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Widyaningrum, Rosalia Nugraheni. "Mesoporous silica-supported catalysts to enhance hydrogen production during cellulose pyrolysis". Thesis, The University of Sydney, 2011. https://hdl.handle.net/2123/28917.
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Pyrolysis of biomass has been studied worldwide as a potential path to produce hydrogen from renewable sources. Major problem in a non-catalytic biomass pyrolysis is tar formation, which causes complication in the utilization of product gas. Elimination of tar requires a high temperature, and it leads to low energy efficiency since tar itself contains high potential energy.
The utilization of metal catalysts is considered an effective method to reduce tar content and subsequently increase the hydrogen production. Nickel catalyst has been previously investigated for its tar cracking activity and identified as one of the best catalysts, but it has a drawback when used at high temperature because sintering of metal particle and carbon deposition occur. To address this challenge, a suitable catalyst support and promoter are required to minimize sintering and enhance the activity of nickel catalyst.
This project approached the issue by studying the potential catalyst supports and the effect of promoter in the catalytic activity of nickel catalyst. Three catalyst supports: mesoporous silica SBA-15 (Santa Barbara Amorphous), MCF (Mesocellular Foam), and commercial y-Alz03 were investigated, and palladium was chosen as a promoter. Mesoporous silica SBA-15 and MCF were synthesized using sol-gel method with Pluronic P123 as a structure directing agent, tetraethyl orthosilicate (TEOS) as a silica source, and 1,3,5-trimethylbenzene as a swelling agent for MCF synthesis. Nickel and palladium were deposited into the supports by wet impregnation techniques. The catalysts were characterized using N2 adsorption-desorption (BET and BJH methods), xray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray fluorescence (XRF). The activity of the catalyst was tested in cellulose pyrolysis using thermogravimetric analyzer coupled to a mass spectroscopy (TGA-MS).
This work studied the role of nickel catalysts in the pyrolysis of cellulose, the role of catalyst supports, and the effect of Pd promoter in increasing the catalytic activity to enhance hydrogen production. The results of this study suggest that mesoporous silica MCF was a good catalyst support because the MCF-supported Ni catalyst gave the highest H2 yield. The H2 yield was 73.5 mL/ g cellulose, which was 1.7 times H2 yield from SBA-15-supported Ni-catalyst, and 3.3 times H2 yield produced by y-Alz03-supported Ni-catalyst. The addition of 0.5 wt% Pd promoter also increased the H2 yield by 14%.
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Iwanow, Melanie [Verfasser], i Burkhard [Akademischer Betreuer] König. "Supported Metal Catalyst Preparation using Deep Eutectic Solvents / Melanie Iwanow ; Betreuer: Burkhard König". Regensburg : Universitätsbibliothek Regensburg, 2020. http://d-nb.info/1215905971/34.
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Min, Byoung Koun. "Scanning tunneling microscopic studies of SiO2 thin film supported metal nano-clusters". Diss., Texas A&M University, 2004. http://hdl.handle.net/1969.1/2737.
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This dissertation is focused on understanding heterogeneous metal catalysts supported on oxides using a model catalyst system of SiO2 thin film supported metal nano-clusters. The primary technique applied to this study is scanning tunneling microscopy (STM). The most important constituent of this model catalyst system is the SiO2 thin film, as it must be thin and homogeneous enough to apply electron or ion based surface science techniques as well as STM. Ultra-thin SiO2 films were successfully synthesized on a Mo(112) single crystal. The electronic and geometric structure of the SiO2 thin film was investigated by STM combined with LEED, Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS). The relationship between defects on the SiO2 thin film and the nucleation and growth of metal nano-clusters was also investigated. By monitoring morphology changes during thermal annealing, it was found that the metal-support interaction is strongly dependent on the type of metal as well as on the defect density of the SiO2 thin film. Especially, it was found that oxygen vacancies and Si impurities play an important role in the formation of Pd-silicide. By substituting Ti atoms into the SiO2 thin film network, an atomically mixed TiO2-SiO2 thin film was synthesized. Furthermore, these Ti atoms play a role as heterogeneous defects, resulting in the creation of nucleation sites for Au nano-clusters. A marked increase in Au cluster density due to Ti defects was observed in STM. A TiO2-SiO2 thin film consisting of atomic Ti as well as TiOx islands was also synthesized by using higher amounts of Ti (17 %). More importantly, this oxide surface was found to have sinter resistant properties for Au nano-clusters, which are desirable in order to make highly active Au nano-clusters more stable under reaction conditions.
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Kamiuchi, Naoto. "Studies on Nano-structures and Catalytic Activities of Oxide-supported Precious Metal Catalysts". 京都大学 (Kyoto University), 2010. http://hdl.handle.net/2433/120878.
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Wang, Shengye. "Algal and alginate based beads and foams as sorbents for metal sorption and catalyst supports for 3-nitrophenol hydrogenation". Thesis, Montpellier, 2019. http://www.theses.fr/2019MONTG001.
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Ce travail décrit la synthèse d'une série de matériaux à base de biomasse d'alginate et d'algues; ces matériaux ont été conçus sous différentes formes: billes et mousses. Des procédés spécifiques ont été mis au point pour l’utilisation directe de la biomasse algale (AB, sans ajout d’autres polymères) avec le souci de développer un processus de synthèse simple et respectueux de l’environnement (production réduite de sous-produits et sans additif supplémentaire). Ces matériaux ont été testés pour la décontamination d’effluents contenant des métaux lourds (Pb(II) et Cu(II)), mais également pour la valorisation des métaux (métaux du groupe platine, PGM: Pd(II) et Pt(IV)). Différents paramètres opératoires ont été testés afin d'évaluer les capacités de sorption et les étapes limitantes, mais également d'identifier des stratégies d’amélioration des performances d’adsorption. L’incorporation de poly(éthylèneimine) (PEI) est une méthode prometteuse pour augmenter la densité de groupes réactifs (fonctions amines). Différents procédés ont été testés: (a) l'incorporation de particules de PEI réticulées avec du glutaraldéhyde (billes hétérogènes: ABA/PEI), et (b) le greffage homogène de PEI sur de l'alginate (suivi de la réticulation par le glutaraldéhyde) (billes homogènes HABA/PEI). La spectroscopie FTIR et l'analyse MEB& MEB-EDX ont été utilisées pour interpréter les mécanismes de fixation ainsi que pour caractériser la structure des matériaux. Dans une deuxième étape, les matériaux sélectionnés ont été testés pour la catalyse supportée en utilisant la réaction d'hydrogénation du 3–nitrophénol (3-NP). Les résultats sont structurés en 3 parties développées successivement: (a) synthèse des billes d’alginate, AB et AB/PEI et étude de l’adsorption de métaux lourds et de PGMs, (b) comparaison des propriétés d’adsorption du Pd(II) par les billes composites AB/PEI préparées par les voies homogène et hétérogène (et leur application aux tests en catalyse supportée), et (c) la synthèse de mousses poreuses (préparées par réaction entre l’alginate et la PEI) appliquées à l’adsorption du Pd(II) et à la catalyse supportée en réacteur à lit fixe.Si la PEI a un effet limité sur la fixation des métaux lourds (interaction avec les groupes carboxyliques de la biomasse d'alginate ou d'algues), sa présence améliore l’adsorption des métaux dans le cas des PGMs (les groupes amine protonés ont une forte affinité pour les espèces chloro-anioniques du Pd(II)) en particulier pour les billes d'alginate et AB. Tous les adsorbants ont une préférence pour le Pb(II) par rapport au Cu(II) et pour le Pd(II) par rapport au Pt(IV); la présence de PEI limite la sélectivité du matériau pour le Pb(II) et le Pd(II). La capacité de fixation et la stabilité des billes composites d'alginate/PEI ont été améliorées en utilisant le mode de synthèse homogène (la PEI étant dispersée de manière homogène dans la bille avant la réticulation par le glutaraldéhyde). Les deux supports (billes hétérogènes ou homogènes) chargés en Pd(II) (ensuite réduit) ont permis des performances catalytiques comparables bien qu’inférieures à celles des catalyseurs classiques, mais le mode homogène améliore la stabilité à long terme du matériau. Le conditionnement du support catalytique sous forme de mousse a permis de tester la réaction catalytique dans un système à lit fixe : le conditionnement sous forme de mousse améliore les propriétés de transfert de masse par rapport aux billes et la constante de vitesse apparente n'est que légèrement réduite après 30 cycles de fonctionnementThis work describes the synthesis of a series of materials based on alginate and algal biomass (AB); these materials have been designed under different shapes: beads and foams. Special processes have been developed for directly using the algal biomass (without adding other polymers) with the double objective of simple processing and environmentally-friendly manufacturing (reduced production of sub-products and without additional resources). These materials have been tested first for metal recovery for heavy metal decontamination (Pb(II) and Cu(II)) but also for the valorization of metals (platinum groups metals, PGMs: Pd(II) and Pt(IV)). These studies were performed investigating various operating conditions in order to evaluate sorption capacities and limiting steps but also to identify the processes to be used for improving sorption performance. The incorporation of poly(ethyleneimine), PEI, is a promising method for increasing the density of highly reactive groups (amine functions). Different processes have been tested: (a) the incorporation of particles of PEI crosslinked with glutaraldehyde (heterogeneous beads: ABA/PEI), and (b) the homogeneous grafting of PEI on alginate (followed by glutaraldehyde crosslinking) (HABA/PEI beads). Several techniques have been used for characterizing the sorption process and the structure of developed sorbents, including FTIR spectroscopy, SEM & SEM-EDX analysis. In a second step selected materials have been tested for supported catalysis using the simple reaction of hydrogenation of 3–nitrophenol (3-NP) as a test reaction. The results are structured in 3 parts successively developed: (a) synthesis of alginate, AB and AB/PEI beads and testing for sorption heavy metals and PGMs, (b) comparison of Pd(II) sorption properties of AB/PEI composite beads prepared by the homogeneous and the heterogeneous routes (and their application to supported catalytic tests), and (c) synthesis of highly porous foams (prepared by reaction of alginate with PEI) and the testing of Pd(II) sorption and Pd-supported catalysis (in fixed-bed reactor). While PEI hardly affects the sorption of heavy metals (due to direct interaction with carboxylic groups of alginate or algal biomass), the presence of PEI strongly improves metal binding in the case of PGMs (the protonated amine groups strongly bind chloro-anionic PGM species). All the sorbents have a preference for Pb(II) over Cu(II) and for Pd(II) over Pt(IV), especially for alginate and AB beads because the presence of PEI limits the selectivity of the material for Pb(II) and Pd(II). Both the sorption capacity and the stability of composite alginate/PEI beads were improved while using the homogeneous synthesis mode (the PEI polymer being homogeneously dispersed in the bead before glutaraldehyde crosslinking). The two supports (heterogeneous vs. homogeneous beads) loaded with Pd(II) and subsequently reduced gave comparable catalytic performance (lower than conventional catalysts) but the homogeneous mode improves the long-term stability. The conditioning of the catalytic support as a foam allows testing the catalytic reaction in fixed-bed system: the conditioning improves mass transfer properties compared to beads and the apparent rate constant is only slightly reduced after operating 30 cycles
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CORVA, MANUEL. "Experimental modeling of nanostructured and single metal atom supported catalysts at close-to-ambient conditions". Doctoral thesis, Università degli Studi di Trieste, 2019. http://hdl.handle.net/11368/2991050.
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This Thesis work deals with the growth and characterization of model nanostructured surface systems in ultra-high vacuum environment (UHV, <10−9 mbar) and with their evolution at near ambient pressure (NAP, 0.1 - 100 mbar) conditions. The investigations are performed with the aid of specific in situ techniques (IR-Vis SFG, NAP-XPS, etc.) in order to probe the structural, electronic, chemical and catalytic properties of the models.
The latter span from ordered lattices of metal nanoparticles to 2D metallorganic crystals, where stabilized mono-metallic centers act as the active cores. These systems, based on single metal atom centers, represent the main topic of this manuscript and they will be referred to as Single Metal Atom Catalysts (SMAC).
The discussion of the scientific findings will first focus on the evolution of graphene supported Pt nanoclusters in CO atmosphere, varying both surface temperature and CO pressure to test the stability of the nanostructures. As degradation of this nanosystem occurs at realistic reaction conditions, the attention was shifted to the design and synthesis of model SMAC systems, where the single metal atom is stabilized in a metallorganic cage, thus preventing structural degradation.
A first, prototype SMAC model system consisted of a single layer of Nickel tetraphenyl porphyrins (Ni-TPPs) deposited on the Cu(100) surface. We proved that, following to NO exposure, a hyponitrite species (N2O2) readily forms at the Ni sites already at UHV conditions and is stable at room temperature. The NO conversion is observed only on the NiTPP monolayer interacting with the underlying copper surface, showing that the substrate plays a major role, governing the properties of the nanostructured system through trans-effects associated with a strong surface-to-molecule charge transfer.
A single Iron Phthalocyanine (FePc) layer was instead considered for a model carbonylation reaction. The metalorganic molecules were deposited both on a single foil of graphene, grown on the Ir(111) surface (FePc/GR), and on an alumina ultra-thin film, grown on the Ni3Al(111) surface (FePc/alumina). In both cases, we exploited CO adsorption to probe the molecular active sites.
On the FePc/GR layer, IR-Vis SFG evidenced unexpected CO stretching modes in 1-10 mbar CO at 300 K. We ascribe the observed vibrational features to the production of long-lived molecular excitons (induced by the visible radiation). The long lifetime of these excitons and their efficient production through singlet-fission mechanisms represent intriguing findings for innovative organic devices for solar energy conversion. We also investigated the interaction of the same system with gas-phase CO2 We found that oxidation of the underlying graphene support yields the control of the charge transfer to the active sites, thus reducing the threshold pressure for CO2 adsorption and activation at 300 K by at least two orders of magnitude.
As CO2 catalytic conversion is hindered by its low reactivity, enhancing its adsorption to metal sites is crucial in the framework of the efficient conversion of this waste gas to valuable chemicals. A practical route to alter the mesoscopic properties of the single metal atom centers has been found, and in parallel we proved a novel graphene oxidation route employing molecular oxygen at near ambient pressure.
Concerning instead the FePc/alumina film, we demonstrated that decoration by Cu nanoclusters
tunes the surface potential energy, inducing a different symmetry in the molecular overlayer lattice, scarcely affecting the reactivity of the metallic sites, as proved by the vibrational modes of adsorbed CO molecules. Thus, we succeeded in tailoring the motif of a self-assembled metallorganic layer while preserving its active sites properties.This Thesis work deals with the growth and characterization of model nanostructured surface systems in ultra-high vacuum environment (UHV, <10−9 mbar) and with their evolution at near ambient pressure (NAP, 0.1 - 100 mbar) conditions. The investigations are performed with the aid of specific in situ techniques (IR-Vis SFG, NAP-XPS, etc.) in order to probe the structural, electronic, chemical and catalytic properties of the models. The latter span from ordered lattices of metal nanoparticles to 2D metallorganic crystals, where stabilized mono-metallic centers act as the active cores. These systems, based on single metal atom centers, represent the main topic of this manuscript and they will be referred to as Single Metal Atom Catalysts (SMAC). The discussion of the scientific findings will first focus on the evolution of graphene supported Pt nanoclusters in CO atmosphere, varying both surface temperature and CO pressure to test the stability of the nanostructures. As degradation of this nanosystem occurs at realistic reaction conditions, the attention was shifted to the design and synthesis of model SMAC systems, where the single metal atom is stabilized in a metallorganic cage, thus preventing structural degradation. A first, prototype SMAC model system consisted of a single layer of Nickel tetraphenyl porphyrins (Ni-TPPs) deposited on the Cu(100) surface. We proved that, following to NO exposure, a hyponitrite species (N2O2) readily forms at the Ni sites already at UHV conditions and is stable at room temperature. The NO conversion is observed only on the NiTPP monolayer interacting with the underlying copper surface, showing that the substrate plays a major role, governing the properties of the nanostructured system through trans-effects associated with a strong surface-to-molecule charge transfer. A single Iron Phthalocyanine (FePc) layer was instead considered for a model carbonylation reaction. The metalorganic molecules were deposited both on a single foil of graphene, grown on the Ir(111) surface (FePc/GR), and on an alumina ultra-thin film, grown on the Ni3Al(111) surface (FePc/alumina). In both cases, we exploited CO adsorption to probe the molecular active sites. On the FePc/GR layer, IR-Vis SFG evidenced unexpected CO stretching modes in 1-10 mbar CO at 300 K. We ascribe the observed vibrational features to the production of long-lived molecular excitons (induced by the visible radiation). The long lifetime of these excitons and their efficient production through singlet-fission mechanisms represent intriguing findings for innovative organic devices for solar energy conversion. We also investigated the interaction of the same system with gas-phase CO2 We found that oxidation of the underlying graphene support yields the control of the charge transfer to the active sites, thus reducing the threshold pressure for CO2 adsorption and activation at 300 K by at least two orders of magnitude. As CO2 catalytic conversion is hindered by its low reactivity, enhancing its adsorption to metal sites is crucial in the framework of the efficient conversion of this waste gas to valuable chemicals. A practical route to alter the mesoscopic properties of the single metal atom centers has been found, and in parallel we proved a novel graphene oxidation route employing molecular oxygen at near ambient pressure. Concerning instead the FePc/alumina film, we demonstrated that decoration by Cu nanoclusters tunes the surface potential energy, inducing a different symmetry in the molecular overlayer lattice, scarcely affecting the reactivity of the metallic sites, as proved by the vibrational modes of adsorbed CO molecules. Thus, we succeeded in tailoring the motif of a self-assembled metallorganic layer while preserving its active sites properties.
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Xu, Chunbao. "Continuous and batch hydrothermal synthesis of metal oxide nanoparticles and metal oxide-activated carbon nanocomposites". Diss., Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-07302006-231517/.
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Thesis (Ph. D.)--Chemical and Biomolecular Engineering, Georgia Institute of Technology, 2007.Teja, Amyn, Committee Chair ; Kohl, Paul, Committee Member ; Liu, Meilin, Committee Member ; Nair,Sankar, Committee Member ; Rousseau, Ronald, Committee Member.
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Verna, Frédérique. "Etude de l'interaction metal-compose sulfure en catalyse d'hydrogenation". Paris 6, 1988. http://www.theses.fr/1988PA066584.
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Dans la premiere partie de ce travail, l'adsorption de divers composes sulfures sur des catalyseurs palladium sur alumine a ete etudiee dans les conditions de l'hydrogenation en phase liquide et a une temperature inferieure a 100**(o)c. Dans une deuxieme partie, l'etude s'est portee sur l'influence du taux de couverture en soufre sur les proprietes catalytiques de pd/al::(2)o::(3) dans diverses reactions. Hydrogenation du butene-1, du butadiene-1,3, du butyne-1, ainsi que l'isomerisation du butene-1 en butene-2
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Price, Robert. "Metal/metal oxide co-impregnated lanthanum strontium calcium titanate anodes for solid oxide fuel cells". Thesis, University of St Andrews, 2018. http://hdl.handle.net/10023/16018.
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Solid Oxide Fuel Cells (SOFC) are electrochemical energy conversion devices which allow fuel gases, e.g. hydrogen or natural gas, to be converted to electricity and heat at much high efficiencies than combustion-based energy conversion technologies. SOFC are particularly suited to employment in stationary energy conversion applications, e.g. micro-combined heat and power (μ-CHP) and base load, which are certain to play a large role in worldwide decentralisation of power distribution and supply over the coming decades. Use of high-temperature SOFC technology within these systems is also a vital requirement in order to utilise fuel gases which are readily available in different areas of the world. Unfortunately, the limiting factor to the long-term commercialisation of SOFC systems is the redox instability, coking intolerance and sulphur poisoning of the state-of-the-art Ni-based cermet composite anode material. This research explores the ‘powder to power' development of alternative SOFC anode catalyst systems by impregnation of an A-site deficient La0.20Sr0.25Ca0.45TiO3 (LSCT[sub](A-)) anode ‘backbone' microstructure with coatings of ceria-based oxide ion conductors and metallic electrocatalyst particles, in order to create a SOFC anode which exhibits high redox stability, tolerance to sulphur poisoning and low voltage degradation rates under operating conditions. A 75 weight percent (wt. %) solids loading LSCT[sub](A-) ink, exhibiting ideal properties for screen printing of thick-film SOFC anode layers, was screen printed with 325 and 230 mesh counts (per inch) screens onto electrolyte supports. Sintering of anode layers between 1250 °C and 1350 °C for 1 to 2 hours indicated that microstructures printed with the 230 mesh screen provided a higher porosity and improved grain connectivity than those printed with the 325 mesh screen. Sintering anode layers at 1350 °C for 2 hours provided an anode microstructure with an advantageous combination of lateral grain connectivity and porosity, giving rise to an ‘effective' electrical conductivity of 17.5 S cm−1 at 850 °C. Impregnation of this optimised LSCT[sub](A-) anode scaffold with 13-16 wt. % (of the anode mass) Ce0.80Gd0.20O1.90 (CGO) and either Ni (5 wt. %), Pd, Pt, Rh or Ru (2-3 wt. %) and integration into SOFC resulted in achievement of Area Specific Resistances (ASR) of as low as 0.39 Ω cm−2, using thick (160 μm) 6ScSZ electrolytes. Durability testing of SOFC with Ni/CGO, Ni/CeO2, Pt/CGO and Rh/CGO impregnated LSCT[sub](A-) anodes was subsequently carried out in industrial button cell test rigs at HEXIS AG, Winterthur, Switzerland. Both Ni/CGO and Pt/CGO cells showed unacceptable levels of degradation (14.9% and 13.4%, respectively) during a ~960 hour period of operation, including redox/thermo/thermoredox cycling treatments. Significantly, by exchanging the CGO component for the CeO2 component in the SOFC containing Ni, the degradation over the same time period was almost halved. Most importantly, galvanostatic operation of the SOFC with a Rh/CGO impregnated anode for >3000 hours (without cycling treatments) resulted in an average voltage degradation rate of < 1.9% kh−1 which, to the author's knowledge, has not previously been reported for an alternative, SrTiO3-based anode material. Finally, transfer of the Rh/CGO impregnated LSCT[sub](A-) anode to industrial short stack (5 cells) scale at HEXIS AG revealed that operation in relevant conditions, with low gas flow rates, resulted in accelerated degradation of the Rh/CGO anode. During a 1451 hour period of galvanostatic operation, with redox cycles and overload treatments, a voltage degradation of 19.2% was observed. Redox cycling was noted to briefly recover performance of the stack before rapidly degrading back to the pre-redox cycling performance, though redox cycling does not affect this anode detrimentally. Instead, a more severe, underlying degradation mechanism, most likely caused by instability and agglomeration of Rh nanoparticles under operating conditions, is responsible for this observed degradation. Furthermore, exposure of the SOFC to fuel utilisations of >100% (overloading) had little effect on the Rh/CGO co-impregnated LSCT[sub](A-) anodes, giving a direct advantage over the standard HEXIS SOFC. Finally, elevated ohmic resistances caused by imperfect contacting with the Ni-based current collector materials highlighted that a new method of current collection must be developed for use with these anode materials.
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Anderson, J. B. F. "Strong metal-support interactions in titania-supported metal catalysts". Thesis, University of Reading, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372539.
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Zheng, Zhanfeng. "Synthesis and modifications of metal oxide nanostructures and their applications". Thesis, Queensland University of Technology, 2009. https://eprints.qut.edu.au/31728/1/Zhanfeng_Zheng_Thesis.pdf.
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Transition metal oxides are functional materials that have advanced applications in many areas, because of their diverse properties (optical, electrical, magnetic, etc.), hardness, thermal stability and chemical resistance. Novel applications of the nanostructures of these oxides are attracting significant interest as new synthesis methods are developed and new structures are reported. Hydrothermal synthesis is an effective process to prepare various delicate structures of metal oxides on the scales from a few to tens of nanometres, specifically, the highly dispersed intermediate structures which are hardly obtained through pyro-synthesis. In this thesis, a range of new metal oxide (stable and metastable titanate, niobate) nanostructures, namely nanotubes and nanofibres, were synthesised via a hydrothermal process. Further structure modifications were conducted and potential applications in catalysis, photocatalysis, adsorption and construction of ceramic membrane were studied. The morphology evolution during the hydrothermal reaction between Nb2O5 particles and concentrated NaOH was monitored. The study demonstrates that by optimising the reaction parameters (temperature, amount of reactants), one can obtain a variety of nanostructured solids, from intermediate phases niobate bars and fibres to the stable phase cubes. Trititanate (Na2Ti3O7) nanofibres and nanotubes were obtained by the hydrothermal reaction between TiO2 powders or a titanium compound (e.g. TiOSO4·xH2O) and concentrated NaOH solution by controlling the reaction temperature and NaOH concentration. The trititanate possesses a layered structure, and the Na ions that exist between the negative charged titanate layers are exchangeable with other metal ions or H+ ions. The ion-exchange has crucial influence on the phase transition of the exchanged products. The exchange of the sodium ions in the titanate with H+ ions yields protonated titanate (H-titanate) and subsequent phase transformation of the H-titanate enable various TiO2 structures with retained morphology. H-titanate, either nanofibres or tubes, can be converted to pure TiO2(B), pure anatase, mixed TiO2(B) and anatase phases by controlled calcination and by a two-step process of acid-treatment and subsequent calcination. While the controlled calcination of the sodium titanate yield new titanate structures (metastable titanate with formula Na1.5H0.5Ti3O7, with retained fibril morphology) that can be used for removal of radioactive ions and heavy metal ions from water. The structures and morphologies of the metal oxides were characterised by advanced techniques. Titania nanofibres of mixed anatase and TiO2(B) phases, pure anatase and pure TiO2(B) were obtained by calcining H-titanate nanofibres at different temperatures between 300 and 700 °C. The fibril morphology was retained after calcination, which is suitable for transmission electron microscopy (TEM) analysis. It has been found by TEM analysis that in mixed-phase structure the interfaces between anatase and TiO2(B) phases are not random contacts between the engaged crystals of the two phases, but form from the well matched lattice planes of the two phases. For instance, (101) planes in anatase and (101) planes of TiO2(B) are similar in d spaces (~0.18 nm), and they join together to form a stable interface. The interfaces between the two phases act as an one-way valve that permit the transfer of photogenerated charge from anatase to TiO2(B). This reduces the recombination of photogenerated electrons and holes in anatase, enhancing the activity for photocatalytic oxidation. Therefore, the mixed-phase nanofibres exhibited higher photocatalytic activity for degradation of sulforhodamine B (SRB) dye under ultraviolet (UV) light than the nanofibres of either pure phase alone, or the mechanical mixtures (which have no interfaces) of the two pure phase nanofibres with a similar phase composition. This verifies the theory that the difference between the conduction band edges of the two phases may result in charge transfer from one phase to the other, which results in effectively the photogenerated charge separation and thus facilitates the redox reaction involving these charges. Such an interface structure facilitates charge transfer crossing the interfaces. The knowledge acquired in this study is important not only for design of efficient TiO2 photocatalysts but also for understanding the photocatalysis process. Moreover, the fibril titania photocatalysts are of great advantage when they are separated from a liquid for reuse by filtration, sedimentation, or centrifugation, compared to nanoparticles of the same scale. The surface structure of TiO2 also plays a significant role in catalysis and photocatalysis. Four types of large surface area TiO2 nanotubes with different phase compositions (labelled as NTA, NTBA, NTMA and NTM) were synthesised from calcination and acid treatment of the H-titanate nanotubes. Using the in situ FTIR emission spectrescopy (IES), desorption and re-adsorption process of surface OH-groups on oxide surface can be trailed. In this work, the surface OH-group regeneration ability of the TiO2 nanotubes was investigated. The ability of the four samples distinctively different, having the order: NTA > NTBA > NTMA > NTM. The same order was observed for the catalytic when the samples served as photocatalysts for the decomposition of synthetic dye SRB under UV light, as the supports of gold (Au) catalysts (where gold particles were loaded by a colloid-based method) for photodecomposition of formaldehyde under visible light and for catalytic oxidation of CO at low temperatures. Therefore, the ability of TiO2 nanotubes to generate surface OH-groups is an indicator of the catalytic activity. The reason behind the correlation is that the oxygen vacancies at bridging O2- sites of TiO2 surface can generate surface OH-groups and these groups facilitate adsorption and activation of O2 molecules, which is the key step of the oxidation reactions. The structure of the oxygen vacancies at bridging O2- sites is proposed. Also a new mechanism for the photocatalytic formaldehyde decomposition with the Au-TiO2 catalysts is proposed: The visible light absorbed by the gold nanoparticles, due to surface plasmon resonance effect, induces transition of the 6sp electrons of gold to high energy levels. These energetic electrons can migrate to the conduction band of TiO2 and are seized by oxygen molecules. Meanwhile, the gold nanoparticles capture electrons from the formaldehyde molecules adsorbed on them because of gold’s high electronegativity. O2 adsorbed on the TiO2 supports surface are the major electron acceptor. The more O2 adsorbed, the higher the oxidation activity of the photocatalyst will exhibit. The last part of this thesis demonstrates two innovative applications of the titanate nanostructures. Firstly, trititanate and metastable titanate (Na1.5H0.5Ti3O7) nanofibres are used as intelligent absorbents for removal of radioactive cations and heavy metal ions, utilizing the properties of the ion exchange ability, deformable layered structure, and fibril morphology. Environmental contamination with radioactive ions and heavy metal ions can cause a serious threat to the health of a large part of the population. Treatment of the wastes is needed to produce a waste product suitable for long-term storage and disposal. The ion-exchange ability of layered titanate structure permitted adsorption of bivalence toxic cations (Sr2+, Ra2+, Pb2+) from aqueous solution. More importantly, the adsorption is irreversible, due to the deformation of the structure induced by the strong interaction between the adsorbed bivalent cations and negatively charged TiO6 octahedra, and results in permanent entrapment of the toxic bivalent cations in the fibres so that the toxic ions can be safely deposited. Compared to conventional clay and zeolite sorbents, the fibril absorbents are of great advantage as they can be readily dispersed into and separated from a liquid. Secondly, new generation membranes were constructed by using large titanate and small ã-alumina nanofibres as intermediate and top layers, respectively, on a porous alumina substrate via a spin-coating process. Compared to conventional ceramic membranes constructed by spherical particles, the ceramic membrane constructed by the fibres permits high flux because of the large porosity of their separation layers. The voids in the separation layer determine the selectivity and flux of a separation membrane. When the sizes of the voids are similar (which means a similar selectivity of the separation layer), the flux passing through the membrane increases with the volume of the voids which are filtration passages. For the ideal and simplest texture, a mesh constructed with the nanofibres 10 nm thick and having a uniform pore size of 60 nm, the porosity is greater than 73.5 %. In contrast, the porosity of the separation layer that possesses the same pore size but is constructed with metal oxide spherical particles, as in conventional ceramic membranes, is 36% or less. The membrane constructed by titanate nanofibres and a layer of randomly oriented alumina nanofibres was able to filter out 96.8% of latex spheres of 60 nm size, while maintaining a high flux rate between 600 and 900 Lm–2 h–1, more than 15 times higher than the conventional membrane reported in the most recent study.
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Boudouvas, Denis. "Effet du potassium sur un catalyseur composite Fe-Co-C en synthèse d'hydrocarbures". Grenoble INPG, 1989. http://www.theses.fr/1989INPG0092.
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Etude de la promotion par le potassium du catalyseur composite fe-co-c, c'est-a-dire de l'amelioration de son activite catalytique et de sa selectivite en alcenes. L'addition de potassium est realisee soit par impregnation par une solution aqueuse de k#2co#3, soit par la formation intermediaire d'un compose d'insertion avec le carbone de formule kc#3#2. L'evolution de la selectivite des catalyseurs promus et non promus par le potassium est etudiee a des conversions en monoxyde de carbone analogues a celles d'un procede industriel. Des tests catalytiques a faible conversion et des mesures de chimisorption de gaz reagissants sont effectues
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Watts, Andrew M. "Polysiloxane supported metal catalysts". Thesis, University of Bath, 1986. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370993.
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Hickel, Probst Sonia Maria. "Propriétés catalytiques et caractérisation de catalyseurs au nickel déposé sur oxydes de terre rare : influence de l'intéraction métal-support". Poitiers, 1989. http://www.theses.fr/1989POIT2296.
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Etude des modifications des proprietes du nickel sur support d'oxydes de terres rares (lanthane et cerium) en comparant avec d'autres supports. Les caracterisations physicochimiques (reduction chimique, adsorption-desorption a temperature programmee) montrent que les oxydes de terres rares sont des supports facilement reductibles. Toutefois les mesures de chimisorption ne permettent pas de determiner la taille des particules en raison d'interactions electroniques entre le metal et le support. C'est pourquoi, les catalyseurs sont caracterises par des reactions d'hydrogenation. Mise en evidence de centres reactionnels d'adsorption du monoxyde de carbone par spectrometrie infra rouge
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Venable, Margaret Hamm. "Syntheses, structures and support interactions of potential metal oxide catalyst precursors". Thesis, Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/26940.
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Brown, Ronald. "A study of hydrocarbon reactions over supported metal catalysts : support and metal dependence". Thesis, University of Edinburgh, 1990. http://hdl.handle.net/1842/13013.
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Havil, Patrick. "Influence du vieillissement thermique sur les proprietes physico-chimiques et la reactivite des catalyseurs mono et bimetalliques a base de platine et/ou rhodium sur alumine ou sur cerine". Paris 6, 1988. http://www.theses.fr/1988PA066291.
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Une etude systematique de la stabilite des catalyseurs de post-combustion mono et bimetalliques, platine-rhodium, supportes sur alumine et cerine a ete realisee pour un vieillissement thermique a des temperatures variant de 600 a 1100**(o)c. Les catalyseurs ont ete ensuite testes avec un melange de gaz synthetique simulant les conditions reelles. Le vieillissement a lieu principalement en milieu oxydant. Il est du soit au frittage de la phase metallique par grossissement des particules de 1 a 30 nm soit a l'encapsulation ou a la migration des ions platine et rhodium dans le support
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Derule, Hervé. "Influence du degré d'oxydation du métal sur la sélectivité des catalyseurs de synthèse Fischer-tropsch". Poitiers, 1989. http://www.theses.fr/1989POIT2268.
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L'utilisation en phase liquide d'un sel de cobalt totalement reduit par un alkyl metal conduit essentiellement a la formation d'hydrocarbures. Lorsque la reduction est incomplete, on note une production d'alcools limitee dans le temps, avec une selectivite maximale pour la demi-reduction. Par contre en creant des centres metalliques sur un support constitue de cobalt oxyde, la production d'alcools augmente legerement et devient stable. Ainsi la synthese de produits oxygenes necessite la presence simultanee de centres metalliques et oxydes
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Kababji, Ala'a Hamed. "Effects of Diluent Addition and Metal Support Interactions in Heterogeneous Catalysis: SiC/VPO Catalysts for Maleic Anhydride Production and Co/Silica Supported Catalysts for FTS". Scholar Commons, 2009. https://scholarcommons.usf.edu/etd/2035.
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This work begins with an introduction to catalysis focusing on heterogeneous systems and surface science phenomena. A study on the partial oxidation reaction of n-butane to maleic anhydride (MA) is presented in the first part. MA supplies are barely adequate for market requirements due to continued strong demand. Only slight improvement in catalytic performance would be welcome in the industrial community. The vanadium phosphorus oxide (VPO) catalyst was used in this work. The reaction is highly exothermic and the need to properly support the catalyst, not only for good dispersion but adequate heat dissipation is of crucial importance. For this, alpha-SiC commercial powders were used in synthesizing the catalyst due to its high thermal conductivity. Up to 25% MA yields were obtained and the reaction temperature was lowered by up to 28% using SiC/VPO mixed catalysts.
The second part of this work is focused on the Fischer-Tropsch synthesis (FTS) process using cobalt silica supported catalysts. The main objective is the production of synthetic ultra high purity jet fuel (JP5). This is a very timely topic given the energy issues our world is facing. Almost all aspects of the FTS process have been extensively studied, however the effects of calcination temperature and silica support structure on the catalyst performance are lacking in literature. The catalysts were prepared using various silica supports. The catalysts had different drying and calcination temperatures. It was found that lower support surface area and calcination temperature catalysts exhibited higher activity due to lower support cobalt phase interaction. Co/silica catalysts calcined at 573K showed the highest CO conversion and the lowest CH4 selectivity. Catalysts prepared with 300m²/g support surface area exhibited 79.5% C5+ selectivity due to higher reducibility and less metal support interaction.
The properties and performance of various prepared catalysts in both VPO and Co/silica systems are characterized by FTIR, XRD, BET, GC and XPS techniques. Theoretical FTS deactivation by sintering calculations and SiC/VPO particle temperature gradient calculations are presented as well. Finally, conclusions and future work on improving the yield and selectivity and scaling up the bench top setups are also presented.
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Messi, C. "Nanostructured catalytic metal oxides supported over oxide supports of various nature : the iron oxide system". Doctoral thesis, Università degli Studi di Milano, 2008. http://hdl.handle.net/2434/57081.
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Brimacombe, Lyn M. "Activation of methane on supported metal catalysts". Thesis, University of Ottawa (Canada), 1991. http://hdl.handle.net/10393/7805.
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In order to obtain more information required for the catalytic conversion of methane, the interaction of methane and ethylene with various supported metal catalysts was investigated. The metals used were Ni, Fe, Co, Mo, Ru, Rh, Pd, Re, Ir, and Pt, all supported on $\rm Al\sb2O\sb3.$ Silica supported nickel was also used. The technique of temperature programmed reaction was mainly used. This method gives temperatures at which the adsorption and/or the reaction of a gas starts to occur. The present results showed wide differences in the interaction of methane or ethylene with each catalyst. The isothermal reaction of methane was also carried out in order to further investigate the behaviour of the CH$\sb{\rm n}$ species which were formed upon the chemisorption of methane. As a process for converting methane to higher hydrocarbons, the catalytic coupling of methane with ethylene (CH$\sb4$ + $\rm C\sb2H\sb4\to C\sb3H\sb8$) was examined by using the catalysts listed above. At 250 and 350$\sp\circ$C, no propane was produced on any of the catalysts, except for alumina supported platinum. A trace of propane was found in this case for the reaction at 250$\sp\circ$C. The results were discussed based on the interaction of the reactants with these metals as revealed by the temperature programmed reactions.
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Namijo, S. N. "Carbon dioxide hydrogenation over supported metal catalysts". Thesis, Brunel University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379411.
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Kennedy, David Rankin. "Hydrogenation of acetylenes over supported metal catalysts". Thesis, University of Glasgow, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340756.
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McLeod, Alistair Scott. "Monte Carlo studies of supported metal catalysts". Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.624870.
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Briquet, L. G. V. "Modelling active sites of supported metal catalysts". Thesis, University College London (University of London), 2010. http://discovery.ucl.ac.uk/19286/.
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Many chemical processes involving heterogeneous catalysis such as automotive catalysts or the steam reforming process are vital for industry. The chemistry of nanoclustered metal particles is distinctly altered by their interaction with the support. Metal/metal oxide interactions are therefore considered to be crucial to tune the catalytic properties of many catalysts. In order to increase our understanding of the interactions between the metal oxide surface and the metal adsorbate, computational techniques, based on both Density Functional Theory and interatomic potentials, have been used. As the presence of sodium cations in alumina supports can be an issue for the catalyst industry, the segregation of sodium is investigated and compared to available experimental data. It has been found that sodium tends to segregate at a subsurface site in the (0001) α-alumina surface, while the migration of sodium defects is much more facile in γ-alumina. In this thesis, we investigate the interactions of a group of catalytically active metals (nickel, palladium, platinum and gold) with different surfaces of alumina, starting with various faces of α-Al2O3. Although subtly different, the metal/support interaction for each surface is consistent, with metal promoting a charge transfer from the surface oxygen to the top-most aluminium. As water is known to bond strongly to the alumina surfaces, the effect of surface hydroxylation on the adsorption mechanisms has also been investigated. An important stabilisation of the metal is observed with, in some cases, the migration of a proton from the surface to the metal, forming hydride species. To assess further the impact of the surface conditions on the catalytic properties of the metal particle, we also investigated the interactions between the metal and a carbon monoxide probe. All metals show different behaviour toward the carbon monoxide bond length and vibrational frequency. The hydroxylation of the alumina surface has a strong impact on the carbon monoxide/metal complex stability as the carbon monoxide probe enters into competition with the hydride specie bonded to the metal. This investigation allows us to obtain a detailed insight into the nature of the metal support interaction and the active sites of complex catalysts.
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Alvaro, Vasco Filipe Domingues. "Selective catalytic activity of metals supported on metal(IV) phosphates for heterogeneous reduction". Thesis, University of Liverpool, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263780.
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Poupart, Romain. "Nanoparticules métalliques@polymères poreux : matériaux hybrides innovants pour la catalyse supportée". Thesis, Paris Est, 2017. http://www.theses.fr/2017PESC1174/document.
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Les matériaux poreux basés sur les polymères font l’objet de recherches nombreuses et variées depuis leur découvertes et jusqu’à aujourd’hui encore. Leurs propriétés uniques et remarquables, comme par exemple une fonctionnalisation aisée ou une large gamme de porosité accessibles, couplées à leur faible coût de production les rendent attrayant pour de nombreuses applications. Parmi elles, la catalyse supportée est en plein essor, spécialement depuis l’avènement des nanoparticules. Durant ce travail de thèse, nous avons développé différents matériaux polymères pouvant servir de support, se focalisant majoritairement sur trois types de matériaux : des matériaux polymères massiques, des matrices polymères poreuses en capillaire ainsi que des polystyrènes poreux provenant de la dégradation sélective de copolymères diblocs.Dans un premier temps, différentes stratégies ont été employées pour l’immobilisation et la génération de nanoparticules sur les matériaux massiques. L’un a consisté en la synthèse d’un monomère contenant un pont disulfure qui, après réduction, a permis la libération de groupement thiol permettant l’accrochage de nanoparticules d’or. La seconde a consisté à réduire de manière originale les nanoparticules en utilisant un gaz, l’hydrogène. Dans un seconde partie, la synthèse de différentes matrices polymères dans des capillaires a été réalisée. Tout d’abord, une matrice déjà connue de la littérature à base de N-acryloxysuccinimide a été utilisée, après modification via thiol-ène et substitution nucléophile par différentes amines, pour immobiliser des nanoparticules de cuivre ainsi que d’or, respectivement. D’autre part, une nouvelle matrice à partir de carbonate cyclique aura, elle, été utilisée après modification, pour l’immobilisation de nanoparticules de platine. Enfin à partir de copolymères diblocs possédant différentes jonctions entre chaque bloc (un pont disulfure ainsi qu’un acétal), différents polystyrènes poreux ont été obtenus. Les copolymères possédant une jonction acétal à lui été utilisé pour l’immobilisation de nanoparticules d’or, permettant la mise en place des réactions de réduction de nitro, d’homocouplage boronique ainsi que de la mise en cascade de ces deux réactionsPorous materials based on polymers have been the subject of intense and various researches since their discovery until now. Their unique and remarkable properties, like their easy functionalization or their large porosity range reachable for instance, coupled with their low production cost makes them attractive for numerous applications. Among them, supported catalysis is booming, especially since the rising of nanoparticles. During this Ph.D. contribution, we have developed different polymeric materials, which could be used as support, focusing mainly onto three types: bulky materials, porous polymeric matrixes into capillaries and porous polystyrene arising from the selective degradation of diblocks copolymers.Firstly, different strategies have been employed for the immobilization and the generation of nanoparticles onto bulk materials. On the one hand, the synthesis of a monomer, bearing a disulphide bridge which can, after a reduction step, free a thiol moiety allowing us to anchor gold nanoparticles. On the other hand, a new route to reduce nanoparticle has been employed using gaseous hydrogen. In another part, the syntheses of different polymeric matrixes into capillaries have been made. First, we used an already known matrix, based on N-acryloxysuccinimide -after modification step via thiol-ene reaction and nucleophilic substitution by amines- to anchor copper or gold nanoparticles, respectively. Also, a new matrix based on cyclic carbonates has been used, after modification, to immobilized platinum nanoparticles. Finally, starting from diblocks copolymers possessing different junctions between both blocks (disulphide bridge or acetal), porous polystyrenes have been obtained. The copolymers bearing an acetal have been implemented to immobilized gold nanoparticles, catalysing several reactions like nitro reduction, boronic homocoupling as well as the cascade reaction of both
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Roberts, Mark Stephen. "Catalysis by semiconductor supported metal clusters". Thesis, University of Hull, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.327805.
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Swaminathan, Sneha. "Metal Oxide Nanofibers as Filters, Catalyst and Catalyst Support Structures". University of Akron / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=akron1279564885.
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Cairns, Graham R. "Hydrogenation catalysts from supported palladium complexes". Thesis, University of Glasgow, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360177.
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Abdoullah, Mohamad. "Supported transition metal oxides as solid base catalysts". Thesis, University of Huddersfield, 2016. http://eprints.hud.ac.uk/id/eprint/28325/.
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The initial objective of the work studied here was to investigate the effects of isomorphously-substituted transition metals in lattice sites in Layered Double Hydroxides (LDHs) in terms of basicity and catalytic activity in base-catalysed reactions and oxidation reactions. Experiments in which copper(II), nickel(II), cobalt(II), zinc(II) and iron(III) were substituted in the lattice of synthetic hydrotalcites showed that, on calcination, the resultant mixed oxides arising from hydrotalcites containing copper(II) exhibited the greatest enhancement of catalytic activity. Test reactions were the conversion of 4-methylpentan-2-ol to methylisobutylketone, the oxidation of benzyl alcohol and the Henry reaction between benzaldehyde and nitromethane. Results showed conclusively that copper(II) imparted base catalytic activity to the mixed metal oxides formed on calcination of the LDHs. This was confirmed through an extension to the study in which the copper(II) content in the LDHs was varied. It was shown that there is an optimum copper(II) loading, above which additional copper(II) is not effectively incorporated in the LDH lattice. Other supports for copper(II) as an oxide were investigated, on the basis that activity was linked to effective dispersion of copper(II) oxide. A series of copper(II) dispersions on zirconia, on silica and on magnesium oxide were prepared and tested. The zirconia-supported catalysts were the most active so work was concentrated on these. Two methods for preparing copper(II) oxide/zirconia were investigated, using a solid state reaction and using a sol-gel process. Catalysts were prepared with molar copper contents of from 2 to 60 mol%. It was possible to see from powder X-ray diffraction that copper(II) was dispersed in the zirconia matrix at levels up to about 20% depending on the synthetic method. And it was shown that base-catalytic activity of these materials correlated with the amount of fully incorporated copper(II). Activities of these were generally higher than the mixed metal oxides made from the LDHs. For comparison, another, different, approach to incorporating basicity in oxide supports was examined, in which alkylamino groups were tethered to silica supports, specifically a mesoporous molecular sieve form of silica, SBA-15. The activity of these materials were compared with those of the copper(II) based catalysts in the Henry reaction between nitromethane and benzaldehyde. An advantage of these catalysts was exploited by coordinating palladium(II) to the amine groups at different levels to impart oxidation catalytic activity. The resultant materials, in which only part of the amine functionality was coordinated by palladium(II), were tested as bifunctional catalysts, for combined oxidation and base catalytic activity, in the two step reaction between benzyl alcohol and nitromethane, which proceeds via an oxidation step to benzaldehyde followed by a base-catalysed step. The overall conclusion was that copper(II) is effective at imparting base catalytic activity to a range of support oxides, and that it does not have significant activity towards oxidation reactions., contrary to some claims in the literature. Oxidation activity can be obtained alongside base activity by preparing bifunctional catalysts but only through a different approach.
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Chambers, Nick. "Asymmetric heterogeneous reduction over modified supported metal catalysts". Thesis, Keele University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.323719.
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Tsui, Li-Hsin. "Supported metal catalysts for water-gas shift conversion". Master's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/13384.
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Includes bibliographical references.The interests in an alternative, sustainable power generation method has greatly increased in the past decade due to increases in greenhouse gases and its impact on global climate change. The use of fuel cells as a form of energy generation is extremely promising as it converts chemical potential energy directly to electrical energy, bypassing the Carnot cycle limitations. Various types of fuel cells have been developed, with the proton exchange membrane fuel cell (PEMFC) being most promising for mobile and small-scale stationary uses under transient conditions. The PEMFC uses hydrogen and oxygen to generate electrical energy. While oxygen can be obtained from air, hydrogen does not exist in its elemental form; hence a process train is required to refine fuels (such as fossil fuels and bio-fuels) into pure hydrogen. This has been successfully achieved by large-scale industrial plants. A typical fuel processing train consists of a steam reforming stage converting the fuel into syngas. This is followed by a water-gas shift (WGS) stage to convert carbon monoxide, which is a poison for the platinum catalysts within fuel cells, into carbon dioxide. If the CO concentration required is extremely low, a methanation or preferential oxidation stage can be used subsequent to the WGS stage. This study focuses on the water-gas shift stage of the fuel processing train. Industrial base metal WGS catalysts are not suitable for a miniaturized fuel processing train due to the catalysts being developed for continuous operations, as miniaturized fuel processing trains are expected to operate at transient conditions. A slow and controlled reduction process is also required prior to operation, as well as the pyrophoricity of industrial catalysts after reduction. These can pose safety issues with non-technical personnel in household applications (e.g. CHP). PGM-based catalysts have shown high activities for the water-gas shift reaction in literature, are not pyrophoric and do not require lengthy and sensitive reduction processes prior to operation. The objective of this study was to investigate and compare two base metal catalysts (high temperature (HT) shift Fe₃O₄/Cr₂O₃ and low temperature (LT) shift CuO/ZnO/Al₂O₃ catalyst) with a PGM based counterpart, as well as to investigate whether the catalysts are able to achieve a required 1 vol% CO via the water-gas shift reaction. For these investigations a synthetic feedstock was used, based on typical exit concentrations of a steam methane reformer.
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Pellegrini-Bonneau, Laurence. "Vaporeformage d'hydrocarbures lourds en présence de composés soufres". Poitiers, 1988. http://www.theses.fr/1988POIT2318.
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Reformage vapeur selectif du methyl-1-naphtalene en vue d'obtenir le "btx" (benzene-toluene-xylene). Utilisation d'un catalyseur mixte supporte niw/al::(2)o::(3) ou zro::(2). Etude de l'influence de promotteurs alcalins
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Gogolieva, Ganna. "Catalyseurs greffés sur support et libérés sous stimulus externe". Phd thesis, Toulouse, INPT, 2014. http://oatao.univ-toulouse.fr/11916/1/gogolieva.pdf.
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La catalyse organométallique est à l’origine des avancées les plus significatives au cours des dernières années puisqu’elle a permis de découvrir de nouvelles voies d’accès à des molécules complexes; elle a ainsi révolutionné le monde de la synthèse organique. Bien que de nombreuses réactions s’appuyant sur des complexes organométalliques aient été développées, les catalyseurs organométalliques présentent encore deux inconvénients majeurs : leur toxicité, associée la plupart du temps à la présence de métaux lourds, et leur coût lié à la présence à la fois d’un centre métallique et de ligands élaborés. Dès lors de nombreuses recherches ont été lancées dans le but de mettre au point des techniques permettant de séparer simplement le catalyseur métallique des produits formés et de le recycler. C’est dans ce contexte que nous avons cherché à développer de nouveaux catalyseurs supportés pouvant être libérés pendant la réaction afin d’effectuer la catalyse en conditions homogènes et de nouveau greffés au support en fin de réaction afin de pouvoir séparer le catalyseur des produits de la réaction et le recycler ensuite via une nouvelle libération. Cette capacité de passage du catalyseur du support vers la solution et vice-versa est basée sur un complexe de coordination lié au support et appelé «agrafe contrôlable» dont la sphère de coordination peut être modulée via un stimulus externe : soit un complexe du ruthénium avec un stimulus photochimique, soit un complexe du cuivre avec un stimulus électrochimique, tels qu’exploités dans de nombreuses machines moléculaires. Les nanotubes de carbone sont choisis comme support, les ligands de type NHC sont choisis comme ligands de base du système catalytique et des complexes du cuivre ou du ruthénium portant des ligands de type bipyridine, phénantroline ou terpyridine constituent le cœur de l’agrafe contrôlable. Des complexes de palladium basés sur des ligands NHC fonctionnalisés ont été synthétisés en utilisant un motif triazole comme lien entre le centre catalytique et la fonctionnalité impliquée dans la récupération du catalyseur. Les tests catalytiques dans des réactions de Suzuki-Miyaura ont montré que les complexes étaient actifs sur une large gamme de substrats et à des charges catalytiques faibles (jusqu’à 50 ppm) et ce, quelle que soit la fonctionnalité ajoutée. Des complexes du ruthénium portant des ligands terpyridine, bipyridine ou phénantroline ont été synthétisés et caractérisés. Le concept du switch photochimique a été validé sur un système modèle : nous avons pu montrer que sous irradiation à l’aide d’une lampe à vapeur de mercure, le complexe [Ru(II)(terpyridine)(bipyridine)(PhCN)][(PF6)2] était capable de libérer le ligand benzonitrile et que la réaction inverse se produisait par chauffage du complexe [Ru(II)(terpyridine)(bipyridine)(H2O)][(PF6)2] en présence de benzonitrile. D’autre part, des complexes du cuivre portant des ligands de type bis-bipyridine et terpyridine ont été synthétisés et caractérisés. Le concept du switch électrochimique a été validé sur un système modèle : nous avons pu montrer par voltamétrie cyclique qu’en présence de terpyridine, le complexe [Cu(I)(bis-bipyridine)][BF4] pouvait s’oxyder et former un complexe de type [Cu(II)(bipyridine)(terpyridine)][(BF4)2] et que la réaction inverse se produisait par réduction. Ces travaux démontrent le caractère contrôlable des agrafes choisies via un stimulus électrochimique ou photochimique, sur des systèmes modèles. L’obtention de complexes de palladium comportant un ligand NHC-triazole fonctionnalisé, leur bonne activité et la voie de synthèse mise au point valident notre stratégie de récupération et ouvrent de nombreuses perspectives en catalyse.
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Huang, Wei. "Selective hydrogenation on zeolite-supported bimetallic catalysts". Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 0.90 Mb., p. 76, 2005. http://proquest.umi.com/pqdlink?did=1037889271&Fmt=7&clientId=8331&RQT=309&VName=PQD.
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Huang, Wei. "Selective hydrogenation of acetylene on zeolite-supported bimetallic catalysts". Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 173 p, 2008. http://proquest.umi.com/pqdweb?did=1459913421&sid=16&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Brandmair, Maria. "Autothermal reforming of n-hexane over supported metal catalysts". [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=978997700.
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Keegan, Michael Bernard Thomas. "Supported metal catalysts : some aspects of characterisation and function". Thesis, University of Hull, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384806.
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Wells, Peter Philip. "Controlled surface modification of supported platinum group metal catalysts". Thesis, University of Southampton, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438652.
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Hayward, James. "Supported metal catalysts for the production of chemical precursors". Thesis, Cardiff University, 2013. http://orca.cf.ac.uk/53589/.
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Supported metal catalysts have applications across a broad range of industrial processes. The metal species are often the active catalysts in these processes, but supporting these materials upon a different material can produce desirable characteristics in the overall catalyst. These effects can include, but are not limited to, increased dispersion of active material, increased stability of the active material, and, depending on the supporting material, beneficial metal-support interactions can be generated. The production of benzaldehyde from benzyl alcohol is a reaction with high commercial value. Gold-palladium catalysts have been shown to be effective at production of benzaldehyde from benzyl alcohol under relatively mild, solvent-free conditions. It has also been shown that the selectivity of this reaction is dependent upon the acidic or basic character of the support material. Perovskites are a class of highly stable minerals with a general formula of ABO3, with A being a cation with a larger ionic radius than B. The acidic and basic character of a perovskite is strongly determined by the nature of the A cation, which allows for the possibility of adjusting this character by metal substitution. This study investigates the effects of gradual substitution of lanthanum for strontium in vanadate perovskites, and showed that incorporation of the substituted metal is effective up to a certain point, beyond which the material switches to two spate perovskite phases. The substitution of the metal ions was shown to have an effect on the acidic and basic properties of the perovskite materials using the Isopropyl Alcohol (IPA) reaction, which forms different products on acidic or basic sites. Following this, substitution with a wider range of group II metals was investigated and tested, both in the IPA reaction and as supports for precious metals in the production of benzaldehyde. A separate series of investigations were performed on Fischer-Tropsch (FT) catalysts. Fischer-Tropsch is a name given to a wide range of catalytic processes involving the production of hydrocarbons from a mixture of carbon monoxide and hydrogen, known as syngas. The formation of products is generally believed to proceed through a chain-lengthening process using single-carbon units. This leads to a broad distribution of products Abstract as opposed to a single highly selective product, and the selectivity pattern is often described using the Shulz-Florey-Anderson distribution. Much of the work on FT catalysts is involved in modifications of the catalyst system to produce a tighter distribution of products. In this study a series of investigations have been made into the effects that variations of the preparation method of CoMnOx supported on activated carbon. The basic preparation is an impregnation method, and several changes in catalyst activity and selectivity were observed following changes to this. An investigation into the effects of altering the amount of manganese relative to cobalt in the system also highlighted several trends, leading to a greater understanding of the factors affecting the conversion and selectivity of the catalyst system. A separate are of research in FT-style reactions is the production of alcohols from syngas, typically at higher pressures. As in the previous section, these an attempt was made to improve the activity and selectivity of these catalysts by alterations to the preparation methods, and also by alteration of the amount of secondary metal relative to cobalt. The catalysts used in these investigations consisted of CoMoOx supported on activated carbon. The standard preparation used a coprecipitation method based upon a similar method used for the production of CoMoS2 catalysts, which were also investigated in this study. Later investigations, notably those in which the amount of molybdenum relative to cobalt was altered, were prepared using an impregnation method. A series of improvements to a base catalyst were achieved by alteration to the preparation conditions, but more substantial improvements were observed when the alteration of the metal ratios was investigated. With regards to the use of activated carbon as a support material, it was also observed that it was possible to bring about the reduction of the cobalt species, and to a lesser extent the manganese and molybdenum species, by heating the catalysts to a high temperature in an inert atmosphere, namely helium.
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Sewell, Gary Stanton. "The reductive animation of ethanol using supported metal catalysts". Doctoral thesis, University of Cape Town, 1996. http://hdl.handle.net/11427/18294.
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Includes bibliographical references.Silica supported cobalt, nickel and copper are efficient catalysts for the reductive amination of ethanol using ammonia. High selectivity to ethylamine product was obtained between reaction temperatures of 140 and 200°C, between ammonia to ethanol molar ratios ranging from 1 to 4 and between hydrogen to ethanol molar ratios ranging from 2 to 5. Depending on the partial pressures of the ethanol, ammonia and hydrogen feeds, different ethylamine selectivities were obtained. The degree of amine substitution was decreased (i.e. increasing MEA and decreasing DEA and TEA selectivities) by increasing the ammonia partial pressure or by decreasing either the ethanol or hydrogen partial pressures.
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Reynhardt, Jan Petrus Karel. "Carbonylation catalysts based on metal complexed PAMAM-dendrimers supported on mesoporous and periodic mesoporous silica supports". Thesis, University of Ottawa (Canada), 2005. http://hdl.handle.net/10393/29253.
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This thesis describes the synthesis and characterization of various polyamidoamine (PAMAM) dendrimer moieties supported on amorphous mesoporous and periodic mesoporous silica supports. The surface characteristics of the supports are investigated using various methods and found to be intricately involved in the success of the dendrimer synthesis. The dendrimers are phophinomethylated and complexed with either palladium or rhodium and used as catalysts for carbonylation reactions.
The palladium complexed C6-PAMAM dendrimers supported on aminopropyl silica gel are recyclable catalysts for the hydroesterification of olefins and turnover numbers (TON) of up to 1200 are possible.
C2-PAMAM dendrimers supported on LPMCM-41 and Davisil are complexed with rhodium and used as catalysts for the hydroformylation reaction of olefins. These catalysts show how the pore geometry influences the activity and recyclability of the catalysts. The dendrimer-rhodium complexes supported on LPMCM-41 exhibit very high activity and a TOF of up to 1800 h-1 are observed for the hydroformylaton of 1-octene. These catalysts can be recycled effectively by simple filtration. A negative dendrimer effect is observed with the higher generations exhibiting lower activity than the lower generations. The dendrimer-rhodium complexes supported on Davisil also exhibit very high activity and a TOF of up to 1700 h-1 are observed for the hydroformylation of 1-octene. The activity of these catalysts are less dependent on the generation than the LPMCM-41 dendrimers, and excellent activity is observed up to the third generation for the hydroformylation reaction of 1-octene.
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Zhao, Yanyan. "Dinuclear Heterogeneous Catalysts on Metal Oxide Supports:". Thesis, Boston College, 2020. http://hdl.handle.net/2345/bc-ir:109003.
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Thesis advisor: Dunwei WangAtomically dispersed catalysts refer to substrate-supported heterogeneous catalysts featuring one or a few active metal atoms that are separated from one another. They represent an important class of materials ranging from single atom catalysts (SACs) and nanoparticles (NPs). The study of SACs has brought an attention of understanding the reaction mechanism at the molecular level. SACs is a promising field, however, there are still many challenges and opportunities in developing the next generation of catalysts. Catalysts featuring two atoms with well-defined structures as active sites are poorly studied. It is expected that this class of catalysts will show uniqueness in activity, selectivity, and stability. However, the difficulty in synthesizing such structures has been a critical challenge. I tackled this challenge by using a facile photochemical method to generate active metal centers consisting of two iridium metal atoms bridged by O ligands and bound to a support by stripping the ligands of the organometallic complex. My research also unveiled the structure of this dinuclear heterogeneous catalysts (DHCs) by integrating various characterization resources. Direct evidence unambiguously supporting the dinuclear nature of catalysts anchored on metal oxides is obtained by aberration-corrected scanning transmission electron microscopy. In addition, different binding modes have been achieved on two categories of metal oxides with distinguishable surface oxygen densities and interatomic distances of binding sites. Side-on bound DHCs was demonstrated on iron oxide and ceria where both Ir atoms are affixed to the surface with similar coordination environment. The binding sites on the OH-terminated surface of Fe2O3 and CeO2 anchor the catalysts to provide outstanding stability against detachment, diffusion and aggregation. The competing end-on binding mode, where only one Ir atom is attached to the substrate and the other one is dangling was observed on WO3. Evidence supporting the binding modes was obtained by in situ diffuse reflectance infrared Fourier transform spectroscopy. In addition, the synergistic effect between two adjacent Ir atoms and the uniqueness of different coordinative oxygen atoms around Ir atoms were investigated by a series of operando spectroscopy such as X-ray absorption spectroscopy and microscopy at atomic level under the reaction condition. The resulting catalysts exhibit high activities and stabilities toward H2O photo-oxidation and preferential CO oxidation. Density functional theory calculations provide additional support for atomic structure, binding sites modes on metal oxides, as well as insights into how DHCs may be beneficial for these catalytic reactions. This research has important implications for future studies of highly effective heterogeneous catalysts for complex chemical reactions
Thesis (PhD) — Boston College, 2020
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
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Castro, Cevallos Ursula Isabel. "Phenol oxidation catalysed by polymer-supported metal complexes". Doctoral thesis, Universitat Rovira i Virgili, 2009. http://hdl.handle.net/10803/8577.
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Focussing on the treatment of industrial effluents with high content of organic compounds, the advanced oxidation processes (AOPs) develop technologies such as the catalytic wet peroxide oxidation of organic compounds (CWPO). The improvement of this process is based on the variation either of the catalyst or the oxidant source. The present research work proposes to get advantage of the catalytic activity of homogeneous catalysts, avoiding the metal contamination of the reaction media by the heterogenization of Cu(II) ions over polymeric matrices, to finally use them as catalysts in the CWPO of phenol. From the group of synthesised catalysts, it was identified two suitable catalysts: Cu(II) adsorbed onto poly(4-vinylpyridine) with 2% of cross-linking and Cu(II) loaded in poly (DVB-co-VBC) functionalised with imino diacetic acid. Both catalysts demonstrated high catalytic activity without Cu(II) release, concluding that heterogenization of catalysts for the CWPO is an ascertained decision to promote phenol degradation.Entre los tratamiento de efluentes industriales con alto contenido de material orgánico, se encuentran los procesos de oxidación avanzada (AOPs) que desarrollan tecnologías como la oxidación húmedo catalítica con peroxido de hidrógeno de compuestos orgánicos (CWPO). El mejoramiento de éste proceso está basado en la variación tanto del catalizador como de la fuente oxidante. El presente trabajo de investigación propone aprovechar la actividad catalítica de catalizadores homogéneos, evitando la contaminación por metal del efluente mediante la heterogeneización de iones de Cu(II) sobre matrices poliméricas, para luego ser usados como catalizadores en la CWPO del fenol. Del grupo de catalizadores sintetizados, se identificaron dos catalizadores: Cu(II) adsorbido sobre poly(4-vinylpyridine) con 2% de entrecruzamiento y Cu(II) soportado en poli (DVB-co-VBC) funcionalizado con ácido aminodiacetico. Ambos catalizadores demostraron alta actividad catalítica sin liberación de Cu(II), concluyendo que la heterogeneización de catalizadores homogéneos para la CWPO es una decisión acertada cuando se desea promover la degradación del fenol.
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Niemelä, Marita. "Reactions of synthesis gas on silica supported transition metal catalysts /". Espoo : Technical Research Centre of Finland, 1997. http://www.vtt.fi/inf/pdf/publications/1997/P310.pdf.
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Georgiades, G. C. "A study of cyclohexene reactions on supported characterised metal catalysts". Thesis, Brunel University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233346.
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Rollins, K. "The preparation and characterisation of supported metal chloride oxychlorination catalysts". Thesis, Brunel University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370138.
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Hermans, S. "Mixed-metal clusters as precursors for bimetallic supported nanoparticle catalysts". Thesis, University of Cambridge, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603977.
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This thesis describes in a first part the synthesis of new mixed-metal clusters of ruthenium in association with palladium, platinum and tin. The use of monometallic dichloro complexes of Pd or Pt in reactions with negatively charged penta- or hexaruthenium clusters in the presence of a chlorine scavenger has been moderately successful in the case of Pd, but highly successful in the case of Pt. High yields were obtained in many instances. The mixed clusters [Ru5C(CO)14Pt(COD)], [Ru6C(CO)16Pt(COD)], [Ru6C(CO)15(Pt(COD))2] and [{Ru6C(CO)16}2Pt(MeCN)2] were characterised by X-ray crystallography. On the other hand, the use of [Pt(PPh3)4] allowed the isolation and structure determination of [Ru6C(CO)16PPh3] rather than mixed species. The reactivity of [Ru5C(CO)14Pt(COD)] and [Ru6C(CO)16Pt(COD)] with CO, PPh3 and dppm was investigated, and led to the isolation of other mixed-metal and homometallic compounds. The crystal structures of the clusters [Ru5C(CO)11Pt(CO)(dppm)2], [Ru6C(CO)13(dppm)2] and [Ru6C(CO)16Pt3(dppm)2] were determined. Several Ru-Sn mixed clusters were also synthesised, and in particular reactions involving [PPN]2[Ru6C(CO)16] and SnCl4 led to the isolation of [PPN][Ru6C(CO)16SnCl3] and [Ru6C(CO)16SnCl2], which were characterised crystallographically. In a second part, some of the new mixed-metal clusters were used as precursors for nanoparticle heterogeneous catalysts, using the mesoporous silica MCM-41 or carbon nanotubes as supports. A Ru-Pd/MCM-41 catalyst derived from a Pd6Ru6 cluster was shown to be extremely active for the hydrogenation of alkenes to alkanes and of naphthalene to cis-decalin selectively. This material was characterised by STEM and in situ FTIR and EXAFS, which confirmed the bimetallic nature of the nanoparticles and their homogeneous small sizes and dispersion on the support. The shape of the nanoparticles was further assessed by theoretical calculations. A Ru-Sn/MCM-41 catalyst was prepared from [PPN][Ru6C(CO)16SnCl3] and shown to hydrogenate selectively cyclic poly-enes to their mono-enes, under solvent-free and low temperature conditions. This catalyst was also characterised by STEM and in situ FTIR and EXAFS, which indicated that the tin atom is the anchoring point for the bimetallic nanoparticles on the siliceous walls of MCM-41. Finally, the clusters [Ru5C(CO)14Pt(COD)], [Ru6C(CO)16Pt(COD)], [PPN][Ru6C(CO)16SnCl3] and [Ru6C(CO)16SnCl2] were used as ideal precursors for small-sized and evenly dispersed bimetallic nanoparticles supported on carbon nanotubes.
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Kennedy, Mark James. "Catalytic combustion of benzene vapour using carbon supported metal catalysts". Thesis, University of Newcastle Upon Tyne, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.436172.
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