies that the catalyst can be regenerated and reused many times. PtSn@SiO2(0.0118M TEOS) catalyst was tested at several different temperatures to determine its n-butane dehydrogenation kinetic. N-butane dehydrogenation was assumed as the first order reversible reaction, the reaction rate constants and activation energy (72.51kJ/mole) were calculated. In order to understand the relationship between catalyst physical properties and their catalytic performance in n-butane dehydrogenation, PtSn@SiO2 catalysts were characterized with FE-SEM, EDS, BET, XRD, TPR, TEM and ICP-AES.
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Zhang, Liang 1986. "Theoretical study of correlation between structure and function for nanoparticle catalysts." Thesis, 2014. http://hdl.handle.net/2152/28338.
Full textAbstract:
The science and technology of catalysis is more important today than at any other time in our history due to the grand energy and environment challenges we are facing. With the explosively growth of computation power nowadays, computer simulation can play an increasingly important role in the design of new catalysts, avoiding the costly trail-and-error attempts and facilitating the development cycle. The goal to inverse design of new materials with desired catalytic property was once far off, but now achievable. The major focus of this dissertation is to find the general rules that govern the catalytic performance of a nanoparticle as the function of its structure. Three types of multi-metallic nanoparticles have been investigated in this dissertation, core-shell, random alloy and alloy-core@shell. Significant structural rearrangement was found on Au@Pt and Pd@Pt nanoparticle, which is responsible for a dramatic improvement in catalytic performance. Nonlin- ear binding trends were found and modeled for random alloy nanoparticles, providing a prescription for tuning catalytic activity through alloying. Studies of ORR on Pd/Au random alloy NP and hydrogenation reaction on Rh/Ag random alloy NP revealed that binding on individual ensemble should be in- vestigated when large disparity of adsorbate affinity is presented between two alloying elements. In the alloy-core@shell system, I demostrated a general linear correlations between the adsorbate binding energy to the shell of an alloy-core@shell nanoparticle and the composition of the core. This relation- ship allows for interpolation of the properties of single-core@shell particles and an approach for tuning the catalytic activity of the particle. A series of promising catalysts were then predicted for ORR, HER and CO oxidation. As a first attempt to bridge the material gap, bimetallic nano clus- ter supported on CeO₂(111) was investigated for CO oxidation. A strong support-metal interaction induces a preferential segregation of the more reac- tive element to the NC-CeO₂ perimeter, generating an interface with the Au component. (Au-Cu)/CeO₂ was found to be optimal for catalyzing CO oxida- tion via a bifunctional mechanism. O₂ preferentially binds to the Cu-rich sites whereas CO binds to the Au-rich sites. A method called distributed replica dynamics (DRD) is proposed at last to utilize enormous distributed computing resources for molecular dynamics simulations of rare-event in chemical reac- tions. High efficiency can be achieved with an appropriate choice of N [subscript rep] and t [subscript rep] for long-time MD simulation.text
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郭舒婷. "A Degradable Core-Shell Structured Artificial Bone Scaffolds: Manufacturing Techniques and Property Evaluations." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/6aumfe.
Full textAbstract:
碩士逢甲大學
纖維與複合材料學系
103
Human bones are subjected to cracks and defects in the presence of an impact force or being aging. Although bones can self-heal the impaired site, the excessive size of the damage may prevent the bone from recovering completely. In order to cope with this difficulty, an implant for the injured part is thus required, and enables the osteocytes to grow bone tissues via the bone scaffolds that can decompose in one day, and ultimately leads to a full recovery. Bone scaffolds are typically made of porous degradable materials that provide the mechanical support during repair and regeneration of damaged or diseased bone. This study aims to create Core-Shel Structured Artificial Bone Scaffolds with biocompatibility, biodegradation, and heal-promotion. Polyvinyl alchol (PVA) fibers are fabricated into hollow PVA braids by using a braiding machine, and a hydroxyapatite (HA)/gelatin)/PVA mixture is infused into the braids in order to form Core-Shel Structured Artificial Bone Scaffolds. The braids are prepared with different combinations of crosslinking parameters, heat treatment conditions, and HA contents, after which the resulting bone scaffolds are then evaluated for their applications by using surface observation, a porosity test, a compressive strength test, a degradation test, a swelling test, an MTT assay, and an in vivio study. The compressive strength of PVA braids that are crosslinked with glutaraldehyde can be increased by at least 20MPa. A ten-minute heat treatment results in an increase in the compressive strength of PVA braids that is from 23.38MPa to 285.92MPa. However, when being heat-treated for fifteen minutes, the compressive strength is decreased to 142.33MPa. The bone scaffolds have a compressive strength that is increased to 51.7MPa with the addition of 0.4% HA, and it is then decreased to 25.13MPa with the addition of 0.6% HA. The bone scaffolds are proven to have biocompatibility according to the results of cell viability and alkaline phosphatase activity.
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Chiang, Chia-Jung, and 江佳蓉. "M@TiO2 (M= Pd, Au, Ag) catalysts with core/shell structure and application on photocatalytic destruction of dye." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/09517166317203456850.
Full textAbstract:
碩士國立中央大學
化學工程與材料工程研究所
100
The purpose of this study was to develop a catalyst with high efficiency photocatalytic activity and had core/shell structure. It could be applied to the degradation of organic pollutants under UV light illumination. The literature shows that doping noble metal on the surface of titanium dioxide can enhance the photocatalytic activity because noble metal can form active sites to promote the electronic charge transfer in the interface of metal and titanium dioxide. Although the activity of this kind of structure is high, the exposed metal is easy to dissolve or corrosive, leading to catalyst decay. Core/shell structure can be used to overcome this shortcoming, noble metals located in the core, while titanium dioxide is in the shell. In this study, M@TiO2 (M = Pd, Ag, Au) catalysts with core/shell structure were synthesized by sol-gel method with hydrothermal treatment with different preparation parameters. These catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectra (UV-vis DRS), and X-ray photoelectron spectroscopy (XPS). The photoreaction was carried out in a 10 ppm methylene blue solution with two 8w 254 nm UV light and 250W halogen lamp as the light source. The concentration of MB in the degradation samples were measured by UV-vis spectrometer (UV-vis). This thesis is divided into two parts, the first part is on the preparation of M@TiO2 (M = Pd, Ag, Au) with core/shell structure and its photocatalystic activity. The TEM micrographs results show that the particle size of metal cores was about 3-12nm, and the shell thickness of titanium dioxide was about 6-20nm. The XRD pattern results show that Pd@TiO2 has highest crystallinity. The photoreaction was carried out in a 10 ppm methylene blue solution with two 8w 254 nm UV light and 250W halogen lamp as the light source. Pd@TiO2 had the highest activity under UV light and halogen lamp illumination. Because Pd@TiO2 had higher crysallinity, lower band gap energy, and higher absorption at visible region. The second part is on discussion different preparation parameters: metals loading amount, and hytrothermal time, and found the relationship with the photocatalystic activity by methylene blue degradation under the UV light illumination. The optimal amounts of Pd, Ag, and Au loading were 0.5 wt. %, 0.5 wt. %, 1.0 wt. %.The optimal hytrothermal time was 18 hours. Furthermore, the sample for 18 hour had the highest activity due to the highest crystallinity. From these results, the photocatalytic activity of M@TiO2 (M = Pd, Ag, Au) catalyst mainly depended on the crystallinity of TiO2, the kind of metals, the amount of noble metal loading and the OH group contents. Keywords: titanium dioxide, core/shell structure, photocatalyst, palladium, silver, gold, sol-gel method, hydrothermal method, methylene degradation.
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Hsiu-HsienWen and 溫修賢. "Green synthesis of Fe3O4-chlorophyllin core-shell nanostructure for catalyst, antioxidant, and MRI contrast enhancement." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/6ju6mf.
Full text
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Wu, Jia-Long, and 吳佳龍. "Bimetallic Co/Cu core-shell catalyst for hydrogen production from simulated waste plastics gasification syngas." Thesis, 2019. http://ndltd.ncl.edu.tw/cgi-bin/gs32/gsweb.cgi/login?o=dnclcdr&s=id=%22107NCHU5087055%22.&searchmode=basic.
Full textAbstract:
碩士國立中興大學
環境工程學系所
107
Due to the shortage of fossil fuels and the sustainability of nuclear fuels, the development of renewable energy has been received high attention. Furthermore, the management of a huge amount of plastic waste is also a critical environmental issue. Recycling of plastics through thermal treatments not only can treat plastic waste but also can generate renewable energy and valuable products such as hydrogen. This technology not only to solve waste management but also produce renewable energy to achieve waste recycling In this study, silica dioxide supported catalyst has been prepared through the polyol method, and the metal active phase was coated by the polyol method. The as-prepared catalyst was applied to catalytic gasification of simulated syngas derived from plastic wastes. Several operating conditions have been studied to evaluate the best parameter in terms of hydrogen production. The effects of catalyst preparing parameters and operating conditions on hydrogen production from simulated syngas derived from plastic waste gasification were investigated. The results of the characteristic analysis show that the Co@SiO2 catalyst prepared by the polyol method has a Co metal particle size range of 30 ± 16 ~ 37 ± 7 nm, which has high hydrogen production activity, while the Cu@SiO2 catalyst has poor hydrogen production activity. and the addition of Cu metal can limit the sintering of the Co catalyst particles, thereby producing more hydrogen.
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Chi, Luo-Shau, and 羅紹綺. "Hydrophilic CdSe@ZnS and FeOx@Au Core-Shell Structured Nanoparticles by Liquid Phase Chemical Synthesis Method." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/07810352605377770127.
Full textAbstract:
碩士逢甲大學
材料科學所
97
Advancements of nanotechnology have been established enormously in many fields such as thin film solar cells, magnetic fluidics, quantum dots in energy and biomedical applications for past few years. The aim of this thesis is to develop wet chemical synthetic processes to fabricate both core-shell structured CdSe@ZnS quantum dots and FeO¬x¬@Au nanoparticles with optimized process conditions. The use of ultraviolet-visible (UV-Vis) light absorption spectroscopy and transmission electron microscopy (TEM) is to investigate the microstructure and growth mechanism of nanoparticles as well as optical properties of nanoparticles. The optical properties of CdSe@ZnS quantum dots are determined by the quantum confinement effect and its energy band structure. It is interesting for us to examine the influences of red-shift, absorption bandwidth and photoluminescence (PL) simulated bandwidth of synthesized CdSe@ZnS particles. As for the FeOx@Au nanoparticles, the combined effect of surface resonance derived from Au nanoparticles and superparamagnetism contributed from iron oxide nanoparticles has a strong connection with its particle size and morphology. The motivation of this study is to explore a reliable processing route to obtain CdSe@ZnS quantum dots with high quantum yield and high PL stability as well as the FeOx@Au with desirable magnetic and hypothermia characteristics. The results of our study show that a satisfyingly high quantum yield of CdSe@ZnS quantum dots close to 70% can be achieved using combined OA/ODE/HAD complexing agents and size and shape uniformity of FeOx@Au nanoparticles are reached by using micro-emulsion method.
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Chen, Chun-Ming, and 陳均銘. "Production of carbon nanotubes with controllable diameter by catalytic cracking of methane using Fe@Al2O3 core-shell catalyst." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/8w2rvu.
Full textAbstract:
碩士國立中興大學
環境工程學系所
106
In this study, we used a novel core-shell catalyst to catalyze methane cracking reaction for the production of carbon nanotubes. We found that the carbon nanotubes with a controllable diameter can be produced by tuning the pore size of the shell. A novel and simple synthetic approach toward core–shell Fe@Al2O3 nanoparticles was developed in this study. Fe@Al2O3 nanostructures were formed by the immersion of Fe@C nanoparticles with Al precursor in deionized water. The as-synthesized core-shell catalyst was applied to convert the methane into carbon nanotubes. The structure property and morphological nature of the fresh and used catalysts were confirmed by different characterization analysis such as SEM, TEM, BET. Moreover, the purity and species of the nanocarbon materials were also identified by Raman spectroscopy and thermogravimetric analysis. According to the experimental results, it was known that the core-shell catalyst affects the structural characteristics at different calcination temperatures and Al/Fe molar ratios. In the case of Al/Fe=1.5 mole ratio, there are relatively more γ-Fe2O3, which is favorable for catalytic formation of methane into carbon nanotubes. For the calcining temperature of 750 °C, the most appropriate core-shell bonding ability is provided to prevent the core-shell structure from being destroyed. In the case of CTAB/Al=1 mole ratio, the core- shell catalyst catalyzes the cracking of methane to produce 135.9 mgC/gcat./h of carbon, and the methane conversion is as high as 95%. The pore size of the shell changed with the CTAB concentration, and further produced a carbon nanotube with a tunable diameter. From the analysis results, it was found that the average diameter is 19.24 nm at CTAB/Al=0; the average tube diameter is 28.59 nm at CTAB/Al=0.5; average tube diameter is 58.06 nm at CTAB/Al=1. In addition, the catalytic performance of the core-shell catalyst in the methane cracking at different temperatures and reaction gas concentrations was investigated. It was found that the Fe@Al2O3 core-shell catalyst exhibits up to 90% of methane conversion under any reaction temperature (700 °C, 750 °C, 800 °C) and initial methane concentrations (3%, 5%, 10%). Compared with traditional supported catalysts, core-shell catalyst is more suitable for high-temperature environments. The methane conversion remains at 95% for nearly 3 hours under 800 ℃ reaction temperature. This work gives a vision towards the design and synthesis of advanced catalysts for chemical vapor deposition.
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Chen, Chia-Ying, and 陳佳瑩. "The study of Ni/SiO2@Al2O3 core-shell catalyst for hydrogen production from simulated waste plastics gasification syngas." Thesis, 2019. http://ndltd.ncl.edu.tw/cgi-bin/gs32/gsweb.cgi/login?o=dnclcdr&s=id=%22107NCHU5087052%22.&searchmode=basic.
Full textAbstract:
碩士國立中興大學
環境工程學系所
107
Due to the depletion of energy, the development of renewable energy has been received high attention. The management of the huge amount of plastic waste is also a critical environmental issue. Recycling of plastics through thermal treatments not only can treat plastic waste but also can generate renewable energy and valuable products. In this study, the core-shell catalyst was applied to catalytic gasification of simulated syngas derived from plastic wastes simulated plastic gasification syngas. The Ni/SiO2 particles were prepared by the polyol method, and the Ni/SiO2@Al2O3 core-shell catalyst was prepared by sol-gel method. The effects of catalyst preparing parameters and operating conditions on hydrogen production from simulated syngas derived from plastic waste gasification were investigated. Besides, the as-prepared catalysts were characterized via FESEM, XRD, and TEM instruments. The effect of catalytic activity on hydrogen production was investigated by different amount of nickel loadings. It was found that the 5Ni/SiO2 exhibited the best hydrogen yield. The 5Ni/SiO2 particles were deposited with Al precursor in the different molar ratio are immersed in deionized water to form Ni/SiO2@Al2O3 core-shell nanostructure, and calcined at 750 °C. The bonding ability can prevent the core structure from being destroyed. The activity test shows that when the amount of Ni metal is higher, the amount of Ni metal active phase supported on the support increases, and the active base can be increased. The hydrogen production activity is high when the molar ratio is Ni/Al=1/1.5, the best catalytic activity for hydrogen production rate (22.26mmol/g-h) and methane conversion (95%)was obtained.
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林有良. "Preparation of Fe-core Pt-shell nano-catalysts and applicaation of cathodic catalyst in proton-exchange membrane fuel cells." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/39467943307652213222.
Full textAbstract:
碩士國立臺灣師範大學
化學系
95
The Fe-core Pt-shell electrocatalysts using step by step reducing process were synthesized and characterized for the purpose of the fuel cell cathode oxygen reduction reaction. The synthesized catalysts were characterized in terms of structural morphology and catalytic activity by XRD, TEM, EDX and electrochemical measurements. In addition, we also synthesized the Pt、FePt、CoPt and FeCoPt alloy catalysts. The all nanoparticles size were 4-8nm . In order to improve activity and stability, the catalysts were loaded on the carbon black and heat-treated at 500◦C . The catalyzed ORR kinetics were also studied with using the rotating disk electrode (RDE) method. Compared to catalytic properties of the Pt、FePt、CoPt and FeCoPt alloy catalysts, the result of Fe-core Pt-shell electrocatalysts was the highest ORR activity. The results showed that the synthesized Fe-core Pt-shell catalysts have futher promotion in the ORR catalytic activity.
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Elshewy, Ahmed M. "Efficient C-O and C-N bond forming cross-coupling reactions catalyzed by core-shell structured Cu/Cu2O nanowires." Thesis, 2013. http://hdl.handle.net/10754/306734.
Full textAbstract:
Oxygen and Nitrogen containing compounds are of utmost importance due to their interesting and diverse biological activities. The construction of the C-O and C–N bonds is of significance as it opens avenues for the introduction of ether and amine linkages in organic molecules. Despite significant advancements in this field, the construction of C-O and C–N bonds is still a major challenge for organic chemists, due to the involvement of harsh reaction conditions or the use of expensive catalysts or ligands in many cases. Thus, it is a challenge to develop alternative, milder, cheaper and more reproducible methodologies for the construction of these types of bonds. Herein, we introduce a new efficient ligand free catalytic system for C-O and C-N bond formation reactions.
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"Development of Platinum-copper Core-shell Nanocatalyst on Multi-Walled Carbon Nanotubes for Proton Exchange Membrane Fuel Cells." Master's thesis, 2012. http://hdl.handle.net/2286/R.I.14854.
Full textAbstract:
abstract: With a recent shift to a more environmentally conscious society, low-carbon and non-carbon producing energy production methods are being investigated and applied all over the world. Of these methods, fuel cells show great potential for clean energy production. A fuel cell is an electrochemical energy conversion device which directly converts chemical energy into electrical energy. Proton exchange membrane fuel cells (PEMFCs) are a highly researched energy source for automotive and stationary power applications. In order to produce the power required to meet Department of Energy requirements, platinum (Pt) must be used as a catalyst material in PEMFCs. Platinum, however, is very expensive and extensive research is being conducted to develop ways to reduce the amount of platinum used in PEMFCs. In the current study, three catalyst synthesis techniques were investigated and evaluated on their effectiveness to produce platinum-on copper (Pt@Cu) core-shell nanocatalyst on multi-walled carbon nanotube (MWCNT) support material. These three methods were direct deposition method, two-phase surfactant method, and single-phase surfactant method, in which direct deposition did not use a surfactant for particle size control and the surfactant methods did. The catalyst materials synthesized were evaluated by visual inspection and fuel cell performance. Samples which produced high fuel cell power output were evaluated using transmission electron microscopy (TEM) imaging. After evaluation, it was concluded that the direct deposition technique was effective in synthesizing Pt@Cu core-shell nanocatalyst on MWCNTs support when a rinsing process was used before adding platinum. The peak power density achieved by the rinsed core-shell catalyst was 618 mW.cm-2 , 13 percent greater than that of commercial platinum-carbon (Pt/C) catalyst. Transmission electron microscopy imaging revealed the core-shell catalyst contained Pt shells and platinum-copper alloy cores. Rinsing with deionized (DI) water was shown to be a crucial step in core-shell catalyst deposition as it reduced the number of platinum colloids on the carbon nanotube surface. After evaluation, it was concluded that the two-phase surfactant and single-phase surfactant synthesis methods were not effective at producing core-shell nanocatalyst with the parameters investigated.Dissertation/Thesis
M.S.Tech Technology 2012
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Ling-ChenHsiang and 向苓甄. "Preparation of Core / Double Shell Structured Silicon/Carbon Nanocomposite for Anode Material of Lithium-Ion Batteries with Long Cycling Stability." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/g8bsg4.
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Al, Mana Noor. "Design of Embedded Metal Catalysts via Reverser Micro-Emulsion System: a Way to Suppress Catalyst Deactivation by Metal Sintering." Diss., 2016. http://hdl.handle.net/10754/614070.
Full textAbstract:
The development of highly selective and active, long-lasting, robust, low-cost and environmentally benign catalytic materials is the greatest challenge in the area of catalysis study. In this context, core-shell structures where the active sites are embedded inside the protecting shell have attracted a lot of researchers working in the field of catalysis owing to their enhanced physical and chemical properties suppress catalyst deactivation. Also, a new active site generated at the interface between the core and shell may increases the activity and efficiency of the catalyst in catalytic reactions especially for oxide shells that exhibit redox properties such as TiO2 and CeO2. Moreover, coating oxide layer over metal nanoparticles (NPs) can be designed to provide porosity (micropore/mesopore) that gives selectivity of the various reactants by the different gas diffusion rates. In this thesis, we will discuss the concept of catalyst stabilization against metal sintering by a core-shell system. In particular we will study the mechanistic of forming core-shell particles and the key parameters that can influence the properties and morphology of the Pt metal particle core and SiO2 shell (Pt@SiO2) using the reverse micro-emulsion method. The Pt@SiO2 core-shell catalysts were investigated for low-temperature CO oxidation reaction. The study was further extended to other catalytic applications by varying the composition of the core as well as the chemical nature of the shell material.
The Pt NPs were embedded within another oxide matrix such as ZrO2 and TiO2 for CO oxidation reaction. These materials were studied in details to identify the factors governing the coating of the oxide around the metal NPs. Next, a more challenging system, namely, bimetallic Ni9Pt NPs embedded in TiO2 and ZrO2 matrix were investigated for dry reforming of methane reaction at high temperatures. The challenges of designing Ni9Pt@oxide core-shell structure with TiO2 and ZrO2 and their tolerance of the structure to the conditions of dry reforming of methane will be discussed.
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Cochell, Thomas Jefferson. "Synthesis and characterization of nano- structured electrocatalysts for oxygen reduction reaction in fuel cells." 2013. http://hdl.handle.net/2152/21691.
Full textAbstract:
Proton exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) are two types of low-temperature fuel cells (LTFCs) that operate at temperatures less than 100 °C and are appealing for portable, transportation, and stationary applications. However, commercialization has been hampered by several problems such as cost, efficiency, and durability. New electrocatalysts must be developed that have higher oxygen reduction reaction (ORR) activity, lower precious metal loadings, and improved durability to become commercially viable. This dissertation investigates the development and use of new electrocatalysts for the ORR. Core-shell (shell@core) Pt@Pd[subscript x]Cu[subscript y]/C electrocatalysts, with a range of initial compositions, were synthesized to result in a Pt-rich shell atop a Pd[subscript x]C[subscript y]-rich core. The interaction between core and shell resulted in a delay in the onset of Pt-OH formation, accounting in a 3.5-fold increase in Pt-mass activity compared to Pt/C. The methanol tolerance of the core-shell Pt@PdCu₅/C was found to decrease with increasing Pt-shell coverage due to the negative potential shift in the CO oxidation peak. It was discovered that Cu leached out from the cathode has a detrimental effect on membrane-electrode assembly performance. A spray-assisted impregnation method was developed to reduce particle size and increase dispersion on the support in a consistent manner for a Pd₈₈W₁₂/C electrocatalyst. The spray-assisted method resulted in decreased particle size, improved dispersion and more uniform drying compared to a conventional method. These differences resulted in greater performance during operation of a single DMFC and PEMFC. Additionally, Pd₈₈W₁₂/C prepared by spray-assisted impregnation showed DMFC performance similar to Pt/C with similar particle size in the kinetic region while offering improved methanol tolerance. Pd₈₈W₁₂/C also showed comparable maximum power densities and activities normalized by cost in a PEMFC. Lastly, the activation of aluminum as an effective reducing agent for the wet- chemical synthesis of metallic particles by pitting corrosion was explored along with the control of particle morphology. It was found that atomic hydrogen, an intermediate, was the actual reducing agent, and a wide array of metals could be produced. The particle size and dispersion of Pd/C produced using Al was controlled using PVP and FeCl₂ as stabilizers. The intermetallic Cu₂Sb was similarly prepared with a 20 nm crystallite size for potential use in lithium-ion battery anodes. Lastly, it was found that the shape of Pd produced with Al as a reducing agent could be controlled to prepare 10 nm cubes enclosed by (100) facets with potentially high activity for the ORR.text
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Nie, Zhihong. "Developing New Strategies for the Preparation of Micro- and Nano-structured Polymer Materials." Thesis, 2008. http://hdl.handle.net/1807/16729.
Full textAbstract:
This thesis described the development of new strategies for the preparation of micro- and nano-structured polymer materials. In particular, this thesis focused on: i) the synthesis of polymer particles in microreactors, and ii) the self-assembly of inorganic nanorods.
First, this thesis presented the synthesis of polymer particles and capsules with pre-determined sizes and narrow size distributions (CV<2%) in continuous microfluidic reactors. The method includes (i) the emulsification of monomers in a microfluidic flow-focusing device and (ii) in-situ solidification of droplets via photopolymerization. This microfluidic synthesis provides a novel strategy for the control over the shapes, compositions, and morphologies of polymer particles. In particular, we demonstrated the control over particle shapes by producing polymer ellipsoids, disks, rods, hemispheres, plates, and bowls. We produced polymer particles loaded with dyes, liquid crystals, quantum dots, and magnetic nanoparticles. We generated core-shell particles, microcapsules, Janus and three-phasic polymer particles. Control over the number of cores per droplet was achieved by manipulating the flow rates of liquids in the microchannels. We further investigated the hydrodynamic mechanism underlying the emulsification of droplets, which helps in guiding scientists and engineers to utilize this technique.
Second, we described the self-assembly of inorganic nanorods by using a striking analogy between amphiphilic ABA triblock copolymers and the hydrophilic nanorods tethered with hydrophobic polystyrene chains at both ends. We organized metal nanorods in structures with various geometries such as nanorings, nanochains, bundles, bundled nanochains, and nanospheres by tuning solely the quality of solvents. The self-assembly was tunable and reversible. This approach paved the way for the organization of anisotropic nanoparticles by using the strategies that are well-established for the self-assembly of block copolymers. We further described a systematic study of the self-assembly of polymer-tethered gold nanorods as a function of solvent composition in the system and the molecular weight of the polystyrene blocks. We found that the structure of the polymer pom-poms played an important role on the organization of polymer-tethered gold NRs. The 'supramolecular' assembly was governed by the competition between the end-to-end and side-by-side association of NRs and resulted in the controlled variation of the plasmonic properties of NRs, reflected in a 3-D plasmonic graph.