Дисертації з теми "Silicon catalysis"
Щоб переглянути інші типи публікацій з цієї теми, перейдіть за посиланням: Silicon catalysis.
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся з топ-50 дисертацій для дослідження на тему "Silicon catalysis".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Переглядайте дисертації для різних дисциплін та оформлюйте правильно вашу бібліографію.
1
Chigondo, Fidelis. "Continuous flow synthesis of silicon compounds as feedstock for solar-grade silicon production." Thesis, Nelson Mandela Metropolitan University, 2016. http://hdl.handle.net/10948/4529.
Анотація:
This thesis describes the key steps in the production of high purity (solar-grade) silicon from metallurgical-grade silicon for use in the production of photovoltaic cells as alternative renewable, environmentally benign and cheap energy source. The initial part of the project involves the development and optimization of a small chemical production platform system capable of producing alkoxysilanes from metallurgical-grade silicon as green precursors to solar-grade silicon production. Specifically, the main aim of the study was to synthesize trialkoxysilanes in continuous flow mode, although the synthesis on monosilane was also done in batch mode. The alkoxylation reaction was carried out in a traditional slurry phase batch reactor, packed bed flow tubular reactor and also attempted in a continuous flow falling film tubular reactor. The effect of key parameters which affect the silicon conversion and selectivity for the desired trialkoxysilane were investigated and optimized using ethanol as a reagent model. The synthesis was then extended to the other alcohols namely methanol, n-propanol and n-butanol. Copper catalysts which were tested in the alkoxylation reaction included: CuCl, Cu(OH)2, CuO and CuSO4. CuCl and Cu(OH)2 showed comparable activity in the batch mode but the former was more efficient in the packed bed flow tubular reactor. Cu(OH)2 could be used as a non-halide catalyst but its activity is limited to short reaction cycles (<10 h). The uncatalysed reaction resulted in negligible reaction rates in both types of reactors. High temperature catalyst pre-heating (>500 oC) resulted in a lower rate of reaction and selectivity than when slightly lower temperatures are used (<350 oC) in both reactors, although much difference was noticed in the packed bed flow tubular reactor. Synthesis in the batch reactor needed longer silicon-catalyst activation time, higher pre-heating temperature and higher catalyst amounts as compare to the packed bed flow tubular reactor. Reaction temperature and alcohol flow rate influenced the reaction in both methods. The optimum reaction temperature range and alcohol flow rate was comparable in both reactors (230 to 240 oC) and 0.1mL/min respectively. The effect of alcohol R-group (C1 to C4) on the reaction revealed that conversion and selectivity generally decrease with an increase in carbon chain length in both methods. Ethanol showed highest selectivity (>95% in batch and >97% in flow) and conversion (about 88% in batch and about 64% in flow) as compared to all other alcohols studied showing that it could be the most efficient alkoxylation alcohol for this reaction. Overally, the packed bed flow tubular reactor resulted in higher selectivity to trialkoxysilanes than the batch system. Performing the reaction under pressure resulted in increased conversion but selectivity to the desire trialkoxysilane diminished. Synthesis in a continuous flow falling film tubular reactor was not successful as it resulted in very poor conversion and selectivity. Monosilane was successfully synthesized from the disproportionation of triethoxysilane using homogeneous and heterogeneous catalysts in batch mode. The results obtained from homogeneous catalysis showed that the reaction can be conducted at room temperature. The heterogeneous catalysis method resulted in slow conversion at room temperature but mild heating up to 55 oC greatly improved the reaction. Conducting the reaction under neat conditions produced comparable results to reactions which were carried out using solvents. The disproportionation reaction was best described by the first order kinetic model. The results obtained in this research indicate that the packed bed flow tubular reactor can be utilized with future modifications for continuous flow synthesis of alkoxysilanes as feedstock for the solar-grade silicon production.
2
Beveridge, Nicola Louise. "Characterisation of silicon-silicon hydroxide catalysis bonds for future gravitational wave detectors." Thesis, University of Glasgow, 2012. http://theses.gla.ac.uk/3526/.
Анотація:
The first generation of gravitational wave detectors are currently undergoing significant upgrades to increase their sensitivity by a factor of ten. These upgrades include the installation of quasi-monolithic silica suspensions in an attempt to reduce the thermal noise of the test masses and their suspensions. Fused silica fibres are welded to fused silica interface pieces, called ‘ears’, which provide suitable welding points onto the sides of the mirror when bonded to the mirror using the high strength chemical jointing technique of hydroxide-catalysis bonding. Plans are developing for the design of potential ‘future generation’ gravitational wave detectors. These detectors may operate at cryogenic temperatures to further reduce thermal noise. Silicon is a prime candidate material for use in the test masses and their suspensions because of its desirable thermo-mechanical properties in the cryogenic regime. With some adaptation, hydroxide catalysis bonding may also be a viable technique for use in third generation detectors; however, to evaluate its suitability it is essential to quantify both the strength of silicon-silicon bonds at cryogenic temperatures and the mechanical loss of such bonds, as this has a direct effect on the contributions of the bond to the overall thermal noise of a bonded suspension. To make bonding of silicon components possible, the bonding surfaces must ideally have a thin coating of SiO2, with which the hydroxide can react to form the bond. In Chapters 3 and 4, the strength of hydroxide catalysis bonds between silicon blocks at room and cryogenic temperatures is investigated. Chapter 3 investigates the minimum required thickness of SiO2 necessary for a successful bond. The bond strength, tested using a 4-point bend strength test, is found to reduce significantly with oxide layer thicknesses below 50 nm at cryogenic temperature. A Weibull analysis of the results showed a characteristic strength of approximately 41MPa at 77K and 35MPa at room temperature for samples with a minimum oxide layer of 50 nm. In chapter 4 the effect on the oxide layer deposition method and the purity of the silicon ingot on the strength of the bond are studied. Bend strength tests were performed on hydroxide-catalysis bonds formed between silicon samples of different crystallographic orientation and purity that had been oxidised using a range of methods. The three methods used were; dry thermal oxidation, ion beam sputtering and e-beam deposition. It was found that the method used influenced the strength of the resulting bond, with the e-beam deposited layers producing the weakest samples. It is postulated that the reason for the lower strength of the e-beam samples is correlated with the lower density of this type of coating compared with other coating methods. The mechanical loss of the bond between silicon cantilevers between 10K and 250K was measured in Chapter 5. The experimental set up is described, the results are presented and then analysed to establish an upper limit of 0.12 for the second bending mode below 100K. The lowest loss measured was 0.06 at 12K.
3
Leung, Jane Jing. "Molecular hybrid photocathodes based on silicon for solar fuel synthesis." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/288001.
Анотація:
Artificial photosynthesis is broadly defined as the process of solar energy conversion into chemical fuels and represents a promising route towards alleviating the global energy crisis. In this context, the development of photocathodes for the use in photoelectrochemical cells is an attractive approach for the storage of solar energy in the form of a chemical energy carrier (e.g. H$_{2}$ and CO$_{2}$-reduction products from H$_{2}$O and CO$_{2}$). However, molecular catalyst-based photocathodes remain scarcely reported and typically suffer from low efficiencies and/or stabilities due to inadequate strategies for interfacing the molecular component with the light-harvesting material, with benchmark systems continuing to rely on precious metal components. In this thesis, the straightforward preparation of a p-silicon|mesoporous titania|molecular catalyst photocathode assembly that is active towards proton reduction in aqueous media is first established. The mesoporous TiO$_{2}$ scaffold acts as an electron shuttle between the silicon and the catalyst, while also stabilising the silicon from passivation and enabling a high loading of molecular catalysts. When a Ni bis(diphosphine)-based catalyst is anchored on the surface of the electrode, a catalytic onset potential of +0.4 V vs. RHE and a high turnover number of 1 $\times$ 10$^{3}$ was obtained from photoelectrolysis under UV-filtered simulated solar irradiation at 1 Sun after 24 hours. Notwithstanding its aptitude for molecular catalyst immobilisation, the Si|TiO$_{2}$ photoelectrode showed great versatility towards different types of catalysts and pH conditions, highlighting the flexible platform it represents for many potential reductive catalysis transformations. The Si|TiO$_{2}$ scaffold was extended towards solar CO$_{2}$ reduction via the immobilisation of a novel phosphonated cobalt bis(terpyridine) catalyst to achieve the first precious metal-free, CO$_{2}$-reducing molecular hybrid photocathode. Reducing CO$_{2}$ in both organic-water and purely aqueous conditions, the activity of this photocathode was shown to be affected by its environment and reached record turnover numbers for CO production by a molecular photocathode under optimal conditions, maintaining stable activity for more than 24 hours. Critically, in-depth electrochemical and in situ resonance Raman and infrared spectroelectrochemical investigations provided key insights into the nature of the surface-bound Co complex under reducing conditions. While demonstrating the power and precision offered by such in situ spectroelectrochemical techniques, these studies ultimately alluded to a catalytic mechanism that contrasts with that reported for the in-solution (homogeneous) catalyst. Overall, this affords a distinct mechanistic pathway that unlocks an earlier catalytic onset and enables photoelectrochemical activity. Finally, in the context of improving product selectivity in molecular-based CO$_{2}$ reduction, polymers based on the cobalt bis(terpyridine) motif were synthesised and immobilised on inverse opal-type electrodes designed specifically to accommodate large molecules. Rational design of the polymers' co-monomers was aimed towards the provision of an artificial environment for the active complex that would influence product selectivity, which was ultimately demonstrated by the improvement of a H$_{2}$:CO product ratio of 1:2 (molecule) to 1:6 (polymer). Further studies of this all-in-one system included modulating its degree of cross-linkage as well as a CO$_{2}$ reducing demonstration photocathode on a Si|inverse-opal TiO$_{2}$ scaffold.
4
Tymowski, Benoît de. "Fischer Tropsch synthesis on conductive silicon carbide based support." Thesis, Strasbourg, 2012. http://www.theses.fr/2012STRAF019/document.
Анотація:
La synthèse de Fischer-Tropsch (SFT) permet la transformation d'un mélange de gaz de synthèse, i.e. H2 et CO, issu des différentes matières premières (charbon, gaz naturel ou biomasse) en hydrocarbures synthétiques. Les catalyseurs généralement utilisés en SFT sont à base de fer ou de cobalt supporté sur alumine ou silice. Dans ce travail, le carbure de silicium (SiC) a été proposé comme nouveau support de remplacement pour la SFT. Les résultats obtenus ont montré que les catalyseurs à base de cobalt supporté sur du SiC, contenant essentiellement des mésopores, sont actifs et sélectifs pour la réaction de SFT par rapport aux catalyseurs traditionnels supportés sur alumine ou silice. L'activité en SFT peut être améliorée en utilisant de l'éthanol comme solvant d'imprégnation ou en ajoutant un promoteur tel que le ruthénium. Le dopage du support de départ par du Ti02 contribue également à une forte augmentation de l'activité en SFT grâce à la formation de petites particules de cobalt présentant une activité en SFT plus élevée. La forte interaction entre le Ti02 et le cobalt permet également d'améliorer d'une manière considérable la stabilité du catalyseurThe Fischer-Tropsch synthesis (FTS) allows the transformation of a mixture of synthesis gas, i.e. H2 and CO, into valuable liquid hydrocarbons. The catalysts generally used in FTS are based on iron or cobalt supported on alumina or silica. ln the present work, silicon carbide (SiC) has been proposed as a replacement media to traditional supports. The results obtained indicate that the mesoporous SiC containing cobalt catalyst exhibits a good FTS activity and an extremely high selectivity towards liquid hydrocarbons compared to other FTS catalysts supported on alumina or silica. The FTS activity on the Co/SiC catalyst can be improved by changing the impregnation solvent or by promoting the cobalt phase with trace amount of noble metal. The doping of the SiC support with Ti02 phase also significantly improves the FTS activity keeping a similar high selectivity thanks to the formation of small cobalt particles in contact with the Ti02 phase
5
Rae, James. "Copper-catalysed silicon and boron functionalisation of heterocycles and allenes." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/coppercatalysed-silicon-and-boron-functionalisation-of-heterocycles-and-allenes(a86718c0-18b4-4092-a2bd-b978797153db).html.
Анотація:
Silicon holds a privileged position in organic chemistry as the carbon-silicon bond can be utilised in many important transformations. As such, developing practical and efficient methods for the enantioselective and regioselective insertion of silicon into organic molecules is a worthy challenge in chemical synthesis. To this end, we have developed an affordable copper-catalysed protocol for the asymmetric silylation of lactones, lactams and amides, providing silylated products with up to > 99:1 er and in good yields. Furthermore, we have demonstrated the synthetic utility of this protocol in the target synthesis of natural or biologically active molecules. We also present the first copper-catalysed silylation of allenes using a silylborane reagent. This affords useful allyl- or vinylsilane building blocks with high regioselectivity, efficiency and a large functional group tolerance. The allylcopper intermediates can be intercepted by aldehydes in a diastereoselective three-component coupling to furnish homoallylic alcohols. We extend this concept to the copper-catalysed three-component coupling of boron, allenes and imines, providing access to homoallylic amines with a vinylborane motif.
6
Pap, A. E. (Andrea Edit). "Investigation of pristine and oxidized porous silicon." Doctoral thesis, University of Oulu, 2005. http://urn.fi/urn:isbn:9514277759.
Анотація:
Abstract
While numerous publications deal with the properties and applications of porous silicon (PS), some of the related topics are not complete or could be investigated from different aspects. Therefore, the main objective of this thesis is to provide novel information associated with the optical and chemical properties of PS.
For the investigations, various PS samples are manufactured by electrochemical dark etching of boron-doped p+-type Si wafers. Amongst others, (i) the wavelength-dependent refractive indices of freestanding PS monolayers having different porosities were obtained from optical transmission and reflection spectra in the 700–1700 nm wavelength range, and compared to those calculated from Bruggeman's effective medium approximation (EMA). The refractive indices of the PS samples are shown to be described well with the EMA. In addition, optical scattering at the air-PS interface was demonstrated. (ii) Multilayer stacks are created by alternating the porosities of PS layers within the same sample to form Bragg filters. The Bragg conditions of the filters are calculated and compared to optical transmission measurements. (iii) The oxidation of PS membranes in dry air is investigated with emphases on the reaction kinetics and on the structural changes of the porous matter. As revealed, oxidation proceeds faster in PS than in Si bulk. The formed SiO2 is amorphous and causes stress in the lattice of the residual Si skeleton. (iv) The effect of oxidation extent of PS layers on the growth mechanism of multi-walled carbon nanotubes (CNTs) is investigated. The density of the CNT network is found proportional to the oxidation extent of the substrates. (v) Finally, the chemically-reductive nature of PS is studied and exploited via the immersion plating method to deposit palladium and silver nanoparticles in the nanopores and on the surface of PS samples.
The presented novel results have potential in silicon-based technologies, including integrated active and passive optical components (waveguides, filters, antireflection coatings, optical gas/liquid sensors), electronic devices (electrochemical gas/liquid sensors, diodes, field effect devices) and selective chemical catalysis (substrates, growth templates).
7
Wieting, Joshua Merlin. "Silanediol-Catalyzed Stereoselective Functionalization of Heterocycles." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1448891366.
8
Lee, Kang-sang. "New Concepts and Catalysts for Enantioselective Synthesis of C-C, C-Si, and C-B Bonds." Thesis, Boston College, 2010. http://hdl.handle.net/2345/1739.
Анотація:
Thesis advisor: Amir H. HoveydaChapter 1. The development of chiral monodentate N-heterocyclic carbenes (NHCs) is presented. Structurally varied twenty-eight new chiral imidazolinim salts, NHC precursors, were synthesized and characterized. Chapter 2. The first example of Cu-catalyzed enantioselective conjugate additions of alkyl- and arylzinc reagents to unactivated cyclic enones is presented. Transformations are promoted in the presence of 2.5-15 mol % of a readily available chiral NHC-based Cu complex, affording the desired products bearing all-carbon quaternary stereogenic centers in 67-98% yield and in up to 97% ee. Catalytic enantioselective reactions can be carried out on a benchtop, with undistilled solvent and commercially available (not further purified) Cu salts. Chapter 3. A new class of enantioselective conjugate addition (ECA) reactions that involve aryl- or alkenylsilylfluoride reagents and are catalyzed by chiral non-C2-symmetric Cu-based NHC complexes are presented. Transformations have been designed based on the principle that a catalytically active chiral NHC-Cu-aryl or NHC-Cu-alkenyl complex can be accessed from reaction of a Cu-halide precursor with in situ-generated aryl- or alkenyl-tetrafluorosilicate. Reactions proceed in the presence of 1.5 equivalents of the aryl- or alkenylsilane reagents and 1.5 equivalents of tris(dimethylamino)sulfonium difluorotrimethylsilicate. Desired products are isolated in 63-97% yield and 73.5:26.5-98.5:1.5 enantiomeric ratio (47%-97% ee). Chapter 4. An efficient Cu-catalyzed protocol for enantioselective addition of a dimethylphenylsilanyl group to a wide range of cyclic and acyclic unsaturated ketones, esters, acrylonitriles and dienones is presented. Reactions are performed in the presence of 1-5 mol % of commercially available and inexpensive CuCl, a readily accessible monodentate imidazolinium salt as well as commercially available (dimethylphenylsilyl)pinacolatoboron. Cu-catalyzed 1,4- and 1,6-conjugate additions afford the enantiomerically enriched silanes in 72%-98% yield and 90:10->99:1 enantiomeric ratio (er) with up to >25:1 of Z:E selectivity. Chapter 5. A Cu-catalyzed method for enantioselective boronate conjugate additions to trisubstituted alkenes of acyclic a,b-unsaturated carboxylic esters, ketones, and thioesters is presented. All transformations are promoted by 5 mol % of a chiral monodentate NHC-Cu complex, derived from a readily available C1-symmetric imidazolinium salt, and in the presence of commercially available bis(pinacolato)diboron. Reactions are efficient (typically, 60% to >98% yield after purification) and deliver the desired boryl carbonyls in up to >98:2 enantiomer ratio (er). In addition, metal-free, nucleophilic activation of a B-B bond has been exploited in the development of a highly efficient method for conjugate additions of commercially available bis(pinacolato)diboron to cyclic or acyclic a,b-unsaturated carbonyls. Reactions are readily catalyzed by 2.5-10 mol % of a simple NHC. A variety of cyclic and acyclic unsaturated ketones and esters can serve as substrates. Transformations deliver boryl carbonyls bearing tertiary as well as quaternary B-substituted carbons in up to >98% yield
Thesis (PhD) — Boston College, 2010
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
9
Douglas, Rebecca Claire. "Aspects of hydroxide catalysis bonding of sapphire and silicon for use in future gravitational wave detectors." Thesis, University of Glasgow, 2016. http://theses.gla.ac.uk/7993/.
10
Mungondori, Henry Heroe. "Development of a visible light active, photo-catalytic and antimicrobial nanocomposite of titanium dioxide and silicon dioxide for water treatment." Thesis, University of Fort Hare, 2012. http://hdl.handle.net/10353/471.
Анотація:
The aim of this study was to prepare composite materials based on titanium dioxide (TiO2) and silicon dioxide (SiO2), and to evaluate their photo-catalytic and antimicrobial properties. Carbon and nitrogen doped TiO2nano-particles were prepared via a sol gel synthesis, which is a simple hydrolysis and condensation technique. In situ doping was carried out using glucose and urea as carbon and nitrogen sources respectively. Doping increased the spectral response of titanium dioxide photo-catalyst, allowing it to utilise the visible region which is much wider than the UV region (about 40 % of the solar spectrum), thus making it a more efficient photo-catalyst. The carbon and nitrogen doped TiO2-SiO2nano-particles were immobilized on glass support material to allow for easy separation of the spent photo-catalyst after the photo-degradation process. Tetraethyl orthosilicate (TEOS) was employed as both a binder and precursor for silicon dioxide. A mixture of TiO2 and TEOS in a 1:1 ratio was allowed to polymerize on a glass support which had been treated with hydrofluoric acid to introduce OH groups. The prepared photo-catalytic material was characterized by FT-IR, XRD, DRS, TEM, EDX, and BET analyses. Carbon was found to be more effective as a dopant than nitrogen. It brought about a band gap reduction of 0.30 eV and a BET surface area of 95.4 m2g-1 on the photo-catalyst as compared to a gap reduction of 0.2 eV and surface area of 52.2 m2g-1 for nitrogen doped TiO2. On the other hand, introduction of SiO2 allowed utilization of visible light by the TiO2-SiO2 nano-composite leading to an improved rate of photo-degradation of both methyl orange and phenol red. However, the immobilization of TiO2 on support material made it less effective towards inactivation of E. coli ATCC 25922 bacterial cells when compared to powdered TiO2 which was able to inactivate about 98 % of the bacterial cells within an hour of treatment.
11
Naha, Sayangdev. "Growth Model, Synthesis of Carbon Nanostructures and Alteration of Surface Properties Using Them." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/28559.
Анотація:
Flame synthesis is recognized as a much cheaper and higher throughput process for carbon nanotube/nanofiber (CNT/CNF) production compared to conventional catalytic processes like chemical vapor deposition (CVD). Nanostructured carbon materials, such as carbon nanotubes and nanofibers, exhibit superhydrophobic behavior over a range of pH values, including for corrosive liquids. Part of this research reports the development of a rapid on-demand process for the synthesis of superhydrophobic surfaces on silicon (Si) discs using an ethylene-air nonpremixed flame. Such superhydrophobic behavior, combined with increase in effective surface area due to carbon nanostructure (CNS) deposition and corresponding desirable size (nanoscale roughness) attract the growth and attachment of microbial colonies to these CNS-enhanced substrates. This has potentially high-impact application in microbial fuel cells (MiFCs) whereby stainless steel (SS) meshes coated with flame-deposited CNS are used as anodes and the electrons produced by attaching biofilms can generate electricity in a fuel cell. However, despite such and many other applications and promise of carbon nanotubes (CNTs), their production is generally based on empirical principles. There are only a few CNT formation models that predict the dependence of CNT growth on various synthesis parameters. Typically, these do not incorporate a detailed mechanistic consideration of the various processes that are involved during CNT synthesis. Herein, this need is addressed and a model is presented for catalytic CNT growth that integrates various interdependent physical and chemical mechanisms involved in CNT production. It is validated by comparing its predictions with experimental measurements for CVD synthesis of CNTs and a concise parametric study is presented. The results are extrapolated for flame synthesis that is recognized as a desirable cost-effective process for the bulk synthesis of CNTs, as already mentioned. The last part of this dissertation discusses an extension of the CNT growth model to silicon nanowire/nanowhisker (SiNW) synthesis. SiNWs are synthesized by a number of methods â catalysis by a metal (involving vapor-liquid-solid or VLS growth mode), molecular beam epitaxy, thermal evaporation and laser ablation to name a few. Our model pertains to metal-catalyzed VLS growth mode.Ph. D.
12
Han, Tingting. "Highly active and efficient metal-decorated silicon-based nanostructured photoelectrodes for water splitting solar cells." Doctoral thesis, Universitat de Barcelona, 2020. http://hdl.handle.net/10803/670880.
Анотація:
With the burning of large amounts of traditional fossil fuels, global environmental pollution is getting worse and worse, and energy crisis is becoming more serious for meeting human’s life demand. In order to solve these problems, it’s imperative to find renewable and clean energy sources. Although solar is one of the most abundant renewable energy on earth, it’s difficult to collect and store.
As a non-polluting energy, hydrogen is a highly promising candidate to replace fossil fuels. Sunlight can be used to split water into hydrogen, producing chemical energy stored in hydrogen bonds. This easy way of producing clean fuels (hydrogen) has attracted the attention of both industry and academy. Photoelectrochemical (PEC) water splitting is one of the most promising methods to produce hydrogen by utilizing solar energy, due to the simple structure, low fabrication cost and good performance of the prepared cells. In these cells, a semiconductor photoelectrode is immersed in an electrolyte, and when illuminated, hydrogen and/or oxygen can be generated on its surface by electrolysis.
To obtain better performance for PEC water splitting devices, it’s extremely significant to select proper semiconductors for absorbing light, catalysts for enhancing the PEC performance and electrolytes containing various ions. Silicon has garnered very much interest as semiconductor photoelectrodes due to its low cost and proper band gap (1.1 eV). However, the electrolyte can oxidize and/or corrode its surface, resulting in a reduction of its performance. Metal catalysts are often used to avoid the degradation of silicon photoelectrodes, and to enhance their activity in the electrolyte. However, the degree of protection can be reduced after some periods of time, and consequently the lifetime of the semiconductor photoelectrodes is still the main bottleneck of this PEC water splitting technology. Besides, tuning the pH of the electrolytes or the chemical composition of the electrolytes including special species could improve the activity and stability of the cells.
In this PhD thesis I present a deep study about the ageing mechanisms of Ni layers with different thicknesses as protective and catalytic coatings on n-type Si photoanodes for PEC water splitting in strong alkaline condition. Before and after performed long-time PEC characterizations, we comprehensively analyzed the photoanodes at nano and atomic scales using atomic force microscopy (AFM) and electron microscopy. By investigating the morphology changes and the chemical composition of the photoanodes after long operation times, we find that the ageing mechanisms extremely rely on the thickness of the Ni coating layer. The activity of
the 2 nm nickel coated silicon photoanode decays faster than thicker ones due to the formation of a thick interfacial SiOX film and the extensive penetration of potassium impurities into the NiOX layer. Whilst the photoanodes with more than 5 nm Ni coatings show longer stability, and the degradation is due to the formation of holes in the NiOX layer. Then, using 5 nm Ni-based n-Si photoanodes, we analyzed the effect of different alkaline electrolytes for PEC water splitting. Although the photoanodes show lower onset potential at high pH electrolyte, we also developed an advanced electrolyte (a mixture of potassium hydroxide (KOH) and lithium hydroxide (LiOH), pH 12.5) that shows good activity and stability for metal-based silicon photoelectrodes. Furthermore, we also designed, fabricated and tested n-3C-SiC/p-Si photocathodes for PEC water splitting in KOH, and observed an enhancement of PEC performance due to the catalytic and plasmonic resonance effects of the noble metal nanoparticles (NPs) introduced. By tuning the size and shape of Au NPs on the photocathodes, higher saturated photocurrent can be achieved. And Pt NPs coated n-3C-SiC/p-Si photocathodes show lowest onset potential and highest saturated photocurrent for PEC performance.La quema de grandes cantidades de combustibles fósiles para satisfacer la demanda energética stá empeorando la contaminación ambiental cada vez más, y la crisis energética se está volviendo más grave. La división de agua mediante fotoelectroquímica (PEC, por sus siglas en inglés) utilizando luz solar es uno de los métodos más prometedores para producir combustible hidrógeno de forma limpia, debido a la estructura simple, el bajo costo de fabricación y el buen rendimiento. En las células fotoelectroquímicas, un fotoelectrodo semiconductor se sumerge en un electrolito y, cuando se ilumina, se puede generar hidrógeno y/u oxígeno en su superficie mediante electrólisis. Para obtener un mejor rendimiento, es extremadamente importante seleccionar semiconductores adecuados para absorber la luz, catalizadores para mejorar el rendimiento, y electrolitos que contienen varios iones. El silicio ha suscitado mucho interés debido a su bajo costo y a sus propiedades eléctricas (banda prohibida de 1.1eV). Sin embargo, debido a su inestabilidad en el electrolito, los catalizadores metálicos a menudo se usan para evitar la degradación de los fotoelectrodos de silicio y para mejorar su actividad en el electrolito. Dado que el grado de protección se puede reducir después de algunos períodos de tiempo, la vida útil de los fotoelectrodos de semiconductores sigue siendo el principal cuello de botella de esta tecnología de división de agua PEC. Además, ajustar el pH o la composición química de los electrolitos, incluidas las especies especiales, podría mejorar la actividad y la estabilidad de las células. En esta tesis, he estudiado el uso de niquel como capa protectora y catalizadora sobre fotoelectrodos de silicio, y hemos analizados su envejecimiento bajo condiciones de funcionamiento reales. También he desarrollado un electrolito avanzado (una mezcla de hidróxido de potasio [KOH] e hidróxido de litio (LiOH), pH 12.5) que muestra una buena actividad y estabilidad para los fotoelectrodos de silicio a base de metal. Además, también diseñamos, fabricamos y testeamos fotocatodos n-3C-SiC/p-Si cubiertos con nanopartículas de metales nobles para la división de agua PEC en KOH, y observamos una mejora en el rendimiento de PEC debido a los efectos de resonancia catalítica y plasmónica de las nanopartículas introducidas.
13
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.
14
Nasrallah, Houssein. "Immobilisation de complexes à base de ruthénium par des interactions non-covalentes pour le recyclage en métathèse des oléfines." Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLS005.
Анотація:
L'objectif de cette thèse est le développement de nouvelles stratégies d'immobilisation de complexes de ruthénium sur des supports insolubles par des interactions non-covalentes pour le recyclage aisé de ces catalyseurs dans la métathèse des oléfines. Tout d'abord, un rappel bibliographie sur le développement de la métathèse des oléfines, de sa découverte jusqu'à nos jours, est présenté. Ensuite trois approches différentes d'immobilisation de catalyseurs de métathèse sont détaillées afin de réaliser le recyclage en tenant compte des défis concernant cette réaction. Une procédure d'immobilisation des catalyseurs par formation de complexes à transfert de charge (CTC) réversibles entre le catalyseur et le support est tout d'abord étudiée dans ces conditions. En se basant sur les résultats obtenus dans ces conditions, une approche plus économique a alors été développée qui consiste en l'immobilisation d'un catalyseur commercial par formation de liaisons hydrogène avec les sites silanols d'un simple support de silice. Finalement, un autre type de support à base de carbone structuré (rGO) a été employé dans l'étude de l'immobilisation de complexes de ruthénium tagués par un fragment pyrène via la formation d'interactions π- π (π-stacking).La performance des différents matériaux catalytiques a d'abord été évaluée dans la réaction test de métathèse d'oléfines (RCM du DEDAM). Ensuite, autres types de métathèses (ènyne, CM et l'homo-métathèse de l'oléate de méthyle) ont été testées pour étendre l'application de ces matériaux.Le développement de ces approches d'immobilisation est également accompagné par des études mécanistiques, en se basant sur l'effet boomerang, connu pour ces réactions.Ce travail a été réalisé dans le cadre du projet ANR CD2I CFLOW-OM, en collaboration avec des partenaires académiques (ENSC-Rennes, LGPC-Lyon, CPE-Lyon, LCMT-Caen) et industriels (ITERG, NOVANCE, OMEGA-CAT-SYSTEM)Ruthenium complexes immobilization by non-covalent interactions for the recycling in olefin metathesisAbstractThe aim of this thesis is the development of new ruthenium complexes immobilization strategies onto insoluble supports by non-covalent interactions, for their easy recycling in olefin metathesis reactions.First, a bibliographic part is devoted to the development of the olefin metathesis from the discovery until now. Then, three different approaches of metathesis catalysts immobilization are described in order to achieve efficient recycling, considering the important challenges associated to this reaction. Firstly, an immobilization procedure of catalysts by formation of reversible charge transfer complexes (CTC) is described between the appropriated tagged catalyst and the support. Based on the results obtained in these conditions, a more economical approach involved the immobilization of a commercially available catalyst by formation of hydrogen bonds with the silanol sites present in silica. Finally, another type of support namely a structured carbon based support (rGO), was used for the pyrene tagged ruthenium complexes immobilization via formation of non-covalent π- π interactions (π-stacking).The catalytic performances of these solid materials were firstly evaluated in the benchmark reaction of olefin metathesis (RCM of DEDAM). Then, other olefin metathesis reactions were applied to extend the application of these materials (enyne, CM, self-metathesis of methyl oleate).The development of these approaches has also been accompanied by mechanistic studies, based on the boomerang effect, already known for these reactions.This work was performed as part of the ANR project CD2I CFLOW-OM, in collaboration with academic (ENSC-Rennes, LGPC Lyon, CPE Lyon-Caen LCMT) and industrial (ITERG, NOVANCE, OMEGA-CAT- SYSTEM) partners
15
Motos, Blanca. "Silices fonctionnalisées contenant des espèces ioniques pour la catalyse hétérogène." Thesis, Montpellier, Ecole nationale supérieure de chimie, 2011. http://www.theses.fr/2011ENCM0015.
Анотація:
La catalyse hétérogène est en plein développement pour des raisons économiques, de santé et de protection environnementale. Les travaux de cette thèse s'intéressent à la préparation des silices fonctionnalisées par des sous-structures ioniques pour leur application en catalyse hétérogène. D'abord, des matériaux mésoporeux fonctionnalisés par des entités di-aryl imidazoliums ont été préparés par des réactions de post-greffage. En plus, films de type PMO contenant des entités di-aryl imidazoliums ont été synthétisés en présence d'un surfactant anionique. Ensuite, complexes carbéniques N-hétérocycliques du cuivre et du palladium supportés ont été préparés et appliqués en tant que catalyseurs organométalliques dans des réactions A3 (Cu-NHC) et de couplage de Suzuki (Pd-NHC). Les silices fonctionnalisées avec des entités imidazoliums ont également été utilisées en tant qu'organocatalyseurs des réactions de Henry et dans de cycloaddition du dioxyde de carbone aux époxydes. Des matériaux de type ‘PMO' contenant des entités amines/ammoniums ainsi que des sous-structures zwitterioniques ont été utilisés en réactions organocatalysées de Henry et BiginelliHeterogenous catalysis is an area in continuous development due to economical, health and environmental issues. This thesis deals with the preparation of i-silica materials for the posterior application in heterogeneous catalysis. First, di-aryl imidazolium containing silica materials were synthesized by post-grafting reactions on mesoporous SBA-15. Moreover, di-alkyl imidazolium containing PMO films were prepared in presence of an anionic surfactant. Then, supported copper and palladium N-heterocyclic carbenes were synthesized from di-aryl imidazolium silica and applied to A3 reactions (Cu-NHC) and Suzuki cross-coupling reactions (Pd-NHC). Imidazolium functionalized silicas were also utilized as heterogeneous organocatalysts in Henry reactions and in reactions of cycloaddition of carbon dioxide to epoxides. Finally, PMO type materials containing amine/ammonium and zwitterionic substructures were applied to Henry and Biginelli organocatalysed reactions, respectively
16
Chauvier, Clément. "Nouvelles réactions d'hydroboration et d'hydrosilylation par transfert avec des réducteurs renouvelables à base d'acide formique." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS359/document.
Анотація:
Les ressources fossiles que sont le gaz ou le pétrole permettent non seulement de couvrir la majeure partie des besoins énergétiques mondiaux, mais fournissent également les briques élémentaires carbonées utiles à des pans entiers de l’industrie chimique. L’utilisation massive de ces combustibles fossiles pose toutefois un problème écologique majeur, le réchauffement climatique, qui se doublera à terme d’un problème de disponibilité de ces ressources. Pour pallier ces difficultés, une des solutions envisagées consiste à abandonner progressivement les hydrocarbures fossiles au profit de ressources carbonées renouvelables telles que le CO₂ ou la biomasse lignocellulosique pour le stockage de l’énergie et/ou comme sources de produits chimiques. Cette entreprise, qui se propose de transformer des substrats fortement oxygénés contenant des liaisons C=O et C–O, requiert fondamentalement un apport d’énergie sous la forme de transferts d’électrons dans des réactions de réduction pour former des liaisons C–H qui préexistent dans les produits dérivés du pétrole. Dans ce contexte, le présent travail doctoral se propose en premier lieu de définir les attributs d’un réducteur renouvelable, c’est-à-dire d’une espèce chimique adaptée à la réduction – limitée à des transferts d’hydrure – de ressources renouvelables oxygénées tel que le CO₂. Les avantages et inconvénients de différentes sources d’hydrure (H₂, acide formique, hydroboranes et hydrosilanes) seront ainsi analysés à la lueur de considérations thermodynamiques et cinétiques et la renouvelabilité de ces réducteurs sera discutée. Dans un second temps, les propriétés réductrices de nouveaux réducteurs renouvelables que sont les formiates de bore et de silicium seront étudiées. Ces composés combinent une source d’hydrure renouvelable, l’acide formique, avec un élément oxophile du groupe principal dont les propriétés stéréoéléctroniques sont modulables. Par un dialogue entre expérience et théorie, il sera démontré que ces composés peuvent avantageusement remplacer les hydroboranes ou hydrosilanes, non renouvelables, dans différents processus réducteurs qui seront unifiés derrière le concept plus général d’hydroélémentations par transfertThe utilization of cheap and abundant sustainable resources such as carbon dioxide or biomass derivatives as source of fuel and chemicals imposes the development of efficient reduction methods, able to promote the conversion of C-O bonds (π and σ) into C-H bonds in an energy and atom efficient manner. Within the realm of C-O reduction methods, the utilization of main group element-based hydrides (e.g. LiAlH₄ or NaBH₄) has proven highly beneficial in terms of selectivity and versatility in the reduction of various functional groups, including poorly electrophilic CO₂. This behavior not only stems from the positive kinetic attributes of these reductants in hydride transfer reactions but also from the oxophilicity of the main group elements that ensures the reductions are downhill processes. Yet, the latter appealing features comes at an energetic price, and the preparation of main group hydrides mainly relies on energy-demanding processes, which in turn limit the recyclability of these reductants. With the goal in mind to circumvent these limitations while preserving the beneficial properties of the main-group element during reduction, one of the major objectives of the research project presented therein was to study the unknown reductive chemistry of boryl formate and silyl formates. The latter indeed combine a renewable hydride source (formic acid can be obtained by 2e electroreduction of CO₂) linked directly to the main group element by the oxygen atom of the formate, which hints at the recyclability of this class of main group element-based reductants. Through a joint experimental and theoretical study, it will be demonstrated that these compounds can advantageously replace non-renewable hydroboranes or hydrosilanes in various reducing processes, which will be unified behind the more general concept of transfer hydroelementation
17
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.
Анотація:
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.
18
Harms, Stefan Mathias. "The oligomerisation of propene over nickel oxide silica alumina." Master's thesis, University of Cape Town, 1987. http://hdl.handle.net/11427/22157.
Анотація:
Bibliography: pages 129-132.A synthesis techniQue was developed for the preparation of a nickel oxide sil ica alumina catalyst. The propene oligomerisation activity and the selectivity of the catalysts prepared by homogeneous decomposition deposition (HDD) were investigated and compared with nickel oxide silica alumina catalysts prepared by the techniQues of impregnation (IMP) and co-precipitation (SG). Amongst others. the effect of the nickel content. reacti6n temperature and pressure, and water content of the feed, on the activity and selectivity. were investigated. Also investigated were the lifetime of the various catalysts and, in the case of HDD type catalysts. the ability to oligomerise high molecular weight hydrocarbons (Cb). Nickel oxide silica alumina prepared by the HDD method is more active for the propene oligomerisation than catalysts prepared by the IMP and SG methods. The product spectrum in the case of IMP and HDD type catalysts are similar, with a propene dimer (Cb) being the main product. In the case of SG type catalysts. however. a shift to heavier products was observed, i.e., propene dimer (Cb) and trimer (Cq) were formed in eQual Quantities. It is proposed that the increase in activity of HDD type catalysts was due to a large extent of metal dispersion and distribution and a stronger interaction between the metal and the support. It is also proposed that the metal is readily accessible to the reactant molecules. The activity and selectivity of catalysts prepared by the HDD method were independent of the nickel content. This was not the case for IMP and SG type catalysts. both of which showed decreasing activity with increasing nickel content when the nickel content was increased beyond 5 wt%. The lifetimes of the various catalysts were also examined. From the results obtained. over the first 10 h. the lifetime of HOD type catalysts was superior to that of the other catalysts studied. The activity and selectivity of the various catalysts were sensitive to the reaction conditions. Thus moving into the vapour phase. by either increasing the temperature at a fixed pressure or decreasing the pressure at a fixed temperature. was in each case acCompanied by a shift to heavier products and a decrease in activity.
19
Battisti, Marcos Valerio. "Investigação teórica sobre a possibilidade dos porfirinatos de silicio(IV) catalisarem O2 e NO: uma abordagem termodinâmica." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/75/75131/tde-14092007-143358/.
Анотація:
A busca por materiais catalíticos fora dos metais de transição foi o objetivo dessa tese. Principalmente se considerarmos a escassez dos metais nobres como matéria prima para a catálise de moléculas diatômicas, em especial o oxigênio e o óxido de nitrogênio. A primeira molécula está diretamente relacionada com à obtenção de energia em células a combustível, especificamente, o ânodo das células a combustível. A segunda molécula está relacionada diretamente a eletroredução de íons nitrato, ou seja, na formação de uma molécula diatômica muito estável quimicamente e muito tóxica. Por isso foi utilizada a DFT (Teoria do Funcional da Densidade) para a realização de diversas simulações a 298,15K e 1 atm, com moléculas no estado gasoso de porfirinatos de silício (IV) reagindo com O2 e NO para a confirmação catalítica dos porfirinatos. Para isso foram utilizados os conjuntos de base 3-21G, 6-31G, 6-31G* e 6-31G(d), que mostraram tendências catalíticas dos porfirinatos estudados. Assim, por exemplo, pode-se evidenciar a tendência de hidrólise do porfirinato de silício (IV) através dos cálculos, já observado e demonstrado através de medidas experimentais. Porfirinatos de silício (IV) e octaetilporfirinatos de silício (IV) mostram a mesma tendência de formação de ligação química com O2 , forma de \"ponte\", diferenciando nos valores absolutos de DG e DH, e na ligação do O2 com o anel porfirínico. Com porfirinato, o oxigênio ligou-se com o silício e com o carbono meso; já com o octaetilporfirinato, o O2 ligou-se com o silício e com o nitrogênio do anel, promovendo uma ruptura de ligação entre o silício (presente no centro das porfirinas) e o nitrogênio do anel. A mesma tendência foi observada quando foram adicionadas hidroxilas nos carbonos meso do anel porfirínico, demonstrando que a presença de grupos doadores de elétrons nos carbonos meso não fortalece as ligações silício e nitrogênio presentes no sistema, e um átomo de cloro como contra-íon também não influencia no resultado final da reação. Quando reagimos o sistema com hidrogênio, observa-se a formação de duas moléculas de água fracamente ligadas ao sistema. Octaetilporfirinato de silício (IV) reagiu apenas com duas moléculas de NO, sendo observado a formação de uma estrutura pentagonal sobre o silício, rompendo-se duas ligações entre silício e nitrogênio do anel porfirínico. Quando colocado hidroxilas e cloro no sistema octaetilporfirinato de silício (IV), observou-se a reação apenas com uma molécula de NO, ligada ao nitrogênio do anel, sem a formação de NO+, comum em sistemas porfirínicos cujo átomo central é ferro, por exemplo. Também observou-se a tendência de formação do íon amônio e água, quando é colocado no sistema moléculas de hidrogênio para reagir com o NO preso ao anel porfirínico. Na prática, tanto os porfirinatos de silício (IV) quanto os octaetilporfirinatos de silício (IV) possuem contra-ions, sendo o mais comum o cloreto. Por isso, o estudo da labilidade do íon cloreto com as moléculas estudadas foi de fundamental importância na determinação da tendência desses sistemas. Assim pode-se inferir, por exemplo, que o cloreto é substituído pela molécula de oxigênio numa reação entre esses dois reagentes. Para finalizar, CO e H2 não reagiram com os porfirinatos de silício (IV), mostrando uma forte tendência à repulsão, devido à diferença de fase nos orbitais atômicos.The search for catalytic materials out of the transition metals was the objective of this thesis. Mainly if we consider the scarcity of noble metals as raw materials for the catalysis of diatomic molecules, especially oxygen and nitrogen oxides. The first molecule is directly related to the getting of energy in fuel cells, specifically, the anode of the fuel cells. The second molecule is related directly to the electroreduction of nitrate ions, in other words, in the formation of a very stable diatomic molecule and also very poisonous. Therefore, DFT was used (Density Functional Theory) for the accomplishment of several simulations, at 298,15K and 1 atm, with molecules in the gaseous state of silicon porphyrinatos (IV) reacting with O2 and NO for their catalytic confirmation. For that, the bases 3-21G, 6-31G, 6-31G * and 6-31G(d) were used to study the catalytic tendencies of the porphyrinatos here studied. For instance, the tendency of hydrolysis of silicon porphyrinato (IV) can be evidenced through theoretical calculations, as already observed and demonstrated through experimental works. Silicon porphyrinatos (IV) and silicon octaethilporphyirinatos (IV) showed the same tendency of forming a chemical bond with O2. They form a \"bridge\" changing the absolute values for DG and DH, and form a O2 bond with the porphyrinic ring. With porphyrinatos, the oxygen binds to silicon and to meso carbon; but with octaethilporphyirinato, the O2 binds to silicon and to the nitrogen of the ring, promoting a rupture between the silicon (present in the center of the porphyrins) and the nitrogen of the ring. The same tendency was observed when hydroxyls were added in the meso carbons of the porphyrinic ring showing that the presence of donor groups of electrons in the meso carbons does not strengthen the silicon and nitrogen bonds presented in the system, and a chlorine counter-ion does not influence the final result of the reaction as well. When we reacted the system with hydrogen, the formation of two weak molecules of water bound to the system is observed. Silicon octaethilporphyrinato (IV) just reacted with two NO molecules, and was observed the formation of a pentagonal structure on silicon breaking two bonds between silicon and nitrogen of the porphyrinic ring. When one puts hydroxyls and chlorine in the system silicon octaethilporphyrinato (IV), the reaction was only observed with a molecule of NO bound to the nitrogen of the ring without the formation of NO+ common in porphyrinic systems where the central atom is iron, for example. Also, it was observed the tendency of formation of the ammonium ion and water when we put in the system molecules of hydrogen to react with the NO linked to the porphyrin ring. In practice, as the silicon porphyrinatos (IV) as the silicon octaethilporphyrinatos (IV) possess counter-ions, where the most common is with chloride. Therefore, the study of the lability of the ion chloride with the studied molecules was of fundamental importance in the determination of the tendency of these molecular systems. From there, for instance, we could observe that the chloride is substituted by the oxygen molecule in a reaction between the two reactants. To conclude, CO and H2 did not react with the silicon porphyrinatos (IV) showing a strong tendency to repulsion due to the phase difference in the atomic orbitals.
20
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.
Анотація:
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.
21
Pascaretti, Mathieu. "Catalyse synergique οr/silicium par activatiοn d’οrganοsilanes et d’hydrοsilanes au mοyen de cοmplexes d’Au(Ι) : dévelοppements et applicatiοns". Electronic Thesis or Diss., Normandie, 2024. http://www.theses.fr/2024NORMLH01.
Анотація:
Depuis le début des années 2000, la catalyse à l'or s'est particulièrement développée en chimie organique, offrant de nouvelles méthodes de synthèse très efficaces, généralement dans des conditions très douces. Ces avancées ont également conduit à une utilisation abondante en glycoscience, mais malgré d'importantes percées, l'application de la catalyse à l'or en glycochimie est typiquement limitée aux modes conventionnels d'activation des donneurs de sucres, dans lesquels le complexe d'or reste strictement confiné au rôle d'un acide σ- ou π-Lewis. Les travaux de recherche présentés au travers de ce manuscrit tendent à introduire un nouveau paradigme dans les réactions de glycosylation catalysées par l'or, en développant des réactions d'alcynylations catalytiques dans lesquelles le complexe d'or devrait surmonter les difficultés intrinsèques de ces couplages en contribuant à l'activation simultanée du donneur de sucre et de l'aglycone alcyne, sur la base d'une stratégie originale de catalyse synergique or/silicium. La combinaison idéale de catalyseur à l'or et de contre-ion a été recherchée (L et X) pour atteindre une réactivité catalytique et un contrôle stéréochimique optimums à la fois pour la réaction d’alcynylation de glycosides saturés simple mais aussi pour l’alcynylation de glycals. La découverte d’un impact important d’un contre-ion du complexe d’Au(I) jusque-là encore inexploité en catalyse synergique or/silicium associée à une phosphine fortement désactivante a permis d’étendre le champ d’application de la catalyse synergique or/silicium au-delà de l’alcynylation des glycosidesSince the early 2000s, gold catalysis has developed particularly well in organic chemistry, offering new highly efficient synthetic methods, generally under very mild conditions. These advances have also led to abundant use in glycoscience, but despite important breakthroughs, the application of gold catalysis in glycochemistry is typically limited to conventional modes of sugar donor activation, in which the gold complex remains strictly confined to the role of a σ- or π-Lewis acid. The research work presented through this manuscript tends to introduce a new paradigm in gold-catalysed glycosylation reactions, by developing catalytic alkynylation reactions in which the gold complex should overcome the intrinsic difficulties of these couplings by contributing to the simultaneous activation of the sugar donor and the alkyne aglycone, based on an original gold/silicon synergistic catalysis strategy. The ideal combination of gold catalyst and counterion was sought (L and X) to achieve optimum catalytic reactivity and stereochemical control both for the alkynylation reaction of simple saturated glycosides and for the alkynylation of glycals. The discovery of a major impact of a hitherto unexploited Au(I) complex counterion in synergistic gold/silicon catalysis associated with a strongly deactivating phosphine has made it possible to extend the field of application of synergistic gold/silicon catalysis beyond the alkynylation of glycosides
22
Müller, Robert [Verfasser], Martin [Akademischer Betreuer] Kaupp, and Carsten [Akademischer Betreuer] Strohmann. "Quantum-chemical studies of inorganic electronic structure and reactivity : from unusual silicon and germanium compounds to transition-metal catalysis / Robert Müller. Gutachter: Martin Kaupp ; Carsten Strohmann. Betreuer: Martin Kaupp." Berlin : Technische Universität Berlin, 2014. http://d-nb.info/1066163480/34.
23
Peiris, Thelge Manindu Nirasha. "Development and characterization of silica and titania based nanostructured materials for the removal of indoor and outdoor air pollutants." Diss., Kansas State University, 2012. http://hdl.handle.net/2097/14891.
Анотація:
Doctor of PhilosophyDepartment of Chemistry
Kenneth J. Klabunde
Solar energy driven catalytic systems have gained popularity in environmental remediation recently. Various photocatalytic systems have been reported in this regard and most of the photocatalysts are based on well-known semiconducting material, Titanium Dioxide, while some are based on other materials such as Silicon Dioxide and various Zeolites. However, in titania based photocatalysts, titania is actively involved in the catalytic mechanism by absorbing light and generating exitons. Because of this vast popularity of titania in the field of photocatalysis it is believed that photocatalysis mainly occurs via non-localized mechanisms and semiconductors are extremely important. Even though it is still rare, photocatalysis could be localized and possible without use of a semiconductor as well. Thus, to support localized photocatalytic systems, and to compare the activity to titania based systems, degradation of organic air pollutants by nanostructured silica, titania and mixed silica titania systems were studied. New materials were prepared using two different approaches, precipitation technique (xerogel) and aerogel preparation technique. The prepared xerogel samples were doped with both metal (silver) and non-metals (carbon and sulfur) and aerogel samples were loaded with Chromium, Cobalt and Vanadium separately, in order to achieve visible light photocatalytic activity. Characterization studies of the materials were carried out using Nova BET analysis, DR UV-vis spectrometry, powder X-ray diffraction, X-ray photoelectron Spectroscopy, FT-IR spectroscopy, Transmission Electron Microscopy, etc. Kinetics of the catalytic activities was studied using a Shimadzu GCMS-QP 5000 instrument using a closed glass reactor. All the experiments were carried out in gaseous phase using acetaldehyde as the model pollutant. Kinetic results suggest that chromium doped silica systems are good UV and visible light active photocatalysts. This is a good example for a localized photocatalytic activity. In contrast, our xerogel system shows comparatively high visible light photocatalytic activity for the titania based system, showing the importance of non-localized nature of photocatalysis. The Cobalt doped silica system shows interesting dark catalytic activity towards acetaldehyde and several other pollutants. Thus, in summary, based on the different activities we observed during our studies these materials could be successfully used to improve the quality of both indoor and outdoor air.
24
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.
Анотація:
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.
25
Chiaranussati, Preeyanuj. "NMR studies of silicas and platinum/ silica catalysts." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319580.
26
Attoui, Mariam. "Nanocatalyseurs hélicoïdaux chiraux à base de polyoxométallates pour les réactions d’oxydation énantiosélectives." Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0447/document.
Анотація:
Les matériaux chiraux à base de polyoxométallates (POMs) ont montré un intérêt croissant ces dernières années, à cause de leurs propriétés remarquables et de leurs applications potentielles, notamment dans le domaine de la catalyse. L’objectif de cette thèse était de concevoir une série d’hybrides hélicoïdaux chiraux à base de polyoxométallates (NANOPOM) énantiopurs, pour des applications en catalyse hétérogène d’oxydation. Deux approches ont été utilisées pour préparer ces nouveaux matériaux. La première consiste à immobiliser les unités POM sur des nanohélices et des nanorubans de silice par couplage électrostatique et par adsorption directe du POM sur les nano-objets, car ces structures sont plus stables et moins sensibles à l’environnement extérieur. La deuxième approche consiste à fixer le POM sur des nanorubans et des nanohélices organiques préparés par auto-assemblage d’amphiphile gemini 16-2-16 (L)- ou (D)-tartrate et du POM dans l’eau. La caractérisation de ces hybrides NANOPOM par des techniques de microscopie (TEM, HR-TEM et EDX) et de spectroscopie (RMN 31P, UV-Vis, DRIFT et Raman) a permis de mettre en évidence la structure des hybrides et notamment le greffage du POM. Ces matériaux sont généralement stables, et l’induction de chiralité des supports chiraux sur le POM a été confirmée par dichroïsme circulaire, mettant en évidence l’énantiopureté de ces NANOPOMs. Ces NANOPOMs sont actifs et recyclables pour l’oxydation de sulfures, mais aucune énantiosélectivité significative n’a été observée. Les résultats obtenus durant la thèse sont encourageants et permettent d’envisager de nouveaux systèmes NANOPOMs basés sur l’incorporation du POM dans les structures hélicoïdales lors de la formation du gel, suivi d’une solidification du système organique par une couche de silice, afin d’augmenter la stabilité, propriété indispensable pour les applications en catalyseChiral polyoxometalates (POMs)-based materials have attracted particular attention in recent years due to their remarkable properties and potential application, especially in the field of catalysis. The goal of this thesis is to design a series of enantiopure nanohelical structures based on polyoxometalates (NANOPOM), for their use as heterogeneous oxidation catalysts. Two approaches were used to prepare these new materials. The first one based on the immobilization of POMs on silica nanohelices and nanoribbons by electrostatic and direct adsorption grafting. These inorganic structures increase the stability and make them less sensitive to external environment. The second approach is to include POM units within the structure of organic nanoribbons and nanohelices during self-assembly of 16-2-16 (L)- or (D)-tartrate gemini amphiphile and POM in water. The characterization of these NANOPOM hybrids by using various techniques such as 31P NMR, UV-Vis, DRIFT, Raman, TEM, HR-TEM and EDX was performed and confirms the structure of these materials, especially the grafting of POM to helical supports. These materials are generally stable, and the induction chirality to the POM anion was confirmed by circular dichroism, highlighting the enantiopurity of these NANOPOM materials. The catalytic properties of these POM hybrids have been tested in the oxidation of sulfides. They are active and recoverable catalysts, unfortunately with no significant enantioselectivity observed in the condition used. We expect that new NANOPOM systems in which POM units are introduced within the structure of nanostructure during gel formation, followed by silica transcription will be more stable, an important feature for their use as recoverable catalyst
27
Elbert, Bryony L. "The synthesis and applications of cyclic alkenylsiloxanes." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:a332365e-22f2-4449-b517-3fd8a62ea8a3.
Анотація:
This thesis describes the development of robust methodology to access cyclic alkenylsiloxanes, and their subsequent application in Hiyama-Denmark cross couplings. An early chapter shows the identification of Lindlar reduction conditions capable of generating cyclic alkenylsiloxanes from alkynylsiloxanes in high yields. The use of such species in Hiyama-Denmark cross coupling is then examined, with particular emphasis on the development of fluoride-free conditions, previously unreported for this class of organosilane. A ring-size dependent orthogonality is revealed, where 5-membered cyclic alkenylsiloxanes cross couple under basic conditions, while 6-membered analogues are inert. The origins of this effect are investigated experimentally and theoretically, leading to the proposal of detailed mechanisms for coupling. In the final chapter, the methodology that has been developed is applied to total synthesis. The great potential of the orthogonality uncovered is demonstrated with the highly convergent construction of anti-inflammatory natural product resolvin D3 by sequential, one-pot, orthogonal cross couplings.
28
Açıkel, Müge Artok Levent. "Silica Supported N-Heterocyclic Carbenes:Active and Reusable Heterogeneous Catalysts for Mizoroki-Heck Reactions/." [s.l.]: [s.n.], 2004. http://library.iyte.edu.tr/tezler/master/kimya/T000496.pdf.
29
O'Brien, Jeannette M. "New Catalysts and Catalytic Methods for Cycloadditions and Conjugate Additions to Alpha, Beta-Unsaturated Carbonyls." Thesis, Boston College, 2012. http://hdl.handle.net/2345/bc-ir:103617.
Анотація:
Thesis advisor: Marc L. SnapperChapter 1. A Practical Synthesis of 3-Acyl Cyclobutanones by [2 + 2] Annulation. Mechanism and Utility of the Zn(II)-Catalyzed Condensation of alpha-Chloroenamines with Electron-Deficient Alkenes. We have developed a catalytic method for the synthesis of highly functionalized 3-acyl cyclobutanones which are useful building blocks for a variety of natural products. Methods for cyclobutanone synthesis have traditionally been limited to Lewis-acid promoted rearrangement of oxaspiropentanes or cyclizations of ketene and syntheses involving keteneiminium salts have required stoichiometric quantities of a Lewis acid. Furthermore, the mechanism for these types of cyclizations remains unknown. This portion of my research focused on an efficient, catalytic method for the synthesis of 3- acyl cyclobutanones and providing insight into the mechanism for cycloaddition. Chapter 2. Enantioselective Synthesis of Boron-Substituted Quaternary Carbons by NHC-Cu-Catalyzed Boronate Conjugate Additions to Unsaturated Carboxylic Esters, Ketones, or Thioesters. We have developed an enantioselective NHC-Cu-catalyzed conjugate addition of boronate esters to acyclic, trisubstituted alpha, beta-unsaturated carbonyl compounds. Enantioselective conjugate addition of a boronic acid pinacol ester through the use of bis(pinacolato)diboron [B2(pin)2,] to alpha, beta-unsaturated aliphatic and aryl esters promoted by 5 mol % of an NHC-Cu catalyst afforded tertiary beta-boryl carbonyls in high efficiency and enantioselectivity. Trisubstituted alpha, beta-unsaturated esters and thioesters were found to be reactive substrates in the presence of a stoichiometric quantity of methanol. Chapter 3. Metal-Free Catalytic C-Si Bond Formation in an Aqueous Medium and C-B Bond Formation in a Protic Medium. Enantioselective NHC-Catalyzed Silyl and Boryl Conjugate Additions to Cyclic and Acyclic alpha, beta-Unsaturated carbonyls. We have developed a method for enantioselective metal-free silyl conjugate additions through the use of dimethylphenylsilyl) boronic acid pinacol ester [PhMe2SiB(pin)] catalyzed by chiral N-heterocyclic carbenes (NHCs) in basic aqueous thf. Optimization of metal-free conditions demonstrated that the presence of water was required for high efficiency. alpha, beta-Unsaturated cyclic ketones and lactones were examined as substrates, and acyclic ketones, esters and aldehydes were also competent substrates for silyl conjugate addition. beta-Silyl carbonyls were isolated in up to >98% yield and >98:2 er. Chapter 4. Elucidation of Mechanism for Enantioselective NHC-Catalyzed Silyl Conjugate Addition. We propose a catalytic cycle for NHC-catalyzed enantioselective silyl conjugate addition. Mechanistic studies of NHC-catalyzed enantioselective silyl conjugate additions are presented. Optimization of conditions for an inefficient alpha, beta-unsaturated electron-deficient ketone provided insight into the roles for dbu and water. Kinetic data indicate that conjugate addition is first order in PhMe2SiB(pin) and carbene, and DFT calculations support the formation of an NHC-silyl anion as a reactive intermediate in the catalytic cycle
Thesis (PhD) — Boston College, 2012
Discipline: Chemistry
30
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.
Анотація:
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
31
Launez, Rémy. "Immobilisation d'organocatalyseurs sur supports inorganiques et évaluation de leur activité en condition de flux continu." Thesis, Université Paris-Saclay (ComUE), 2015. http://www.theses.fr/2015SACLS212/document.
Анотація:
Le but de notre projet était de mettre au point un procédé éco-compatible d’organocatalyse asymétrique hétérogène en flux continu. Pour réaliser ce procédé, nous avons choisi d’utiliser la cupréine, un alcaloïde dérivé de la quinine comme organocatalyseur bifonctionnel. La silice (un matériau inorganique mésoporeux) a été choisie comme support pour l’hétérogénéisation du catalyseur. La cupréine immobilisée sur silice a ensuite été testée comme organocatalyseur de la réaction d’addition de Michael asymétrique entre le trans-β-nitrostyrène (accepteur de Michael) et le diméthyl malonate (donneur de Michael) en condition de flux continu.Nous avons tout d’abord immobilisé la cupréine sur deux types de silice selon trois stratégies différentes. Chaque stratégie nous a permis d’obtenir le support greffé avec des quantités de cupréine allant de 0,2 à 0,4 mmol par gramme de silice, ainsi que des silices greffées possédant des caractéristiques différentes selon les stratégies envisagées.L’évaluation de l’activité catalytique de la cupréine greffée sur silice a ensuite été réalisée en milieu hétérogène en batch. Différents solvants biosourcés ont alors été testés comme solvants alternatifs pour la réaction d’addition de Michael. Le 2-MeTHF s’est révélé être un bon solvant et a été choisi pour les expériences de catalyse en flux continu. Les résultats obtenus en catalyse avec la cupréine greffée sur silice sont comparables à ceux en milieu homogène (excès énantiomériques supérieur ou égale à 85 % et conversion supérieure à 96 %) exceptés pour la fréquence de rotation (TOF, mol de substrat converti/mol de catalyseur/durée de réaction) qui est trois fois plus faible en milieu hétérogène (0,2 h-1 pour 0,6 h-1 en milieu homogène).Enfin, cette réaction d’addition de Michael a été réalisée en flux continu avec les différentes silices greffées. La fréquence de rotation de la cupréine a été multipliée par deux (0,4 h-1) et le nombre de rotation (TON, mol de substrat converti/mol de catalyseur) a lui aussi été augmenté, passant de 16 en milieu hétérogène en batch à 63 en condition de flux continu. Finalement, différents dérivés du trans-β-nitrostyrène (Chloré, phénolique et méthoxy en position 4) ont été testés avec succès.Ainsi, à notre connaissance, nous avons réalisé la première réaction d’addition de Michael entre le trans-β-nitrostyrène et le diméthyl malonate, organocatalysée en milieu hétérogène en batch et en flux continu par la cupréine immobilisée sur silice, en utilisant un solvant biosourcé. Nous avons réussi à mettre au point le procédé de catalyse hétérogène en flux continu permettant de recycler facilement le catalyseur et aussi d’augmenter la productivité de la cupréine immobilisée par rapport au milieu hétérogène en batch, tout en conservant une conversion et une énantiosélectivité équivalente à celles en milieu homogèneThe aim of our project was to develop an eco-friendly process based on heterogeneous asymmetric organocataysis in continuous flow conditions. To succeed in this development, we chose to use a quinine-derived bifunctional organocatalyst: cupreine. Silica, a mesoporous inorganic material, was chosen as the support to immobilize this organocatalyst. The grafted cupreine was then tested as catalyst for the asymmetric Michael addition between the trans-β-nitrostyrene (Michael acceptor) and the dimethyl malonate (Michael donor) in continuous flow condition.First, we immobilized the catalyst on two types of silica, following three different strategies. The various cupreine-grafted silicas we obtained were functionnalized with 0.2 to 0.4 mmol of cuprein per gram of silica. Each one of them possessed specific characteristics depending of the followed strategy.The assessment of the catalytic activity of immobilized silica was then performed in batch condition. Different bio-based solvents were used for the Michael addition. 2-MeTHF was chosen as the best solvent among those tested and used in continuous flow. Immobilized cupreine proved to be as efficient in heterogenous condition as in homogenous (enantiomeric excess was superior or equal to 85 % and conversion better than 96 %), except for turn over frequency (TOF, mol of converted substrate/mol of catalyst/reaction time) which is three times lower in hetereogeneous condition (0.2h-1 to 0.6 h-1 in homogenous condition).Michael addition of trans-β-nitrostyrene to dimethyl malonate was then realized in continuous flow condition, using the various silica-supported catalysts. Turn over frequency of cupreine was doubled (0.4 h-1) and the turn over number (mol of converted substrate/mol of catalyst) increased from 16 to 63 in continuous flow condition. Derivatives of trans-β-nitrostyrene (chlorinated, phenolic and methoxylated in position 4) were successfully tested in continuous flow.To the best of our knowledge, we realized the first asymmetric Michael addition between trans-β-nitrostyrene and the dimethyl malonate, catalysed by silica-supported cupreine in batch and in continuous flow, using a bio-based solvent.We successfully developed an eco-friendly process based on heterogeneous organocatalysis in continuous flow. This process favorited an efficient recycling of the supported catalyst, and increased the productivity of grafted cupreine compare to the heterogeneous condition in batch. The enantioselectivity of the cupreine for this reaction was similar in both homogeneous and heterogeneous conditions
32
Wu, Xianchun. "Acidity and catalytic activity of zeolite catalysts bound with silica and alumina." Diss., Texas A&M University, 2003. http://hdl.handle.net/1969.1/561.
Анотація:
Zeolites ZSM-5 (SiO2/Al2O3=30~280) and Y(SiO2/Al2O3=5.2~80) are bound with silica gel (Ludox HS-40 and Ludox AS-40) and alumina (γ- Al2O3 and boehmite) by different binding methods, namely, gel-mixing, powder-mixing and powder-wet-mixing methods. The acidities of the bound catalysts and the zeolite powder are determined by NH3-TPD and FTIR. The textures of these catalysts are analyzed on a BET machine with nitrogen as a probe molecule. The micropore surface area and micropore volume are determined by t-plot method. Micropore volume distribution is determined by Horvath-Kawazoe approach with a cylindrical pore model. Mesopore volume distribution is determined by BJH method from the nitrogen desorption isotherm. Silica from the binder may react with extra-framework alumina in zeolites to form a new protonic acid. SiO2-bound catalysts have less strong acidity, Bronsted acidity and Lewis acidity than the zeolite powder. Also, the strength of strong acid sites of the zeolites is reduced when silica is embedded. Micropore surface area and micropore volume are reduced by about 19% and 18%, respectively, indicating some micropores of ZSM-5 are blocked on binding with silica. SiO2-bound ZSM-5 catalysts have less catalytic activity for butane transformation (cracking and disproportionation) and ethylene oligomerization than ZSM-5 powder. When alumina is used as a binder, both the total acid sites and Lewis acid sites are increased. Micropore surface area and micropore volume of ZSM-5 powder are reduced by 26% and 23%, respectively, indicating some micropores of ZSM-5 are blocked by the alumina binder. Alumina-bound catalysts showed a lower activity for butane transformation and ethylene oligomerization than ZSM-5 powder. Alkaline metals content in the binder is a crucial factor that influences the acidity of a bound catalyst. The metal cations neutralize more selectively Bronsted acid sites than Lewis acid sites. Alkaline metal cations in the binder and micropore blockage cause the bound catalysts to have a lower catalytic activity than the zeolite powder.
33
Widyaningrum, Rosalia Nugraheni. "Mesoporous silica-supported catalysts to enhance hydrogen production during cellulose pyrolysis." Thesis, The University of Sydney, 2011. https://hdl.handle.net/2123/28917.
Анотація:
Pyrolysis of biomass has been studied worldwide as a potential path to produce hydrogen from renewable sources. Major problem in a non-catalytic biomass pyrolysis is tar formation, which causes complication in the utilization of product gas. Elimination of tar requires a high temperature, and it leads to low energy efficiency since tar itself contains high potential energy.
The utilization of metal catalysts is considered an effective method to reduce tar content and subsequently increase the hydrogen production. Nickel catalyst has been previously investigated for its tar cracking activity and identified as one of the best catalysts, but it has a drawback when used at high temperature because sintering of metal particle and carbon deposition occur. To address this challenge, a suitable catalyst support and promoter are required to minimize sintering and enhance the activity of nickel catalyst.
This project approached the issue by studying the potential catalyst supports and the effect of promoter in the catalytic activity of nickel catalyst. Three catalyst supports: mesoporous silica SBA-15 (Santa Barbara Amorphous), MCF (Mesocellular Foam), and commercial y-Alz03 were investigated, and palladium was chosen as a promoter. Mesoporous silica SBA-15 and MCF were synthesized using sol-gel method with Pluronic P123 as a structure directing agent, tetraethyl orthosilicate (TEOS) as a silica source, and 1,3,5-trimethylbenzene as a swelling agent for MCF synthesis. Nickel and palladium were deposited into the supports by wet impregnation techniques. The catalysts were characterized using N2 adsorption-desorption (BET and BJH methods), xray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and x-ray fluorescence (XRF). The activity of the catalyst was tested in cellulose pyrolysis using thermogravimetric analyzer coupled to a mass spectroscopy (TGA-MS).
This work studied the role of nickel catalysts in the pyrolysis of cellulose, the role of catalyst supports, and the effect of Pd promoter in increasing the catalytic activity to enhance hydrogen production. The results of this study suggest that mesoporous silica MCF was a good catalyst support because the MCF-supported Ni catalyst gave the highest H2 yield. The H2 yield was 73.5 mL/ g cellulose, which was 1.7 times H2 yield from SBA-15-supported Ni-catalyst, and 3.3 times H2 yield produced by y-Alz03-supported Ni-catalyst. The addition of 0.5 wt% Pd promoter also increased the H2 yield by 14%.
34
Hondow, Nicole S. "The synthesis of new heterogeneous Fischer-Tropsch catalysts : the incorporation of metal aggregates in mesoporous silicas." University of Western Australia. School of Biomedical, Biomolecular and Chemical Sciences, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0083.
Анотація:
Transition metals have been extensively studied as catalysts, and certain metals are known to be highly selective and active for certain processes. It is possible to use metal clusters as models for reactions occurring at metal surfaces, but it is often found that in practical applications these complexes are unstable and break down. It is possible to support or stabilise a metal species on, or in, an inorganic framework, making heterogeneous catalysts. A study of metal cluster chemistry with mixed-donor phosphine ligands was conducted, with several new ruthenium complexes synthesised. The chemistry of metal-sulfur interactions is applicable to the removal of sulfur from crude oil, and in an investigation to this chemistry, the bifunctional ligand HSCH2CH2PPhH was added to ruthenium clusters (Chapter 2). The addition of this sulfur-phosphine ligand to the cluster [Ru3([mu]-dppm)(CO)10] produced the carbonyl substituted cluster [Ru3([mu]-dppm)(H)(CO)7(SCH2CH2PPhH)] and the bridged complex [Ru3([mu]-dppm)(H)(CO)8(SCH2CH2PPhH)Ru3([mu]-dppm)(CO)9], as well as recovery of the starting material. Further reactions with this ligand were examined with [Ru3(CO)12] and other complexes were synthesised with different clusters and ligands (Chapter 2). The M41S materials, MCM-41 and MCM-48, are well ordered porous materials with high surface areas (Chapter 3). The incorporation of three different types of metal species, metallosurfactants, metal clusters and nanoparticles, into these materials was examined in an attempt to make heterogeneous catalysts for the Fischer-Tropsch process. The success of this was studied using characterisation techniques such as powder X-ray diffraction, transmission electron microscopy and BET surface area measurements. Metallosurfactants containing either copper or cobalt were added directly to the synthesis of the porous materials in an attempt to incorporate the metals into the framework structure of the porous silica (Chapter 3). This resulted in well ordered iv porous materials, but the successful incorporation of the metal species was found to be dependent on several factors. Organometallic clusters containing metals such as copper, iron and ruthenium, with supporting carbonyl ligands, were added post-synthesis to MCM-41 and MCM-48 (Chapter 4). Various reaction conditions were examined in attempts to ensure small particle formation. The optimum incorporation of nanoparticles containing iron and platinum was found to occur when a suspension of pre-made and purified nanoparticles was added post-synthesis to the M41S materials (Chapter 4). These materials resulted in porous silicas with well dispersed, small metal particles. The optimum conditions for the calcination of these new materials were determined, in an attempt to remove the ligands and stabilisers and retain the small metal particle size (Chapter 5). Testing for the Fischer-Tropsch process was conducted in a fixed bed reactor through which a flow of synthesis gas containing carbon monoxide and hydrogen could pass over the material (Chapter 5). Analysis by gas chromatography showed that the major product produced by all materials tested was methane, but other hydrocarbons were produced in small amounts, including hexane.
35
Roussey, Arthur. "Preparation of Copper-based catalysts for the synthesis of Silicon nanowires." Thesis, Lyon 1, 2012. http://www.theses.fr/2012LYO10164.
Анотація:
Les travaux dans cette thèse ont pour objectif la synthèse de catalyseurs (nanoparticules de cuivre) de taille contrôlée pour la synthèse de nanofils de silicium dans des conditions compatibles CMOS, c'est-à-dire en évitant l'utilisation de l'or comme catalyseur et pour des croissances basse température (<450°C). Les résultats obtenus ont permis de montrer que les techniques de chimie de surface classiquement utilisées pour la préparation de catalyseurs sur des supports 3D (silice, nitrure de titane…) sont directement applicables et transférables sur des supports 2D (wafer de silicium recouvert de films fins de SiO2, SiOx et TiN). Nous avons par exemple pu préparer des nanoparticules de cuivre de taille contrôlée (de 3 nm à 40 nm de diamètre moyen suivant les conditions expérimentales et supports). De plus, les mécanismes de formation des nanoparticules en fonction des propriétés de surface des matériaux étudiés ont été démontrés en combinant diverses techniques d'analyses de surface. La croissance de nanofils de silicium à partir de ces catalyseurs sur substrats 2D a également été réalisée avec succès dans des procédés à basse température. Il a notamment été montré l'existence d'un diamètre minimum critique à partir de laquelle la croissance basse température était possibleThe work presented in this PhD thesis aimed at the preparation of copper nanoparticles of controllable size and their utilization as catalysts for the growth of silicon nanowires in a process compatible with standard CMOS technology and at low temperature (< 450°C). The growth of silicon nanowires by Chemical Vapor Deposition (CVD) via the catalytic decomposition of a silicon precursor on metallic nanoparticles at low temperature (Vapor Solid-Solid process) was demonstrated to be possible from an oxidized Cu thin film. However, this process does not allow the control over nanowires diameter, which is controlled by the diameter of the nanoparticle of catalyst. In this PhD is presented a fully bottom-up approach to prepare copper nanoparticles of controllable size directly on a surface without the help of external stabilizer by mean of surface organometallic chemistry. First, the preparation of copper nanoparticles is demonstrated on 3D substrates (silica and titanium nitride nanoparticles), along with the fine comprehension of the formation mechanism of the nanoparticles as a function of the surface properties. Then, this methodology is transferred to planar (2D) substrates typically used in microelectronics (silicon wafers). Surface structure is demonstrated to direct the Cu nanoparticles diameter between 3 to 40 nm. The similarities between the 2D and 3D substrates are discussed. Finally, the activity of the Copper nanoparticles in the growth of Silicon nanowire is presented and it is demonstrated that in our conditions a critical diameter may exist above which the growth occurs
36
Kaya, Sarp. "Structural and catalytic investigations on vanadium oxide nanoparticles supported on silica films grown an a Mo(112) substrate." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2007. http://dx.doi.org/10.18452/15639.
Анотація:
Die breite Anwendung von Modellsystemen, um heterogene katalytische Prozesse zu verstehen, basiert darauf, die Lücke der strukturellen Komplexität zu überbrücken zwischen heutigen technischen Katalysatoren, bestehend aus einem Metalloxid sowie einem darauf geträgerten Metall, sowie kristallinen Metallen und planaren Metall/Oxid-Systemen, welche dazu benutzt werden, Struktur-Reaktivitäts-Beziehungen mittels einer Fülle von Surface Science-Methoden zu untersuchen. In der vorliegenden Arbeit liegt das Hauptaugenmerk auf so genannten Vanadiumoxid-‚Monolagen’-Katalysatoren, die insbesondere für Oxidationsreaktionen von Methanol eingeführt wurden. Mittels eines ‚bottom-up’-Ansatzes wurden Silica-geträgerte Vanadiumoxid-Modellkatalysatoren untersucht. Durch Kombination einer Reihe experimenteller Techniken wurde die Oberfläche von Mo(112), die als Substrat für den Silica-Film diente, im Detail untersucht und die atomare Struktur des Silica-Films wurde ermittelt. Adsorption von Wasser und das Wachstum von Vanadiumoxid-Nanopartikeln auf dem Silica-Film und schließlich die Reaktivität von Vanadiumoxid/Silica-Systemen gegenüber Methanol wurden untersucht. Im Gegensatz zu früher vorgeschlagenen Modellen sollte eine Sauerstoff-induzierte p(2×3)-Überstruktur, die sich auf einer Mo(112)-Oberfläche ausbilded, angenommen werden als ein eindimensionales Oberflächenoxid, bei dem sich Mo=O-Gruppen bevorzugt entlang der [-1-11]-Richtung der Mo(112)-Oberfläche ausbilden. Monolagen-Silica-Filme, die auf Mo(112) gewachsen wurden, bestehen aus einem zweidimensionalen Netz von SiO4-Tetraedern. In Abhängigkeit der Bedingungen, unter denen der Film präpariert wurde, kann die Struktur durch zusätzlich auf dem Mo-Substrat adsorbierte Sauerstoff-Atome verändert werden. Die Defekt-Struktur schließt Antiphasen-Domänengrenzen ein, die durch eine Verschiebung um die halbe Gitterkonstante entlang der [-110]-Richtung gebildet werden, und eine geringe Dichte von Punkt-Defekten, die höchstwahrscheinlich Silizium-Fehlstellen darstellen. Wasser dissoziiert nicht auf dem Monolagen-Silica-Film. Eine Wasser-Struktur, die geordnet bezüglich des Silica-Films ist, wurde bei 140 K beobachtet, was der guten Übereinstimmung der Gitterkonstanten von Silica-Film und hexagonalem Eis geschuldet ist. Amorphe Lagen festen Wassers, die die Oberfläche bei 100 K homogen bedecken, wurden als reaktive Lagen für Vanadiumoxid-Partikel benutzt, um die ‚Nasschemie’ nachzubilden, wie sie in der Präparation technischer Katalysatoren zum Einsatz kommt. Die Ergebnisse verdeutlichen, dass die Eis-Lagen die Bildung von hydratisierten Vanadiumoxid-Nanopartikeln, welche teilweise von V=O und V-OH-Gruppen terminiert werden, begünstigen. Die Dehydratisierung geschieht oberhalb 500 K, wobei eine V-terminierte Oberfläche entsteht. Methanol dissoziiert auf dehydratisierten Vanadiumoxid-Partikeln, und Methoxy-Spezies sind auf der Oberfläche stabil bis 500 K, allerdings nur in der Gegenwart von V-Plätzen. Die Produktion von Formaldehyd, die bei etwa 550 K stattfindet, ist stark abhängig von der Struktur der Oberfläche der Vanadiumoxid-Partikel und weist ein Maximum bei einem spezifischen Verhältnis zwischen V- und V=O-Oberflächenplätzen auf. Die hier vorgestellten Ergebnisse könnten unser Verständnis von katalytischen Reaktionen auf molekularer Ebene bedeutend vorantreiben.The widespread use of model systems for understanding the heterogeneous catalytic processes is based on bridging the structural complexity gap between present generation of supported metal and metal oxide technical catalysts and crystalline metal and planar metal/oxide systems, which are utilized to investigate structure-reactivity relationships by a large variety of surface science techniques. In this thesis, we focused on a concept of so-called ''monolayer'' vanadium oxide catalysts, which have been introduced particularly for methanol oxidation reactions. Following a bottom-up approach, silica supported vanadium oxide model catalysts were investigated. Combining a number of experimental techniques, the surface of Mo(112) used as a substrate for the silica films was characterized in detail and the atomic structure of the silica film was determined. Adsorption of water and growth of vanadium oxide nanoparticles on the silica films, and finally the reactivity of vanadium oxide/silica systems towards methanol were studied. In contrast to the previously suggested models, an oxygen induced p(2×3) superstructure formed on a Mo(112) surface should be considered as one dimensional surface oxide where Mo=O groups are formed preferentially along the [-1-11] direction of the Mo(112) surface. Monolayer silica films grown on Mo(112) surfaces are composed of two-dimensional network of SiO4 tetrahedra. Depending on the film preparation conditions, the structure can be altered by additional oxygen atoms adsorbed on the Mo substrate. The defect structure includes antiphase domain boundaries which form by a half-lattice shift along the [-110] direction and a low density of point defects, most probably silicon vacancies. Water does not dissociate on the monolayer silica film. An ordered structure of water with respect to silica film was observed at 140 K owing to good lattice matching between the silica film and hexagonal ice. Amorphous solid water layers homogenously covering the surface at 100 K were used as reactive layers for vanadium oxide particles in order to mimic ''wet chemistry'' used in preparation of technical catalysts. The results revealed that ice layer assisted the formation of hydrated vanadium oxide nanoparticles partially terminated by V=O and V-OH groups. The dehydration takes place above 500 K, thus exposing V-terminated surface. Methanol dissociates on dehydrated vanadium oxide particles and methoxy species are stable on the surface up to 500 K only in the presence of vanadium terminated surface sites. Formaldehyde production which takes place at ~550 K is strongly affected by the surface structure of the vanadium oxide particles and exhibits a maximum at specific ratio between V- and V=O sites on the surface. The results presented may have a strong impact on our understanding of the catalytic reactions at the molecular level.
37
Aksın, Özge Artok Levent. "The activity of silica immobilized palladium N-heterocyclic carbene complexes toward Mizoro-Heck reaction and their characterization/Özge Aksın;thesis advisor Levent Artok." [s.l.]: [s.n.], 2005. http://library.iyte.edu.tr/tezler/master/kimya/T000341.pdf.
Анотація:
Thesis (Master)--İzmir Institute of Technology, İzmir, 2005.Keywords: Palladium, Immobilization, Heck Reaction, Palladium-N-Heterocyclic Carbene, Carbon-Carbon Coupling. Includes bibliographical references (leaves. 89-104).
38
Zamboulis, Alexandra. "Silices hybrides pour l'organocatalyse asymétrique." Thesis, Montpellier, Ecole nationale supérieure de chimie, 2010. http://www.theses.fr/2010ENCM0004.
Анотація:
L'organocatalyse asymétrique est un domaine en plein développement. L'immobilisation de ce type de catalyseurs pourrait présenter de multiples avantages. Ces travaux de thèse s'intéressent à la préparation de silices hybrides organiques/inorganiques par voie sol-gel et aux applications de ces matériaux en organocatalyse asymétrique. La première partie du manuscrit est consacrée à une présentation bibliographique du sujet. Dans la deuxième partie, l'utilisation de la L-proline comme modèle est décrite. Des matériaux contenant un fragment L-proline ont été préparés et leurs performances catalytiques évaluées pour une réaction d'aldolisation asymétrique. Les processus à l'origine des propriétés catalytiques modérées de ces catalyseurs supportés sont discutés. La troisième partie porte sur le catalyseur de Takemoto, organocatalyseur bifonctionnel contenant un groupement donneur de liaisons hydrogène et une fonction amine tertiaire. Les différentes stratégies envisagées pour préparer des dérivés silylés de ce catalyseur sont exposées. Enfin, la nanostructuration de silsesquioxanes par le biais de liaisons hydrogène entre fonctions thiourée est présentéeAsymmetric organocatalysis is a blossoming area of research. Immobilisation of this kind of catalysts could present numerous advantages. This thesis deals with the sol-gel synthesis of organic/inorganic hybrid silicas and their applications in asymmetric organocatalysis. The first part of this work is dedicated to a bibliographic presentation of this area of research. In the second part, the use of L-proline as a model is described. Hybrid materials containing a L-proline component were prepared and their catalytic performances were evaluated in an asymmetric aldolisation reaction. The processes accounting for the moderate performances of these materials are discussed. The third part relates the synthetic strategies used to prepare silylated derivatives of the Takemoto catalyst, a bifunctional catalyst containig a H-bond donnor and a tertiary amine. Finally the nanostructuring of bridged silsesquioxanes through H-bonding interactions between thiourea cross-linkers is presented
39
Kababji, Ala'a Hamed. "Effects of Diluent Addition and Metal Support Interactions in Heterogeneous Catalysis: SiC/VPO Catalysts for Maleic Anhydride Production and Co/Silica Supported Catalysts for FTS." Scholar Commons, 2009. https://scholarcommons.usf.edu/etd/2035.
Анотація:
This work begins with an introduction to catalysis focusing on heterogeneous systems and surface science phenomena. A study on the partial oxidation reaction of n-butane to maleic anhydride (MA) is presented in the first part. MA supplies are barely adequate for market requirements due to continued strong demand. Only slight improvement in catalytic performance would be welcome in the industrial community. The vanadium phosphorus oxide (VPO) catalyst was used in this work. The reaction is highly exothermic and the need to properly support the catalyst, not only for good dispersion but adequate heat dissipation is of crucial importance. For this, alpha-SiC commercial powders were used in synthesizing the catalyst due to its high thermal conductivity. Up to 25% MA yields were obtained and the reaction temperature was lowered by up to 28% using SiC/VPO mixed catalysts.
The second part of this work is focused on the Fischer-Tropsch synthesis (FTS) process using cobalt silica supported catalysts. The main objective is the production of synthetic ultra high purity jet fuel (JP5). This is a very timely topic given the energy issues our world is facing. Almost all aspects of the FTS process have been extensively studied, however the effects of calcination temperature and silica support structure on the catalyst performance are lacking in literature. The catalysts were prepared using various silica supports. The catalysts had different drying and calcination temperatures. It was found that lower support surface area and calcination temperature catalysts exhibited higher activity due to lower support cobalt phase interaction. Co/silica catalysts calcined at 573K showed the highest CO conversion and the lowest CH4 selectivity. Catalysts prepared with 300m²/g support surface area exhibited 79.5% C5+ selectivity due to higher reducibility and less metal support interaction.
The properties and performance of various prepared catalysts in both VPO and Co/silica systems are characterized by FTIR, XRD, BET, GC and XPS techniques. Theoretical FTS deactivation by sintering calculations and SiC/VPO particle temperature gradient calculations are presented as well. Finally, conclusions and future work on improving the yield and selectivity and scaling up the bench top setups are also presented.
40
Moitra, Nirmalya. "Silices hybrides fonctionnelles : matériaux dérivés d'alcaloïdes pour organocatalyse ; réactions "click" pour le sol˗gel." Thesis, Montpellier, Ecole nationale supérieure de chimie, 2011. http://www.theses.fr/2011ENCM0003.
Анотація:
Cette thèse s'intéresse à la préparation de silices hybrides organique/inorganiques à base de fragments alcaloïdes cinchona, et à une nouvelle méthode de synthèse de précurseurs silylés hydrolysables via une réaction ‘click' de CuAAC. La première partie de ce travail est dédiée à une présentation bibliographique du domaine de la catalyse supportée sur matériaux hybrides, et est principalement focalisée sur l'organocatalyse supportée, un champ de recherche en plein développement. Dans la seconde partie, différentes méthodes d'immobilisation d'alcaloïdes dans une matrice de silice sont décrites, dans le but de les utiliser comme organocatalyseurs pour une réaction de décarboxylation asymétrique. La troisième partie est dédiée à une nouvelle méthode de préparation de précurseurs silylés via une réaction de CuAAC. Cette méthodologie montre un potentiel important pour la formation de nouveaux composés fonctionnels. Finalement, la synthèse de nanoparticules de silice mésoporeuse contenant des groupes azoture ou alcyne et leur post-fonctionalisation sont présentéesThis thesis deals with the preparation of organic-inorganic hybrid silica based on cinchona alkaloids fragments and with a new method of synthesis for hydrolysable silylated precursors via CuAAC “click” reactions. The first part of this work is dedicated to a bibliographic presentation of the area of supported catalysis on hybrid materials and is mainly focused on supported organocatalysis, an emerging area of research. In the second part, different methods for immobilization of alkaloids within a silica matrix are described aiming at using them as organocatalysts for an asymmetric decarboxylation reaction. The third part is devoted to a new method of preparation of silylated precursors by CuAAC “click” reactions. This methodology shows a high potential in the formation of new functional compounds. Finally the synthesis of mesoporous silica nanoparticles bearing azide or alkyne groups and their post-functionalization by CuAAC reactions are presented
41
Popoff, Nicolas. "Préparation et caractérisation de complexes du groupe IV supportés sur silice et silice mono-fonctionnalisée : catalyseurs pour la polymérisation des oléfines." Thesis, Lyon 1, 2011. http://www.theses.fr/2011LYO10229.
Анотація:
Ce manuscrit est consacré à l'élaboration et la caractérisation de nouveaux catalyseurs à base de métaux de transition du groupe IV neutres ou cationiques, supportés sur silice ou silices mono-fonctionnalisées, pour la polymérisation d'alpha-oléfines. Dans un premier temps une nouvelle méthode de préparation de catalyseurs neutres, pour la polymérisation des oléfines, a été mise au point, par greffage de TiCl4 sur des silices déshydroxylées à 200 ou 700°C (notées SiO2-200 ou SiO2-700) donnant une espèce unique [≡SiO-TiCl3] qui, activée par le réducteur de Mashima conduit à un catalyseur neutre, actif en polymérisation de l'éthylène, selon un mécanisme faisant intervenir un couplage oxydant, avec une activité maximale de 260 kgPE.molTi -1.h-1. De même, d'autres catalyseurs neutres ont été mis au point pour la polymérisation de l'éthylène selon le même mécanisme. Les complexes M(CH2Ph)4 (M=Ti, Zr) ont été greffés et caractérisés sur SiO2-200 et SiO2-700, en utilisant notamment des complexes isotopiquement enrichis en carbone-13, pour donner les espèces bien définies [(≡SiO)2M(CH2Ph)2] et [≡SiO-M(CH2Ph)3] respectivement. L'activation de ces espèces neutres par B(C6F5)3 pour obtenir des espèces cationiques plus électrophiles ne permet qu'une amélioration faible de l'activité. Dans la deuxième partie de ce travail l'introduction d'un bras espaceur de type phénoxy entre la surface de la silice et le complexe organométallique a été étudiée. Un nouveau matériau [(≡SiO)2AlO-C6H4-OH.(Et2O)] a été obtenu en deux étapes par greffage de AliBu3 sur SiO2-700 donnant l'espèce unique [(≡SiO)2AliBu.(Et2O)] suivi d'une réaction de protolyse par l'hydroquinone. Les complexes tetrabenzyl zirconium et titane ont été greffés sur ce support. Ces espèces de surface ont été ensuite activées par B(C6F5)3 et une amélioration notable de l'activité a été obtenue en polymérisation de l'éthylène. Cette méthodologie a été étendue au complexe métallocène 100% enrichit (C5Me5)Zr(13CH3)3 selon trois approches. Soit par greffage direct sur ce nouveau matériau, puis activation par B(C6F5)3, soit par réaction avec ce support, modifié par HB(C6F5)2 ou [B(C6F5)3][NEt2Ph]. Cependant, quelle que soit la méthode utilisée, l'espèce active cationique obtenue présente une liaison covalente Zr-O avec la surface et un contre-anion [MeB(C6F5)3]- et une activité maximale de 510 kgPE.molZr -1.h-1, supérieure à celle obtenue sur la siliceThis work deals with the preparation and characterization of new, neutral or cationic group IV complexes, supported on silica or mono-functionalized silica, for alpha-olefins polymerization. In a first part, a new preparation for an olefin polymerization catalyst based on TiCl4, was proposed. Grafting on silica dehydroxylated at 200 and 700°C (SiO2-200 and SiO2-700) yielded the unique species [≡SiO-TiCl3] which, upon activation by Mashima’s reductant, led to a neutral active polymerization catalyst, following an oxidative coupling mechanism, and reaching an activity of 260 kgPE.molTi -1.h-1. Similarly, neutral catalysts acting along the same mechanistic pathways, were developed by grafting M(CH2Ph)4 (M=Ti, Zr) to yield the well defined species [(≡SiO)2M(CH2Ph)2] and [≡SiO-M(CH2Ph)3] on SiO2- 200 and SiO2-700 respectively. The ensuing activation by B(C6F5)3 in order to yield cationic species, did not increase the activity considerably.In the second part of this work, a new material was prepared in order to introduce of a phenoxy spacer between the surface and the complex. Reaction of AliBu3 with SiO2-700 yielded the unique species [(≡SiO)2AliBu.(Et2O)] which was then reacted with hydroquinone. The tetrabenzyl Ti and Zr complexes were successfully grafted on this support. These species were then activated by B(C6F5)3 and a notable increase in the resulting polymerization activities were observed. This methodology was extended to 100\% enriched complexes (C5Me5)Zr(13CH3)3 following three approaches. Either direct grafting on this new material, followed by B(C6F5)3 activation, or by reaction with the support, previously altered by HB(C6F5)2 or [B(C6F5)3][NEt2Ph]. Either way, the active cationic active species obtained presents a covalent Zr-O bond with the surface, with the associated counter-ion [MeB(C6F5)3]- with a maximum activity of 510 kgPE.molZr-1.h-1, higher than its the silica counterpart
42
Wang, Zichun. "Catalytic conversion of biomass- and petrochemical-derived model compounds over acidic catalysts." Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/13679.
Анотація:
Silica-aluminas (SA) as solid acids are widely used in the chemical, food, pharmaceutical and petrochemical and bio-refining industries. Their acidic properties depend on their local structure. For the first time, the presence of large amount of surface available AlV species on amorphous SA (ASA) was revealed by 27Al MQMAS NMR spectroscopy in this thesis. These AlV species can enhance the strength of neighboring SiOH groups evidenced by 1H-27Al D-HETCOR. Indeed, significantly enhancing the acidity of ASA at the same Al loading was achieved via increasing AlV concentration by applying higher combustion enthalpy solvent. In H/D exchanged with benzene-d6, ASA exhibited 4 times lower activation energy compared to zeolite H-ZSM-5, which was due to the assistance of AlV species. In the conversion of phenylglyoxal to ethyl mandelate, the performance of ASA correlated well with the enhanced Brønsted acidity, confirmed by using silica-zirconia catalyst. At the same conditions, ASA obtained a 10 times higher TOF than dealuminated zeolite HY. This was attributed to the free diffusion of molecules on ASA surface, confirmed by using [Al]MCM-41. Selective dehydration of glycerol on solid acids is important for the production of the value-added acrolein for sustainable bio-refinery. Most efforts focus on developing strong BAS to improve the acrolein production, since LAS produce by-product acetal. With Al-exchange zeolite H-ZSM-5, the significant increase of the acrolein yield was achieved via the cooperative dehydration between the BAS and LAS. In chemoselective hydrogenation of acetophenone, the selectivity was influenced by electronic properties of noble metal, indicated by FTIR investigation. Solid-state NMR spectroscopy studies revealed electronic properties depends on the strength of BAS covered by metal nanoparticles. Increasing the number of uncovered BAS on the supports can improve the performance of supported metal catalyst with similar product selectivity.
43
Tichauer, Ruth Elena. "In silico screening of NRas protein oncogenic mutations : new structural and physico-chemical insights into the catalytic activity." Electronic Thesis or Diss., Toulouse 3, 2019. http://www.theses.fr/2019TOU30028.
Анотація:
Les protéines Ras jouent un rôle majeur dans le développement cellulaire. Faisant partie de la catégorie de petites GTPases, elles sont dotées d'un mécanisme fonctionnant tel un interrupteur moléculaire qui, dans leur cas, contrôle la transmission de signaux de croissance cellulaire. Liées au GTP, ces protéines adoptent une conformation leur permettant d'interagir avec des effecteurs en aval et, ainsi, activer la réplication et différenciation cellulaires. La réaction d'hydrolyse du GTP qui se déroule en leur centre, est accompagnée d'un changement conformationnel qui met fin à ces interactions, conduisant ainsi à l'état inactif de Ras, lié au GDP. Des mutations spécifiques de résidus bien déterminés entraînent une baisse du taux d'hydrolyse, laissant ainsi Ras liée au GTP. Or, de fortes concentrations de cette forme active de Ras ont été associées à une prolifération cellulaire anormale, caractéristique de la dissémination de tissus cancéreux. Il apparaît alors que l'élucidation des mécanismes employés par Ras pour accélérer le clivage du GTP constitue une étape majeure dans le développement de thérapies ciblées contre le cancer. Elles consisteraient à rétablir, au sein des mutants oncogéniques, un taux d'hydrolyse proche à celui mesuré au sein du type sauvage. Dans le but de mieux comprendre au niveau atomique les propriétés catalytiques de Ras, nous avons mené des simulations de dynamique moléculaire (MD) en décrivant le domaine G à différents niveaux de théorie (Mécanique Moléculaire (MM), Semi-empirique et Théorie de la Fonctionnelle de la Densité (DFT)). Ces calculs ont été réalisés pour les formes sauvage et mutées au niveau du résidu 61 de NRas. Ils ont été couplées à des caractérisations biomécaniques des complexes protéine-ligand étudiés, en utilisant la méthode des modes statiques. Cette méthode permet d'identifier des points chauds, réactifs, de la biomolécule et qui, suivant le critère de contrainte choisi, ont une influence mécanique sur la fonction GTPase de la protéine. Par conséquent, ils pourraient servir en temps que sites appropriés pour héberger des molécules médicamenteuses contenant des groupes chimiques spécifiques qui faciliteraient l'hydrolyse du GTP. Tout d'abord, les résultats obtenus montrent que le positionnement des molécules d'eau dans le cite actif est crucial pour catalyser efficacement la réaction. En effet, la répartition précise du solvant, observée dans le type sauvage, est perdue au sein des mutants de NRas considérés ici. Cette distribution différente des molécules d'eau ainsi que les modifications structurales du site actif engendrées par les substitutions du résidu Gln 61, ont un impact direct sur la densité électronique du GTP. Cette dernière présente un profil de type GDP au sein de la protéine de type sauvage uniquement, comme déterminé expérimentalement dans des études précédentes. Il apparaît donc que les mutations oncogéniques de Gln 61 perturbent cet effet catalytique majeur de NRas. Parmi trois propositions faites au cours de cette thèse sur des modifications à apporter à la forme mutée Q61R de NRas, une est présentée pendant la soutenance tandis que toutes les trois sont décrites dans le manuscript. Les groupes chimiques insérés au niveau du site identifié permettent de rétablir une distribution de l'eau comme celle observée dans le type sauvage. Pour terminer, lors de la soutenance uniquement, un chemin réactionnel alternatif de l'hydrolyse enzymatique du GTP est proposéRas subfamily of small GTPase proteins holds a key position in cell proliferation pathways. Indeed, the transmission of cell growth signals is controlled by proteins belonging to it. In their GTP-bound conformation, these proteins interact and activate downstream effectors of cell replication and differentiation. The hydrolysis reaction that takes place in their center, terminates these interactions, thereby leading to the GDP-bound inactive state. Point mutations of key residues lead to a hydrolysis rate drop that keeps Ras in a GTP-bound active state. Now, high concentrations of active Ras have been associated to abnormal cell proliferation, emblematic of cancerous tissues dissemination. With this into consideration, the elucidation of Ras mechanisms for accelerating GTP cleavage appears as a major step in the development of cancer targeted therapies that would consist in restoring the hydrolysing capabilities within oncogenic Ras to a wild-type rate. In an attempt to gain insight into Ras catalysing properties at the atomic level, unconstrained Molecular Dynamics (MD) simulations describing the G domain at different levels of theory (Molecular Mechanics (MM), Semi-empirical and Density Functional Theory (DFT)) were carried out for NRas member in its wild-type and Gln 61 mutated forms. These simulations were coupled to biomechanic characterisations of the complexes under inspection employing the static modes approach. The latter method, allows the identification of hot spots {\it i.e.} responsive residues of the biomolecule, that have a mechanical influence on the GTPase function of the protein. Hence, they could serve as suitable sites to host drug-like molecules containing specific chemical groups that would facilitate GTP hydrolysis. The obtained results show that water molecules positioning is crucial for efficiently catalysing the reaction that takes place in NRas center. Indeed, the precise positioning observed within the wild-type is lost within the mutants studied here. Furthermore, the active site structural modifications undergone upon Gln 61 substitutions, together with solvent distribution in it, impact directly GTP electronic density. The latter is accommodated to a GDP-like state within the wild-type protein only, as experimentally determined in previous investigations. Thus, oncogenic Gln 61 mutations impair this major catalysing effect. Among three engineered NRas proteins of the Q61R mutated form, proposed during this thesis, one is presented during the defence while the three are described in the manuscript. The chemical groups inserted at the identified site enable the recovery of water distribution as within the wild-type. To end, during the defence only, an alternative reaction pathway of the enzymatic reaction is proposed
44
Scriba, Manfred R. "Silicon nanoparticle sysnthesis through thermal catalytic pyrolysis." Master's thesis, University of Cape Town, 2006. http://hdl.handle.net/11427/6550.
Анотація:
Includes bibliographical references.Nanoparticles are considered as fundamental building blocks of nanotechnology and, silicon nanoparticles in particular, will form the basis of applications in single electron transistors, floating gate memory devices, solid state lighting, chemical sensors and flexible electronics, including solar cells and luminescent materials, printed on paper. A remaining key challenge however in the development of applications is the reproducible and reliable production of nanomaterial in sufficient quantities. Historically nanoparticles have been manufactured by top-down approaches such as milling, laser ablation or etching, and bottom-up synthesis such as colloidal chemistry and gas phase pyrolysis. The chemical processes in the latter are generally equivalent to those in the chemical vapour deposition (CVD) of compact films. Due to its simplicity and the relatively straight-forward construction of the hot wire chemical vapour deposition (HWCVD) reactor, this method is further investigated as a suitable route to nanoparticle production. The objective of this research is thus to produce Si nanoparticles (powder) in sufficient quantities, through thermal catalytic pyrolysis, while maintaining control of the important properties namely size, size distribution, composition and crystallinity.
45
Nzahou, Ottou Winnie. "Organopolymérisations du méthacrylate de méthyle induites par les carbène N-hétérocycliques et par des paires de Lewis organiques." Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0303/document.
Анотація:
Deux carbènes N-hétérocycliques (NHCs) de type imidazol-2-ylidène ont été étudiés en tant qu’amorceurs organiques pour la polymérisation directe de monomères vinyliques de type (méth)acrylates d’alkyle, principalement le méthacrylate de méthyle(MMA), en l’absence tout autre activateur. Une différence de réactivité a été mise en évidence en fonction des substituants du carbène et de la nature du substrat. Des études théoriques ont permis de rationaliser les résultats expérimentaux par l’influence des effets électroniques et stériques intervenant au cours des réactions mises en jeu. Un NHC en particulier a été ensuite utilisé comme véritable catalyseur de la polymérisation du MMA en présence d’alcools comme amorceurs. En utilisant des macroamorceurs hydroxylés de type poly(oxyde d’éthylène), des copolymères amphiphiles ontété ainsi synthétisés. Des études théoriques ont encore une fois permis d’identifier les mécanismes réactionnels de cette polymérisation. Enfin, des paires de Lewis composées d’un acide à base de silicium et d’une base de typeNHC ou phosphine trialkyle(aryle) ont été ensuite utilisées comme système d’activation de polymérisation du MMA. Ce type de polymérisation est basé sur une activation duale du monomère par effet coopératif de la base et de l’acideThe reactivity of imidazol-ylidene N-heterocyclic carbenes (NHCs) as direct initiators for the polymerization of miscellaneous (meth)acrylic monomers, mainly methylmethacrylate (MMA), has been screened in the absence of any other co-activator.Different reactivities have been observed according to the structure of the NHC and thenature of the substrate. Computational studies allowed rationalizing steric and electroniceffects involved in these reactions.The use of a peculiar NHCs as catalyst for the polymerization of MMA using alcohols as initiators has then been investigated. This simple and efficient method also allows achieving amphiphilic block copolymers by using hydroxylated poly(ethylene oxide)s asmacro-initiators. Combined computational and experimental investigations have provided insights into the mechanism of polymerization.Various Lewis pairs including a silicon-based compound as acid and NHC or a trialkyl(aryl)phosphine as base, have been investigated to trigger an efficient polymerization of MMA.In this case, the polymerization is expected to proceed via a cooperative/dual activation mechanism
46
Modiba, Fortunate Mofao. "Tin Catalyst preparation for Silicon Nanowire synthesis." University of the Western Cape, 2018. http://hdl.handle.net/11394/6516.
Анотація:
>Magister Scientiae - MScSolar cells offer SA an additional energy source. While Si cells are abundantly available they are not at an optimal efficiency and the cost is still high. One technology that can enhance their performance is SiNW. However, material properties such as the diameter, porosity and length determine their effectiveness during application to solar cell technology. One method of growing SiNW uses Sn catalysts on a Si substrate. As the properties of the Sn nanoparticle govern the properties of the SiNW, this thesis investigates their formation and properties by depositing a Sn layer on a Si wafer and then subjecting it to different temperatures, during process the layer forms into nanoparticles. At each temperature the morphology, composition and crystallinity will be determined using XPS, SEM, TEM and EDS. Thus, in Chapter 1 there is an overview, Chapter 2 deals with techniques used in this study, Chapter 3 will give the quantitative and qualitative results on the XPS analysis and Chapter 4 will illustrate the structural behaviour of the annealed Sn film samples.
47
Polisski, Sergej. "Porous silicon/noble metal nanocomposites for catalytic applications." Thesis, University of Bath, 2010. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.545317.
Анотація:
Today, bulk silicon is one of the best studied semiconductors. However, in its different nano-modifications, e.g. as porous silicon, totally new properties are exhibited. Despite the fact, that porous silicon is widely known and has been extensively studied since the 1990s, many unique features of this material are still unexplored. In this work, specific functionalities of porous silicon prepared, utilising both solid (via electrochemical or stain etching processes) and gas phase (from silane) syntheses, were investigated. Since this study was in-part industry oriented, the emphasis has been placed upon the investigation of porous silicon nanostructures, made from low cost metallurgical grade polycrystalline silicon powder. It has been previously demonstrated that porous silicon exhibits a very large, hydrogenated internal surface area (up to 500 m2 g−1). It is verified in this work, that morphological properties of this material result in a high reductive potential of its internal surface due to hydrogen passivation. Therefore, in this thesis, we would like to show that porous silicon-based reactive templates are promising for their applications in nanometal-supported catalysis. We used salts of platinum, gold, palladium, silver and their mixtures, which were reduced on the silicon nanocrystalline internal surface, resulting in formation of metal nanoparticles embedded into porous silicon matrix. Various experimental techniques were used to evaluate the morphology, size and composition of metal nanoparticles, as well as their growth rates. Hydrogen effusion experiments proved the crucial difference between porous silicon and other chemically inert supporting templates for the process of metal nanoparticles formation. The catalytic activity of the synthesised materials was evaluated in gas phase conversion of CO to CO2. Furthermore, the new porous silicon-based catalysts were tested in gas/liquid phase reactions as well, using hydrogenation, oxidation, dehalogenation and C-C coupling class reactions. Following the trends of “state of the art” current Si technology, we present the design of the developed flow microreactor, based on patterned Si wafer, which can be implemented in future work to catalyse selected reactions. Results obtained in this work suggest that porous silicon matrices are promising supports for metal nanoparticle based catalysis.
48
Utting, Katherine Alice. "Silica supported mild base catalysts." Thesis, University of York, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.423602.
49
Peyralans, Jerome Jean-Pierre. "Silasultones as silicon-based Lewis acid catalysts : synthesis and activity." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.412759.
50
Papafilippou, Alexandros. "Development of low-oxidation state nitrogen, carbon and silicon catalysts." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/23646.
Анотація:
This PhD thesis is focused on the development of novel low-oxidation state main group catalysis for organic synthesis. More specifically, the major objective has been to explore and design non-toxic and effective catalysts based on the following isoelectronic species: nitreones [nitrogen(I)], carbones [carbon(0)], and silylones [silicon(0)]; the corresponding central nonmetal atom in these molecules is in the formal low-oxidation state ‘+I’ and ‘0’, respectively. These species have been calculated to be strong Lewis and Brønsted bases. In addition, compared with established base catalysts such as N-heterocyclic carbenes (NHCs), nitreones, carbones, and silylones formally possess an additional lone pair of electrons at the central atom. In turn, these species may be used in base catalysis or as ligands in metal catalysis, and in the context of frustrated Lewis pair (FLP) or dual catalysis. The Lewis basicity of these N(I), C(0), and Si(0) compounds has been assessed with 11B NMR analysis using a variety of boron Lewis acids. These boron binding data have been compared with results obtained using NHCs as a Lewis base. Nitreones –more specifically cyclopropen-imines– have been explored in base catalysis. These N(I) Lewis bases have been uncovered to catalytically activate a variety of silicon-based pro-nucleophiles for subsequent bond formation with carbonyl and imine derivatives as well as aziridines. Successfully used pro-nucleophiles include TMS–CN, TMS– CF3, TMS–N3, and TMS–Cl. The characteristic features of this unprecedented cyclopropenimine Lewis base catalysis include low catalyst loading, mild reaction conditions, and broad substrate scopes. Various “normal” imines have proved to be catalytically inactive under the same conditions. In a similar context, carbones and silylones have been used to develop novel catalytic umpolung reactions, which turned out to be too challenging at this stage. Importantly though, silylones have been shown to activate the B–H bond of suitable pro-nucleophiles. Finally, several carbone–metal complexes have been synthesized and characterized. These novel species may be used in Lewis acid or dual catalysis after appropriate activation of the corresponding metal site.