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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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Jungius, Hugo. "Model inverse electro-catalyst investigations of metal support interactions." Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/413849/.
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Gold supported titania nano-particle surfaces have been synthesised in order to understand supported electrochemical mechanisms through an inverse catalyst. The catalyst process investigated was the electro-oxidation of CO which is known to be promoted on Au nano-particles on a titania support. Synthesis proceeded via physical vapour deposition (PVD) of titanium onto a gold surface (both polycrystalline and 111 crystal), followed by alloying and oxidation to form discrete particles of titania on the surface, with variations in density of particles achieved by control of the initial titanium coverages. Scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) measurements indicate these particles develop with consistent triangular and hexagonal shapes, with average diameters of 11.5 and 20 nm observed depending on alloying temperature. The procession of titanium deposition on the gold surface and subsequent alloy formation was followed by X-ray photoelectron spectroscopy (XPS) measurements, with the formation of pure TiO2 revealed once synthesis was complete, with minimal modification to the final electronic state of the underlying gold. Electrochemical testing in an acidic environment provides evidence for alteration of the electrooxidation of CO on these modified gold surfaces. A deactivation of the CO oxidation is observed with initial addition of titania, explained by the blocking of CO adsorption on the surface. This is followed by significant subsequent increases in activity with increasing densities of titania particles, with decreasing over-potential and increasing current density observed as the titania coverage increases. This observed effect on CO oxidation activity with titania coverage in the inverse system provides significant evidence for the action of either reactant spill-over or Ti-Au interface sites as being responsible for the changes in activity observed for titania modified gold systems, whether in the inverse or standard form.
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Mogorosi, Ramoshibidu Patrick. "Metal-support interactions on Fe-based Fischer-Tropsch catalysts." Doctoral thesis, University of Cape Town, 2012. http://hdl.handle.net/11427/5438.
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Includes abstract.<br>Includes bibliographical references.<br>‘Metal support interactions’ is a term used to describe a phenomenon whereby the interaction between the active metal and the support material is strong enough to affect the catalytic activity and selectivity of the active phase. Primarily, there are two theories described in literature to explain the manner in which the development of these interactions alters catalytic behavior in supported catalysts. The first theory is ‘the contact affect’, which is generally associated with partially reducible supports such as TiO2 [Tauster et al., 1978]. It is believed that the intimate contact between the partially reduced surface of the support and the surface of the active phase results in the creation of special contact sites at the interface. These sites are thought to be responsible for the improved activity observed in TiO2 supported catalysts [Burch and Flambard, 1982; Vannice and Sudhakar, 1984; Tauster, 1987]. The second theory is ‘the ligand effect’. With this hypothesis, it is proposed that the development of chemical bonds at the interface between the active metal and the support material is responsible for the altered catalytic behavior in supported catalysts [Qing et al., 2011; Sou et al., 2012]. The presence of these bonds is believed to alter the strength of CO and H2 absorption on the surface of the active phase, resulting in different activity and selectivity. These chemical bonds might be viewed as ligand attachments [Haller and Resasco, 1989], holding the active metal in place. The ligand effect is commonly associated with irreducible support material such as silica [Hou et al., 2008; Sou et al., 2012] and alumina [Taniguchi, et al., 1988; Wan et al., 2007]. The aim of this study was to investigate metal support interactions as a ligand effect. The objective was to prepare model catalysts and modify the surface of the iron oxide using alkoxide compounds, viz. tetra ethoxy-silane (TEOS) and titanium butoxide (TBO), to generate the Fe-O-Si and Fe-O-Ti interactions respectively in a controlled and varying manner in order to investigate how these interactions affect the behaviour of the catalysts. The presence of both the surface silicate and surface titanate groups in the calcined catalyst precursor was confirmed using DRIFTS. Characterization of the calcined samples, containing Fe2O3, showed an overall decrease in the average crystallite size with increasing alkoxide loading (for both TEOS and TBO). However, this effect was more severe for the TEOS modified samples.
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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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DEMRI, HARIK OJAMILA, and J. P. HINDERMANN. "Etude des interactions metal-support et metal-promoteur sur des catalyseurs a base de rhodium." Université Louis Pasteur (Strasbourg) (1971-2008), 1992. http://www.theses.fr/1992STR13101.
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Le but du present travail est l'etude des interactions metal-support et metal-promoteur (th, zr, ce, y, na. . . ) dans la reaction co+h#2 sur des catalyseurs au rhodium. L'utilisation combinee de differentes methodes (adsorption, microscopie electronique a transmission (met)), spectroscopie infra-rouge a transformee de fourier (ir-tf), thermodesorption programmee (tpd) et thermoreaction programmee (tpsr) a permis de tirer les conclusions suivantes: la difference de taille des particules metalliques observee par les methodes d'adsorption et par la microscopie electronique montrent qu'une partie du promoteur est situee sur les cristallites metalliques. Les faces (100) semblent preferentiellement recouvertes (ir-tf); les differences d'activite et de selectivite ne sont pas dues a des variations de tailles de particules; un nouveau mode d'adsorption de co coordine par le carbone au metal et par l'oxygene au support est confirme avec la plupart des promoteurs; la probabilite de dissociation est accrue en presence de promoteurs (tpd); la thermoreaction programmee de co adsorbe avec l'hydrogene suggere que deux mecanismes de formation de methane sont possibles: l'un par dissociation de co, l'autre par hydrogenation partielle de co avec rupture de la liaison c-o; l'intermediaire acyle dans la synthese de l'ethanol est stabilise et mis en evidence (tpd, ir-tf)
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Macheli, Lebohang. "Inverse model systems to investigate metal-support interactions in Fischer-Tropsch catalysis." Doctoral thesis, Faculty of Engineering and the Built Environment, 2019. http://hdl.handle.net/11427/30921.
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This thesis aims to gain insight into the effects of metal-support interaction in Co/SiO2 catalysts using an inverse model system by modifying Co3O4 nanocrystallites with silanes (i.e. tetraethoxysilane, trimethyl chlorosilane, triphenyl ethoxysilane). It is postulated that the formation of Co-O-Si will alter the catalytic properties of the cobalt site to which silane is bonded and the adjacent ligand-free sites. The desire is to understand the effects of metal support interactions obtained after reduction of the model system on its performance in FischerTropsch synthesis, which was used as a test reaction, taking into account the change in the reducibility and metal surface area. Cobalt oxide was synthesize using sodium dodecylsulphate assisted oxidative precipitation or cobalt carbonyl decomposition and was contacted with the respective silanes in different solvents. The presence of silanes on the surface of cobalt oxide both prior and after reduction was confirmed using infrared spectroscopy. Modification of cobalt oxide with the silanes does not affect the morphology of cobalt oxide nano-crystallite and may have formed silicate islands on the surface of cobalt oxide. The presence of the silane retards the reduction process by changing the activation energy required for the reduction process. The presence of this material on the surface of cobalt decrease the surface area. However, the catalytic activity increased drastically. The interaction of Co3O4 with tetraethoxysilane was manipulated by using different solvents (mixtures) (i.e. anhydrous environment vs acid/base hydrolysing environment). For the modification in anhydrous environment, the formation of silica on the surface of Co3O4 is facilitated by heat treatment. However, in hydrous environment, the formation of silica on the surface of Co3O4 is initiated by the hydrolysis of tetraethoxysilane. The effects of modification using different solvent was tested in the Fischer-Tropsch synthesis. The modification under acid catalysed hydrolysis facilitate the formation of Co-O-Si contact points followed by increase catalytic activity compared to catalysts modified in other solvents. An insight about the effects of calcination on the interaction of silica and cobalt was obtained by calcining a modified sample at different temperatures. Low temperature (573 K) calcination facilitate stronger interactions. The interaction becomes weaker in increasing temperature up to 873 K. Calcination at temperature from 973 K-1173 K result in very strong interaction that leads to the formation of Co2SiO4. To further obtain an enlightenment regarding the electronic effects caused by the modification of cobalt oxide with silane, silanes of different electronic behaviour were used. In addition to electron withdrawing tetraethoxysilane, electron donor silane (triphenyl ethoxysilane and trimethyl chlorosilane) were used to modify the surface of cobalt oxide. While the activity was increased, the product selectivity was altered differently by the different silanes used.
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Traversaz, Olivier. "Etude des interactions relatives metal-metal et metal-support mises en jeu lors de la preparation de catalyseurs bimetalliques supportes." Paris 6, 1992. http://www.theses.fr/1992PA066621.
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Ce travail a porte sur la preparation de catalyseurs bimetalliques supportes par depot selectif, en solution aqueuse, d'un deuxieme metal present sous forme de sel, sur un premier metal supporte. Les parametres (nature et composition du milieu d'impregnation, ph. . . ) regissant le depot, sur le support d'une part et sur le premier metal d'autre part, ont ete etudies. Les resultats nous ont permis de preparer des catalyseurs palladium-cuivre et platine-cuivre deposes sur des billes d'alumine, en operant en deux etapes : - penetration du cuivre au coeur du grain au moyen d'un agent complexant (acide citrique). - declenchement de l'interaction metal-metal au moyen d'un agent reducteur (acide formique). La realisation de l'interaction metal-metal a ete verifiee en utilisant des methodes de caracterisation telles que : reduction en temperature programmee, infra-rouge du monoxyde de carbone, et microscopie electronique. Les catalyseurs palladium-cuivre ont ete testes en reacteur discontinu lors de l'hydrogenation selective du butadiene et du butyne. L'effet bimetallique se traduit par une promotion de l'activite pour de faibles teneurs en deuxieme metal
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Dyasi, Nontsikelelo. "Model systems for the investigation of metal-support interactions in cobalt based Fischer-Tropsch." Master's thesis, Faculty of Engineering and the Built Environment, 2021. http://hdl.handle.net/11427/33639.
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The catalyst used plays a pivotal role in the optimization of the Fischer Tropsch (FT) synthesis. Cobalt (Co)-based catalysts have been widely used in low temperature Fischer Tropsch synthesis for the production of longer chain olefins [1]. The interaction between the support and the active metal, Co, has been observed to affect the activity and selectivity of the FT synthesis [2]. In order to investigate metal support interactions independent of other support effects, the inverse method was used in the synthesis of model catalysts [3]. The inverse method mimics the interface bond between the support and the active metal, resulting in CoO-Si bond formation. By exposing Co nanoparticles (NPs) to a dilute solution of an alkoxide, tetraethyl orthosilicate (TEOS) or triphnyl ethoxy silane (TPEOS), Co-O-Si bond (ligand) is expected to form until it reaches equilibrium state. The concentration of the dilute alkoxide solution can be varied to observe its effect on the surface coverage of the Co NPs with the alkoxide. XRD analysis of the modified cobalt nanoparticles showed that there was no evidence of the formation of a crystalline silica phase as those characteristic diffraction lines were absent. The TPR profiles showed a shift to higher reduction temperatures with increasing silica loading suggesting that the surface modification results in retardation of reduction of the cobalt nanoparticles. CO-TPD studies of the model catalyst indicated that the total number of active sites available for CO adsorption and bond cleavage decreases upon surface modification, but it leads to a more facile CO bond cleavage as evidenced by decrease in energy of dissociation. The activity of these materials in the Fischer Tropsch synthesis decreased with increasing silicon content for the oxidized cobalt nanoparticles. This was attributed to the decline in the total number of active site available for CO bond cleavage with increasing silicon content. The methane selectivity passes a minimum with increasing silicon content. This may be related to the carbon coverage on the surface of the nanoparticles affecting the chain growth. It is recommended that Fischer Tropsch synthesis studies be conducted on the modified as-synthesized cobalt nanoparticles to compare the performance of the two catalysts.
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Neumann, Sarah [Verfasser], Sebastian [Akademischer Betreuer] Kunz, Sebastian [Gutachter] Kunz, and Marcus [Gutachter] Bäumer. "Heterogeneous Catalysis with supported Nanoparticles : Particle Size Effects and Metal-Support Interactions / Sarah Neumann ; Gutachter: Sebastian Kunz, Marcus Bäumer ; Betreuer: Sebastian Kunz." Bremen : Staats- und Universitätsbibliothek Bremen, 2019. http://d-nb.info/1203298927/34.
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Spence, Stephanie L. "Tuning the Morphology and Electronic Properties of Single-Crystal LiNi0.5Mn1.5O4-δ". Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/100790.
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The commercialization of lithium-ion batteries has played a pivotal role in the development of consumer electronics and electric vehicles. In recent years, much research has focused on the development and modification of the active materials of electrodes to obtain higher energies for a broader range of applications. High voltage spinel materials including LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4-δ</sub> (LNMO) have been considered as promising cathode materials to address the increasing demands for improved battery performance due to their high operating potential, high energy density, and stable cycling lifetimes. In an effort to elucidate fundamental structure-property relationships, this thesis explores the tunable properties of single-crystal LNMO. Utilizing facile molten salt synthesis methods, the structural and electronic properties of LNMO can be well controlled. Chapter 2 of this thesis focuses on uncovering the effect of molten salt synthesis parameters including molten salt composition and synthetic temperature on the materials properties. A range of imaging, microscopic, and spectroscopic techniques are used to characterize structural and electronic properties which are investigated in tandem with electrochemical performance. Results indicate the Mn oxidation state is highly dependent on synthesis temperature and can dictate performance, while the molten salt composition strongly influences the particle morphology. In Chapter 3, we explore the concept of utilizing LNMO as a tunable support for heterogeneous metal nanocatalysts, where alteration of the support structure and electronics can have an influence on catalytic properties due to unique support effects. Ultimately, this work illustrates the tunable nature of single-crystal LNMO and can inform the rational design of LNMO materials for energy applications.<br>M.S.<br>The development of lithium-ion batteries has been fundamental to the expansion and prevalence of consumer electronics and electric vehicles in the twenty-first century. Despite their ubiquity, there is an ongoing drive by researchers to address the limitations and improve the quality and performance of lithium ion batteries. Much research has focused on altering the composition, structure, or properties of electrodes at the materials level to design higher achieving batteries. A fundamental understanding of how composition and structure effect battery performance is necessary to progress toward better materials. This thesis focuses on investigating the properties of LiNi<sub>0.5</sub>Mn<sub>1.5</sub>O<sub>4-δ</sub> (LNMO). LNMO material is considered a promising cathode material to meet the increasing consumer demands for improved battery performance. Through the synthesis methods, the shape of individual particles and the global electronic properties of LNMO can be tuned. In this work, specific synthesis parameters are systematically tuned and the properties of the resultant LNMO materials are explored. Electrochemical testing also evaluates the performance of the materials and offers insights into how they may fair in real battery systems. In an effort to potentially recycle spent battery materials, LNMO is also utilized as a catalyst support. Alteration of shape and electronic properties of the LNMO support can influence the catalytic properties, or the ability of the material to enhance the rate of a chemical reaction. Overall, this thesis explores how LNMO can be tuned and utilized for different applications. This work provides insights for understanding LNMO properties and direction for the development of future battery materials.
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Kähler, Kevin [Verfasser], Martin [Gutachter] Muhler, and Wolfgang [Gutachter] Grünert. "On the role of metal-support interactions in methanol synthesis and oxidation / Kevin Kähler ; Gutachter: Martin Muhler, Wolfgang Grünert ; Fakultät für Chemie und Biochemie." Bochum : Ruhr-Universität Bochum, 2010. http://d-nb.info/1226426336/34.
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Steib, Matthias [Verfasser], Johannes A. [Akademischer Betreuer] Lercher, Johannes A. [Gutachter] Lercher, and Harald [Gutachter] Klein. "Dry Reforming of Methane – understanding metal support interactions and evaluation of regeneration protocols / Matthias Steib ; Gutachter: Johannes A. Lercher, Harald Klein ; Betreuer: Johannes A. Lercher." München : Universitätsbibliothek der TU München, 2018. http://d-nb.info/1153882582/34.
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Warczinski, Lisa [Verfasser], Christof [Gutachter] Hättig, Robert [Gutachter] Franke, and Reinhold [Gutachter] Fink. "Computational study of metal-support interactions for carbon-supported palladium nanoparticles / Lisa Warczinski ; Gutachter: Christof Hättig, Robert Franke, Reinhold Fink ; Fakultät für Chemie und Biochemie." Bochum : Ruhr-Universität Bochum, 2021. http://d-nb.info/1233484141/34.
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Steib, Matthias Verfasser], Johannes [Akademischer Betreuer] [Lercher, Johannes A. [Gutachter] Lercher, and Harald [Gutachter] Klein. "Dry Reforming of Methane – understanding metal support interactions and evaluation of regeneration protocols / Matthias Steib ; Gutachter: Johannes A. Lercher, Harald Klein ; Betreuer: Johannes A. Lercher." München : Universitätsbibliothek der TU München, 2018. http://d-nb.info/1153882582/34.
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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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Garcia, de Castro Insua Ricardo Antonio. "Catalyseurs d’hydrotraitement modèles à base du Mo et supportés sur α-Al2O3 : étude sur l’incorporation du cobalt, phosphore et triéthylène glycol par une approche de science de surfaces". Electronic Thesis or Diss., Sorbonne université, 2020. http://www.theses.fr/2020SORUS145.
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La genèse de la phase active dans les catalyseurs d’hydrotraitement est influencée par la nature du support. Néanmoins, une description à l’échelle moléculaire des interactions métal-support est encore balbutiante dû aux sites de sorption mal définis du support industriel γ-Al2O3. Une approche de science des surfaces en phase aqueuse a contourné cette limitation en utilisant des monocristaux de α-Al2O3 selon 4 orientations : C(0001), A(112 ̅0), M(101 ̅0), et R(11 ̅02) pour étudier la genèse de MoS2 en contrôlant la spéciation des sites de surface. Cette approche a montré que des propriétés de MoS2 sont contrôlées par les interactions Mo-support qui sont à la fois déterminées par le type de OH de surface. Ce travail vise à se rapprocher aux catalyseurs industriels en intégrant du cobalt, du phosphore, et du TEG. Des techniques de caractérisation de surface ont été utilisées pour étudier cette dépendance. Il est montré que le phosphore interagit de manières diverses selon le support, ce qui conduit à un effet sur la sulfuration. Au contraire, la promotion de MoS2 par le Co ne dépend que de la sulfuration du Mo. Enfin, il est montré que l’absence de l’étape de calcination et l’ajout de TEG diminue les interactions métal-support, menant à des taux de sulfuration plus élevés. L’activité catalytique des catalyseurs promus a été étudiée en hydrodésulfuration du thiophène. Elle est plus importante chez les catalyseurs supportés sur la face A(112 ̅0), ce qui suggère que les interactions métal-support intermédiaires mènent à des activités plus élevées. Ces résultats peuvent donner lieu à la synthèse de catalyseurs plus efficaces au travers du contrôle de la morphologie du support<br>The genesis of the active phase in hydrotreating catalysts is deeply influenced by the nature of the support. However, a fine description of active phase-support interactions at the molecular level is still missing since the traditional support γ-Al2O3 exhibits ill-defined sorption sites. A surface-science approach in aqueous phase circumvented this limitation by using α-Al2O3 single crystals with four different orientations: C(0001), A(112 ̅0), M(101 ̅0), and R(11 ̅02) as surrogates to study the genesis of MoS2 exerting control over surface sites. Such approach revealed that properties of MoS2 were dictated by Mo-support interactions which are, in turn, determined by the nature of surface -OH. The present work aims to take a step further in closing the gap between model and industrial catalysts by incorporating cobalt, phosphorus and TEG in model catalyst formulation. Surface-sensitive techniques are used to expose such dependencies. It is shown that phosphorus interacts differently depending on support orientation, leading to a surface-dependent sulfidation. Conversely, it is shown that cobalt promotion of MoS2 is exclusively dependent on Mo sulfidation. At last, it is shown how omitting calcination and TEG incorporation reduces metal-support interactions leading to higher sulfidation. The catalytic activity of promoted catalysts is studied through a thiophene hydrodesulfurization reaction revealing that A(112 ̅0)-based catalysts display the highest activity. In that sense, intermediate metal-support interactions are key to achieve higher catalytic performance. These results could lead to a new generation of hydrotreating catalysts through control of support morphology
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PENGUILLY, VANESSA DE. "Etude de catalyseurs bimetalliques pt - w supportes sur alumine : vers un suivi moleculaire des interactions metal / support au cours des etapes de la preparation d'un catalyseur a 3 composantes." Paris 6, 1998. http://www.theses.fr/1998PA066587.
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Pour ameliorer les performances du catalyseur classique de reformage pt / al 2o 3-cl, les recherches actuelles s'orientent vers la comprehension exacte des modifications induites sur le platine par l'ajout d'un deuxieme voire d'un troisieme metal. L'etude du systeme pt / alumine modifiee par un depot de tungstene entre dans la lignee de ces etudes. Afin de comprendre et de rationaliser comment le depot initial de tungstates a la surface de l'alumine peut modifier le comportement catalytique du platine metallique, les etapes successives de la preparation d'un catalyseur (impregnation w puis pt, sechage, calcination, reduction) ont ete etudiees en caracterisant le systeme aux niveaux macroscopique et moleculaire par plusieurs techniques comme la spectroscopie uv-visible, la rmn du 1 9 5pt, les reactions en temperature programmee, l'adsorption de co suivie par ir, la microscopie electronique, les titrages h 2-o 2. Le suivi des interactions pt - w - al 2o 3 a permis de montrer que le systeme garde la memoire des conditions initiales de preparation. La structure du tungstate utilise est un parametre aussi important a maitriser que la quantite deposee puisqu'elle determine le mode d'interaction w-surface et controle la mobilite des especes de surface (w et pt) et, par la, notamment la possibilite du recouvrement des particules de platine metallique (effet smsi du w vers le pt). De plus, le tungstene modifie la taille finale des particules de pt soit par une competition directe entre les sites de greffage des deux metaux, soit par une diminution du nombre de platine greffe. Enfin, lors de l'etude des proprietes d'hydrogenation de ces catalyseurs, des proprietes isomerisantes particulieres ont ete mises en avant par rapport au catalyseur monometallique. Elles permettraient, a basse temperature, d'hydrogener les noyaux aromatiques et d'effectuer les premieres etapes de l'isomerisation pour obtenir des carburants qui repondraient aux nouvelles normes anti-pollution.
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Gallais, Patrick. "Dépôt de couches minces de tantale par pulvérisation et étude des interactions TA/SIO :(2) et TA/SI à basses températures." Angers, 1987. http://www.theses.fr/1987ANGE0013.
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Analyse par spectrométrie Auger des couches déposées par pulvérisation cathodique sur des substrats de silicium ou d'oxyde de silicium pour des températures comprises entre 50 et 500c. Certains échantillons sont élaborés en bombardant la couche durant sa formation à l'aide d'ions argon du plasma. Etude de la nature chimique des interactions entre TA et SI ou SIO::(2).
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Holz, Marie Christine [Verfasser], Martin [Gutachter] Muhler, and Wolfgang [Gutachter] Grünert. "Spectroscopic and kinetic investigations of the oxidation of short-chain alcohols over supported Au catalysts to probe metal-support interactions / Marie Christine Holz ; Gutachter: Martin Muhler, Wolfgang Grünert ; Fakultät für Chemie und Biochemie." Bochum : Ruhr-Universität Bochum, 2013. http://d-nb.info/1223172090/34.
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Carrette, Linda Petra Lea. "Characterisation of the strong metal-support interaction (SMSI) in electrocatalysis." Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.286753.
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Dole, Holly. "Connecting Metal-Support Interaction and Electrochemical Promotion Phenomena for Nano-structured Catalysts." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/34610.
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Air pollutants can cause poor air quality; however, the use of heterogeneous catalytic oxidation has been shown to be an efficient and cost-effective removal method. Some examples of commercial application of such catalysts include catalytic convertors in automobiles and industrial process exhausts. Research with regards to improving these technologies has included using less-expensive catalyst materials, increasing catalytic performance, and achieving higher efficiency.
The concept of metal-support interaction (MSI) is one method of altering catalytic performance through changing the properties of the metal catalyst due to the interaction with the support material. Similarly, the phenomenon of electrochemical promotion of catalysis (EPOC) has also been shown to enhance the catalytic activity, however, through the application of a small electrical stimulus to a catalyst-working electrode deposited on a solid electrolyte (e.g. yttria-stablized zirconia). The properties of the metal catalyst are altered due to the movement of ions (in this case, O2-) from the electrolyte. Since its discovery, several factors were identified that are preventing EPOC from being commercialized, including the use of thick film catalysts. Implementing nano-catalysts makes this method competitive with typical heterogeneous catalysts; however, it has not been studied by many research groups. Furthermore, many heterogeneous catalytic studies have been performed separately for each of these phenomena; however, a connection between EPOC and MSI has yet to be fully understood.
The overall objective of this project is to study the concept of EPOC over highly-dispersed nano-catalysts and determine how MSI relates to the change in catalytic activity. Supported nano-catalysts were synthesized, characterized, and evaluated for catalytic performance using model reactions. A reactor was designed to carry out the electrochemical studies, where the EPOC concept was successfully implemented and a relationship with MSI established. Furthermore, additional studies were conducted to determine the role of the O2- in the catalyst support and its relationship to MSI.
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Hajar, Yasmine. "Effect of Electrochemical Promotion and Metal-Support Interaction on Catalytic Performance of Nano-catalysts." Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/39701.
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In heterogeneous catalysis, promoting the activity of the catalytic metals is long known as an important method to make a process more efficient and viable. Noble metals have been promoted classically by a chemical coverage of an ionic solution on the surface of the catalyst or using inert support, e.g., silica or alumina, allowing an increase of the dispersion of the catalyst. Therefore, new methods of promotion needed to be better explored to improve the efficiency of metal and metal oxide catalysts. One way of enhancing the catalyst’s activity is to disperse the noble metal at the nanoscale using an active type of support that is ion-conducting. Not only lattice ions can be exchanged with the surface of the nanoparticles but it can also engage in the oxidation reaction on the surface, resulting in what is known as metal-support interaction (MSI). Another method of improving the catalytic activity is to polarize the catalyst, allowing ions to migrate from a solid electrolyte to the gas-exposed surface, in a phenomenon known as electrochemical promotion of catalysis (EPOC). The change in the ions concentration on the surface would change the adsorption energy of the gaseous reactants and enhance or supress the catalytic rate.
In this thesis, the effect of supporting nanoparticles of noble and non-noble metal (oxides) (Pt, Ru, Ir, Ni) was studied for the case of ionic and ionic-electronic conducting supports (CeO2, TiO2, YSZ). The enhancement in their catalytic rate was found and correlated to an electrochemical property, the exchange current density. Then, using isotopically-labeled oxygen, the oxygen exchange ability of the conductive oxides was evaluated when supporting Ir and Ru nanoparticles and correlated with the results from C3H8 isotopic oxidation reaction, which showed the extent of involvement of oxygen from the support as carried by the isotopically-labeled CO2 produced.
Following this, electrochemical promotion of catalysis experiments were performed for different reactant/catalyst systems (C2H4 - Pt, Ru; C3H8 - Pt; CH4 - Pd, Ni9Pd). In the first system, the main outcome was the functional equivalence found for the MSI and EPOC effect in promoting the catalysts as experiments were performed at different temperatures, reactants partial pressures and polarization values. In the case of C3H8/Pt, the novel dispersion of Pt on an intermediate supporting layer (LSM/GDC) was found as a feasible method to obtain long stability of the catalyst while electrochemically promoting the rate of reaction. For CH4 oxidation, the polarization of the Pd nanoparticles showed continuous oxidation of the bulk of the catalyst resulting in a continuous increase of the catalytic rate. The Ni9Pd synthesized in a way to form a core/double-shell layer of Ni/Pd resulted in an enhanced catalytic rate and enhanced stability compared to stand-alone Pd.
And lastly, to comprehend the ions’ effect in the electrochemical promotion and the non-Faradaic nature of the phenomena, density-functional theory (DFT) modeling was used to demonstrate the increase of the heat of adsorption of reactants depending on their electronegative/positive nature.
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Bertella, Francine. "Structural, promotion and metal-support interaction effects in Co/TiO2 catalysts for Fischer-Tropsch synthesis." Doctoral thesis, Universitat Politècnica de València, 2018. http://hdl.handle.net/10251/107952.
Full textAbstract:
La presente tesis doctoral está centrada en la investigación de los parámetros estructurales que determinan las propiedades catalíticas en la síntesis de Fischer-Tropsch (SFT) de catalizadores de cobalto soportados en TiO2. Por un lado, el estudio de la influencia del polimorfo de óxido de titanio (rutilo vs. anatasa) utilizado como soporte en catalizadores de Co promovidos con Ru ha permitido obtener correlaciones entre la estructura cristalina del soporte, la extensión del efecto SMSI (interacción fuerte metal-soporte) y los resultados catalíticos. Por otro lado, mediante la modificación de las propiedades texturales del soporte TiO2-anatasa con el objetivo de obtener catalizadores con baja, media y alta área superficial se ha podido avanzar en el conocimiento del efecto SMSI y su correlación con las propiedades texturales del soporte. Además, las consecuencias del aumento en área superficial del soporte en la actividad y selectividad de catalizadores CoRu/TiO2 para la SFT se han podido explicar en base a las relaciones establecidas entre estructura y efecto SMSI. Adicionalmente, el uso de técnicas de luz sincrotrón junto con caracterización espectroscópica in situ realizada a presiones superiores a la atmosférica, ha permitido explicar el papel de la adición y concentración de Ru como promotor en catalizadores CoRu/TiO2. Finalmente, se han estudiado tratamientos de reducción-oxidación-reducción (ROR) en catalizadores CoRu/TiO2 con el objetivo de mejorar su actividad catalítica.
Como conclusión general, los conocimientos derivados de los resultados obtenidos en esta tesis doctoral pueden aportar estrategias adecuadas para el diseño de catalizadores de FT mejorados basados en Co empleando TiO2 como soporte.<br>The present doctoral thesis focused on the investigation of the structural parameters that can determine the ultimate catalytic properties for Fischer-Tropsch synthesis (FTS) of TiO2-supported cobalt catalysts. On the one hand, the study of the influence of the titania polymorph (rutile vs. anatase) as support for Ru-promoted Co and Ru nanoparticles (NPs) has allowed to identify some correlations between the TiO2 crystalline phase, the SMSI (strong metal-support interaction) effect, and the catalytic performance for FTS of the catalysts. On the other hand, by preparing CoRu catalysts supported on TiO2-anatase with low, medium, and high surface area, further insights into the SMSI effect and its dependence on the textural properties of the TiO2-anatase support have been gained. Besides, the consequences of increasing the surface area of the support on the activity and selectivity of the catalysts for FTS have been explained based on the established structure-SMSI relationships. Moreover, a detailed study involving the use of in situ synchrotron-based spectroscopic characterizations at pressures higher than the ambient pressure usually applied in most previous works, has been carried out aiming at explaining the role of Ru addition and concentration as promoter in Co/TiO2 catalysts. Finally, reduction-oxidation-reduction (ROR) treatments have been applied on CoRu/TiO2 catalysts to revert the SMSI effect as a feasible strategy to enhance their catalytic activity.
Overall, the results reported in this thesis provide grounds for designing TiO2-supported Co catalysts with improved activity and selectivity for FTS.<br>La present tesi doctoral està centrada en la investigació dels paràmetres estructurals que poden tenir influència en les propietats catalítiques dels catalitzadors que s'han aplicat a la reacció de síntesi de Fischer-Tropsch (SFT). S'ha estudiat la influència del polimorf de titani (rutil o anatasa) utilitzat com a suport de nanopartícules (NPs) de Co i Ru, observant correlacions entre l'estructura cristal·lina del suport, l'efecte SMSI (forta interacció metall-suport) i els resultats catalítics. D'altra banda, es va fer un estudi modificant les propietats texturals de la anatasa amb l'objectiu d'obtenir catalitzadors amb diferent àrea superficial, i s'ha pogut establir un coneixement més profund de l'efecte SMSI i la seua correlació amb les propietats texturals del suport. A més, la influència de l'augment de l'àrea superficial del suport per a la reacció de SFT, en termes d'activitat i selectivitat, han sigut explicats d'acord a les relacions establides entre l'estructura i l'efecte SMSI. Addicionalment, fent ús de tècniques de llum sincrotró juntament amb caracterització in situ realitzada a altes pressions, ha sigut possible explicar el paper de l'addició i concentració de Ru com a promotor en catalitzadors CoRu/TiO2. Finalment, s'han estudiat els tractaments de reducció-oxidació-reducció (ROR) en catalitzadors CoRu/TiO2 amb l'objectiu de millorar la seua activitat catalítica. En resum, els coneixements derivats dels resultats obtinguts en esta tesi doctoral permeten establir estratègies per al disseny de catalitzadors millorats per a la síntesi de FT basats en cobalt utilitzant TiO2 com a suport.<br>Bertella, F. (2018). Structural, promotion and metal-support interaction effects in Co/TiO2 catalysts for Fischer-Tropsch synthesis [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/107952<br>TESIS
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NERY, MONICA PIRES. "THE STUDY OF METAL-SUPPORT INTERACTION ON BARIUM AND CESIUM PROMOTED RUTHENIUM CATALYSTS FOR THE AMMONIA SYNTHESIS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2004. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=6629@1.
Full textAbstract:
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO<br>O processo industrial para a síntese de amônia utiliza um
catalisador de
ferro triplamente promovido, operando em condições
drásticas a temperaturas
entre 400 e 700°C e a uma pressão bastante elevada
(aproximadamente 300
atm). Novos
catalisadores vêm sendo estudados, em substituição ao
ferro, para aumentar ainda
mais a produção de NH3. A principal vantagem dos
catalisadores a base de rutênio
é que eles são menos sensíveis à contaminação pela amônia
que os catalisadores a
base de ferro. O objetivo deste trabalho foi avaliar
catalisadores de rutênio
suportados em zeólitas e hidrotalcita promovidos por
cátions básicos para a
síntese de amônia. Foi verificada a influência do tipo de
suporte nos catalisadores
de rutênio, do tipo e forma de introdução dos precursores
de rutênio, o papel da
adição de cátions promotores (Ba e Cs) sobre a interação
metal-suporte e na
atividade dos catalisadores de rutênio na reação de
síntese de amônia. Os
catalisadores de rutênio suportados na hidrotalcita
apresentaram as maiores
conversões na reação de síntese de amônia. Eles
apresentaram os mais altos níveis
de dispersão e redução das partículas metálicas. O bário,
apesar de ter diminuído
menos a interação do rutênio com o suporte, se mostrou um
promotor mais efetivo
na reação de síntese de amônia que o césio. A ordem de
introdução do bário
apresentou efeitos diferentes, dependendo do suporte,
sobre o desempenho dos
catalisadores de rutênio. O método de impregnação com
carbonila de rutênio se
mostrou o mais efetivo, conduzindo a catalisadores de
rutênio mais básicos e mais
ativos na reação de síntese de amônia.<br>The industrial ammonia synthesis process uses a triple
promoted iron catalyst,
operating at drastic temperature conditions between 673K
and 973K, and high
pressure (300atm). New catalysts have been studied,
replacing iron, to increase
NH3 production. The main advantage of Ru-based catalysts
is that they are less
sensitive to poisoning by ammonia than Fe-based catalysts.
The aim of this work
was to evaluate ruthenium catalysts supported on zeolites
and hydrotalcite
promoted by basic cations for ammonia synthesis reaction.
The influence of the
support type on the ruthenium catalysts and of
introduction way of the ruthenium
precursors was verified. Also the hole of the cationic
promoters (Ba and Cs) on
the metal-support interaction and on the ruthenium
catalysts activity in the
ammonia synthesis reaction was examined. The ruthenium
catalysts supported on
hydrotalcite had the highest conversion in the ammonia
synthesis reaction. They
presented the highest degrees of dispersion and reduction
of metallic particles.
The barium, despite having decreased the interaction
between the ruthenium and
the support, showed to be a more effective promoter on the
synthesis of ammonia
than the cesium. The barium introduction order resulted in
different effects over
the ruthenium catalysts performance depending on the
support. The impregnation
method with ruthenium carbonil was the most effective,
leading to more basic
ruthenium catalysts and more actives in the ammonia
synthesis reaction.
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Panaritis, Christopher. "Metal-Support Interaction and Electrochemical Promotion of Nano-Structured Catalysts for the Reverse Water Gas Shift Reaction." Thesis, Université d'Ottawa / University of Ottawa, 2021. http://hdl.handle.net/10393/41963.
Full textAbstract:
The continued release of fossil-fuel derived carbon dioxide (CO₂) emissions into our atmosphere led humanity into a climate and ecological crisis. Converting CO₂ into valuable chemicals and fuels will replace and diminish the need for fossil fuel-derived products. Through the use of a catalyst, CO₂ can be transformed into a commodity chemical by the reverse water gas shift (RWGS) reaction, where CO₂ reacts with renewable hydrogen (H₂) to form carbon monoxide (CO). CO then acts as the source molecule in the Fischer-Tropsch (FT) synthesis to form a range of hydrocarbons to manufacture chemicals and fuels. While the FT synthesis is a mature process, the conversion of CO₂ into CO has yet to be made commercially available due to the constraints associated with high reaction temperature and catalytic stability.
Noble metal ruthenium (Ru) has been widely used for the RWGS reaction due to its high catalytic activity, however, several constraints hinder its practical use, associated with its high cost and its susceptibility to deactivation. The doping or bimetallic use of non-noble metals iron (Fe) and cobalt (Co) is an attractive option to lower material cost and tailor the selectivity of the CO₂ conversion towards the RWGS reaction without compromising catalytic activity. Furthermore, employing nanostructured catalysts as nanoparticles is a viable solution to further lower the amount of metal used and utilize the highly active surface area of the catalyst. Dispersing nanoparticles on ionically conductive supports/solid electrolytes which contain species like O²⁻, H⁺, Na⁺, and K⁺, provide an approach to further enhance the reaction. This phenomenon is referred to as metal-support interaction (MSI), allowing for the ions to back spillover from the support and onto the catalyst surface. An in-situ approach referred to as Non-Faradaic Modification of catalytic activity (NEMCA), also known as electrochemical promotion of catalysis (EPOC) is used to in-situ control the movement of ionic species from the solid electrolyte to and away from the catalyst. Both the MSI and EPOC phenomena have been shown to be functionally equivalent, meaning the ionic species act to alter the work function of the catalyst by forming an effective neutral double layer on the surface, which in turn alters the binding energy of the reactant and intermediate species to promote the reaction.
The main objective of this work is to develop a catalyst that is highly active and selective to the RWGS reaction at low temperatures (< 400 °C) by employing the MSI and EPOC phenomena to enhance the catalytic conversion. The electrochemical enhancement effect will lower energy requirements and allow the RWGS reaction to take place at moderate temperatures. Catalysts composed of Ru, Fe and Co were synthesized through the polyol synthesis technique and deposited on mixed-ionically conductive and ionically conductive supports to evaluate their performance towards the RWGS reaction and the MSI effect. The nano-structured catalysts are deposited as free-standing nanoparticles on solid electrolytes to in-situ promote the catalytic rate through the EPOC phenomenon. Furthermore, Density Functional Theory (DFT) calculations were performed to correlate theory with experiment and elucidate the role polarization has on the binding energy of reactant and intermediate species.
The high dispersion of RuFe nanoparticles on ion-containing supports like samarium-doped ceria (SDC) and yttria-stabilized zirconia (YSZ) led to an increase in the RWGS activity due to the MSI effect. A direct correlation between experimental and DFT modeling was established signifying that polarization affected the binding energy of the CO molecule on the surface of Ru regardless of the type of ionic species in the solid electrolyte. The electrochemical enhancement towards the RWGS reaction has been achieved with iron-oxide (FeOₓ) nanowires on YSZ. The in-situ application of O²⁻ ions from YSZ maintained the most active state of Fe₃O₄ and FeO towards the RWGS reaction and allowed for persistent-promoted state that lasted long after potential application. Finally, the deposition of FeOₓ nanowires on Co₃O₄ resulted in the highest CO₂ conversion towards the RWGS reaction due to the metal-oxide interaction between both metals, signifying a self-sustained electro-promoted state.
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Udumula, Venkata Reddy. "Synthesis, RNA Binding and Antibacterial Studies of 2-DOS Mimetics AND Development of Polymer Supported Nanoparticle Catalysts for Nitroarene and Azide Reduction." BYU ScholarsArchive, 2015. https://scholarsarchive.byu.edu/etd/6031.
Full textAbstract:
Project I 2-Deoxystreptamine (2-DOS), the most conserved central scaffold of aminoglycosides, is known to specifically recognize the 5'-GU-'3 sequence step through highly conserved hydrogen bonds and electrostatic interactions within and without the context of aminoglycosides (Figure 1a). We proposed that a novel monomeric unnatural amino acid building block using 2-DOS as a template would allow us to develop RNA binding molecules with higher affinity and selectivity than those currently available. Conjugating two or more of the monomeric building blocks by an amide bond would introduce extra hydrogen bonding donors and acceptors that are absent in natural aminoglycosides and increase specificity of binding to a target RNA through a network of hydrogen bonds. In addition, the amide conjugation between the monomeric building blocks places two GU-base recognizing amines at 5 Å… distance, which is equal to the distance of neighboring base stacks in dsRNAs We hypothesized that targeting dsRNAs containing multiple consecutive 5'-GU-'3 sequence steps would become possible by connecting two or more of the monomeric building blocks by amide bonds. According to the proposed hypothesis, we designed three dimeric 2-DOS compounds connected by an amide bond. These three targets include the dimeric 2-DOS substrate connected by an amide bond, the dimeric 2-DOS containing the sugar moiety from Neamine, and a dimeric 2-DOS connected by a urea linker. These compounds were then tested for sequence specific binding against 8 different RNA strands, and for antibacterial activity against E. coli, actinobacter baumannii and klebsiella. Project II A dual optimization approach was used for to enhance the catalytic activity and chemoselectivity for nitro reduction. In this approach the composition of the nanoparticles and electronics effects of the polymer were studied towards nitro reduction. Bimetallic Ruthenium-Cobalt nanoparticles showed exceptional catalytic activity and chemoselectivity compared to monometallic Ruthenium nanoparticles. The electronic effects of the polymer also had a significant effect on the catalytic activity of the bimetallic nanoparticles. The electron-deficient poly(4-trifluoromethylstyrene) supported bimetallic nanoparticles undergo nitro reduction in 20 minutes at room temperature, whereas electron-rich poly(4-methylstyrene) and poly(4-methoxystyrene) supported bimetallic nanoparticles to longer reaction times to go to completion. Electronics of the polymers also effects the change in mechanism of nitroreduction. Polystyrene bimetallic Ruthenium-Cobalt nanoparticles showed excellent yields and chemoselectivity towards nitro functional group in the presence of easily reducible functional groups like alkenes, alkynes, allyl ethers, propargyl ethers. Monometallic ruthenium nanoparticles also showed excellent reactivity and chemoselectivity towards azide reduction in the presence of easily reducible functional groups. Interestingly monometallic ruthenium nanoparticles showed regioselective reduction of primary azides in the presence of secondary and benzylic azides, also aromatic azides can be selectively reduced in the presence of secondary azides. These polystyrene supported nanoparticles are heterogeneous and are easily separated from the reaction mixture and reused multiple times without significant of catalytic activity.
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Macheli, Lebohang. "Silica modified Co3O4 nanocubes as a model system for metal-support interaction in Co/SiO2 catalyst for Fischer-Tropsch synthesis." Master's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/13226.
Full textAbstract:
Includes bibliographical references.<br>The aim of this study was to study the interaction between the silica and cobalt crystallites using a model of Co3O4-nanocubes whose surface was modified with tetraethyl orthosilicate. The model systems were prepared in two steps, viz. synthesis of the cobalt(III,II) oxide nanocubes via the sodium dodecylsulphate assisted oxidative precipitation and a surface modification of the nanocubes with tetraethyl orthosilicate. The obtained morphology and in particular the average crystallite size of Co3O4 nanocubes is affected by the temperature at which the reagents are mixed, the rate at which they are mixed as well as the time of reaction. The modification of the surface of the Co3O4-nanocubes with tetraethyl orthosilicate resulted in the formation of Co-O-Si ligands on the surface of Co3O4. This was confirmed in addition to (amorphous) SiO2 using Fourier transformer infrared (FTIR) spectrometry. The surface treatment did not yield the formation of crystalline silica or a crystalline cobalt silicate phase as indicated by the absence of characteristic diffraction bands using XRD. Furthermore, there was no hard-to reduce material (e.g. cobalt silicate) as the TPR profiles showed only two peaks corresponding to the reduction of Co3O4 to metallic cobalt. The reduction behaviour of Co3O4 nano-cubes was, however, affected by the surface treatment with tetraethyl orthosilicate. A shift in the reduction profile towards higher temperatures was observed with increasing SiO2 loading. This occurs as a result of increased activation energy for the reduction of the model catalysts upon modifying with tetraethyl orthosilicate, which might be ascribed to a strong interaction between cobalt and silica. Surface modification of Co3O4 with SiO2 prohibits sintering and the silica species may act as spacers between the cobalt particles. The Co-O-Si species are still present after the reduction of these model materials and during the Fischer-Tropsch synthesis. The Fischer-Tropsch activity is improved with a maximum activity improvement of about 15 times. The activity enhancement is larger than what is expected based on the increased metal surface area indicating that Co-O-Si surface species may also act as a promoter for the Fischer-Tropsch synthesis.
28
BADRI, AHMED. "Caracterisation de la reduction de la cerine par h#2 et co. Interaction metal support dans les catalyseurs pd/ceo#2." Caen, 1995. http://www.theses.fr/1995CAEN2007.
Full textAbstract:
La reduction d'echantillons de cerine, de differentes textures et surfaces specifiques, a ete suivie par thermogravimetrie et, essentiellement, par spectroscopies d'absorption uv-vis et irtf. L'etat de reduction est spectroscopiquement repere en utilisant: soit des transitions electroniques (ce#3#+-ce#4#+ dans le visible, de ce#3#+ et peut-etre ce#2#+ (excite - ce#3#+ dans l'infrarouge), soit des molecules sondes (especes hydroxyles et methoxy). On montre que la sonde methoxy permet: (i) une mesure de la surface externe de la cerine (reduite ou oxydee), (ii) la caracterisation des lacunes oxygene et sites cationiques de surface, (iii) l'evolution du rapport de reduction surface/volume de la cerine en fonction de la texture et de la temperature de reduction. La morphologie du palladium dans les catalyseurs pd/ceo#2 est determinee par adsorption de co et suivie par spectroscopie irtf en fonction de la temperature de reduction. En absence de chlore dans le support, on met en evidence la formation d'agregats carbonyles pdco, pd#2co et pd#nco#m (n > 2). Pour les catalyseurs reduits, le palladium constitue des structures bidimensionnelles soit denses, type plans (111), soit desorganisee et caracterisee par une bande v(co) vers 1750 cm#-#1. La reduction provoque l'encapsulation du palladium dans le support. L'effet de la chloration du support a ete aborde
29
Luo, Wen. "Tuning the redox properties of cobalt particles supported on oxides by an In-between graphene layer." Thesis, Strasbourg, 2016. http://www.theses.fr/2016STRAF007/document.
Full textAbstract:
L'interaction métal-support (MSI) joue un rôle important dans la catalyse hétérogène. La compréhension et la modification du MSI sont des étapes essentielles pour développer catalyseurs de haute performance. Dans cette thèse, un nouveau concept, qu’il s’agit de recouvrir le support l'oxyde avec un revêtement mono-couche de graphène, a été proposé pour modifier le MSI. L'influence de la couche de graphène sur les interactions de métal (Co et Co-Pt) - oxyde (ZnO et SiO2) et sur les propriétés d'oxydo-réduction des particules métalliques ont été évaluées via des systèmes catalytiques de modèle. Les résultats ont montré que la mono-couche de graphène peut influencer considérablement les états d'oxydation et les morphologies des Co monométallique et Co-Pt bimétallique par rapport aux ceux résultent d’un dépôt direct sur les oxydes nus. En particulier, par calcination sous vide, le graphène protége Co d'être oxydé par ZnO, ce qui conduit à la formation d’un mélange métallique Co-Pt. Co interagit avec les substrats d'oxydes pour former des particules plates qui sont facilement oxydés par O2 en pression faible, tandis que l'insertion d'une couche intermédiaire de graphène entre la couche supérieure métallique et le supporte d’oxyde entraîne la formation des nanoparticules de Co en état très dispersés, qui sont résistants à l'oxydation. Sous la condition de réduction par H2, le graphène favorise clairement la réduction de Co. La quantité de dépôt de Co, le substrat d'oxyde, la température de calcination et l'environnement ont été prouvés pour pouvoir influencer la stabilité de graphène. Ces résultats ouvrent des nouvelles voies possibles d'utiliser le graphène comme promoteur dans des réactions catalytiques à l'avenir<br>The metal-support interaction (MSI) plays an important role in heterogeneous catalysis. Understanding and tuning the MSI are essential steps for developing catalysts with high performance. In this thesis, a new concept, which is coating the oxide supports with a single layer graphene, was introduced to modify the MSI. The influence of graphene layer on the metal (Co and Co-Pt) – oxide (ZnO and SiO2) interactions and on the redox properties of metal particles were evaluated through model catalyst systems. The results showed that single layer graphene can significantly influence the oxidation states and morphologies of both mono Co and bimetallic Co-Pt as compared to the one after direct deposition on bare oxides. In particular, under vacuum annealing, graphene protects Co from being oxidized by ZnO and results in Co-Pt metallic mixture. Co interacts with oxide substrates forming flat particles which are easily oxidized by low pressure O2, while insertion of a graphene interlayer between the metal overlayer and the oxide supports leads to the formation of highly dispersed Co nanoparticles, which are resistant to oxidation. Under H2 reduction condition, graphene evidently facilitates the reduction of Co. The deposition amount of Co, the oxide substrate, the annealing temperature and the environment were proved to influence the stability of graphene. These results explore new directions for the possible future of using graphene as a promoter in catalytic reactions
30
Behafarid, Farzad. "Structure, stability, vibrational, thermodynamic, and catalytic properties of metal nanostructures: size, shape, support, and adsorbate effects." Doctoral diss., University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5121.
Full textAbstract:
Recent advances in nanoscience and nanotechnology have provided the scientific community with exciting new opportunities to rationally design and fabricate materials at the nanometer scale with drastically different properties as compared to their bulk counterparts. In this dissertation, several challenges have been tackled in aspects related to nanoparticle (NP) synthesis and characterization, allowing us to make homogenous, size- and shape-selected NPs via the use of colloidal chemistry, and to gain in depth understanding of their distinct physical and chemical properties via the synergistic use of a variety of ex situ, in situ, and operando experimental tools. A variety of phenomena relevant to nanosized materials were investigated, including the role of the NP size and shape in the thermodynamic and electronic properties of NPs, their thermal stability, NP-support interactions, coarsening phenomena, and the evolution of the NP structure and chemical state under different environments and reaction conditions.<br>Ph.D.<br>Doctorate<br>Physics<br>Sciences<br>Physics
31
Law, Yeuk Ting. "Investigation of reaction networks and active sites in ethanol steam reforming reaction over Ni and Co-based catalysts." Phd thesis, Université de Strasbourg, 2013. http://tel.archives-ouvertes.fr/tel-00869963.
Full textAbstract:
Bimetallic catalysts have been widely exploited to improve the performance of various catalytic reactions. Understanding the surface properties and in particular, bimetallic interaction and support effect of the catalytic components is an important step towards rational catalyst design. In this thesis, Ni-Co thin film on polar ZnO single crystal was studied as a model catalyst for ethanol steam reforming reaction. The aim is to provide fundamental understanding of how the surface characteristics of the catalyst influence the mechanism and the efficiency of the reaction. This study focused firstly on the study of the interaction between Ni and Co in oxidative environment using Xray photoelectron spectroscopy (PES). Oxidation of Co is favoured over nickel and the surface is enriched with cobalt oxide. Secondly, Ni-Co thin film supported on polar Zn and O terminated ZnOwas studied by synchrotron based PES. The as deposited layer interacts readily with ZnO and Co is partially oxidized upon deposition, even at room temperature. The interaction of ethanol with Ni- Co/ZnO-Zn was studied by thermal desorption spectroscopy (TDS). Ethanol decomposes in different pathways on Ni and Co, in which C-C bond scission and methane production are favoured on Ni/ZnO-Zn while dehydrogenation is favoured on Co/ZnO-Zn. Finally, Ni-Co powder was studied byin-situ ambient pressure PES under reaction conditions in order to clarify the correspondence between the active state of the catalyst and the reaction activity. The product selectivity on Co catalyst is distinctly different from Ni and Ni-Co. Also, the decomposition of methyl group and the high amount of CO produced over Co is likely to be the cause for its high level of carbon deposition.
32
Fruth, Jana. "Sensitivy analysis and graph-based methods for black-box functions with on application to sheet metal forming." Thesis, Saint-Etienne, EMSE, 2015. http://www.theses.fr/2015EMSE0779/document.
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Le domaine général de la thèse est l’analyse de sensibilité de fonctions boîte noire. L’analyse de sensibilité étudie comment la variation d’une sortie peut être reliée à la variation des entrées. C’est un outil important dans la construction, l’analyse et l’optimisation des expériences numériques (computer experiments).Nous présentons tout d’abord l’indice d’interaction total, qui est utile pour le criblage d’interactions. Plusieurs méthodes d’estimation sont proposées. Leurs propriétés sont étudiées au plan théorique et par des simulations.Le chapitre suivant concerne l’analyse de sensibilité pour des modèles avec des entrées fonctionnelles et une sortie scalaire. Une approche séquentielle très économique est présentée, qui permet non seulement de retrouver la sensibilité de entrées fonctionnelles globalement, mais aussi d’identifier les régions d’intérêt dans leur domaine de définition.Un troisième concept est proposé, les support index functions, mesurant la sensibilité d’une entrée sur tout le support de sa loi de probabilité.Finalement les trois méthodes sont appliquées avec succès à l’analyse de sensibilité de modèles d’emboutissage<br>The general field of the thesis is the sensitivity analysis of black-box functions. Sensitivity analysis studies how the variation of the output can be apportioned to the variation of input sources. It is an important tool in the construction, analysis, and optimization of computer experiments.The total interaction index is presented, which can be used for the screening of interactions. Several variance-based estimation methods are suggested. Their properties are analyzed theoretically as well as on simulations.A further chapter concerns the sensitivity analysis for models that can take functions as input variables and return a scalar value as output. A very economical sequential approach is presented, which not only discovers the sensitivity of those functional variables as a whole but identifies relevant regions in the functional domain.As a third concept, support index functions, functions of sensitivity indices over the input distribution support, are suggested.Finally, all three methods are successfully applied in the sensitivity analysis of sheet metal forming models
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Kast, Patrick [Verfasser], Robert [Akademischer Betreuer] Schlögl, Thorsten [Akademischer Betreuer] Ressler, and Martin [Akademischer Betreuer] Muhler. "Structure-function relationship of strong metal-support interaction studied on supported Pd reference catalysts / Patrick Kast. Gutachter: Robert Schlögl ; Thorsten Ressler ; Martin Muhler. Betreuer: Robert Schlögl." Berlin : Technische Universität Berlin, 2015. http://d-nb.info/1072684268/34.
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Zhang, Ke [Verfasser], Hans-Joachim [Akademischer Betreuer] Freund, Hans-Joachim [Gutachter] Freund, and Mario [Gutachter] Dähne. "Scanning tunneling microscopy study of strong metal-support interaction in iron oxide based model catalysts / Ke Zhang ; Gutachter: Hans-Joachim Freund, Mario Dähne ; Betreuer: Hans-Joachim Freund." Berlin : Technische Universität Berlin, 2018. http://d-nb.info/1164076469/34.
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Saoud, Khaled Mohammad Eqab. "Carbon Monoxide Oxidation on Nanoparticle Catalysts and Gas Phase Reactions of Small Molecules and Volatile Organics with Metal Cations." VCU Scholars Compass, 2005. http://scholarscompass.vcu.edu/etd/1372.
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This dissertation demonstrates the application of a vapor phase method to synthesize supported and unsupported nanoparticle catalysts for CO oxidation. The method is based on the Laser Vaporization/Controlled Condensation (LVCC) technique. The first part of this dissertation presents the vapor phase synthesis and characterization of gold nanoparticles supported on a variety of oxide supports such as CeO2, TiO2, CuO and MgO.The results indicate that Au nanoparticles supported on CeO2 exhibit higher catalytic activity than Au supported on other oxides. The high activity of the Au/CeO2 catalyst is attributed to the strong interaction of Au with CeO2. The results also indicate that 5% Au loading on CeO2 has higher activity than 2% Au or 10% Au. When comparing the catalytic activity of Au/CeO2 prepared by physical (LVCC) and chemical (deposition-precipitation)methods, it was found that the catalytic activity is higher for Au/CeO2 prepared by the deposition-precipitation method.The effect of alloying Au and Cu nanoparticles on the catalytic activity for low temperature CO oxidation was also investigated. The unsupported Au-Cu alloy nanoparticle catalyst exhibits higher catalytic activity than the activities of the individualcomponents and their physical mixtures. The XRD data of Au-Cu alloy taken after the catalysis test indicates the formation of CuO within the bimetallic nanoparticles, whichimproves the catalytic activity of Au-Cu alloy nanoparticle.The second part of this dissertation investigates the gas phase reactions of Au+ and Cu+ with CO, O2 and H2O molecules using the Laser Vaporization ionization, High-Pressure Mass Spectrometry (LVI-HPMS) technique. The gas phase reactions resulting from the interactions of Au+ with CO and O2 molecules are investigated. Although multiple additions of CO and O2 molecules on Au+ have been observed at room temperature, no evidence was found of the production of CO2. This is attributed to the presence of water molecules which effectively replace the oxygen molecules on Au+ at room temperature.Finally, the role of the metal cations Au+ and Cu+ in initiating the gas phase polymerization of butadiene and isoprene vapors was investigated.
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FERNANDEZ, J. LASSO. "HYDROGEN PRODUCTION FROM RENEWABLE PRIMARY SOURCES." Doctoral thesis, Università degli Studi di Milano, 2016. http://hdl.handle.net/2434/366899.
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ABSTRACT
One of the most attracting renewable sources for energy production is bioethanol, which can be obtained from biomass. Special attention is here focused on the steam reforming reaction of ethanol (SRE) in which the principal product, hydrogen, is an interesting energy vector to produce power, electricity and heat. However, the process has not yet come to maturity and it should be optimized in order to made it industrially available.
To this aim, we focused our work on catalysts synthesis for SRE, trying to couple high activity and durability. Different catalyst formulations based on Ni as active phase, supported over zeolite-BEA, zirconia, titania and lanthana were synthesized and characterized by N2 adsorption/desorption, temperature programmed reduction (TPR), X-rays diffraction, transmission electron microscopy and infra-red Fourier transform spectroscopy. The performance of the catalysts was evaluated for SRE by using absolute ethanol and bioethanol 50 and 90 vol%, obtained from second generation biomass and kindly supplied by Mossi&Ghisolfi. An important aim of the work was the intensification of the process from the energetic point of view, decreasing the energy input to the reformer (endothermal reaction) to better integrate this high temperature stage with the hydrogen purification section and the possible use of Proton Exchange Membrane Fuel Cells (PEM-FC).
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Rico, Pérez Verónica. "Optimization of N2O decomposition RhOx/ceria catalysts and design of a high N2-selective deNOx system for diesel vehicles." Doctoral thesis, Universidad de Alicante, 2013. http://hdl.handle.net/10045/35739.
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Kikkawa, Soichi. "The Design of Active Sites for Selective Catalytic Conversion of Carbon Dioxide." Doctoral thesis, Kyoto University, 2020. http://hdl.handle.net/2433/253303.
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京都大学<br>0048<br>新制・課程博士<br>博士(工学)<br>甲第22467号<br>工博第4728号<br>新制||工||1738(附属図書館)<br>京都大学大学院工学研究科分子工学専攻<br>(主査)教授 田中 庸裕, 教授 江口 浩一, 教授 佐藤 啓文<br>学位規則第4条第1項該当<br>Doctor of Philosophy (Engineering)<br>Kyoto University<br>DFAM
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PASQUALE, LEA. "Structural Evolution of PdCu and PtCu Nanocrystal Catalysts over Redox Treatments." Doctoral thesis, Università degli studi di Genova, 2019. http://hdl.handle.net/11567/973257.
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This thesis presents the main results on the synthesis of PdCu and PtCu bimetallic nanocrystals (NCs) and their application as catalysts for CO oxidation as a probe reaction. Focusing on Cu and keeping constant the NC size and the support material, the role of the noble metal in the alloy/dealloy/migration process of noble metal-Cu alloyed NCs was studied. The role of the support material in the same transformations was also objected of study. NCs with defined size and composition were successfully synthesized by means of colloidal synthesis methods. The NCs were further deposited on a SiO2 support and studies of catalytic activity were performed on NCs exposed to oxidizing and reducing pre-treatments before each catalytic test. The catalytic activity data were also collected on γ-Al2O3 support to investigate the correlation between the activity and the structural properties of such NCs. For this purpose, different analysis techniques were used as routine ex situ methods to characterize these materials. In situ methods such as diffuse reflectance infrared Fourier transform spectroscopy and X-ray absorption fine structure spectroscopy were used to monitor the structure evolution of the metals under controlled conditions. The use of in situ and operando methods has significantly highlighted that the structure of the metallic particles can be dramatically modified under reaction conditions in terms of geometry and chemical composition. The analysis and synthesis techniques and the main results obtained on structural changes in the NC catalysts under different conditions are widely described.
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Wang, Zichun. "Catalytic conversion of biomass- and petrochemical-derived model compounds over acidic catalysts." Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/13679.
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Silica-aluminas (SA) as solid acids are widely used in the chemical, food, pharmaceutical and petrochemical and bio-refining industries. Their acidic properties depend on their local structure. For the first time, the presence of large amount of surface available AlV species on amorphous SA (ASA) was revealed by 27Al MQMAS NMR spectroscopy in this thesis. These AlV species can enhance the strength of neighboring SiOH groups evidenced by 1H-27Al D-HETCOR. Indeed, significantly enhancing the acidity of ASA at the same Al loading was achieved via increasing AlV concentration by applying higher combustion enthalpy solvent. In H/D exchanged with benzene-d6, ASA exhibited 4 times lower activation energy compared to zeolite H-ZSM-5, which was due to the assistance of AlV species. In the conversion of phenylglyoxal to ethyl mandelate, the performance of ASA correlated well with the enhanced Brønsted acidity, confirmed by using silica-zirconia catalyst. At the same conditions, ASA obtained a 10 times higher TOF than dealuminated zeolite HY. This was attributed to the free diffusion of molecules on ASA surface, confirmed by using [Al]MCM-41. Selective dehydration of glycerol on solid acids is important for the production of the value-added acrolein for sustainable bio-refinery. Most efforts focus on developing strong BAS to improve the acrolein production, since LAS produce by-product acetal. With Al-exchange zeolite H-ZSM-5, the significant increase of the acrolein yield was achieved via the cooperative dehydration between the BAS and LAS. In chemoselective hydrogenation of acetophenone, the selectivity was influenced by electronic properties of noble metal, indicated by FTIR investigation. Solid-state NMR spectroscopy studies revealed electronic properties depends on the strength of BAS covered by metal nanoparticles. Increasing the number of uncovered BAS on the supports can improve the performance of supported metal catalyst with similar product selectivity.
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Ngandjong, Alain Cabrel. "Modélisation structurale des clusters d’alliages supportés : effet du support de silice et effet de taille." Thesis, Orléans, 2015. http://www.theses.fr/2015ORLE2070/document.
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Les simulations numériques ont négligé jusqu’ici l’influence du support de silice amorphe sur la structure des nanoparticules métalliques déposées car l’interaction métal-silice amorphe est faible. Toutefois les études expérimentales montrent un effet de troncature sur la structure des nanoparticules. L’idée de ce travail a donc été d’étudier l’influence de ce support sur la structure et la morphologie des nanoparticules d’argent au moyen de la modélisation moléculaire (Monte Carlo et dynamique moléculaire). L’objectif de ce travail a été tout d'abord de déterminer le potentiel interatomique permettant de décrire l’interaction argent-silice. Ce potentiel a été obtenu sur la base des données expérimentales d'angles de mouillages en phase liquide et en phase solide. D’autre part, l'intensité d'interaction argent-silice a été déterminée par calculs DFT sur la cristobalite qui est un polymorphe de la silice cristalline présentant la même densité que la silice amorphe. Les énergies d'adhésions obtenues ont ainsi permis d'ajuster les paramètres du potentiel argent-silice de type Lennard-Jones. L’étude de la stabilité structurale des nanoparticules d'argent supportées à température nulle a été effectuée pour trois degrés d'approximation du support. (1) : un support parfaitement lisse décrit par un puits carré dont la profondeur est reliée à l’énergie d’adhésion, (2) : un support atomique de silice amorphe de surface plane et (3) : un support atomique de silice amorphe présentant une rugosité de surface. L’influence de la température sur la structure a été étudiée par fusion et recristallisation des nanoparticules d’argent sur les deux supports de silice amorphe. Afin d’étudier la stabilité structurale des nanoparticules en température, le calcul d’énergie libre des nanoparticules a été abordé<br>Numerical simulations have so far neglected the influence of amorphous silica substrate on the structure of metallic nanoparticles due to its relatively weak interaction with deposited nanoparticles. However, experimental studies have often shown a truncation effect on the structure of nanoparticles. The idea of this work was to study the influence of this substrate on the structure of silver nanoparticles using molecular modeling (Monte Carlo and molecular dynamics). The objective of this work was firstly to determine silver-silica interatomic potential. This was achieved using experimental data of wetting angles in solid and liquid phase. On the other hand, silver-silica interaction intensity was determined by DFT calculations on cristobalite which is a polymorph of crystalline silica having the same density as amorphous silica. The adhesions energies obtained were used to fit the Lennard-Jones parameters for the silver-silica interaction. The study of the structural stability of silver nanoparticles supported at zero temperature was performed for three levels of approximation of the support. (1): the smooth wall approximation where the support is described by a square-well whose depth is related to the adhesion energy of the nanoparticle, (2): an atomistic model of flat amorphous silica, (3): an atomistic model of rough amorphous silica. The influence of the temperature on the structure was investigated by melting and recrystallization of the silver nanoparticles deposited on the two silica supports. In order to study the temperature stability of the nanoparticles the free energy calculation of the nanoparticles was discussed
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Xu, Zhenxin. "Development of new macroscopic carbon materials for catalytic applications." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAF005/document.
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De nos jours, les matériaux carbonés macroscopiques font face à un nombre croissant d'applications en catalyse, soit en tant que supports, soit directement en tant que catalyseurs sans métal. Cependant, il reste difficile de développer un support de catalyseur hiérarchisé à base de. carbone ou un catalyseur utilisant un procédé de synthèse beaucoup plus simple. À la recherche de nouveaux matériaux carbonés structurés pour la catalyse hétérogène, nous avons exploré le potentiel du feutre de carbone / graphite du commerce (FC / FG). Le but du travail décrit dans cette thèse a été le développement du monolithe FG et FC en tant que catalyseur sans métal pour les réactions d’oxydation en phase gazeuse et en tant que support de catalyseur, notamment pour le palladium, pour les réactions d’hydrogénation en phase liquide, et leur rôle dans la performance de réaction de ces catalyseurs. En raison de leur surface de chimie inerte avec une mouillabilité inappropriée, une telle étude avait pour condition d'activer celles d'origine. Par conséquent, des FG et des FC modifiés bien arrondis ont été synthétisés avec des propriétés physico-chimiques adaptées par une série de procédés de traitement chimique, tels que l'oxydation, l'amination, la thiolation, le dopage à l'azote et au soufre. L’oxydation partielle du sulfure d’hydrogène en soufre élémentaire et l’hydrogénation sélective du cinnamaldéhyde α, β-insaturé, en tant que réactions sensibles à l’effet des propriétés du catalyseur sur l’activité et la sélectivité, combinées à des techniques de caractérisation, ont été choisis pour étudier l’effet de la matériaux carbonés sur le comportement catalytique<br>Nowadays, macroscopic carbon materials are facing an increasing number of applications in catalysis, either as supports or directly as metal-free catalysts on their own. However, it is still challenging to develop hierarchical carbon-based catalyst support or catalyst using a much simple synthesis process. In the quest for novel structured carbon materials for heterogeneous catalysis we explored the potential of commercial carbon/graphite felt (CF/GF). The aim of the work described in this thesis has been the development of GF and CF monolith as metal-free catalyst for gas-phase oxidation reactions and as catalyst support, notably for palladium, for liquid-phase hydrogenation reactions, and their roles in the reaction performance of these catalysts. Due to their inert chemistry surface with inappropriate wettability, a prerequisite for such a study was to activate the origin ones. Therefore, well-rounded modified GFs and CFs were synthesized with tailored physic-chemical properties by a series of chemical treatment processes, such as oxidation, amination, thiolation, nitrogen- and sulfur-doping. The partial oxidation of hydrogen sulfide into elemental sulfur and selective hydrogenation of α, β-unsaturated cinnamaldehyde, as the sensitive test reactions to the influence of the catalyst properties on activity and selectivity, combined with characterization techniques, were chosen to investigate the effect of functionalized carbon materials on the catalytic behavior
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Thevenin, Philippe. "Catalytic combustion of methane." Doctoral thesis, KTH, Chemical Engineering and Technology, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3402.
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<p>Catalytic combustion is an environmentally benign technologywhich has recently reached the stage of commercialization.Palladium is the catalyst of choice when considering gasturbines fuelled with natural gas because of its superioractivity for methane oxidation. Several fundamental issues arestill open and their understanding would result in animprovement of the technology. Hence, the work presented inthis thesis aims at the identification of some of theparameters which govern the combustion activity ofpalladium-based catalysts.</p><p>The first part of this work gives a background to catalyticcombustion and a brief comparison with other existingtechnologies. Paper I reviews some of the issues related tomaterial development and combustor design.</p><p>The second part of this thesis consists of an experimentalinvestigation on palladium-based catalysts. The influence ofthe preparation method onthe properties of these catalystmaterials is investigated in Paper II. Paper III examines theactivity of the following catalysts: Pd/Al2O3, Pd/Ba-Al2O3 andPd/La-Al2O3. Specific attention is given to the metal-supportinteraction which strongly affects the combustion activity ofpalladium. The effect of doping of the support by addition ofcerium is reported in Paper IV.</p><p>Finally, the deactivation of combustion catalysts isconsidered. The various deactivation processes which may affecthigh temperature combustion catalysts are reviewed in Paper V.Paper VI focuses on the poisoning of supported palladiumcatalysts by sulphur species. Palladium exhibits a higherresistance to sulphur poisoning than transition metals.Nevertheless, the nature of the support material plays animportant role and may entail a severe loss of activity whensulphur is present in the fuel-air mixture entering thecombustion chamber.</p><p><b>Keywords</b>: catalytic combustion, gas turbine, methane,palladium, alumina, barium, lanthanum, oxidation, preparation,temperature-programmed oxidation (TPO), decomposition,reoxidation, X-ray photoelectron spectroscopy (XPS),metal-support interaction, deactivation, sulphur, poisoning.The cover illustration is a TEM picture of a 100 nm palladiumparticle supported on alumina</p>
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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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Rankin, Andrew Gordon McLaughlin. "Applications of multinuclear solid-state NMR spectroscopy to the characterisation of industrial catalysts." Thesis, University of St Andrews, 2018. http://hdl.handle.net/10023/12793.
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This thesis describes applications of advanced multinuclear solid-state nuclear magnetic resonance (NMR) experiments to the characterisation of industrially-relevant catalyst materials. Experiments on γ-Al₂O₃ introduce the use of solid-state NMR spectroscopy for the investigation of disordered solids. The existence of Al(V) sites on the surface of this material is demonstrated, showing that removal of adsorbed H₂O may facilitate a rearrangement effect in γ-Al₂O₃ that promotes the formation of these Al environments. A range of aluminium oxide-based supported metal catalysts has been investigated. Studies of these systems by ¹H and ²⁷Al solid-state NMR spectroscopy indicate that a metal-support interaction (MSI) exists between surface cobalt oxide crystallites and the γ-Al₂O₃ support, and is strongest for materials containing small, well dispersed Co oxide crystallites. It is shown that the hygroscopic nature of γ-Al₂O₃ allows the extent of the MSI to be visualised by ¹H MAS NMR, by observing the extent of the proton-metal oxide interaction resulting from the presence of adventitious adsorbed H₂O. The surface/bulk chemistry of Co spinel aluminate materials is also investigated. ¹H, ²⁹Si, ²⁷Al and ¹⁷O solid-state NMR techniques are used to gain insight into the structural nature of silicated alumina catalysts. The combination of isotopic enrichment and dynamic nuclear polarisation (DNP) surface-enhanced NMR spectroscopy can provide a definitive and fully quantitative description of the surface structure of Si-γ-Al₂O₃ (1.5 wt% Si), and the role of adventitious surface water is highlighted. Analysis of silicated aluminas prepared by “sequential grafting” and “single shot” approaches shows that silica growth on γ-Al₂O₃ follows two distinct morphologies. ¹⁷O gas exchange enrichment is also shown to be successful in facilitating ¹⁷O solid-state NMR studies of these materials. It is demonstrated that double (²⁹Si and ¹⁷O) enrichment of Si-γ-Al₂O₃ (1.5 wt% Si) can facilitate access to ²⁹Si-¹⁷O 2D correlation experiments, even at low silica loading. An exploratory investigation of Ti-alumina model catalysts has also been carried out using ¹H, ²⁷Al and ¹⁷O solid-state NMR spectroscopy. These studies indicate that Ti-γ-Al₂O₃ and Ti-Al M50 may be structurally distinct materials.
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Mohotlhoane, Sifiso Alec. "The effect of the presence of species mimicking metal-support interactions adsorbed on a Co(0001) metal surface." Thesis, 2016. http://hdl.handle.net/10539/21752.
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A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, October 2016.<br>The adsorption of molecules on a metal surface is core in heterogeneous catalysis. Surface sensitive techniques such as low energy electron diffraction (LEED), X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD) are key tools to study adsorption geometries and structures of molecules and atoms on a metal surface. As our first model system we investigated the dissociation of NO on Ir{100}. The LEED experimental results showed a p(2 X 2) diffraction pattern at 300 K using. In this study two options were explored: phase mixing where dissociated nitrogen and oxygen are on the same unit cell, as well as phase separation where both nitrogen and oxygen form their own separate unit cell which results in a p(2 x 2) unit cell.
Calculations were done on atop, bridge and hollow sites, with only perpendicular parameters and vibrational amplitude being varied initially. Results for phase mixing calculations gave the lowest R-factor of 0.70 ± 0.11 for atop site. We further considered phase separation for hollow and bridge sites for nitrogen and oxygen respectively because these two sites were found to be the most stable sites using DFT from previous studies.
The lowest R-factors were 0.37 ± 0.06 for nitrogen c(2x2) and 0.24 ± 0.13 for oxygen p(2 X 1) For oxygen significant row pairing of iridium atoms stabilized the structure as mentioned in previous studies. Therefore from our results it is evident that phase separation models the experimental data better than phase mixing. Nitrogen and oxygen form c(2 X 2) and p(2 X 1) overlayer structures respectively which in combination result in a p(2 X 2) pattern that is in agreement with experimental results.
The second system involves enantio-selectivity and chiral resolution at the organic-inorganic interfaces. The d-serine molecule was adsorbed on the Cu{110} surface. Density functional theory (DFT) calculations were used as a benchmark for our CLEED calculations. LEED experiments showed a (- 1 + 2: 40) overlayer pattern for d-serine adsorbed on Cu{110} surface. Three structures from DFT calculations with the lowest energy were used for CLEED calculations.
These structures differed by the way they bond to the surface and molecular interactions. Calculations were carried out on these three structures and the structure with intra-dimer bonding was the best structure. The searches for this structure were further optimized by introducing pairing of the atoms in the row reconstruction on the copper surface and angle search. The lowest value obtained was 0.37 ± 0.09, which suggests that further understanding of this system is needed.
The ultra-high vacuum (UHV) chamber was fully commissioned and is now ready for TPD and XPS studies.<br>LG2017
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Mokoloko, Lerato Lydia. "The effect of metal support interactions between a cobalt catalyst and carbon dots (Cdots) in cobalt fischer-tropsch catalysts." Thesis, 2018. https://hdl.handle.net/10539/26174.
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A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfillment for the degree of Master of Science in Chemistry.
University of the Witwatersrand, Johannesburg,
January 2018<br>The aim of this study was to introduce functionalized carbon dots (Cdots) as potential support and reducing agents for cobalt-based Fischer-Tropsch catalysts. Cdots with different physicochemical properties were synthesized from natural-based product such as ascorbic acid, sucrose and chitosan, using microwave-assisted reactions. Two types of Cdots, namely N-free Cdots (or Cdots) and N-doped Cdots, with particle sizes < 10 nm were produced. Both Cdots and N-doped Cdots have an amorphous structure, containing both sp2 and sp3 type carbon. The surface of Cdots contained mainly hydroxyl and carboxyl functional groups, while N-doped Cdots contained hydroxyl, carbonyl, and nitrogen-based (mainly pyridinic and pyrrolic) functional groups.
Spinel Co3O4 nanoparticles with 10 nm crystallite sizes were synthesized from the “benzyl alcohol route”. Both the spinel Co3O4 nanoparticles and functionalized Cdots were used to prepare the inverse Co3O4/Cdots and Co3O4/N-doped Cdots catalysts. The in-situ XRD results showed that under H2 gas reduction conditions, the Co3O4/Cdots and Co3O4/N-doped Cdots catalysts increased the reduction temperature of Co3O4 to CoO and metallic Co, and Co (fcc) is the predominant form of metallic Co formed. However, when N-doped Cdots were used as both support and reducing agents, Co3O4 was reduced to both Co (fcc) and Co (hcp). The increase in reduction temperature of Co3O4 on Co3O4/Cdots and Co3O4/N-doped Cdots suggest the presence of strong metal to support interactions (SMSIs) between Co3O4 and functionalized Cdots. Further studies on the activity and selectivity of these prepared catalysts will be conducted under F-T reaction process.<br>MT 2018
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Wilde, C. A., Yulia Ryabenkova, I. M. Firth, et al. "Novel rhodium on carbon catalysts for the oxidation of benzyl alcohol to benzaldehyde: A study of the modification of metal/support interactions by acid pre-treatments." 2018. http://hdl.handle.net/10454/17007.
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Yes<br>Rhodium nanoparticles or rhodium organometallic complexes are mainly used in catalysis for reduction or hydroformylation reactions. In this work instead, we explored the capabilities of Rh nanoparticles as an oxidation catalyst, applied to the oxidation of benzyl alcohol to benzaldehyde under very mild conditions (100 °C, and atmospheric pressure) as a model reaction. Here we report the preparation of novel Rh/C catalysts by using an impregnation protocol, with particular emphasis on the pre-treatment of the carbon supports by using HNO3 and HCl, as well as the characterization of these materials by using an array of methods involving TEM, XPS and XRPD. Our preparation method led to a wide Rh particle size distribution ranging from 20 to 100 nm, and we estimate an upper limit diameter of Rh nanoparticles for their activity towards benzyl alcohol oxidation to be ca. 30 nm. Furthermore, a HNO3 pre-treatment of the activated carbon support was able to induce a smaller and narrower particle size distribution of Rh nanoparticles, whereas a HCl pre-treatment had no effect or sintered the Rh nanoparticles. We rationalise these results by HNO3 as an acid able to create new nucleation sites for Rh on the carbon surface, with the final effect of smaller nanoparticles, whereas for HCl the effect of sintering was most likely due to site blocking of the nucleation sites over the carbon surface. The roles of acid centres on the carbon surfaces for the oxidation reaction was also investigated, and the larger their amounts the larger the amounts of by-products. However, by treatment with HNO3 we were able to convert neutral or basic carbons into supports capable to enhance the catalytic activity of Rh, and yet minimised detrimental effects on the selectivity of the oxidation to benzaldehyde.
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Lu, Chun-Mei, and 呂春美. "Naphthalene hydrogenation over Pt/TiO2-ZrO2 and the behavior of strong metal-support interaction(SMSI)." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/60637477374980455645.
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博士<br>國立清華大學<br>化學工程學系<br>88<br>Vapor-phase naphthalene hydrogenation over various supported Pt catalysts was studied in a continuous fixed-bed micro-reactor. Experimental results indicated that the catalytic activity of the catalyst strongly depended on the nature of the support and the pre-reduction temperature. Reaction order was independent of the supports as the reaction was pseudo-first-order with respect to naphthalene in the temperature range studied. By comparing the apparent rate constants over various supported Pt catalysts, Pt supported on TiO2-ZrO2(1/1) reduced at a low temperature, showed the highest activity.For higher pre-reduction temperatures, Pt/TiO2-ZrO2(1:1) exhibited the least suppression of H2 uptake, due to a stabilization effect exerted by ZrO2, which prevents the migration of TiOx moieties and the blockage of the Pt surface. However, the apparent depression of the hydrogenation activity of high temperature reduced Pt/TiO2-ZrO2(1:1) was significantly greater than the suppression of its hydrogen uptake. Furthermore, the decreasing value of the hydrogenation activity relative to the hydrogen uptake, demonstrates electron perturbation between the support and the Pt metal.
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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.<br>text