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1
Grieco, Francesco. "Le rôle de la poussière carbonée dans le milieu interstellaire en tant que catalyseur pour la formation de molécules et la croissance des grains". Electronic Thesis or Diss., CY Cergy Paris Université, 2024. http://www.theses.fr/2024CYUN1306.
Testo completoAbstract (sommario):
Cette thèse présente une étude complète de l'interaction entre les grains de poussière et diverses espèces en phase gazeuse dans le milieu interstellaire. Les principaux résultats impliquent l'utilisation de surfaces comme la glace et le coronène, une surface qui ressemble aux hydrocarbures aromatiques polycycliques (PAH), avec des éléments H et O en phase gazeuse. Nous étudions comment les grains de poussière peuvent catalyser la formation de nouvelles molécules par des processus comme l'adsorption, la diffusion, les réactions de surface et la désorption dans des conditions typiques du milieu interstellaire.La thèse comprend trois chapitres expérimentaux (4, 5 et 6), réalisés au LERMACYU en utilisant la configuration FORMOLISM, qui sont complétés par deux études théoriques (chapitres 8 et 9), menées avec les codes Cloudy et Nautilus à l'UGent. Les expériences se concentrent sur le rôle que jouent les différentes surfaces de grains de poussière et les couches de glace sur les énergies de liaison (BE) des molécules (chapitre 4), sur la formation expérimentale de H2 sur le coronène jusqu'à 250 K (chapitre 5) et sur la formation d'eau solide sur la poussière à des températures allant jusqu'à 85 K (chapitre 6). Plusieurs implications astrophysiques sont également discutées.Les résultats présentés au chapitre 5 montrent comment H2 peut se former dans des nuages moléculaires avec des températures de poussière >20 K et cela est extrêmement pertinent pour expliquer l'efficacité de H2 et de la formation d'étoiles dans les galaxies à fort décalage vers le rouge. Le chapitre 6 donne de nouvelles perspectives sur la formation de manteaux de glace qui pourraient se former à une température plus élevée que celle démontrée précédemment,étant un moyen significatif d'expliquer l'appauvrissement en O élémentaire en phase gazeuse observé dans de telles conditions. De plus, la disparition des PAH lors de la transition des nuages diffus aux nuages denses pourrait s'expliquer par le fait que les grains de poussière commencent à être recouverts par des couches de glace. Dans le chapitre 8, nous étudions l'effet de la formation expérimentale de H2 à haute température sur les PAH sur la localisation du front de dissociation (DF) dans une image PDR classique, en le modélisant avec Cloudy. À partir d'une implémentation de base des résultats expérimentaux du chapitre 5 dans le code, il a été difficile de quantifier cet effet. Cela souligne combien il reste encore beaucoup de travail à faire sur les modèles pour mieux correspondre aux observations. Dans le chapitre 9, certaines questions concernant l'appauvrissement en O dans les nuages translucides et la croissance des grains introduites au chapitre 6 sont abordées avec Nautilus. En utilisant une stratégie innovante, nous avons pu reproduire les appauvrissements en C et O dans des conditions de nuages translucides en les verrouillant dans deux espèces de surface distinctes lors de l'adsorption, reproduisant le rapport de structure moléculaire des carbonates organiques. Cette thèse montre l'incroyable nature catalytique des PAH et leur capacité à permettre des processus de chimisorption pour la formation de molécules à des températures de poussière élevées. Il s'agit d'un résultat important qui peut être lié aux nouvelles découvertes rapportant la possibilité d'avoir une croissance des grains à des nH plus faiblesThis Thesis presents a comprehensive study of the interaction between dust grains andvarious gas-phase species in the ISM. The main results involve the use of surfaces likeices and coronene, a surface that resembles polycyclic aromatic hydrocarbons (PAHs),with gas-phase H and O elements. We investigate how dust grains can catalyze the formation of new molecules through processes like adsorption, diffusion, surface reactions and desorption in typical ISM conditions.The Thesis includes three experimental Chapters (4, 5 and 6), performed at LERMACYUby using the FORMOLISM setup, that are complemented by two theoretical studies(Chapters 8 and 9), conducted with Cloudy and Nautilus codes at UGent. The experiments focus on the role that different dust grain surfaces and ice layers have onthe Binding Energies (BEs) of molecules (Chapter 4), on the experimental formation ofH2 on coronene up to 250 K (Chapter 5) and on the formation of solid water on dustat temperatures up to 85 K (Chapter 6). Several astrophysical implications are alsodiscussed.The results presented in Chapter 5 show how H2 can form in molecular clouds with dusttemperatures >20 K and this is extremely relevant to explain the efficient H2 and starformation in high redshift galaxies. Chapter 6 gives new insights on the formation oficy mantles that could be forming at higher temperature than previously demonstrated,being a significant way to explain the gas-phase elemental O depletion observed in suchconditions. Moreover, the disappearance of PAHs in the transition from diffuse to denseclouds could be explained by the dust grains starting to be covered by ice layers. InChapter 8 we study the effect of the high temperature experimental H2 formation onPAHs on the location of the dissociation front (DF) in a classical PDR picture, bymodelling it with Cloudy. From a basic implementation of the experimental results ofChapter 5 in the code, it has been challenging to quantify such effect. This underlineshow a lot of work still needs to be done on models to better match observations. InChapter 9 some questions regarding O depletion in translucent clouds and grain growthintroduced in Chapter 6 are addressed with Nautilus. By using an innovative strategy,we were able to reproduce C and O depletions in translucent cloud conditions by lockingthem in two separate surface species upon adsorption, reproducing the molecular structure ratio of organic carbonates.This Thesis shows the incredible catalytic nature of PAHs and their capacity to enablechemisorption processes for the formation of molecules at high dust temperatures. Thisis an important result that can be linked to the new discoveries reporting the possibilityof having grain growth at lower nH
2
Fiske, Thomas Haukli. "Correlation of Catalyst Morphology with Attrition Resistance and Catalytic Activity of Fischer-Tropsch Catalysts". Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for kjemisk prosessteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-22778.
Testo completoAbstract (sommario):
Three alumina based support materials for the Fischer-Tropsch synthesis (FTS) catalyst has been prepared and investigated. The three support materials were prepared in order to obtain different mechanical strengths, henceforth denoted weak, medium and strong support. Magnesium modified γ-alumina support material calcined at 950°C and 1050°C were prepared as the medium and strong support respectively, whereas the unmodified alumina was used as the weak support. The modified support materials were both prepared by the incipient wetness impregnation method to obtain 10 wt .% Mg. Several batches were prepared to gain enough material for the planned experiments.Each of the support materials were subject to one crushing process in order to try to alter the particle morphology. The chosen method was determined based on the results from the specialization project. In this project, one method gave a larger change in morphology than other methods. Therefore a ball mill was the method of choice. Unprocessed samples and samples subjected to the ball mill for the three different materials were tested for attrition in an attrition rig, and characterized in terms of morphology using a particle analyzer. The different fractions were also analyzed with respect to particle morphology using an environmental scanning electron microscope (ESEM). FTS catalysts with 12 wt. % Co and 0,5 wt. % Re were prepared from the weak and the medium support materials, both unprocessed and milled fractions, using the incipient wetness impregnation. These four catalyst samples were tested for dispersion using a chemisorption experiment, and for activity and selectivity using a dedicated setup. Results from the particle analyzer showed that the morphology had not been altered as much as expected. Most change in shape occurred for the medium strength support material, but the observed alteration was much less than observed for the same experiment in the specialization project. For the weaker and stronger support, only a slight change was observed, and for the strong support material this change was in the direction of rounder particles. This is probably due to the excellent mechanical strength of the strong support, which leads to grinding of the kinks and corners of the particles and not the breakage of whole particles to smaller and more uneven fragments. With such relative small differences in morphology between the unprocessed and the milled materials, correlations of morphology with other parameters are difficult to obtain. The same correlation as from the specialization project, with rounder particles having a higher attrition resistance, was observed. A slight degree of correlation was also found between particle morphology and dispersion, where more uneven particles gave a slightly higher value of cobalt dispersion.
3
Paliga, James Francis. "Developing Earth-abundant metal-catalysts for hydrofunctionalisation". Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31115.
Testo completoAbstract (sommario):
The iron-catalysed hydromagnesiation of styrene derivatives has been developed further from previous publications, expanding the electrophile scope to enable the regioselective formation of new carbon-carbon and carbon-heteroatom bonds (Scheme A1). A commercially available pre-catalyst and ligand were used to give an operationally simple procedure that did not require prior synthesis of a catalyst. This work also investigated the hydromagnesiation of dienes, using a screen of ligands commonly used in transition metal catalysis. An investigation into the magnesium-catalysed hydroboration of olefins was also carried out. Although mostly unsuccessful, it was demonstrated that in the presence of a magnesium catalyst, a small amount of vinyl boronic ester could be formed from an alkyne (Scheme A2). Simple magnesium salts were also investigated for the reduction of carbonyls. Lastly, this work explored the titanium-catalysed hydrosilylation of olefins, using a novel activation method developed within the group (Scheme A3). The results were compared to those published previously using traditional organometallic activation methods and attempts at identifying conditions to improve chemoselectivity were carried out.
4
Large, Benjamin. "Activation sélective de naphtalènes et synthèse d'architectures polycycliques étendues". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLV070/document.
Testo completoAbstract (sommario):
Comme le naphtalène a récemment émergé comme un socle fondamental en chimie médicinale, le développement de méthodologies menant à des plateformes fonctionnalisées basées sur du naphtalène est devenu un centre d’intérêt majeur de la communauté scientifique. En effet, des conditions expérimentales optimisées sur le benzène ou d’autre noyaux aromatiques ne peuvent pas toujours être transposées au naphtalène. Ces dernières peuvent parfois conduire à des résultats différents, possiblement dû à l’aromaticité plus faible de ce bicycle aromatique.Dans ce contexte, cette thèse s’articule autour du naphtalène et de ses dérivés. Des méthodes variées permettant une fonctionnalisation sélective de différentes positions de cette plateforme, ainsi que des stratégies de synthèses d’architectures polycycliques ont été développées.Notre attention s’est ensuite portée sur des précurseurs du naphtalène, en particulier sur les tetralones. En utilisant une méthode basée sur l’utilisation d’un groupe directeur éphémère, la position 8 de ce bicycle a été arylée, et les différents composés ainsi obtenus ont pu être convertis en d’autre plateformes polycycliques. En complément, des calculs DFT ont permis d’expliquer la régiosélectivité observée lors de la synthèse de fluorenones étendues, et d’étudier le mécanisme d’arylation dirigée des tetralonesBecause naphthalene has recently emerged as a fundamental platform in medicinal chemistry, the development of methodologies leading to diversely functionalised naphthalene-based platforms has become a prime concern of the scientific community. Indeed, experimental conditions previously optimised for benzene and other aromatic rings cannot always be applied to naphthalene. These methods can sometimes lead to different results, as a consequence of the lower aromaticity of the naphthalene core.In this context, this thesis is dedicated to the naphthalene and its derivatives. Various methods to selectively functionalise the different positions of the naphthalene core and synthetic pathways to extended polycyclic architectures were developed.Next, we focused on naphthalene precursors, especially on tetralones. Using a strategy involving a transient directing group, the position 8 of these bicycles was successfully arylated and the resulting compounds were successfully converted into other polycyclic platforms. In addition, DFT calculation have been used to explain the regioselectivity observed during the synthesis of extended fluorenones, and to study the mechanism of directed arylation of tetralones
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Meyer, Simon [Verfasser]. "Carbide Materials as Catalysts and Catalyst Supports for Applications in Water Electrolysis and in Heterogeneous Catalysis / Simon Meyer". München : Verlag Dr. Hut, 2014. http://d-nb.info/1058284967/34.
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Hruby, Sarah Lynn. "Catalytic domains in porous catalysts". [Ames, Iowa : Iowa State University], 2009.
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McGregor, James. "Heterogeneous catalytic hydrogenation and dehydrogenation : catalysts and catalytic processes". Thesis, University of Cambridge, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612796.
Testo completo
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Richardson, John Michael. "Distinguishing between surface and solution catalysis for palladium catalyzed C-C coupling reactions: use of selective poisons". Diss., Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22704.
Testo completoAbstract (sommario):
This work focuses on understanding the heterogeneous/homogeneous nature of the catalytic species for a variety of immobilized metal precatalysts used for C-C coupling reactions. These precatalysts include: (i) tethered organometallic palladium pincer complexes, (ii) an encapsulated small molecule palladium complex in a polymer matrix, (iii) mercapto-modified mesoporous silica metalated with palladium acetate, and (iv) amino-functionalized mesoporous silicas metalated with Ni(II). As part of this investigation, the use of metal scavengers as selective poisons of homogeneous catalysis is introduced and investigated as a test for distinguishing heterogeneous from homogeneous catalysis. The premise of this test is that insoluble materials functionalized with metal binding sites can be used to selectively remove soluble metal, but will not interfere with catalysis from immobilized metal. In this way the test can definitely distinguish between surface and solution catalysis of immobilized metal precatalysts.
This work investigates three different C-C coupling reactions catalyzed by the immobilized metal precatalysts mentioned above. These reactions include the Heck, Suzuki, and Kumada reactions. In all cases it is found that catalysis is solely from leached metal. Three different metal scavenging materials are presented as selective poisons that can be used to determine solution vs. surface catalysis. These selective poisons include poly(vinylpyridine), QuadrapureTM TU, and thiol-functionalized mesoporous silica. The results are contrasted against the current understanding of this field of research and subtleties of tests for distinguishing homogeneous from heterogeneous catalysis are presented and discussed.
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Gill, Christopher Stephen. "Novel hybrid organic/inorganic single-sited catalysts and supports for fine chemical and pharmaceutical intermediate synthesis". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28218.
Testo completoAbstract (sommario):
Thesis (M. S.)--Chemical Engineering, Georgia Institute of Technology, 2009.Committee Chair: Jones, Christopher; Committee Member: Agrawal, Pradeep; Committee Member: Teja, Amyn; Committee Member: Weck, Marcus; Committee Member: Zhang, John.
10
Nguyen, Joseph Vu. "Design, synthesis, and optimization of recoverable and recyclable silica-immobilized atom transfer radical polymerization catalysts". Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6860.
Testo completoAbstract (sommario):
Despite the growing interest in heterogeneous polymerization catalysis, the majority of the polymerization catalysts used industrially are single-use entities that are left in the polymer product. Recoverable and recyclable polymerization catalysts have not reached the industrial utility of single-use catalysts because the catalyst and product separation have not become economical. The successful development of recyclable transition metal polymerization catalysts must take a rational design approach, hence academic and industrial researchers need to further expand the fundamental science and engineering of recyclable polymerization catalysis to gain an understanding of critical parameters that allow for the design of economically viable, recoverable solid polymerization catalysts.
Unfortunately, the rapid development of Atom Transfer Radical Polymerization over the past 10 years has not resulted in its wide spread industrial practice. Numerous reports regarding the immobilization of transition metal ATRP catalysts, in attempts to increase its applicability, have extended the fundamentals of recyclable polymerization catalysis. However, for industrial viability, more research is required in the area of how the catalyst complex immobilization methodology and support structure affect the catalyst polymerization performance, regeneration, and recyclability. A comprehensive rational catalyst design approach of silica-immobilized ATRP catalyst was undertaken to answer these questions and are discussed here.
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Beckler, Robert Kendall. "Polynuclear metal complexes as model mixed oxide catalysts". Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/11897.
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Liu, Hongying. "Syntheses, structures, and catalysis of polynuclear metal complexes". Diss., Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/30561.
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Damian, Karen Serena. "Pd catalysed synthesis of phosphines for homogeneous catalysis". Thesis, St Andrews, 2009. http://hdl.handle.net/10023/907.
Testo completo
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Clarke, Richard John. "Mesopore immobilised bis(oxazoline) catalysts for enantioselective catalysis". Thesis, University of Birmingham, 2003. http://etheses.bham.ac.uk//id/eprint/3578/.
Testo completoAbstract (sommario):
Mesoporous silica materials have the potential to replace many conventional silicas for uses such as supports for heterogeneous catalysis and absorbents. The large pore size and high surface area make them ideal for supporting bulky organometallic catalysts for enantioselective reactions. We have immobilised chiral bis(oxazoline) metal complexes onto the surfaces of some of these versatile supports (MCM-41 and MCM-48) via different tethering strategies. The resulting heterogeneous catalysts were shown to be highly active in the enantioselective cyclopropanation of styrene with ethyl diazoacetate.
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Jenkins, Patrick L. "Electrochemical and catalytic investigation of catalysis by gold". Thesis, Cardiff University, 2005. http://orca.cf.ac.uk/56012/.
Testo completoAbstract (sommario):
The performance of gold/graphite as an oxidation catalyst has been investigated in an electrochemical cell (electrooxidation at ambient temperature and pressure) and in a high pressure reactor (conventional catalytic oxidation typically at 3 bar and 333 K). A range of gold/graphite catalysts having various metal loadings were prepared and characterised by cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The technique of lead underpotential deposition (Pdupd) was used to reveal the presence of {111}, {100}, and {110} facets in the surfaces of the gold microcrystals. Oxidation of 1-propanol to propionic acid, of 2-propanol to acetone, and of glycerol to wide range of products was investigated both in electrooxidation and in conventional catalytic oxidation. Variation of the surface morphology of the gold active phase was achieved by (i) thermal annealing and sintering of the catalysts under air and under hydrogen, (ii) deposition of bismuth onto the gold surface, and (iii) preparation of further catalysts in which Au was deposited onto Pt/graphite. Conventional catalytic oxidation of the 1-propanol, 2-propanol, and glycerol over the full range of gold-containing catalysts is reported. Variations in catalyst structure were accompanied by changes in activity and selectivity, indicating that these reactions were indeed structure sensitive. However, few correlations of these experimental outcomes with the surface states identified by the voltammetric techniques were evident.
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Xu, Jiahui. "Catalytic properties of nano ceria in heterogeneous catalysis". Thesis, University of Oxford, 2010. http://ora.ox.ac.uk/objects/uuid:02e68ff9-ce28-475a-bd08-6b60bcda64e7.
Testo completoAbstract (sommario):
There have been many applications of cerium oxide in oxidation catalysis but the understanding of its role in catalysis is rather limited. This research is concerned with the use of nano-size cerium oxide in methane steam reforming reaction. It is found that addition of cerium oxide to the commercial supported Ni catalysts can dramatically reduce the undesirable carbon deposition (through surface oxidation), which is thermodynamically favorable under low steam conditions. In order to understanding the fundamental role of oxidation activity of the cerium oxide, different sizes of nano-crystallined cerium oxides have been carefully prepared by micro-emulsion technique. Their reactivity is clearly shown to be size dependent. We found that ceria particle sizes of lower than 5.1 nm are able to activate molecular oxygen, which accounts for the unprecedentedly reported critical size effect on oxidation. Characterizations by EPR, XPS, TPR suggest that a substantially large quantity of adsorbed oxygen species (O2 -) is preferentially formed in the small size ceria from air. Also, it is found that the oxygen vacancies are formed in the interface of metal and oxide, and the strength of the metal oxide interaction may influence the formation of the efficient oxygen vacancies, which are responsible for the adsorbed surface oxygen.
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Rosenthal, Daniel Jay. "Estimating the acid site density of silica-alumina by infrared spectroscopy using a selective reactant poison". Thesis, Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/10222.
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Nixon, David J. "Catalytic behaviour of nickel-based catalysts operating on simulated biogas : optimisation through oxygen addition, temperature variation and catalyst modification". Thesis, Keele University, 2013. http://eprints.keele.ac.uk/3818/.
Testo completoAbstract (sommario):
The use of catalytic systems operating on waste products such as biogas offers a potentially attractive alternative for renewable and sustainable energy generation. To investigate the potential viability of such catalytic systems for operation on biogas, a detailed study of nickel-based catalysts for the reforming of simulated biogas (methane:carbon dioxide = 2) to synthesis gas has been undertaken. The influence of oxygen addition in varied concentrations to the simulated biogas mixture has been investigated with regards to catalyst activity, selectivity and stability. This influence has been studied over an extended temperature range from room temperature to 1000 °C. Additionally, the effect of H2S within the simulated biogas mixture on the catalyst activity, selectivity and stability has been studied. Also, the influence of ceria-doping of the nickel catalyst on catalytic behaviour has been investigated. Temperature programmed and conventional catalytic reaction measurements have been used to analyse the catalytic behaviour and long term stability of the catalyst system over a full range of reaction temperatures. Carbon deposits from the simulated biogas reforming were analysed using post-reaction temperature programmed oxidation to assess the extent and nature of carbon deposition. The addition of oxygen significantly increases catalyst activity and shows a variation in product selectivity with temperature. Increased catalyst stability through reduced carbon deposition and increased sulfur tolerance is also observed with oxygen addition. Doping of the nickel catalyst with ceria enhances the influence of oxygen, apart from at high oxygen levels where total oxidation of methane is prevalent. Catalyst regeneration from sulfur poisoning has also been shown through oxygen addition to the simulated biogas mixture and ceria-doping of the nickel catalyst. Fuel cell studies have shown the successful operation of solid oxide fuel cells on simulated biogas and the substantial improvements in electrical performance through addition of oxygen and increased temperature.
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Guo, Chris. "Alkane Oxidation Catalysis by Homogeneous and Heterogeneous Catalyst". Thesis, The University of Sydney, 2005. http://hdl.handle.net/2123/622.
Testo completoAbstract (sommario):
Abstract Cobalt-based complexes are widely used in industry and organic synthesis as catalysts for the oxidation of hydrocarbons. The Co/Mn/Br (known as "CAB system") catalyst system is effective for the oxidation of toluene. The Co/Mn/Br/Zr catalyst system is powerful for the oxidation of p-xylene, but not for the oxidation of toluene. [Co3O(OAc)5(OH)(py)3][PF6] (Co 3+ trimer 5) is more effective than [Co3O(OAc)6(py)3][PF6] (Co 3+ trimer 6) as a catalyst in the CAB catalyst system. Higher temperatures favour the oxidation of toluene. Zr 4+ does not enhance the oxidation of toluene. Zr 4+ could inhibit the oxidation of toluene in the combination of Co/Br/Zr, Co/Mn/Zr or Co/Zr. NHPI enhances the formation of benzyl alcohol, but the formation of other by-products is a problem for industrial processes. Complex(es) between cobalt, manganese and zirconium might be formed during the catalytic reaction. However, attempts at the preparation of complexes consisting of Co/Zr or Mn/Zr or Co3ZrP or Co8Zr4 clusters failed. The oxidation of cyclohexane to cyclohexanone and cyclohexanol is of great industrial significance. For the homogeneous catalysis at 50 o C and 3 bar N2 pressure, the activity order is: Mn(OAc)3 �2H2O > Mn12O12 cluster > Co 3+ trimer 6 > [Co3O(OAc)3(OH)2(py)5][PF6]2 (Co 3+ trimer 3) > Co 3+ trimer 5 > Co(OAc)2 �4H2O > [Co2(OAc)3(OH)2(py)4][PF6]-asym (Co dimerasym) > [Co2(OAc)3(OH)2(py)4][PF6]-sym (Co dimersym); whereas [Mn2CoO(OAc)6(py)3]�HOAc (Mn2Co complex) and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. But at 120 o C and 3 bar N2 pressure, the activity order is changed to: Co dimerasym > Co(OAc)2 �4H2O > Co trimer 3 and Mn(OAc)3 �2H2O > Co 3+ trimer 6 > Mn2Co complex > Co 3+ trimer 5 > Co dimersym > Mn12O12 cluster. The molar ratio of the products was close to cyclohexanol/cyclohexanone=2/1. Mn(II) acetate and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. Among those cobalt dimers and trimers, only the cobalt dimerasym survived after the stability tests, this means that [Co2(OAc)3(OH)2(py)4][PF6]-asym might be the active form for cobalt(II) acetate in the CAB system. Metal-substituted (silico)aluminophosphate-5 molecular sieves (MeAPO-5 and MeSAPO-5) are important heterogeneous catalysts for the oxidation of cyclohexane. The preparation of MeAPO-5 and MeSAPO-5 and their catalytic activities were studied. Pure MeAPO-5 and MeSAPO-5 are obtained and characterised. Four new pairs of bimetal-substituted MeAPO-5 and MeSAPO-5(CoZr, MnZr, CrZr and MnCo) were prepared successfully. Two novel trimetal-subtituted MeAPO-5 and MeSAPO-5 (MnCoZr) are reported here. Improved methods for the preparation of four monometal-substituted MeAPO-5 (Cr, Co, Mn and Zr) and for CoCe(S)APO-5 and CrCe(S)APO-5 are reported. Novel combinational mixing conditions for the formation of gel mixtures for Me(S)APO-5 syntheses have been developed. For the oxidation of cyclohexane by TBHP catalysed by MeAPO-5 and MeSAPO-5 materials, CrZrSAPO-5 is the only active MeSAPO-5 catalyst among those materials tested under conditions of refluxing in cyclohexane. Of the MeAPO-5 materials tested, whereas CrCeSAPO-5 has very little activity, CrZrAPO-5 and CrCeAPO-5 are very active catalysts under conditions of refluxing in cyclohexane. MnCoAPO-5, MnZrAPO-5 and CrAPO-5 are also active. When Cr is in the catalyst system, the product distribution is always cyclohexanone/cyclohexanol equals 2-3)/1, compared with 1/2 for other catalysts. For MeAPO-5, the activity at 150 o C and 10 bar N2 pressure is: CrZrAPO-5 > CrCeAPO-5 > CoZrAPO-5. For MeAPO-5 and MeSAPO-5, at 150 o C and 13 bar N2 pressure, the selectivity towards cyclohexanone is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5; and the selectivity towards cyclohexanol is: MnZrAPO-5 > CrZrAPO-5 > MnCoAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5. Overall the selectivity towards the oxidation of cyclohexane is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5. The amount of water in the system can affect the performance of CrCeAPO-5, but has almost no effect on CrZrAPO-5. Metal leaching is another concern in potential industrial applications of MeAPO-5 and MeSAPO-5 catalysts. The heterogeneous catalysts prepared in the present work showed very little metal leaching. This feature, coupled with the good selectivities and effectivities, makes them potentially very useful.
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Guo, Chris. "Alkane Oxidation Catalysis by Homogeneous and Heterogeneous Catalyst". University of Sydney. Chemistry, 2005. http://hdl.handle.net/2123/622.
Testo completoAbstract (sommario):
Abstract Cobalt-based complexes are widely used in industry and organic synthesis as catalysts for the oxidation of hydrocarbons. The Co/Mn/Br (known as "CAB system") catalyst system is effective for the oxidation of toluene. The Co/Mn/Br/Zr catalyst system is powerful for the oxidation of p-xylene, but not for the oxidation of toluene. [Co3O(OAc)5(OH)(py)3][PF6] (Co 3+ trimer 5) is more effective than [Co3O(OAc)6(py)3][PF6] (Co 3+ trimer 6) as a catalyst in the CAB catalyst system. Higher temperatures favour the oxidation of toluene. Zr 4+ does not enhance the oxidation of toluene. Zr 4+ could inhibit the oxidation of toluene in the combination of Co/Br/Zr, Co/Mn/Zr or Co/Zr. NHPI enhances the formation of benzyl alcohol, but the formation of other by-products is a problem for industrial processes. Complex(es) between cobalt, manganese and zirconium might be formed during the catalytic reaction. However, attempts at the preparation of complexes consisting of Co/Zr or Mn/Zr or Co3ZrP or Co8Zr4 clusters failed. The oxidation of cyclohexane to cyclohexanone and cyclohexanol is of great industrial significance. For the homogeneous catalysis at 50 o C and 3 bar N2 pressure, the activity order is: Mn(OAc)3 �2H2O > Mn12O12 cluster > Co 3+ trimer 6 > [Co3O(OAc)3(OH)2(py)5][PF6]2 (Co 3+ trimer 3) > Co 3+ trimer 5 > Co(OAc)2 �4H2O > [Co2(OAc)3(OH)2(py)4][PF6]-asym (Co dimerasym) > [Co2(OAc)3(OH)2(py)4][PF6]-sym (Co dimersym); whereas [Mn2CoO(OAc)6(py)3]�HOAc (Mn2Co complex) and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. But at 120 o C and 3 bar N2 pressure, the activity order is changed to: Co dimerasym > Co(OAc)2 �4H2O > Co trimer 3 and Mn(OAc)3 �2H2O > Co 3+ trimer 6 > Mn2Co complex > Co 3+ trimer 5 > Co dimersym > Mn12O12 cluster. The molar ratio of the products was close to cyclohexanol/cyclohexanone=2/1. Mn(II) acetate and zirconium(IV) acetate hydroxide showed almost no activity under these conditions. Among those cobalt dimers and trimers, only the cobalt dimerasym survived after the stability tests, this means that [Co2(OAc)3(OH)2(py)4][PF6]-asym might be the active form for cobalt(II) acetate in the CAB system. Metal-substituted (silico)aluminophosphate-5 molecular sieves (MeAPO-5 and MeSAPO-5) are important heterogeneous catalysts for the oxidation of cyclohexane. The preparation of MeAPO-5 and MeSAPO-5 and their catalytic activities were studied. Pure MeAPO-5 and MeSAPO-5 are obtained and characterised. Four new pairs of bimetal-substituted MeAPO-5 and MeSAPO-5(CoZr, MnZr, CrZr and MnCo) were prepared successfully. Two novel trimetal-subtituted MeAPO-5 and MeSAPO-5 (MnCoZr) are reported here. Improved methods for the preparation of four monometal-substituted MeAPO-5 (Cr, Co, Mn and Zr) and for CoCe(S)APO-5 and CrCe(S)APO-5 are reported. Novel combinational mixing conditions for the formation of gel mixtures for Me(S)APO-5 syntheses have been developed. For the oxidation of cyclohexane by TBHP catalysed by MeAPO-5 and MeSAPO-5 materials, CrZrSAPO-5 is the only active MeSAPO-5 catalyst among those materials tested under conditions of refluxing in cyclohexane. Of the MeAPO-5 materials tested, whereas CrCeSAPO-5 has very little activity, CrZrAPO-5 and CrCeAPO-5 are very active catalysts under conditions of refluxing in cyclohexane. MnCoAPO-5, MnZrAPO-5 and CrAPO-5 are also active. When Cr is in the catalyst system, the product distribution is always cyclohexanone/cyclohexanol equals 2-3)/1, compared with 1/2 for other catalysts. For MeAPO-5, the activity at 150 o C and 10 bar N2 pressure is: CrZrAPO-5 > CrCeAPO-5 > CoZrAPO-5. For MeAPO-5 and MeSAPO-5, at 150 o C and 13 bar N2 pressure, the selectivity towards cyclohexanone is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5; and the selectivity towards cyclohexanol is: MnZrAPO-5 > CrZrAPO-5 > MnCoAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5. Overall the selectivity towards the oxidation of cyclohexane is: CrZrAPO-5 > CrZrSAPO-5 > CrCeAPO-5 > CrAPO-5 > MnCoAPO-5 > MnZrAPO-5. The amount of water in the system can affect the performance of CrCeAPO-5, but has almost no effect on CrZrAPO-5. Metal leaching is another concern in potential industrial applications of MeAPO-5 and MeSAPO-5 catalysts. The heterogeneous catalysts prepared in the present work showed very little metal leaching. This feature, coupled with the good selectivities and effectivities, makes them potentially very useful.
21
Solmi, Matilde Valeria. "Synthèse d'acides carboxyliques à partir de substrats oxygénés, de CO2 et de H2". Thesis, Lyon, 2018. http://www.theses.fr/2018LYSE1287/document.
Testo completoAbstract (sommario):
Les acides carboxyliques aliphatiques sont utilisés dans de nombreux secteurs industriels et leur importance économique augmente. Ils sont actuellement produits en grande quantité, grâce à des procédés utilisant le C0 qui est principalement non- renouvelable. L'anhydride carbonique est une molécule potentiellement écologique, renouvelable et abondante. Cette thèse décrit l'étude et l'optimisation d'un système catalytique homogène de Rh, utilisé pour produire des acides carboxyliques aliphatiques à partir de substrats oxygénés, C02 et H2. Le système consiste en un précurseur de Rh, un additif à base d'iodure et un ligand PPh3, fonctionnant dans un réacteur discontinu sous une pression de C02 et de H2. Les conditions de réaction ont été optimisées pour chaque classe de substrats étudiés: alcools primaires et secondaires, cétones, aldéhydes et époxydes. 30 molécules différentes ont été converties en acides carboxyliques, conduisant à des rendements jusqu'à 80%. En plus, le système a été étudié avec une approche de « Design of Experiment », ce qui a permis d'obtenir des informations supplémentaires concernant les paramètres étudiés. Le mécanisme de réaction et les espèces catalytiques actives ont été étudiés par différentes manipulations comme des réactions compétitives, des expériences de RMN et l'utilisation de molécules marquées. La réaction est composée de transformations non catalytiques et de deux étapes catalytiques. La réaction se déroule à travers une réaction de reverse Water Gas Shift (rWGSR) transformant le C02 et l'H2 en C0 et H20, qui sont consommés dans l'hydrocarboxylation suivante de l'alcène formé in situ pour livrer l'acide carboxylique. Le système catalytique est similaire aux catalyseurs traditionnels à base du Rh pour les réactions de carbonylation et de Water Gas Shift. Le PPh3 est nécessaire pour fournir des ligands supplémentaires, permettant au catalyseur de fonctionner avec une quantité minimale de ligand toxique de C0. En plus, un système catalytique hétérogène a été étudié pour la même réaction. « Single Atom Catalysts » (SACs) reçoit beaucoup plus d'attention que les solutions catalytiques, car il présente à la fois les avantages des catalyseurs homogènes (sélectivité, haute activité) et des catalyseurs hétérogènes (séparation et recyclage faciles). Des atomes de rhodium simples dispersés sur du graphène dopé avec l'N ont été synthétisés et caractérisés, obtenant des informations concernant la structure chimique et physique du matériau. Finalement, ils ont été testés ainsi que les catalyseurs pour l'activation du C02, la production d'acides carboxyliques, les réactions d'hydrogénation et d'hydrogénolyseAliphatic carboxylic acids are used in many industrial sectors and their importance from an economical point of view is increasing. They are currently produced in large quantities, through processes exploiting the mostly non-renewable C0 as C1 synthon. Carbon dioxide is a potential environmentally friendly, renewable and abundant C1 building block. The aim of this work is to provide a catalytic protocol converting C02, H2 and oxygenated substrates to obtain useful chemicals, like carboxylic acids.To this end a homogeneous catalytic Rh system, used to produce aliphatic carboxylic acids starting from oxygenated substrates, C02 and H2 was investigated and optimized. The system consists of a Rh precursor, iodide additive and PPh3 ligand working in a batch reactor under C02 and H2 pressure. The reaction conditions were optimized for each class of investigated substrates: primary alcohols, secondary alcohols, ketones, aldehydes and epoxides. The reaction scope was investigated and 30 different molecules were converted into carboxylic acids, leading to yields of up to 80%. ln addition, the system was studied using a Design of Experiment approach, obtaining additional information regarding the studied parameters.The reaction mechanism and the catalytically active species were studied, by different experiments like competitive reactions, NMR and labelling experiments. This investigation resulted in a deeper knowledge of the reaction pathway, composed of some non-catalytic transformations and two catalytic steps. The reaction proceeds through a reverse Water Gas Shift Reaction (rWGSR) transforming C02 and H2 into C0 and H20, which are consumed in the following hydrocarboxylation of the in-situ formed alkene to give the final carboxylic acid product. The catalytic system is similar to traditional Rh carbonylation and Water Gas Shift catalysts. The PPh3 is needed to supply additional ligands allowing the catalyst to work in reaction conditions with a minimal amount of toxic C0 ligand. ln addition, a heterogeneous catalytic system was investigated for the same reaction. Single atom catalysts (SACs) are receiving much attention as catalytic solution, since they have both the advantages of homogeneous (selectivity, high activity) and heterogeneous (easy separation and recycling) catalysts. Single Rh atoms dispersed on N-doped graphene were synthesized and characterized, obtaining information regarding the chemical and physical structure of the material. Eventually, they were tested as catalysts for C02 activation, carboxylic acid production, hydrogenation and hydrogenolysis reactions
Aliphatische Carbonsauren werden in vielen industriellen Bereichen verwendet und ihre wirtschaftliche Bedeutung nimmt zu. Sie werden derzeit in gror.en Mengen hergestellt, indem das meistens nicht erneuerbare Kohlenmonoxid als C1-Synthon genutzt wird. Kohlendioxid ist ein potenziell umweltfreundlicher, erneuerbarer und abundanter C1-Baustein. Das Ziel dieser Arbeit ist die Entwicklung eines Protokolls zur katalytischen Umwandlung von C02, H2 und sauerstoffhaltigen Substraten, um nützliche Chemikalien, wie Carbonsauren zu erhalten. Zu diesem Zweck wird ein homogenes Rh-Katalysatorsystems zur Herstellung aliphatischer Carbonsauren aus sauerstoffhaltigen Substraten, C02 und H2 untersucht und optimiert. Das System besteht aus Rh-Prakursor, lodid-Additiv und PPh3 als Ligand, die in einem Batchreaktor unter C02 und H2 eingesetzt werden. Die Reaktionsbedingungen wurden für folgende Substratklassen optimiert: primare Alkohole, sekundare Alkohole, Ketone, Aldehyde und Epoxide. Es wurden insgesamt 30 verschiedene Substrate mit Ausbeuten bis zu 80% zu Carbonsauren umgesetzt. Darüber hinaus wurde das System mit einem ,,Statistische Versuchsplanung"-Ansatz untersucht, um zusatzliche lnformationen zu den untersuchten Parametern zu erhalten. Mechanismus und katalytisch aktive Spezies wurden durch verschiedene Experimente wie Konkurrenzreaktionen, NMR- und Markierungsexperimenten untersucht. Dies erschloss den Reaktionsweg, der aus mehreren nicht-katalytischen Transformationen und zwei katalytischen Schritten besteht. Die Reaktion verlauft durch eine ,,reverse Wassergas-Shift-Reaktion" (rWGSR), die C02 und H2 in C0 und H20 umwandelt. Diese werden wiederum bei der nachfolgenden Hydrocarboxylierung des in-situ gebildeten Alkens unter Bildung der Carbonsaure verbraucht. Das katalytische System ahnelt herkômmlichen Rh-Carbonylierungs- und WGSR-Katalysatoren. PPh3 fungiert als zusatzlicher Ligand, der es dem Katalysator ermôglicht unter den gleichen Reaktionsbedingungen mit minimaler Menge toxischen C0 als Liganden zu arbeiten. Zusatzlich wurde ein heterogenes katalytisches System für die gleiche Reaktion untersucht. ,,Single atom catalysts" (SACs) erhalten gror.e Aufmerksamkeit als neue Katalysatorklasse. Sie kombinieren die Selektivitat und hohe Aktivitat homogener und die einfache Abtrennung und Recycling heterogener Katalysatoren Verschiedene Katalysatoren aus auf N-dotiertem Graphen dispergierten Rh-Atomen, wurden synthetisiert und charakterisiert. Dadurch wurden lnformationen über die chemische und physikalische Struktur des Materials gewonnen und als Katalysatoren für C02-Aktivierung, Carbonsauresythese, Hydrierung und Hydrogenolyse getestet
22
Ellis, Ieuan. "Interstitial modification of palladium for partial hydrogenation reactions". Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:7c8c294c-0583-4a61-98e5-4c32d76cbf89.
Testo completoAbstract (sommario):
Heterogeneous catalysis is a key industrial process involved in the synthesis of nearly all chemicals currently produced. The environmental impact of these processes is huge so improvements must be made to current catalysts. Should a new material provide better yields at lower energy cost the benefits to both the industry and the planet are significant. There are many ways to change the behaviour of a catalyst, the addition of dopants, the selective blocking of active sites, and changing the strength of the support interaction to name a few. One technique that has become increasingly investigated is interstitial modification, the insertion of a light element into a metal lattice to change the metal's catalytic properties. The work presented in this thesis devises greener synthetic routes to the known Pd-interstitialB/C catalyst and investigates potential routes to a novel interstitial material, Pd-interstitialLi/C. Initially, successful verification of interstitial modification comes from the characteristic increase in palladium lattice parameter from 3.89 to 4.00 Å and the blocking of the β-hydride formation. Initial catalytic screening determines the synthetic route which yields the most active catalyst which subsequently undergoes thorough characterisation. The wealth of evidence generated confirms the interstitial location of lithium within the palladium lattice, as well as adding to the current understanding of the Pd-interstitialB/C material. EELS analysis on Pd-interstitialB is the closest to direct observation of boron within the palladium lattice to date. PDF on Pd-interstitialLi shows 13.7 % of the palladium octahedral interstitial sites are occupied by lithium. This is the first report of interstitial lithium within palladium to date. The effect of the interstitial modification on catalytic hydrogenation by two elements that have opposite effects on the surface electronics of the host palladium gives intriguing results. The effect on catalysis varies depending on the conditions investigated. This bank of hydrogenation data allows an informed choice as to which interstitial material would be best suited to the gas or liquid phase catalytic hydrogenation under investigation.
23
Boopalachandran, Praveenkumar. "Catalytic studies of supported Pd-Au catalysts". Texas A&M University, 2006. http://hdl.handle.net/1969.1/3826.
Testo completoAbstract (sommario):
Although Pd-Au high-surface area catalysts are used in industry to improve
activity and selectivity, a thorough understanding of the nature of these enhancements is
lacking. A molecular-level understanding of catalytic reactions under actual reaction
conditions is the ultimate goal. This thesis is mainly focused on the application of Pd-Au
supported catalysts for vinyl acetate synthesis and CO oxidation reactions using highsurface
area catalysts. We have attempted to improve the conventional Pd-Au based
catalyst by synthesizing novel acetate-based and polymer-based catalysts. The
corresponding catalytic reactivity and selectivity were measured and compared to
conventional Pd-Au based catalyst systems. Subsequent characterization was performed
using characterization techniques, such as, X-ray diffraction (XRD) and transmission
electron microscopy (TEM).
From our bimetallic catalytic studies, it was evident that the addition of Au to Pd
leads to increased reactivity and selectivity. This surface modification is an important
factor in the altered reaction kinetics for vinyl acetate (VA) synthesis and CO oxidation
reactions. Promoted and unpromoted Pd-Au/SiO2/K+ catalyst were used for VA synthesis
and the effect of pre-adsorbed O2, acetic acid and the role of oxygen were explored. The VA reaction rate of novel acetate-based Pd-Au/SiO2 catalyst was 3.5 times
higher than conventional Pd-Au catalysts. Also, 100% selectivity was obtained for
acetate-based Pd-Au/SiO2 at 130 oC and the VA formation rate was comparable to that of
conventional Pd-Au catalysts. Therefore, the acetate-based Pd-Au/SiO2 catalyst seems
very promising and can be explored further. Also, Pd(1):Au(4)/SiO2 catalysts
demonstrate 100% CO conversion at much lower temperatures (90 oC) compared with
other Pd-Au based catalysts. Furthermore, we were successful in obtaining sufficient CO
oxidation activity with increased metal loading (5 wt%) and these catalysts did not
deactivate under above-ambient reaction temperature conditions, which make 1:4 Pd-
Au/SiO2 catalyst a good candidate for further exploration in CO oxidation reactions.
24
Iniesta, Beteta Ester. "Supramolecular Catalytic Systems: Synthesis, Characterization and Application in Catalysis". Doctoral thesis, Universitat Rovira i Virgili, 2021. http://hdl.handle.net/10803/671551.
Testo completoAbstract (sommario):
Aquesta tesi doctoral abasta el disseny i el desenvolupament de catalitzadors supramoleculars derivats de metalls de transició per a la seva aplicació com a catalitzadors en transformacions d'interès.
La primera part d'aquesta tesi doctoral està centrada en el desenvolupament de catalitzadors de coure(I) regulats supramolecularment i la seva aplicació en reaccions d'inserció d'espècies carbèniques metàl·liques a enllaços O–H, generant derivats α-alquil/aril-α-alcoxi/ariloxi. S’abordà el disseny, preparació, caracterització i aplicació dels catalitzadors de coure(I) derivats de lligands bisoxazolina. Aquests estudis van demostrar que l'activitat catalítica es podia modular amb l'ús de molècules externes (agents de regulació), que interaccionaven amb la cadena polioxietilènica del lligand (centre de regulació) a través d'interaccions supramoleculars de tipus ió-dipol. L'eficiència d'aquesta aproximació es demostrà en reaccions d’inserció de carbens metàl·lics sobre alcohols estructuralment diversos (derivats cicloalquílics, alquílics i arílics). Aquesta metodologia es va utilitzar també per a preparar intermedis sintètics avançats de compostos amb rellevància biològica.
La segona part d'aquesta tesi doctoral està centrada en l'ús d'interaccions de tipus halogen per formar l'esquelet de complexos metàl·lics. Es descriu la síntesis de nous complexos supramoleculars de platí(II) i pal·ladi(II) mitjançant l'assemblatge de dos blocs constituents que contenen fosfines com a grups coordinants, així com grups capaços de formar enllaços de tipus halogen. Es va caracteritzar en dissolució i a l’estat sòlid un conjunt de complexos estructuralment diversos de platí(II) i pal·ladi(II) derivats de difosfines (supramoleculars). Es va realitzar un ampli estudi dels intermedis de reacció que van conduir als complexos de platí(II) finals. Es proposa una racionalització mecanística de la formació dels complexos de platí(II) finals. El complex XBPhos-Pt va resultar ser inactiu en reaccions de ciclació d’enins i d’hidrofenilació de l’etilè. Es presenten estratègies d’activació del complex XBPhos-Pt i anàlegs per a noves transformacions químiques.Esta tesis doctoral abarca el diseño y desarrollo de catalizadores supramoleculares derivados de complejos de metales de transición para su aplicación como catalizadores en transformaciones de interés. La primera parte de esta tesis doctoral se centra en el desarrollo de catalizadores de cobre(I) regulados supramolecularmente para su aplicación en reacciones de inserción de especies carbénicas metálicas a enlaces O–H, generando derivados α-alquilo/arilo-α-alcoxi/ariloxi. Se abordó el diseño, preparación, caracterización y aplicación de los catalizadores de cobre(I) derivados de ligandos bisoxazolina. Estos estudios demostraron que la actividad catalítica podía modularse con el uso de moléculas externas (agentes de regulación), que interaccionaban con la cadena polioxietilénica del ligando (centro de regulación) a través de interacciones supramoleculares de tipo ion-dipolo. La eficiencia de esta aproximación se demostró en reacciones de inserción de carbenos metálicos sobre alcoholes estructuralmente diversos (derivados cicloalquílicos, alquílicos y arílicos). Esta metodología se utilizó también para preparar intermedios sintéticos avanzados de compuestos con relevancia biológica. La segunda parte de esta tesis doctoral se centra en el uso de interacciones de tipo halógeno para formar el esqueleto de complejos metálicos. Se describe la síntesis de nuevos complejos supramoleculares de platino(II) y paladio(II) mediante el ensamblaje de dos bloques constituyentes que contienen fosfinas como grupos coordinantes, así como grupos capaces de formar enlaces de tipo halógeno. Se caracterizó en disolución y en estado sólido un conjunto de complejos estructuralmente diversos de platino(II) y paladio(II) derivados de difosfinas (supramoleculares). Se realizó un estudio de los intermedios de reacción que condujeron a los complejos de platino(II) finales. Se propone una racionalización mecanística para la formación de los complejos de platino(II) resultantes. El complejo XBPhos-Pt fue inactivo en reacciones de ciclación de eninos e hidrofenilación del etileno. Se presentan estrategias de activación del complejo XBPhos-Pt y análogos para nuevas transformaciones químicas.
This doctoral thesis encompasses the design and development of supramolecular catalysts derived from transition metal complexes and their application as catalysts in transformations of interest. The first part of the thesis focusses on the development of supramolecularly regulated copper(I) catalysts for the insertion of metal carbenes into O–H bonds leading to synthetically useful α-alkyl/aryl-α-alkoxy/aryloxy derivatives. The design, preparation, characterization and application of supramolecularly regulated copper(I) catalysts derived from bisoxazoline ligands is described. Our studies demonstrate that the catalytic performance of these systems can be modulated by the use of an external molecule (i.e. the regulation agent), which interacts with the polyethyleneoxy chain on the ligand (i.e. the regulation site) via supramolecular ion-dipole interactions. This approach has been applied to an array of structurally diverse alcohols (cycloalkyl, alkyl and aryl derivatives). Moreover, this methodology has been used to synthesize advanced synthetic intermediates of biologically relevant compounds. The second part of this thesis focusses on the use of halogen bonding interactions to construct the skeleton of metal complexes. The synthesis of new supramolecular platinum(II) and palladium(II) complexes by assembling two building blocks that incorporate phosphines as ligating groups, as well as complementary binding motifs for the assembly through halogen bonding, are reported. A set of structurally diverse platinum(II) and palladium(II) complexes derived from (halogen-bonded) diphosphines have been characterized in solution and in the solid state. A broad study of the reaction intermediates that led to the platinum(II) complexes has been performed. A tentative mechanistic rationalization for the formation of the platinum(II) complexes is proposed. The complex XBPhos-Pt has proved to be unreactive as a catalyst in cyclizations of enynes and in the hydrophenylation of ethylene. Strategies towards the activation of XBPhos-Pt and analogues for new chemical transformations are presented.
25
Fan, Yinan. "Rational synthesis of plasmonic/catalytic bimetallic nanocrystals for catalysis". Thesis, Sorbonne université, 2022. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2022SORUS189.pdf.
Testo completoAbstract (sommario):
Parmi les différents nanocatalyseurs, ceux constitués de nanoparticules de métaux nobles méritent une attention particulière en raison de leurs propriétés électroniques, chimiques et même optiques (dans le cas de transformations renforcées par les plasmons). Le platine ou le palladium sont bien connus pour leurs remarquables propriétés catalytiques, mais ils sont chers et leurs ressources sont limitées. En outre, les nanocatalyseurs monométallique ne peuvent conduire qu'à une gamme limitée de réactions chimiques. Ainsi, notre stratégie a été de développer des nanocatalyseurs bimétalliques composés de deux éléments métalliques qui peuvent présenter des effets synergiques entre leurs propriétés physicochimiques et une activité catalytique accrue. Nous avons ainsi conçu des nanocatalyseurs bimétalliques de type cœur-coquille composés d'un cœur en argent et d'une coquille en platine. L'intérêt est de combiner les activités catalytiques élevées et efficaces de la coquille de platine avec le cœur d'argent hautement énergétique, capable de renforcer les activités de la coquille grâce à ses propriétés plasmoniques. En outre, ces nanoparticules bimétalliques présentent souvent une activité catalytique supérieure en raison de la modification de la distance inter-atomique Pt-Pt (c'est-à-dire l'effet de contrainte). Dans ce travail de thèse, les nanoparticules Ag@Pt ont été synthétisées via un processus en deux étapes utilisant d'une part des nanoparticules d'Ag synthétisées chimiquement comme germes et d'autre part des complexes platine-oleylamine qui sont ensuite réduits à la surface des germes à une température contrôlée. Différentes tailles de germes d'Ag de 8 à 14 nm avec une très faible distribution de taille (<10%) ont été obtenues en ajustant le temps de réaction, la rampe de température, la concentration en précurseur d'Ag et la température finale pendant la synthèse. Différentes épaisseurs de coquille (de 1 à 6 couches atomiques) ont été obtenues en ajustant le rapport entre les concentrations de précurseur de platine et de germe d'argent. L'activité catalytique des nanoparticules Ag@Pt a été testée en considérant une réaction modèle de réduction du 4-nitrophénol en 4-aminophénol par NaBH4 en phase aqueuse. Nous avons observé que l'épaisseur de la coquille de Pt et la taille du noyau d'Ag influençaient les propriétés catalytiques et conduisaient à une activité catalytique accrue par rapport à l'argent ou au platine pur. Ceci a été attribué à des effets synergiques. De plus, nous avons observé une augmentation de l'activité catalytique des nanoparticules Ag et Ag@Pt sous irradiation lumineuse. Ce phénomène a été corrélé à la génération d'électrons chauds dans les noyaux d'Ag. Afin de développer une plateforme de nanocatalyse supportée, nous avons fabriqué des auto-assemblages 3D appelés aussi supercristaux composés de nanoparticules d'Ag@Pt obtenus spontanément après dépôt sur un substrat solide en raison de leur distribution de taille étroite et de leur forme homogène. L'activité catalytique de ces supercristaux pour la réaction d'évolution de l’hydrogène (HER) a été étudiée en suivant in situ par microscopie optique la production de nanobulles de gaz H2. Trois comportements distincts dans l'activité photo-catalytique (activité, activité intermittente et non-activité) ont été observés sur les supercristaux dans la même région d'intérêt. En outre, 50 % des assemblages ont été déterminés comme étant actifs pour l'HER qui a été démontrée comme étant accompagnée par une corrosion oxydative de l’argentAmong several nanocatalysts, those based on noble metal NPs deserve particular attention because of their electronic, chemical and even optical properties (in the case of plasmonic-enhanced transformations). Platinum or palladium are well known for their remarkable catalytic properties, but they are expensive and their resources are limited. In addition, single component nanocatalysts can only lead to a limited range of chemical reactions. Thus, our strategy was to develop bimetallic nanocatalysts composed of two metal elements that can exhibit synergistic effects between their physicochemical properties and enhanced catalytic activity. We have thus designed bimetallic nanocatalysts of the core-shell type composed of a silver core and a platinum shell. The interest is to combine the high and efficient catalytic activities of the platinum shell surface with the highly energetic silver core capable of enhancing the activities of the shell through its plasmonic properties. In addition, these bimetallic NPs often exhibit superior catalytic activity due to the modification of the Pt-Pt atomic bonding distance (i.e. the strain effect). In this thesis work, Ag@Pt NPs have been synthesized via a two-step process using chemically synthesized spherical Ag NPs as seeds on the one hand and platinum complexes with oleylamine on the other hand which are then reduced on the surface of the seeds at a controlled temperature. Different Ag seed sizes from 8 to 14 nm with a very low size distribution (<10%) have been obtained by adjusting the reaction time, temperature ramp, Ag precursor concentration and final temperature during the synthesis. The control of the shell thicknesses (from 1 to 6 atomic layers) has been possible by adjusting the ratio of platinum precursor to silver seed concentrations. The catalytic activity of the core-shell Ag@Pt NPs was tested by a model reaction of reduction of 4-nitrophenol to 4-aminophenol by NaBH4 in aqueous phase. We have observed that the thickness of the Pt shell and the size of the Ag core influence the catalytic properties and led increased catalytic activity compared to pure silver or platinum. This was attributed to synergistic effects. Furthermore, we have observed an enhancement of the catalytic activity of Ag and Ag@Pt NPs under light irradiation. This is correlated to the generation of hot electrons in the Ag core. Finally, in order to develop a supported nanocatalysis platform, 3D self-assemblies also called supercrystals composed of Ag@Pt nanoparticles have been spontaneously obtained after deposition on a solid substrate due to their narrow size distribution and homogeneous shape. The catalytic activity of these supercrystals for the hydrogen evolution reaction (HER) has been studied by following in situ by optical microscopy the production of H2 gas nanobubbles. Three distinct behaviors in photo-catalytic activity (activity, intermittent activity and non-activity) have been observed on the supercrystals in the same region of interest. In addition, 50% of the assemblies were determined to be active for HER which was shown to be accompanied by oxidative corrosion of silver
26
Reddy, P. K. "Exploration of catalysts and catalysis under near working conditions". Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2018. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/4577.
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Warren, James Patrick. "Catalytic chemistry of the rhodium/ceria system : model catalysts and dispersed catalysts". Thesis, University of Cambridge, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627214.
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Sonqishe, Thantaswa Millecent. "Treatment of brines using commercial zeolites and zeolites synthesized from fly ash derivative". Thesis, University of the Western Cape, 2008. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_6127_1297842299.
Testo completoAbstract (sommario):
The objectives of this project was to ameroliate two waste materials, namely Acid Mine Drainage and Fly Ash and recover the solid residues for conversion into an adsorbent to treat brine. The solid residues were then converted into zeolite P through low temperature hydrothermal treatment. The adsorption capacity of the solid residues, zeolite P derived from the solid residues was compared to the commercial zeolite Y and fresh Arnot fly ash. The quality of the resulting water was assessed using different analytical methods before the reaction with adsorbents and after the reaction and a comparison was done based on the removal efficiency of elements Zeolite P from solid residues was successfully synthesized as confirmed by XRD, BET and FTIR. Brine treatment with fly ash, solid residues, zeolite P and commercial zeolite Y adsorbents was done concentration on the following major elements Na, K, Mg, Ca and Si. Zeolite P had higher or similar removal efficiency that the commercial zeolite Y for the following elements K, Ca and Mg. Fly ash is the only adsorbent that managed to reduce the concentration of Na in brine and also had a good removal efficiency of Mg. Si leached out of all the adsorbents which could be ascribed to Si being the major component of these adsorbents which could indicate some dissolution of these adsorbents under the conditions tested. Overall, zeolite P did not completely remove the major elements, especially for Na, but did result in a cleaner waste stream which would improve brine processing.
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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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Ashraf, Muhammed Arfan. "Biomimetic ligands for transition metals". Thesis, King's College London (University of London), 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391261.
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Linganiso, Linda Zikhona. "Adsorption studies on supported gold catalysts using temperature programmed desorption (TPD)". Thesis, Wits University, 2007. http://hdl.handle.net/10539/20167.
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Wojcik, Karolina. "D-glucosamine as "green" substrate in synthesis of ligands for asymetric catalysis". Phd thesis, Université Claude Bernard - Lyon I, 2012. http://tel.archives-ouvertes.fr/tel-00974873.
Testo completoAbstract (sommario):
Several ligands derived from D-glucosamine, designed for different catalytic reactions havebeen synthesized. The ligands for homogeneous catalysis based on 1,2-glucodiamine wereprepared, and used in reactions of allylic alkylation, hydrogenation and Michael addition.Supported Aqueous Phase Catalyst (SAPC) system was prepared from D-glucosamine anduse with very good results in Suzuki Miyaura cross coupling reactions. Catalyst was alsorecycled. Attempt to prepare ligands grafted on SBA-silica matrix were made as well asligands containing poly(ethylene) glycol moiety.
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Chenneberg, Ludwig. "Nouvelles avancées en catalyse photoredox : applications en chimie radicalaire de synthèse et en catalyse duale". Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066305/document.
Testo completoAbstract (sommario):
L’objectif principal des travaux de recherche décrits dans ce manuscrit de thèse, est de concevoir de nouvelles méthodes de synthèse en chimie radicalaire et organométallique, de les associer dans une catalyse duale afin qu’elles puissent être appliquées à l’élaboration de briques moléculaires élaborées. Nous avons développé dans une première étude une alternative photocatalytique à la réaction de désoxygénation classique de Barton-McCombie d’alcools secondaires et tertiaires par l’hydrure de tributylétain. Celle-ci repose sur l’utilisation d’un précurseur O-thiocarbamate dérivé d’alcools pouvant être réduit par catalyse photorédox. Une étude mécanistique, basée sur des expériences de fluorescence et de voltammétrie cyclique, est aussi présentée. Dans une seconde étude, une élégante méthode de génération de radicaux alkyles non stabilisés, par photooxydation de « ate-complexes » de bore ou d’espèces hypervalentes à base de silicium est présentée. Ces radicaux sont piégés en présence d’accepteurs radicalaires ou engagés dans une catalyse duale avec des complexes de NickelVisible-light photoredox catalysis has emerged as a very powerful strategy to generate radical species replacing more and more tin-mediated or stoichiometric redox methodologies. The main objective of the research described in this Ph. D. thesis is to develop new synthetic methodologies in radical and organometallic chemistry, and merge them in a dual catalysis process for the preparation of elaborated molecular building blocks. In a first study, we report a photocatalytic alternative of Barton-McCombie deoxygenation based on a visible-light photoreduction of O-thiocarbamates derived from secondary and tertiary alcohols. A mechanistic investigation is presented based on fluorescence quenching and cyclic voltammetry experiments. In a second study, a challenging method of generation of unstabilized alkyl radicals by photooxidation of borate salts or hypervalent silicon species is reported. These radicals are trapped by free radical scavengers or engaged in a photoredox/nickel dual catalysis
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Ebadi, pour Negisa. "Développement de systèmes catalytiques à base de Ca pour la polymérisation sélective de glycérol". Electronic Thesis or Diss., Centrale Lille Institut, 2021. http://www.theses.fr/2021CLIL0027.
Testo completoAbstract (sommario):
Bien que de très nombreuses applications soient recensées pour valoriser le glycérol coproduit par la filière biodiesel (à raison de 100 kg de glycérol par tonne de biocarburant), les solutions potentiellement les plus lucratives basées sur des transformations chimiques avancées n’atteignent aujourd’hui que rarement le stade commercial. Ceci est principalement dû à (i) une instabilité réglementaire sur les licences de production de biodiesel menaçant ainsi la disponibilité du glycérol et (ii) un prix du glycérol pouvant par conséquent fluctuer de manière imprévisible. Faire évoluer le concept d’unité de production de biodiesel, où le glycérol est le coproduit principal, en un concept de bioraffinerie oléagineuse, où notamment des produits à haute valeur ajoutée dérivés du glycérol sont produits avec le biodiesel, permettra de s’affranchir des incertitudes règlementaires liées à la production du biodiesel tout en favorisant un développement rapide des technologies de valorisation du glycérol par évolution d’unités de production existantes. Dans ce contexte, ce projet de thèse basé sur des résultats préliminaires très prometteurs de notre équipe vise à développer un procédé catalytique de valorisation efficace du glycérol en polyglycérols linéaires (PGs). Les PGs présentent une biocompatibilité exceptionnelle récemment démontrée. Ils possèdent en outre des applications directes (pharmacie, alimentation, etc.), et de grands industriels le voient aussi de plus en plus comme une base pour l’obtention d’autres molécules, notamment les esters de PGs, diversifiant considérablement les champs d’applications finaux (émulsifiants, stabilisateurs, etc.). Le programme de recherche proposé permettra de mieux comprendre et d’optimiser en retour un système catalytique performant et robuste, dans un contexte régional particulièrement propice (Hub2 de l’I-SITE, producteurs de biodiesel, plateformes REALCAT et UPCAT, CPER-FEDER Archi-CM, etc.)Although many applications are listed to valorize glycerol as a co-produced of the biodiesel sector (at a rate of 100 kg of glycerol per ton of biofuel), the most potential solutions based on advanced chemical transformations today reach rarely the commercial stage. This is mainly due to (i) instability on biodiesel production licenses, thus threatening the availability of glycerol and (ii) a price of glycerol that can fluctuate unpredictably. In the concept of biodiesel production unit, where glycerol is the main co-product, into a concept of oilseed biorefinery, where in particular glycerol-derived products with high added value are produced with biodiesel, will make it possible to overcome uncertainties related to the production of biodiesel while promoting the rapid development of glycerol valorization technologies through the evolution of existing production units. In this context, this thesis project based on very promising preliminary results from our team aims to develop a catalytic process for the efficient valorisation of glycerol in linear polyglycerols (PGs). PGs have recently demonstrated exceptional biocompatibility. They also have direct applications (pharmacy, food, etc.), and large manufacturers also see it increasingly as a base for obtaining other molecules, including PGs esters. The proposed research program will provide a better understanding and optimization of a powerful and robust catalytic system in a particularly favorable regional context
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Shiels, Rebecca Anne. "Synthesis, characterization, and evaluation of silica and polymer supported catalysts for the production of fine chemicals". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/29629.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Chemical Engineering, Georgia Institute of Technology, 2008.Committee Chair: Dr. Christopher Jones; Committee Member: Dr. Dennis Hess; Committee Member: Dr. Hang Lu; Committee Member: Dr. Marcus Weck; Committee Member: Dr. Pradeep Agrawal. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Han, Xu. "Development of innovative methodologies in phosphine organocatalysis and enantioselective gold(I)-catalysis". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS568.
Testo completoAbstract (sommario):
Les phosphines jouent un rôle central dans la chimie organique moderne. Dans le domaine de la catalyse, les composés organophosphorés peuvent être appliqués soit en tant qu’organocatalyseurs dans de nombreuses transformations, soit en tant que ligands en catalyse organométallique. Au cours de cette thèse, nous avons utilisé les phosphines dans ces deux applications : en organocatalyse et en catalyse asymétrique à l’or(I). Dans la première partie, nous avons développé une réaction d’addition de Michael/réaction de Wittig intramoléculaire. Nous avons judicieusement choisi la phosphine utilisée ainsi que l’agent réducteur afin de permettre la réduction in situ de l’oxyde de phosphine correspondant. De nombreux dérivés 1,2-dihydroquinolines diversement fonctionnalisés ont pu être isolés avec de bons rendements. Parallèlement à cela, une nouvelle réaction d’oléfination a pu être découverte, donnant accès à des dérivés succinates. Un mécanisme réactionnel a pu être proposé, en se basant notamment sur des expériences de deutération. Dans un deuxième temps, nous nous sommes intéressés au développement de réactions énantiosélectives catalysées par des complexes chiraux d’or(I), et utilisant des substrats énynes. Une première réaction de cyclisation d’énynes-1,5, suivie d’une addition nucléophile a été développée en utilisant des complexes d’or de structure TADDOL-phosphoramidite-AuCl. Ce catalyseur a permis l’obtention de vingt dérivés cyclopentènes avec de bons rendements et des excès énantiomériques atteignant 94% ee. Finalement, des substrats énynes-1,6 correctement substitués ont été utilisés dans une réaction de cyclisation, suivie d’un piégeage intramoléculaire, afin de donner accès à des composés tétracycliques et pentacycliques complexes. Les composés racémiques ont été isolés avec de bons rendements et la version asymétrique a également été développée, par l’utilisation de complexes chiraux d’or(I)Phosphines play a major role in modern organic chemistry. In the field of catalysis, organophosphorus derivatives can be applied as catalysts in numerous transformations by itself, as organocatalysts, or as ligands in organometallic catalysis. This thesis focused on the application of phosphines both in phosphine organocatalysis and in asymmetric gold(I) catalysis. In the organophosphorus catalysis part, we have developed a phosphine-catalyzed Michael addition/Wittig reaction by using a well-chosen cyclic phosphine catalyst. In this process, silane was used as reducing agent to selectively reduce in situ the phosphine oxide. A series of highly functionalized 1,2-dihydroquinolines were prepared. Besides, a new olefination process was discovered for the synthesis of succinate derivatives. Detailed mechanism research was carried out with H/D exchange experiments. In the asymmetric gold(I) catalysis part, we have developed two new methodologies based on cyclization reactions of 1,n-enyne substrates. A 1,5-enyne cyclization/nucleophilic addition reaction was first developed with an acyclic TADDOL-derived phosphoramidite-Au(I) complex. Twenty examples were carried out with good to excellent yields and up to 94% enantiomeric excess. For the 1,6-enyne cyclization/intramolecular nucleophilic addition sequence, we have synthesized a range of racemic tetracyclic and pentacyclic compounds in high yields. The enantioselective version of this transformation was carried out successfully with both high reactivity and enantioselectivity
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Lopes, Silva Susana. "Développement de nouveaux catalyseurs d'hydrotraitement basés sur l'encapsulation d'hétéropolyoxometallates dans des silices mésostructurées : application à la production de carburants propres". Thesis, Lyon, École normale supérieure, 2013. http://www.theses.fr/2013ENSL0799/document.
Testo completoAbstract (sommario):
Le développement de technologies plus propres et économes en énergie amène aujourd’hui l’industrie du raffinage à modifier ses stratégies de préparation de catalyseurs et à se tourner vers l'utilisation plus massive de catalyseurs hétérogènes plus actifs, sélectifs, stables et régénérables.Récemment une méthode originale a été développée par Dufaud et al. (J. Mater. Chem., 2009, 19, 1142-1150) pour encapsuler des polyoxométallates (POMs) dans les murs des silices mésoporeuses. Le projet de thèse a visé l’élaboration de nouveaux catalyseurs basés sur cette nouvelle méthodologie qui devrait conduire à des systèmes à haute teneur en métal actif Mo/W bien dispersé, avec une meilleure proximité spatiale entre le Mo/W et son promoteur. Afin de mettre en évidence cette proximité, différentes voies ont été envisagées :i) synthèse en deux étapes comportant l'encapsulation des POMs dans les murs de SBA-15, suivie d’une imprégnation à sec des promoteurs (Ni(NO3)2 ou Co(NO3)2)ii) synthèse en une seule étape comportant l'imprégnation à sec de POMs substitués Co3PCoMo11O40H, Ni3PNiMo11O40H, Co3/2PMo12O40 ou Ni3/2PMo12O40 iii) préparation traditionnelle par co-Imprégnation à sec d’une silice SBA-15 par une solution de POMs et Ni(NO3)2 ou Co(NO3)2, afin de mettre en évidence non seulement l'intérêt de la nouvelle méthode de préparation mais aussi le gain lié à l'utilisation de supports de type SBA-15 (par rapport aux supports aluminiques conventionnels) ayant des caractéristiques texturales aussi remarquables. L’effet du traitement de sulfuration sur ces solides a été étudié et l’évaluation des propriétés catalytiques de ces matériaux a été réalisée sur des molécules modèles en hydrogénation du toluène, hydrodésulfuration du thiophène et du 4,6-DMDBT. A partir des résultats obtenus, une des stratégies de synthèse a été optimisée, en vue de l'élaboration de matériaux encore plus actifsEconomic growth in the developing countries over the past decade has increased the global demand for crude oil. It is projected that the global crude slate will become sourer, with a sulfur content above 1.3 wt%. An overall aim of policymakers is thus to ensure that transportation fuels do not surpass a sulfur content of 10 ppm. Several solutions are possible to achieve the nowadays goals, that affect either the process or the catalyst. The latter solution, which does not involve significant additional costs for refiners, is therefore the most studied. One way to improve the nowadays catalysts would be to increase the content of active metal (eg cobalt and molybdenum in the case of CoMo systems). Nevertheless, at higher metal loadings, the formation of refractory species such as CoMoO4 or Co3O4 by sintering during calcination and/or sulfidation steps has been reported for alumina-Supported catalysts. This PhD project is based on the development of new hydrotreating catalysts, through a 2-Step one-Pot method : synthesis of polyoxometalates-Containing mesoporous SBA-15 materials, followed by incipient wetness impregnation of active phase promoter. The encapsulation of these species within the silica matrix would prevent the agglomeration of large particles during sulfidation reactions and could thus lead to systems with high content of active metal well dispersed over the support. One aim of this study was to evaluate the potential of these catalysts in the hydrotreating of several feedstocks, such as diesel oil, gasoline or vegetal oil. A second objective was the understanding of the nature of the different interactions between the active phase precursors and the support, according to each preparation technique.The non-Promoted hybrid catalyst showed a better dispersion of the metallic phase in the oxide state, compared to the catalysts prepared by incipient wetness impregnation, which can be correlated with stronger interactions between encapsulated POM and silica functionalities, such as siloxanes and silanols, as evidenced by Raman spectroscopy. However, the wide-Angle XRD showed the presence of MoO3 crystallites. HRTEM analyzes of the sulfided catalysts showed different species on this catalyst: small MoS2 slabs and metal particles (∼ 1 nm) mainly in the walls but also on the surface of pores; curved MoS2 slabs at mesopores surface leaving the entrance of the pore free; MoS2 hanks blocking the pores.This catalyst showed a relatively low sulfidation rate (determined by XPS), which could be associated with the presence of refractory species already present before activation. Thus, the toluene conversion represented per MoS2 clearly showed the interest of the catalyst prepared by this innovative method, presenting an intrinsic activity two-Fold higher than that of the catalyst prepared by dry impregnation.The subsequent impregnation of the active phase promoter of the hybrid catalyst (Pr(NO3)2, Pr = Ni or Co; 4
38
Ye, Wei. "Catalytic oxidation of methane over supported palladium catalysts". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0003/MQ40128.pdf.
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Persson, Katarina. "Bimetallic palladium catalysts for catalytic combustion of methane". Licentiate thesis, Stockholm, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-332.
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Huang, Zhenyu. "Magnetic resonance studies of catalysts and catalytic reactors". Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612201.
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Lenden, Philip. "Tandem catalytic processes involving Rhodium-catalysed intermolecular hydroacylation". Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:e63f5fd7-f92f-47dd-b06f-face73729804.
Testo completoAbstract (sommario):
This work describes the extension of rhodium-catalysed intermolecular hydroacylation to encompass some tandem catalytic processes, wherein a further catalytic process is enacted on the product of an intermolecular hydroacylation reaction in “one pot”. Chapter 1 entails an overview of the development of hydroacylation chemistry, with a focus on the different types of catalytic systems which have been used to facilitate this transformation. A brief description of some precedented examples of tandem catalytic processes which include a hydroacylation reaction is also included. Chapter 2 describes the intermolecular hydroacylation of chelating aldehydes and propargylic alkynes to form γ-hydroxy-α,β-enones, and their subsequent acid-catalysed cyclisation to form substituted furans in a "one-pot" procedure. Additionally, a tandem intermolecular hydroacylation/double-bond isomerisation protocol for the synthesis of 1,4-dicarbonyl compounds is detailed, and the subsequent transformation of this class of compounds to heterocycles is included. Chapter 3 focuses on the development of tandem catalytic hydroacylation/reductive processes, wherein a hydroacylation product undergoes a reduction which is catalysed by the hydroacylation catalyst. Chapter 4 describes an attempt to utilise the rhodium-catalysed conjugate addition of arylmetal species to enomes to create a tandem alkyne hydroacylation/conjugate addition process. Chapter 5 encompasses the use of a small range of different solvents in rhodium-catalysed hydroacylation, in an attempt to find higher-boiling alternatives to acetone and a "green" alternative to the commonly used DCE.
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Beach, Nicholas James. "Metathesis Catalysts in Tandem Catalysis: Methods and Mechanisms for Transformation". Thèse, Université d'Ottawa / University of Ottawa, 2012. http://hdl.handle.net/10393/22731.
Testo completoAbstract (sommario):
The ever-worsening environmental crisis has stimulated development of less wasteful “green” technologies. To this end, tandem catalysis enables multiple catalytic cycles to be performed within a single reaction vessel, thereby eliminating intermediate processing steps and reducing solvent waste. Assisted tandem catalysis employs suitable chemical triggers to transform the initial catalyst into new species, thereby providing a mechanism for “switching on” secondary catalytic activity.
This thesis demonstrates the importance of highly productive secondary catalysts through a comparative hydrogenation study involving prominent hydrogenation catalysts of tandem ring-opening metathesis polymerization (ROMP)-hydrogenation, of which hydridocarbonyl species were proved superior. This thesis illuminates optimal routes to hydridocarbonyls under conditions relevant to our ROMP-hydrogenation protocol, using Grubbs benzylidenes as isolable proxies for ROMP-propagating alkylidene species. Analogous studies of ruthenium methylidenes and ethoxylidenes illuminate optimal routes to hydridocarbonyls following ring-closing metathesis (RCM) and metathesis quenching, respectively. The formation of unexpected side products using aggressive chemical triggers is also discussed, and emphasizes the need for cautious design of the post-metathesis trigger phase.
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Smallwood, Keith. "Catalysis and photocatalysis by platinized titanium dioxide and other catalysts". Thesis, University of Nottingham, 1993. http://eprints.nottingham.ac.uk/12591/.
Testo completoAbstract (sommario):
The gas-phase, thermal hydrogenations of propene and cyclopropane over various titania-supported metal catalysts have been investigated. Catalysts were prepared either by a photodeposition or a thermal reduction method. Absolute initial hydrogenation rates were calculated from total gas pressure vs time measurements. The activities of all catalysts were found to be very dependent upon catalyst state, as modified by reductive or oxidative pretreatments. These results are discussed in terms of reversible strong metal-support interactions, initiated via hydrogen spillover. For 0.5 %mass Pt on Ti02, the order of reaction with respect. to hydrocarbon was 0.5. An adsorption mechanism involving the alkylidene species is proposed as one possible explanation of this result. A negative order of reaction with respect to hydrogen was recorded. A Langmuir-Hinshelwood mechanism, involving competitive adsorption of hydrocarbon and hydrogen at supported metal sites, is proposed. Differences in behaviour between catalysts prepared by photodeposition and the thermally-prepared catalyst were observed during the hydrogenation studies. These include different apparent activation energies, maximum reaction rates at differing propene: hydrogen ratios and irreversible degradation of all photodeposited catalysts during cyclopropane hydrogenation. These differences are taken as being strongly indicative of differences in supported metal morphologies, arising as a consequence of the preparative routes employed. Temperature programmed desorption and scanning electron microscopy studies were undertaken in an attempt to establish and characterise these potential morphological differences. Although the results of these studies were, at best, inconclusive, the possible nature of such supported metal morphological differences is discussed on the basis of available evidence generated within this and other, similar, studies. The liquid-phase photocatalytic dehydrogenation of propan-2-ol, using the same catalysts, was also briefly investigated. Variations in measured activation energies suggest that photodeposited catalysts in the 'as prepared' state are contaminated with variable levels of impurity residues, particularly chloride ions.
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Carter, Christabel Anne. "Asymmetric phase transfer catalysis : towards catalysts with a chiral anion". Thesis, University of Leeds, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.399654.
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Monti, Chiara. "Development of new catalysts for asymmetric catalysis via combinatorial chemistry". Thesis, University of Sheffield, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398589.
Testo completo
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Neate, Peter Gregory Nigel. "Pathways to sustainable catalysis : from novel catalysts to mechanistic understanding". Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/25441.
Testo completoAbstract (sommario):
Catalysis allows for the controlled formation of new bonds, whilst reducing both time and energy expenditure in the process. Catalysis has traditionally been the realm of precious metals, which have been used to carry out a bewildering array of reactions. However, there is an ever-increasing drive for the development of catalytic methodology employing sustainable and environmentally benign catalysts. Two such candidates are organocatalysis, omitting the need for metals where possible, or the use of iron catalysis. Two key areas to the advancement of the of field catalysis are the identification and development of new catalysts as well as an understanding of the mechanisms of established catalytic processes. Novel catalysts can provide many benefits such as enhanced or even novel reactivity, access to new classes of substrates or simply be more readily accessible compared with previously developed catalysts. To this end, the first example of Lewis-base-catalysis using the recently developed cyclopropenimine motif is reported. This was exploited in the trifluoromethylation of aldehydes and ketones using the Rupert-Prakash reagent (Scheme A-1). Scheme A-1 Cyclopropenimine-catalysed trifluoromethylation of aldehydes and ketones Developing an understanding of catalytic methodologies in the terms of their mechanism and active species is also a key area in catalysis. Insight into these can direct the expansion of these systems in terms of both more effective catalysts and tailoring reaction conditions as examples. The iron-catalysed hydromagnesiation of styrene derivatives was studied in detail. This culminated in a proposed mechanism, involving a novel hydride transfer process (Scheme A-2). Studies were carried out using a combination of kinetic analysis and in situ Mössbauer spectroscopy, as well as successfully isolating and studying the reactivity of a catalytically-relevant, formal iron(0)-species.
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Konrad, Tina Maria. "Chiral phanephos derived catalysts and their application in asymmetric catalysis". Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/4499.
Testo completoAbstract (sommario):
The research presented in this thesis is a project funded by the EU-network of the Marie Curie project NANO-HOST in collaboration with partner institutes. The aims of this network are to develop innovative methods for the preparation, recovery and reuse of single-site, nanostructured catalytic materials, and further on apply them in combination with specifically engineered reactors for a sustainable production process for making high value fine chemicals. One part of this project was to prepare chiral diphosphine ligands and their complexes for currently challenging reactions, such as asymmetric carbonylations (homogeneous catalysis). Catalytic studies of these chiral diphosphine ligands were carried out in asymmetric hydroxy-and alkoxy-carbonylations and hydrogenation reactions. The second part of this project was the heterogenisation of these chiral homogeneous complexes through collaborations with the network partners and furthermore their catalytic behavior was studied.
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Paterson, A. James. "Exploitation of synergy in oxidation catalysis with bimetallic aluminophosphate catalysts". Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/192867/.
Testo completoAbstract (sommario):
A series of novel bimetallic aluminophosphate catalysts were prepared with the simultaneous isomorphous substitution of cobalt (III) and manganese (III) for aluminium (III) and titanium (IV) replacing phosphorus (V). By substituting simultaneously for both Al (III) and P (V) in the ordered microporous aluminophosphate AlPO-5, the potential for catalytic application as either a solidacid or redox catalyst is produced. The bimetallic hydrothermal synthesis produced a phase pure and highly crystalline microporous catalyst which displayed properties not seen in monometallic AlPO-5 materials. These catalysts were fully characterized by physical, diffraction, spectroscopic and electrochemical techniques including powder X-ray diffraction, diffuse reflectance UV/Visible spectroscopy, cyclic voltammetry, extended X-ray absorption fine structure, X-ray absorption near edge spectra, scanning electron microscopy and surface/elemental (BET and ICP) methods. A significant change was observed when two metals were combined in the same structural framework, leading to an enhancement in the catalyst performance over the monometallic analogues. EXAFS indicated a change in the relative bond lengths, thought to be as a result of compensation in the structural distortion, similarly UV/Visible spectroscopy highlighted a change in the tetrahedral environment around the titanium centre when in combination with a redox metal. These catalysts were tested for the ammoximation of cyclohexanone using benign reagents to produce cyclohexanone oxime, a vital precursor in the production of nylon-6. Currently produced through hazardous processes, the ammoximation of cyclohexanone with metal substituted catalysts provides a more environmentally favourable solution. The use of a redox metal such as cobalt (III) in combination with titanium (IV) was shown to facilitate higher catalytic conversions compared with the monometallic AlPO-5 analogues while maintaining the high oxime selectivity. Similarly the epoxidation of cyclohexene with the solid oxidant acetylperoxyborate (APB) indicated a significantly higher conversion with the CoIIITiIVAlPO-5 catalyst. The substitution of two metals to replace both aluminium and phosphorus sites clearly influences and modifies the nature of the active site and provides an enhanced catalytic performance for ammoximation and epoxidation reactions. This synergy exerted through bimetallic substitution provides an important alternative approach to academic and industrial application of metal substitution within heterogeneous catalysis
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Peneau, Virginie. "Activation of hydrocarbons and their catalytic oxidation by heterogeneous catalysis". Thesis, Cardiff University, 2014. http://orca.cf.ac.uk/74614/.
Testo completoAbstract (sommario):
The targets of this thesis were the selective oxidation of hydrocarbons under mild conditions, using cheap and environmentally friendly oxidants and initiators. Three projects are treated; the oxidation of an alkane using O2 and a co-oxidant, the oxidation of toluene using TBHP (tert-butyl hydroperoxide) and finally the oxidation of propane using hydrogen peroxide. C-H bond activation, O2 activation and high conversion with high selectivity were essential points to investigate. In the first project, alkane oxidation was studied in presence of a co-oxidant. The co-oxidant has for purpose to initiate the activation of the alkane and O2, as well as prevent the over-oxidation of the alkane. The co-oxidation of octane using benzaldehyde has been investigated using 1 wt. % AuPd/ C catalyst; the hypothesis is that benzaldehyde oxidation would use a radical mechanism able to activate octane to octanol. Also, the coupling of octanol with activated benzaldehyde would prevent the over-oxidation of octanol by the formation of an ester; octylbenzoate. The aim of the second study was to investigate the selective oxidation of toluene using TBHP at 80 °C with supported noble metal nanoparticle catalysts prepared by sol-immobilisation techniques. Au, Pd and Pt have been use to form mono, bi and trimetallic catalysts of different morphology supported on C and TiO2. These catalysts have been tested for toluene oxidation. The catalyst showing the best activity has been used for further investigation such as reuse test, using H2O2 as oxidant or O2 activation. The third project target was to oxidise propane using H2O2 in mild conditions. 2.5 wt. % Fe/ ZSM-5 (30) has been used to investigate reaction conditions in order to optimise the system. This catalyst has been acid treated; standard and treated catalysts were characterised and analysed to identify the structure and active sites. Role of supports and metals (mono and bimetallic) has been explored in order to improve this system.
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Kieffer, Raphaëlle. "Développement de nouveaux catalyseurs pour la dépolymérisation de la lignine par voie d’oxydation". Thesis, Lyon 1, 2015. http://www.theses.fr/2015LYO10124/document.
Testo completoAbstract (sommario):
La lignine est l'un des biopolymères les plus importants sur Terre. Elle est extraite des plantes et représente la plus grande source de noyaux aromatiques dans la biomasse. De nombreux projets ayant pour but la dépolymérisation de la lignine en molécules de faibles poids moléculaires, valorisables par les industries chimiques, sont de plus en plus développés au vu du fort potentiel de cette bio-ressource. Le but de notre projet était de développer un nouveau système catalytique pour la dépolymérisation de la lignine. Nous nous sommes intéressés à la conception de nouveaux catalyseurs homogènes et hétérogènes, basés sur la structure connue du complexe Fe(TAML). Nous avons étudié leurs réactivité et stabilité en conditions de catalyse oxydante, et les avons comparés aux caractéristiques du Fe(TAML) existant. Pour ce faire, l'étude catalytique a été réalisée sur des molécules modèles de la lignine, dans le but d'éviter les problèmes analytiques liés à la structure du polymère. Dans un premier temps, nous présenterons la stratégie de fonctionnalisation du ligand TAML connu afin d'obtenir de nouveaux complexes qui puissent être greffés sur un support de silice. Dans un deuxième temps, nous parlerons des résultats de la catalyse oxydante en conditions homogènes et hétérogènes, et de l'influence du changement de la structure des ligands sur l'activité des catalyseursLignin is one of the most abundant biopolymers on earth. It is issued from plants and represents the largest source of aromatics in biomass. Projects aiming at depolymerizing lignin to obtain value-added small molecules for the chemical industry are more and more developed due to the high potential of this bio-resource. The goal of our project was to develop a new catalytic system for the depolymerization of lignin. We have been interested in designing new homogeneous and heterogeneous catalysts based on the known structure of the Fe(TAML) complex. We have studied their reactivity and stability under oxidative catalysis conditions, and have compared them to the characteristics of the existing Fe(TAML). To do so, the catalysis study has been realized on lignin small model molecules to avoid the analytical problems related to a polymer backbone. In a first hand, we will present the strategy of functionalization of the known TAML ligand to design new complexes to be grafted on a silica support. In a second hand, we will talk about the results of oxidative catalysis in homogeneous and heterogeneous conditions, and the influence of the ligand structure change on the activity of the catalysts