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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
461

Iridium Catalysed Asymmetric Hydrogenation of Olefins and Dynamic Kinetic Resolution in the Asymmetric Hydrogenation of Allylic Alcohols

Liu, Jianguo January 2017 (has links)
The work described in this thesis is focused on exploring the efficacy of iridium-catalysed asymmetric hydrogenation of precursors to chiral alcohols and chiral cyclohexanes. A range of allylic alcohols including γ,γ-dialkyl allylic alcohols and (Z)-allylic alcohols were prepared and evaluated in the asymmetric hydrogenation using iridium catalysts resulting in chiral alcohols in high yields and excellent enantioselectivity. This methodology was applied in the formal synthesis of Aliskiren, an efficient renin inhibitor drug, using the asymmetric hydrogenation of an allylic alcohol as a key-step. Another project concerned the dynamic kinetic resolution of racemic secondary allylic alcohols using Ir-N,P catalysts under hydrogenation conditions. A range of secondary allylic alcohols and protected alcohols were evaluated in the asymmetric hydrogenation via dynamic kinetic resolution using Ir-N,P catalysts. The corresponding chiral saturated alcohols were formed in good yield with excellent diastereoselectivites (up to 95/5) and enantioselectivities (&gt;99% ee). The last part of this thesis is directed towards the development of highly regio- and enantioselective asymmetric hydrogenation of 1,4-cyclohexadienes and its application in the preparation of useful chiral cyclohexenone intermediates. Non-functionalised, functionalised and heterocycle-containing cyclohexadienes were evaluated. Good yield of regioselectively mono-hydrogenated silyl protected enol ethers were obtained in most cases with excellent enantioselectivity. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 5: Manuscript.</p>
462

The Effect of Oxidation and Support on TiO2(110)-Supported Pdn (n=1-7) Clusters

Ong, S. Vincent 21 November 2011 (has links)
First principles theoretical studies based on a gradient-corrected density functional approach have been carried out on the atomic and electronic properties and oxidation of Pdn (n=1-7) clusters supported on the TiO2(110) surface. The studies are aimed to address some of the fundamental issues related to the properties of supported Pdn clusters used as catalysts in oxidation reactions. Of those issues are the following: What are the atomic structures of Pdn clusters on the TiO2 surface? Upon oxidation, do O atoms from a dissociated O2 molecule spill over onto the underlying TiO2 sup- port? How strongly does spillover oxygen bind? What is the microscopic mechanism for the experimentally observed strong metal support interaction (SMSI) state where the Pd catalyst becomes encapsulated by the surface? Is this related to spillover oxygen? How do the properties of the Pdn clusters change when the TiO2 surface is marked with oxygen vacancies? As will be shown, the ground state geometries of supported Pdn clusters are driven by competing effects including intra-cluster interactions favoring compact structures and cluster support interactions favoring geometries that flatten out in the TiO2(110) surface channel. When exposed to O2, a single Pd atom only activates the O-O bond while all other clusters energetically favor a broken O-O bond. For PdnO2 (n=2-7), while one O is adsorbed on the Pdn cluster, the second O spills over to a lattice Ti site binding at the Pd-Ti interface. The binding strength of these spillover atoms is calculated to be surprisingly high, which is identified to be a result of long-range ionic interactions between Pd and spilled over oxygen. When oxygen spills onto lattice Ti sites, composite TiO motifs are formed that can exchange sites with Pd atoms with a minimal energy, opening the pathway for Ti migration and strong metal support interactions. For the TiO2 surface with oxygen vacancies, clusters bound at the vacancy site possess atomic and electronic properties that resemble bulk palladium. The theoretical findings are compared with recent experiments and are believed to provide insight toward developing a fundamental understanding of supported Pdn clusters as oxidation catalysts.
463

Transestérification des huiles végétales par l’éthanol en conditions douces par catalyses hétérogènes acide et basique / Transesterification of vegatable oils by ethanol in mild conditions by acid and base heterogeneous catalysts

Hamad, Berna 09 December 2009 (has links)
Le biodiesel est un mélange d’esters mono-alkyl utilisé comme carburant alternatif au diesel. Il est obtenu par transestérification des huiles végétales ou de graisses animales par un alcool léger.L’objectif de ce travail consiste en la recherche de catalyseurs solides acides ou basiques capables de promouvoir la réaction de transestérification de l’huile de colza par l’éthanol en conditions aussi douces que celles utilisées en catalyse homogène basique. Pour cela, deux séries de solides acides et basiques ont été préparées et caractérisées par différentes techniques (ATG-ATD, DRX, Isotherme N2). Les propriétés acides et basiques de ces solides ont également été étudiées par calorimétrie et spectroscopie Infra Rouge. Des corrélations entre les activités initiales et les propriétés acides ou basiques de ces catalyseurs ont été recherchées. L’influence des principaux paramètres réactionnels a été examinée sur le catalyseur acide et le catalyseur basique, les plus actifs. Puis une étude cinétique comparative a été réalisée. Enfin la valorisation in situ du glycérol, produit secondaire de la réaction, a été considérée.Nous avons pu montrer que le sel de césium de l’acide 12-tungstophosphorique est le catalyseur acide le plus actif, dans la gamme de solides acides étudiés. Ceci s’explique par la présence de sites acides de BrØnsted forts aptes à promouvoir la réaction en conditions douces de température. Par ailleurs, il est capable de réaliser l’éthérification in situ du glycérol par l’éthanol. En catalyse basique, le nouveau catalyseur préparé, la zircone échangée au césium, est le catalyseur le plus actif parmi les bases solides étudiées. Ce catalyseur est stable dans le milieu réactionnel après élimination par lavage à chaud des espèces Cs labiles. La comparaison des deux catalyseurs montre que la catalyse basique est nettement plus rapide que la catalyse acide. L’étude cinétique permet de proposer des différences mécanistiques entre ces deux types de catalyseurs. / Biodiesel is a mixture of mono-alkyl esters used as alternative fuel. It can be obtained by transesterification of vegetable oils or animal fats with light alcohols.The objective of this work is the research of acid and basic solid catalysts able to promote the transesterification reaction of rapeseed oil with ethanol in conditions as mild as those used in homogeneous base catalysis. For this, two series of solid acids and bases were prepared and characterized by various characterization techniques (TGA-DTA, XRD, Isothermal N2). Calorimetry and Infrared Spectroscopy have also been used to characterize acid and basic properties. Correlations between initial activity and the acidic or basic properties of these catalysts have been investigated. The influence of the main reaction parameters was examined on the most active acid and basic solid. A comparative kinetic study then allowed us to propose reaction mechanisms. Finally the in situ valorisation of glycerol, a by product of the reaction, was carried out.We have shown that the cesium salt of 12-tungstophosphoric acid catalyst is the most active among the solid acids studied. This is explained by the presence of strong BrØnsted acid sites that are able to promote the reaction under mild temperature conditions. This catalyst is capable of achieving in situ etherification of glycerol with ethanol. In base catalysis, the newly prepared catalyst, zirconia exchanged with Cesium, is the most active catalyst among the solid bases studied. This catalyst is stable in the reaction medium after removal of the labile Cs species by hot washing. Comparison of the two catalysts shows that the base catalysis is much faster than acid catalysis. A kinetic comparative study allows us to propose mechanistic differences between these two types of catalysts.
464

Sélectivation de catalyseurs au nickel : modification et caractérisation contrôlées par site / Selectivation of nickel catalysts : controlled-site modification and characterization

Deghedi, Layane 08 December 2009 (has links)
L’objectif de cette étude est de préparer des catalyseurs bimétalliques Ni-X/SiO2, de les caractériser, et de comparer leur activité en hydrogénation du styrène en éthylbenzène,ainsi que leur sélectivité en hydrogénation de la double liaison oléfinique du styrène, par rapport à l’hydrogénation du noyau benzénique. L’élément X est greffé de manière contrôlée sur le nickel, et est choisi selon son électronégativité, soit inférieure (Zr), soit égale (Sn), soit supérieure (Au) à celle du nickel, dans le but d’étudier les effets géométriques et/ou électroniques qu'il pourrait induire. Parmi les échantillons préparés, le catalyseur Ni-Au/SiO2s’est révélé presque aussi actif que le catalyseur non dopé et nettement plus sélectif dans l’hydrogénation du styrène en éthylbenzène. / The aim of the present study is to prepare silica-supported Ni-X bimetallic catalysts, tocharacterize them, and to compare their catalytic activity in the hydrogenation of styrene, as well as their selectivity in the hydrogenation of the styrene’s olefinic double bond instead of the hydrogenation of the aromatic ring. The element X is grafted in a controlled way on the supported nickel particles, and is chosen according to its electronegativity, which is eitherlower (Zr), or equivalent (Sn), or higher (Au) than the electronegativity of Ni, in order to study the geometrical and/or electronic effects due to the doping of Nickel. Among the prepared samples, the Ni-Au/SiO2 catalyst has exhibited high activity and high selectivity in the hydrogenation of styrene into ethylbenzene, which makes the doping of Ni by Au apromising alternative for PyGas selective hydrogenation catalysts.
465

Synthèse de bio-liquide de seconde génération par hydroliquéfaction catalytique de la lignine / Synthesis of second generation fiofuels by catalytic hydroliquefaction of lignin

Joffres, Benoît 15 November 2013 (has links)
Actuellement, la transformation de la biomasse en bio-carburant ou molécules pour l'industrie chimique fait l'objet de nombreuses recherches. La lignine, en tant que coproduit de l'industrie papetière et de l'éthanol cellulosique, est une ressource des plus disponibles qui pourait être utilisée pour la production d'aromatiques ou de composés phénoliques. Cependant, cette macromolécule constituée d'unités propylphénoliques liées par des liaisons éthers nécessite d'être dépolymérisée. Ce travail porte sur la compréhension des mécanismes de liquéfaction par hydroconversion catalytique d'une lignine de paille de blé extraite par un procédé papetier à la soude. Dans un premier temps, nous avons mené une caractérisation poussée de cette lignine à l'aide de diverses techniques qui nous a permis de proposer une structure modèle. Ensuite, nous avons mis en place un mode opératoire de conversion et un protocole de récupération des produits. La réaction est réalisée en réacteur semi-ouvert à 350°C en présence d'H2 (8MPa), d'un solvant donneur d'hydrogène (tétraline) et d'un catalyseur d'hydrotraitement NiMoP/Al2O3 sulfuré. Les produits se répartissent en une phase liquide (liquéfiat), une phase gaz, une lignine résiduelle et des solides non-solubles dans le THF. Un taux de conversion a été défini comme le rendement en produits non-solides et les valeurs maximales atteintes sont de 81% pds après 28h de réaction avec un excellent bilan matière. Les fractions récupérées ont ensuite été caractérisées en détail avec des techniques d'analyse adaptées. Grâce à ce protocole d'analyse, nous avons pu observer que le solvant permet d'éviter la formation de solides et que le catalyseur intervient principalement sur l'hydrodésoxygénation et l'hydrogénation des molécules issues de la dépolymérisation de la charge. Enfin, nous avons suivis la réaction au cours du temps, ce qui nous a permis de présenter une ébauche de schéma réactionnel. Les premières étapes de conversion sont la décarboxylation, l'hydrogénolyse des OH aliphatiques et la rupture des liaisons éthers entre les unités élémentaires de la lignine, qui entraînent sa dépolymérisation. Puis des processus plus lent se produisent comme l'élimination des groupes méthoxy, principalement par déméthylation suivi de déshydroxylation. Ainsi, les principaux produits obtenus sont des composés phénoliques et des composés désoxygénés / Nowadays, the transformation of lignocellulosic biomass is deeply investigated in order to provide biofuels and chemicals. Lignin, a by-product of pulp and bio-ethanol industry, is an available resource which could be used for the production of aromatic and phenolic compounds. However, this macromolecule mainly made of propylphenolic units linked by ether functions needs to be depolymerized. This work focuses on the study of liquefaction mechanisms by catalytic hydroconversion of wheat straw lignin extracted by a soda pulping. In the first part of this study, an in-depth characterization of this lignin was carried out using techniques. A structure of our lignin was proposed as a result. Then, a procedure was developed to perform the catalytic hydroconversion and recover the products. Catalytic experiments were carried out in a semi-batch reactor at 350°C, using H2 (8 MPa), a hydrogen donor solvent (tetralin) and a sulfide NiMoP/Al2O3 catalyst. The recovered products were separated into a liquid phase, gases, a lignin residue and THF insoluble solids. A conversion of 81 wt% of lignin into non-solid products was reached after 28h of reaction with an excellent mass balance. The characterization of the different fractions was carried out using techniques. Thanks to this protocol, we were able to point out the role of the H-donor solvent for preventing solid formation as well as the role of the catalyst for hydrodeoxygenation and hydrogenation of the depolymerized products. Finally, the catalytic hydroconversion of the lignin was carried out with the different residence times, which helps understanding the transformations occurring during the conversion. At the beginning of the reaction, we observed decarboxylation, hydrogenolysis of aliphatic OH and cleavage of ether linkages between the phenolic units of the lignin. Then, we observed elimination of methoxy groups, mainly by demethylation followed by dehydroxylation. Finally, the main products obtained during the reaction were phenolic and deoxygenated compounds such as aromatics, naphthenes and alkanes
466

[en] SYNTHESIS AND CHARACTERIZATION OF NANOCOMPOSITES OF OXIDES AND METALLIC NICKEL FOR USE AS CARBON NANOTUBES CATALYST / [pt] SÍNTESE E CARACTERIZAÇÃO DE NANOCOMPOSITOS DE ÓXIDOS E NÍQUEL METÁLICO PARA USO COMO CATALISADORES DE NANOTUBOS DE CARBONO

RONALD BEYNER MEJIA SANCHEZ 07 October 2014 (has links)
[pt] Foram desenvolvidos nanocompósitos de óxidos dopados com níquel metálico pelo processo Sol-Gel modificado pelo uso do PVA (Álcool Polivinílico) na função de matriz de crescimento dos nanocompósitos. Os precursores dos óxidos foram os nitratos de seus próprios metais. Foram sintetizados três tipos de nanocompósitos óxido de magnésio, óxido de alumínio e óxido de zinco. O trabalho envolveu quatro etapas principais: levantamento bibliográfico, desenvolvimento e caracterização dos nanocompósitos e uso dos nanocompósitos como catalisadores na síntese de nanotubos de carbono. O desenvolvimento dos nanocompósitos foi motivado pela necessidade de materiais com tamanho e estrutura controláveis para emprego como catalisadores pela indústria. Na síntese dos nanocompósitos foi usada uma relação de PVA/ Água de 1/12 que depois foi variada para avaliar a influência sobre a força de hidrólise, a relação entre metal da matriz e níquel metálico foi de 9:1, em porcentagem em massa. Também foi avaliada a influência do surfactante Dodecil Sulfato de sódio (SDS) e do hidróxido de amônio na síntese dos nanocompósitos. Os nanocompósitos sintetizados neste trabalho foram testados como catalisadores no crescimento de nanotubos de carbono pela técnica de High Vacuum Chemical Vapor Deposition (CVD). Os catalisadores utilizados tinham tamanho de cristalito aproximado de 11nm no caso de óxido de magnésio e de 5 nm no caso do óxido de alumínio, o níquel metálico formado nestes suportes estava bem disperso e com dimensões estimadas de 3nm. Nanotubos de carbono de uma camada e mais de uma camada foram obtidas somente quando o suporte do níquel metálico era o óxido de magnésio. Os nanotubos foram caracterizados por Raman e microscopia eletrônica de varredura. / [en] Metallic Nickel and oxide nanocomposite have been developed by Sol-Gel process modified by the use of PVA (polyvinyl alcohol) as a matrix for the growth of the nanocomposites. The oxides precursors were nitrates from their own metal. Three types of oxides were synthetized, magnesium oxide, aluminum oxide and zinc oxide. This work is presented in four sections: literature survey, development and characterization of nanocomposites and the use of nanocomposites as catalysts in the synthesis of carbon nanotubes. The development of these nanocomposites was motivated by the need for materials with controllable size and structure for use as catalysts in industry. The synthesis of the nanocomposites used a ratio of PVA / water of 1/12 that was later varied to evaluate the influence of the force of hydrolysis, the relationship between the matrix oxide metal and metallic nickel was 9:1 in mass percentage. The influence of the surfactant sodium dodecyl sulfate (SDS) and the ammonium hydroxide was also evaluated in the nanocomposites synthesis. The nanocomposites synthesized in this work were tested as catalysts in the growth of carbon nanotubes by the technique of High Vacuum Chemical Vapor Deposition (CVD). The catalysts used had a crystallite size of approximately 11nm in the case of magnesium oxide and 5 nm in the case of aluminum oxide, metallic nickel formed on these supports was well dispersed with a size of 3nm. Single layer and multiple layer carbon nanotubes were obtained only when magnesium oxide was the nickel substrate. The nanotubes were characterized by Raman and scanning electron microscopy.
467

Electronic, Structural, and Catalytic Analyses of Iron Pincer Complexes and Methods for the Direct Functionalization of Lactide

Mako, Teresa Louise January 2017 (has links)
Thesis advisor: Amir Hoveyda / Chapter 1: A review of recent iron catalyzed cross coupling advances. Abstract: Herein, advances in iron catalyzed cross coupling from 2010-2015 are thoroughly reviewed. Newly developed protocols and the mechanistic work that has been conducted to gain understanding of these systems are discussed. Specific emphasis is placed on the techniques used for mechanistic investigations. Chapter 2: Cross coupling applications of pyridyl(diimine) iron complexes. Abstract: Versatile and redox noninnocent pyridyl(diimine) iron complexes were explored for catalytic ability in iron catalyzed cross coupling reactions. These complexes were found active for the coupling of benzyl halides and aryl Grignard reagents, producing moderate yields. Although active for the coupling of cyclohexyl chloride and aryl Grignard reagents, the catalytic ability of these complexes was not general for alkyl halides, and the majority of substrates readily underwent β- hydride elimination. Mechanistic studies indicated the role of PDIFe(I)Ph and PDIFe(0)(N2)2 as offcycle species. Additionally, these complexes were employed for the Suzuki-type coupling of alkyl halides with 1,1-bis(boronates), leading to the conclusion that the processes were instead base catalyzed. Chapter 3: Electronic structure analysis and catalytic applications of carbeno(diamidine) iron complexes. Abstract: Iron(II) pincer complexes carbeno(diamidine) iron dibromide [(CDA)FeBr2] and bis(N-heterocyclic carbene)pyridine iron dibromide [(CNC)FeBr2] were examined by magnetic circular dichroism and density functional theory studies to invesitgate the effect that NHC moieties have on electronic structure and bonding in tridentate pincer ligands. The increased Fe-C bonding and pincer-donating abilities that result from NHC incorporation have a direct impact on spin state and observed ligand fields. Additionally, the position of the NHC moiety on the tridentate ligand and the overall geometry of the molecule were found to effect the net donor ability of the pincers and the strength of the iron-pincer interactions. Three new variations of the CDA ligand were developed and evaluated for catalytic ability in olefin hydrogenation and atom transfer radical polymerization reactions. While iron CDA complexes were found to be mediocre catalysts for both transformations, a cobalt CDA dimer complex was developed that showed promising catalytic activity for olefin hydrogenation. Chapter 4: The direct functionalization of lactide. Abstract: In an effort to provide cyclic diesters that could generate useful and biodegradable polymers, the direct functionalization of lactide was pursued. Lactide undergoes ring opening under a wide range of conditions, and thus traditional methods used for the functionalization of lactones could not be employed here. Typical routes for the formation of cyclic diesters involve multi-step syntheses and low yielding cyclization reactions. Herein, C-H activation and soft enolization have been identified as promising avenues toward the direct functionalization of lactide. Palladium catalyzed C-H activation was not amenable for lactide, however, soft enolization techniques led to low yields of the desired functionalized product. / Thesis (MS) — Boston College, 2017. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.
468

Investigations into the use of Ring Closing Metathesis to form 5-, 6-, 7- and 8-membered benzo-fused heterocylces

Panayides, Jenny-Lee 01 November 2006 (has links)
Student Number : 0002306V - MSc dissertation - School of Chemistry - Faculty of Science / The first part of the dissertation involves the use of ring closing metathesis (RCM) and ruthenium mediated isomerisation-RCM tandem reactions to form a wide range of nitrogencontaining benzo-fused heterocycles. Those synthesized include the 6-membered isoquinolines, the 7-membered benzazepines and the 8-membered benzazocines. In order to put these compounds into perspective, a review of selected naturally occurring nitrogencontaining benzo-fused heterocycles is included along with some of their synthetic approaches. Of major significance is our utilization of the Wits methodology allowing one to access the 6-, 7- and 8-membered ring systems from a common synthetic intermediate. The 1,2,3,6-tetrahydro-2-benzazocines were all obtained after RCM in excellent yields (82-99%). We were also able to show that some ofthe protecting groups used were easily removed and that the ring could be hydrogenated after RCM to yield the 1,2,3,4,5,6-hexahydro-2- benzazocines. The isoquinolines were synthesized in 78% and 27% yield for the Ac- and Tsprotected compounds respectively, with no product isolated for the Boc- or SO2Bn-protected compounds. These poor results, caused a change to our strategy and we then used a “combinatorial-type” approach for the synthesis of the 2,5-dihydro-1H-2-benzazepines and the 2,3-dihydro-1H-2-benzazepines with yield of 9, 47, 58 and 82% and 8, 26, 39 and 82% obtained respectively for the RCM reaction Futhermore, we attempted the synthesis of the substituted 4-phenyl isoquinolines and 5-phenyl benzazepines, but we found that the systems would not undergo RCM even at high temperatures and with large amounts of Grubbs II metathesis catalyst. A short review is given in the second part of the dissertation concerning the naturally occurring and pharmaceutically useful indenols, indenones and indanones. It further highlights how our methodology was extended to include the synthesis of 4-isopropoxy-5- methoxy-1H-inden-1-ol (X), 4-isopropoxy-5-methoxy-1H-inden-1-one (X) and 4-isopropoxy- 5-methoxy-1H-indanone (X) through the use of ruthenium-mediated isomerisation and RCM from a similar common intermediate. We have shown the synthesis of 3-substituted indenols, indenones and indanones using the same synthetic procedure, but by changing the reaction temperature during RCM. This dissertation also answers many of the questions posed during the post-doctoral work of Coyanis. Namely, we were able to support our proposed mechanism that the conversion of the unsubstituted indenol to the indenone was occurring via a dehydrogenative-oxidation, through the use of 1H NMR studies that were coupled with an ICP-MS analysis. To the best of our knowledge, this is the first reported use of the Grubbs II catalyst (or its degradation products) in a tandem RCM-oxidation procedure by our group recently.
469

Synthesis of nanostructured silica for use as a support for iron Fischer-Tropsch catalysts

Khoabane, Keneiloe 23 May 2008 (has links)
ABSTRACT Nanostructured silica materials were synthesised by the sol-gel process using simple hydroxyacids as template precursors, and these materials were employed as supports for a low temperature iron Fischer-Tropsch (FT) catalyst. Thus, this thesis is divided into two parts: (I) the synthesis of nanostructured silica gels, and (II) their use as catalyst supports in the FT reaction. PART I The effects of synthesis conditions, acidic and basic template precursors and their amounts, synthesis temperature, duration of hydrolysis and ageing, solvent concentration, organic co-solvent, and the synthesis procedure used on the morphology of the silica materials were studied. The synthesised silica gels were characterised by TEM, SEM, BET, TGA, and XRD. Mixtures of different morphologies were obtained with all the hydroxyacids used and the studies revealed that the morphology of the resultant silica gels was largely determined by the type of the hydroxyacid used. The use of oxalic acid produced materials with 4-9 % micropores and a mixture of meso- and macropores mainly consisting of hollow tubes and hollow spheres; the use of D-gluconic and L-tartaric acids produced mesoporous materials mainly consisting of hollow spheres and sheets with folds, respectively; while the use of stearic and cinammic acids produced macroporous materials mainly consisting of solid spheres and undeveloped particles, respectively. The silica gels formed were found to be amorphous in nature, despite the different morphologies that existed in them, and were also thermally stable.Studies involving the use of oxalic and D-gluconic acids showed that the key to the shape of the resultant morphologies resided in the shape of the template crystals formed in solution under specific synthesis conditions. The template shape depended on the type of the template precursor (i.e. both the acid and the base) and its amount. It was also observed that under certain conditions, both at elevated temperatures (≥ 55 oC) and at high water concentrations (> 50 %), the template dissolved and this led to low yields of shaped morphologies (i.e. hollow spheres and tubes). The solvent concentration to produce a maximum tube yield (in the case of oxalic acid) and hollow sphere yield (in the case of D-gluconic acid) was found to require about 25- 50 % water. Very well-developed tubes were also obtained at this concentration (i.e. with oxalic acid). Long hydrolysis and ageing times (i.e. > 2 h) of the sols and gels, respectively, resulted in the formation of surface attached colloidal particles and of tubes and hollow spheres with decreased wall thicknesses. Pre-formation of the template prior to addition of TEOS produced materials with lower surface areas, higher tube yields and bigger tube sizes when compared with materials synthesised by forming the template together with the silica gel. PART II Two types of silica gels were used as supports for an iron FT catalyst; the nanostructured silica gels (tubes with surface area 109 m2/g and spheres with surface area 245 m2/g ) and a commercial silica gel (Davisil silica, surface area 273 m2/g - consisting of undeveloped particles). The effect of varying the potassium promotion levels and of the support morphology on the catalyst activity and selectivity in the FT reaction was studied at 250 oC, in a slurry operated CSTR.It was observed that an increase in the potassium loading up to 0.5 wt % in the Davisil silica catalyst led to a decrease in the catalyst FT and water gas shift (WGS) activity, and methane selectivity. However, the efficiency of the catalyst to produce hydrocarbons increased with an increase in potassium loading up to 0.5 wt %. Increasing the potassium level up to 0.9 wt % led to a slight increase in both the catalyst activity and methane selectivity, and a decrease in the catalyst efficiency. For the silica tubes catalyst, increasing the potassium loading to 0.5 wt % led to an increase in the catalyst activity and methane selectivity, while increasing the potassium level up to 0.9 wt % led to a decrease in the catalyst activity. For both supports, increasing the potassium loading led to an increase in the selectivity towards high molecular weight hydrocarbons, olefins (relative to paraffins) and terminal olefins (relative to internal olefins). While the Davisil silica and the silica tube catalysts remained more or less stable throughout the reaction, the activity of the silica spheres catalyst declined rapidly with time. The nanostructured silica gel supported catalysts both showed higher activities and methane selectivities, but lower efficiencies when compared to the Davisil silica catalyst. Although the selectivity of all three catalysts towards olefins were similar, their selectivity towards high molecular weight hydrocarbons decreased in the order Davisil silica > silica spheres > silica tubes. Elongated needlelike Fe nanoparticles (NPs) were obtained in the silica tubes catalyst, semi hexagonal Fe NPs were formed in the silica spheres catalyst, while the Fe NPs could not be distinguished from the support in the Davisil silica catalyst. After the reaction, the surface areas of all three catalysts were found to have decreased and the catalysts to have sintered. The nanostructured silica supported catalysts showed the presence of Fe nanozones surrounded by a layer of amorphous carbon, while only agglomerated particles of Fe and some carbon rich regions were observed in the Davisil silica catalyst. No evidence of alteration of the morphology of the nanostructured silica supports was observed after the reaction.
470

Model Based Catalyst Control

Irman, Svraka, Linus, Österdahl Wetterhag January 2019 (has links)
A one dimensional discretized model of a two brick three way catalyst (TWC) system was developed and implemented in MATLAB, Simulink and TargetLink in collaboration with Volvo Cars and Linköpings Universitet - ISY. The purpose of this thesis was to increase system understanding and create a model based TWC control for further development at Volvo Cars. A total of 50 states were modelled, including emission concentrations (O2, CO, C3H6, C3H8, H2, NOx, CO2, H2O), temperature and oxygen buffer level (OBL). A model based control structure was implemented in the form of five separate PID-controllers enabling possibilities to control the OBL of each separate slice of each brick individually and through simple reference handling. The control structures includes anti-windup, feedforward control and feedback safety for model reset during sensor indication of leakage. Specific equipment and software used included MATLAB, Simulink, TargetLink, Volvo SULEV30 TWC and testing rigs. Overall increase in system understanding was achieved in comparison with contemporary TWC modelling and control, as well as sufficient system performance in regard to estimate emissions, simulation duration and pedagogical value. Concluding thoughts of the thesis revolve the complexity of the actual TWC modelling, parameter estimation as well as control. The model presented in this thesis has great potential of describing TWC systems but with great effort during parameter estimation. With ECU performance available in temporary vehicle production year 2019, a complex model may be combined with a simple control strategy whilst a simple model may be combined with a complex control strategy.

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