Tesi sul tema "Modern catalysis"
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1
Werner, Emilie. "Catalysis at the origin of life and catalysis today, a 3.8-billion-year jump". Electronic Thesis or Diss., Strasbourg, 2024. https://publication-theses.unistra.fr/public/theses_doctorat/2024/Werner_Emilie_2024_ED222.pdf.
Testo completoAbstract (sommario):
La catalyse, permettant une réactivité sélective et accrue, est exploitée aussi bien en chimie de synthèse qu’en biologie. Cette thèse l’abordera à deux temporalités différentes. Dans un premier temps, les processus chimiques aux origines de la vie seront étudiés au travers de deux types de catalyse non enzymatique : la catalyse par les métaux rares et la cocatalyse métal/coenzyme. Cette dernière serait un produit de l’évolution pour s’affranchir d’environnements rares et permettre à la chimie prébiotique de se propager vers des milieux communs. Dans un deuxième temps, la catalyse métallique moderne sera discutée. Une nouvelle variante azotée du réarrangement de Piancatelli sera décrite avec des nucléophiles sulfoximines, permettant d’accéder directement et avec de bons rendements à des 4-sulfoximinocyclopenténones inédites, structures prometteuses pour des applications en chimie médicinaleCatalysis enables selective and enhanced reactivity and is harnessed in both synthetic chemistry and biology. This thesis will discuss this concept at two different time points. Firstly, the chemical processes at the origins of life will be studied through two types of non-enzymatic catalysis: rare metal catalysis and metal/coenzyme cocatalysis. The latter is thought to be a product of evolution to become independent from rare environments and enable prebiotic chemistry to spread to more common media. Secondly, modern metal catalysis will be examined. A new aza-variant of the Piancatelli rearrangement will be described with sulfoximine nucleophiles, giving direct access to unprecedented 4-sulfoximinocyclopentenone scaffolds in good yields. These structures hold promises for applications in drug discovery
2
Falletta, E. "¿RE-DISCOVERING¿ AN OLD MATERIAL, POLYANILINE, FOR MODERN APPLICATIONS". Doctoral thesis, Università degli Studi di Milano, 2014. http://hdl.handle.net/2434/229552.
Testo completoAbstract (sommario):
The chemical industry of the forthcoming years will be shaped by a number of emerging global megatrends strictly related to the growth and aging of the world population (nine billion people in 2050). This will result in demand of innovative materials able to solve new needs in different fields: health, communication, energy, environmental sustainability, etc. In this diversified context, conducting organic polymers (COPs) are expected to play an important role thanks to their polyhedric properties. Among them, polyaniline is one of the more investigated COPs owing to its peculiar properties which make it a potential substitute of conventional materials in different fields (electronics, fenestration, textile industry, sensors and many others).
However, to date many aspects related to its synthesis and application are still open. Scope of the present work is to provide alternative eco-friendly methods to the traditional synthetic routes towards PANI-based materials and enlarge their present applications in view of the novel requirements. This study has been organized in three main sections. In the first section a new green protocol will be present to prepare PANI/metal oxides nanocomposites, innovative materials in the field of EMI shielding. For the first time the double role of magnetic nanoparticles, as catalysts of the reaction and magnetic fillers of the final products, will be illustrated.
Conducting/magnetic materials are particularly tempting for their ability to reduce the electromagnetic interferences (EMI) originated by the increasing use of electronic devices and telecommunication equipment. Preliminary results in terms of their microwave absorbing properties will be shown.
The possibility to improve the health and quality of life for millions of people worldwide is, in fact, the overall goal of tissue engineering. Nanostructured PANI in form of fibers or wires could find application as novel conductive scaffolds in neuronal or cardiac stimulations. In the second section, the possibility to produce highly pure polyaniline nanofibers by electrospinning technique will be showed. These materials, characterized by high values of conductivity and cytocompatibility, could represent an alternative to traditional solutions for cardiac and neuronal stimulation.
Regarding the third section of the work, the amazing piezoresistive properties of PANI, especially in form of film, will be for the first time herein presented. Herein, the extraordinary high GF values of PANI-based films (more than 10 times higher than those of commercial piezoresistors) will be reported. The mechanical monitoring in large and small scale (buildings/touch-technology) needs of highly sensitive stress/strains sensors and PANI-based materials are particularly promising in this sector. All these characteristics contribute to make PANI and its composites innovative materials which could offer new solutions for many challenges of the future.
3
Sharma, Giriraj. "Modeling of selective catalytic reduction (SCR) of nitric oxide with ammonia using four modern catalysts". Texas A&M University, 2004. http://hdl.handle.net/1969.1/2785.
Testo completoAbstract (sommario):
In this work, the steady-state performance of zeolite-based Cu-ZSM-5, vanadium based honeycomb monolith catalysts (V), vanadium-titanium based pillared inter layered clay catalyst (V-Ti PLIC) and vanadium-titanium-tungsten-based honeycomb monolith catalysts (V-Ti-W) was investigated in the selective catalytic reduction process (SCR) for NO removal using NH3 in presence of oxygen. The objective is to obtain the expression that would predict the conversion performance of the catalysts for different values of the SCR process parameters, namely temperature, inlet oxygen concentration and inlet ammonia concentration.
The NOx emission, its formation and control methods are discussed briefly and then the fundamentals of the SCR process are described. Heat transfer based and chemical kinetics based SCR process models are discussed and widely used rate order based model are reviewed.
Based on the experimental data, regression analysis was performed that gives an expression for predicting the SCR rate for the complete temperature range and the rate order with respect to inlet oxygen and ammonia concentration. The average activation energy for the SCR process was calculated and optimum operating conditions were determined for each of the catalyst.
The applicable operating range for the catalyst depends on the NO conversion as well as on the ammonia slip and the N2O and NO2 emission. The regression analysis was repeated for the applicable range and an expression was obtained that can be used to estimate the catalyst performance.
For the Cu-ZSM-5, the best performance was observed for 400oC, 660 ppm inlet ammonia concentration and 0.1% inlet oxygen concentration. For the V based honeycomb monolith catalyst, the best performance was observed for 300oC, 264 ppm inlet ammonia concentration and 3% inlet oxygen concentration. For the V-Ti based PLIC catalyst, the best performance was observed for 350oC, 330 ppm inlet ammonia concentration and 3% inlet oxygen concentration. For the V-Ti-W based honeycomb monolith catalyst, the best performance was observed for 300oC, 330 ppm inlet ammonia concentration and 3% inlet oxygen concentration. The conversion performance of all of these catalysts is satisfactory for the industrial application. At the operating conditions listed above, the N2O emission is less than 20 ppm and the NO2 emission is less than 10 ppm.
The results were validated by comparing the findings with the similar work by other research groups. The mechanism of SCR process is discussed for each of the catalyst. The probable reactions are listed and adsorption and desorption process are studied. The various mechanisms proposed by the researchers are discussed briefly.
It is concluded that V-Ti-W and Cu-ZSM-5 catalyst are very promising for SCR of NOx. The expressions can be used to estimate the conversion performance and can be utilized for optimal design and operation. The expressions relate the SCR rate to the input parameters such as temperature and inlet oxygen and ammonia concentration hence by controlling these parameters desired NOx reduction can be achieved with minimal cost and emission.
4
Filippov, Igor 1971. "Metal-mediated hydrodenitrogenation catalysis: Designing new models". Diss., The University of Arizona, 1998. http://hdl.handle.net/10150/282749.
Testo completoAbstract (sommario):
Reduction of Ta(DIPP)₂Cl·OEt₂(DIPP= 2,6-OC₆H₃ⁱPr₂) with 2 equiv. of NaHg in the presence of 3,5-lutidine results in cyclometalation of DIPP to give TaCl(DIPP)-(OC₆H₃ⁱPr-η²(C,C)-CMe =CH₂)(3,5-lutidine)₂ (10) in moderate yield. Metallacycle 10 was also isolated from the reaction of (η⁶-C₆Me₆)Ta(DIPP)₂Cl with 3,5-lutidine. Examination of both crude reaction mixtures by ¹H NMR revealed 10 to be the major product without any indication of the formation of η²-lutidine species. These observations suggest that η²(N,C)-coordination of 3,5-lutidine is kinetically incompetitive with respect to the cyclometalation of DIPP by d² tantalum. Such undesired reactivity of DIPP can be potentially inhibited by the use of linked aryloxide ligands to prevent close approach of metalatable C-H bonds of DIPP to the metal center. An efficient route to a family of silane-linked aryloxides was developed. Tris(2-hydroxy-3-isopropylphenyl)methylsilane (H₃TIPSI, 59), bis(2-hydroxy-3-isopropyl-phenyl)diphenylsilane (H₂BIPSI, 61), and bis(2-hydroxy-3-isopropylphenyl)dimethyl-silane (H₂BIPSI, 60) were obtained via deprotection of the parent silane-linked anisoles. The anisoles were prepared in high yields by treating 2-methoxy-3-isopropyl-phenyllithium·0.5TMEDA (27·0.5TMEDA) with an appropriate amount of chloroalkylsilanes. The deprotection was carried out employing BBr₃ in CH₂Cl₂ followed by hydrolysis of the intermediate boron ethers in the presence of a non-nucleophilic base to avoid protiodesilylation. Additionally, a significantly improved synthesis of 1,2-bis(3-isopropyl-2-hydroxyphenyl)ethane (H₂BIPP, 40) employing 27·0.5TMEDA as a starting reagent is reported. 2-Methoxyphenyllithium 27·0.5TMEDA was prepared via catalytic ortho-directed metalation of 2-isopropylanisole, and the mechanistic aspects of such metalations are presented. Trinuclear complex (AlBr₂)₃TIPSI (55) was isolated from the reaction of Me₃TISPI with 3 equiv. of AlBr₃ in benzene at 60°C. Preliminary reactivity studies show that Me₃TIPSI (49) and Me₂BIPSI (51) can be reacted with TaBr₅ under similar conditions to give Br₃Ta(MeTIPSI)(THF)₂ (62) and Br₃Ta(BIPP)OEt₂ (63), respectively, after appropriate reaction work ups.
5
Huang, Jin-Mo. "Model Development for the Catalytic Calcination of Calcium Carbonate". Thesis, North Texas State University, 1987. https://digital.library.unt.edu/ark:/67531/metadc331193/.
Testo completoAbstract (sommario):
Lime is one of the largest manufactured chemicals in the United States. The conversion of calcium carbonate into calcium oxide is an endothermic reaction and requires approximately two to four times the theoretical quantity of energy predicted from thermodynamic analysis. With the skyrocketing costs of fossil fuels, how to decrease the energy consumption in the calcination process has become a very important problem in the lime industry.
In the present study, many chemicals including lithium carbonate, sodium carbonate, potassium carbonate, lithium chloride, magnesium chloride, and calcium chloride have been proved to be the catalysts to enhance the calcination rate of calcium carbonate. By mixing these chemicals with pure calcium carbonate, these additives can increase the calcination rate of calcium carbonate at constant temperatures; also, they can complete the calcination of calcium carbonate at relatively low temperatures. As a result, the energy required for the calcination of calcium carbonate can be decreased.
The present study has aimed at developing a physical model, which is called the extended shell model, to explain the results of the catalytic calcination. In this model, heat transfer and mass transfer are two main factors used to predict the calcination rate of calcium carbonate. By using the extended shell model, not only the catalytic calcination but also the inhibitive calcination of calcium carbonate have been explained.
6
Pagani, Adriana Siviero. "Estudo cinetico do craqueamento catalitico de moleculas modelo de hidrocarbonetos em catalisadores de FCC". [s.n.], 2009. http://repositorio.unicamp.br/jspui/handle/REPOSIP/267085.
Testo completoAbstract (sommario):
Orientadores: Jose Roberto Nunhez, Gustavo Paim ValençaTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
Made available in DSpace on 2018-08-13T11:29:24Z (GMT). No. of bitstreams: 1 Pagani_AdrianaSiviero_D.pdf: 5130407 bytes, checksum: b53a0b1f8d58411a68c3cb683c12eba0 (MD5) Previous issue date: 2009
Resumo: O 1-octeno, 2,2,4-trimetil-pentano e n-octano foram utilizados como moléculas modelo para o estudo experimental e de modelagem do craqueamento catalítico na superfície de dois catalisadores comerciais (PETROBRAS), compostos por zeólita USY e matriz (SiO2-Al2O3) com impregnação de terras raras (CTR) e sem a impregnação de terras raras (STR), ambos desativados pelo método vapor. Os testes de craqueamento catalítico foram realizados em fase gasosa em reator tubular de leito fixo, construído em quartzo, na faixa de temperatura de 325 a 685 K para o 1-octeno, 725 a 950 K para o 2,2,4-trimetil-pentano e 815 a 975 K para o n-octano à pressão atmosférica. O catalisador STR apresentou valores de taxa de giro (s-1) maiores que os encontrados para o CTR. As energias de ativação aparente apresentaram a seguinte ordem decrescente: n-octano (STR: 180 kJ mol-1 e CTR: 192 kJ mol-1) > 2,2,4-trimetil-pentano (STR: 121 kJ mol-1 / CTR: 127 kJ mol-1) > 1-octeno (STR: 18 kJ mol-1 / CTR: 23 kJ mol-1). Os mecanismos de reações foram determinados para as três moléculas modelo através dos produtos de reação determinados experimentalmente e considerando as famílias de reações de iniciação, isomerização, transferência de hidrogênio, adsorção/dessorção e cisão-ß/oligomerização. A modelagem do craqueamento catalítico foi desenvolvida segundo a teoria da colisão, a teoria do estado de transição e as propriedades termodinâmicas das espécies envolvidas nos mecanismos. As taxas de giro da modelagem cinética apresentaram uma diferença com as taxas de giro experimentais de aproximadamente 20%.
Abstract: The 1-octene, 2,2,4-trimethylpentane and n-octane were used as model molecules in an experimental and modeling study for the catalytic cracking on the surface of commercial catalysts (PETROBRAS) that are composed of USY zeolite and matrix with rare earth impregnation (CTR) and without rare earth impregnation (STR), both deactivated by steam method. The experimental tests were carried out in the gas phase, in a fixed bed tubular reactor made of quartz in the temperature range of 325 to 685 K for the 1-octene, 725 to 950 K for the 2,2,4-trimethylpentane and 815 to 975 K for the n-octane at atmospheric pressure. The catalyst STR showed higher values of turnover rate (s-1) than the catalyst CTR. The apparent activation energies showed the following decreasing order: n-octane (STR: 180 kJ mol-1 and CTR: 192 kJ mol-1) > 2,2,4-trimethylpentane (STR: 121 kJ mol-1 / CTR: 127 kJ mol-1) > 1-octene (STR: 18 kJ mol-1 / CTR: 23 kJ mol-1). The reactions mechanisms were determined for the three model molecules with the reaction products obtained experimentally and considering the families of reactions of initiation, isomerization, hydride transfer, adsorption/desorption and ß-scission/oligomerization. The modeling of the catalytic cracking was developed according to the collision theory, the transition state theory and the thermodynamics properties of the adsorbed species involved in the mechanisms. The model turnover rates showed a difference between the experimental turnover rates near 20 %.
Doutorado
Desenvolvimento de Processos Químicos
Doutor em Engenharia Química
7
Harle, Gavin John. "Polyoxometalate models for Fischer-Tropsch Catalysts". Thesis, University of Newcastle Upon Tyne, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.519568.
Testo completo
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Hayward, J. J. "Studies in modern organic chemistry : catalytic, technological and structural". Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603905.
Testo completoAbstract (sommario):
This thesis describes work done within the Ley group on a variety of projects, with a particular focus upon modern methods of synthesis. Chapter 1 initially describes work directed towards examining the use of the proline tetrazole catalyst 1.16 as a catalyst for aminations of carbonyl compounds. A novel ionic liquid-based system was developed to investigate this reaction as an oscillatory flow process. Chapter 2 gives an overview of the three enabling technologies that are of principal interest to the Ley group in general and this thesis in particular – microwave chemistry, polymer-supported reagents and flow chemistry (Fig 8888A). Chapter 3 describes the total synthesis of Siphonazole B. Our approach to this molecule was designed to make use of the enabling technologies described above, but also to evaluate them – particularly flow-based methods. With this in mind a left-hand fragment synthesis is devised and executed in the flow domain, and several approaches to the left-hand fragment investigated, culminating in the completed total synthesis. Siphonazole B is a bis-oxazole natural product, a class of molecules that has been of interest to our group for some time. Oxazoles and other aromatic heterocycles are ubiquitous within organic chemistry, whether one considers natural products (such as the siphonazoles) or pharmaceuticals (Fig 8888B). Chapter 4 chronicles our studies towards a new synthesis of thiazolothiophenes. During the course of these studies we describe a new class of conjugated betaines (shown above) which appear to exhibit an unusual S …. S interaction in the solid state, which we have investigated crystallographically and computationally.
9
Ndi, Cornelius Ndi. "Synthesis of Chemical Models of Hydrolase Enzymes for Intramolecular Catalysis". Digital Commons @ East Tennessee State University, 2011. https://dc.etsu.edu/etd/1356.
Testo completoAbstract (sommario):
Most nuclease enzymes can hydrolyze phosphoester bonds (in DNA and RNA) by using metal ions cofactors that coordinate and activate water molecules in the enzymes' active sites. However, there are some hydrolase enzymes (including nucleases) that can function without the aid of metal ions. 2,6-Di(1H-imidazol-2-yl)phenol, a model compound for hydrolase enzyme, was synthesized by the reaction between ethylenediamine and dimethyl-3-carboxysalicylate, initially resulting in the formation of diimidazoline. The diimidazoline was subsequently aromatized to the diimidazole by dehydrogenation over palladium. The overall reaction yield was low; therefore, other dehydrogenation transformation reactions were tried but all failed to improve the yield. Converting this diimidazolphenol into diimidazolphenyl monophoshpate derivative was attempted but failed to give desired products.
Synthesis of 2,2'-anthracene-1,8-diylbis-1H-imidazole, another model compound for hydrolase enzymes, was attempted using dimethyl-1,8-anthracenedicarboxylate, but synthesis was unsuccessful due to solubility problem.
10
Isenogle, Melanie R. "Anna Atkins: Catalyst of Modern Photography Through The First Photobook". Bowling Green State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1522796885194359.
Testo completo
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Brown, Darryl Edward. "Kinetic models for the Pt/CeO₂ catalysed water-gas shift reaction". Master's thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/27914.
Testo completoAbstract (sommario):
As the global population grows, so does the world's demand for energy. Consequently, there exists an increased interest in the development of fuel cells for power generation due to their low greenhouse gas emissions. For fuel cells to be a successful power source, a reliable hydrogen source is required. Ultimately, the goal is for hydrogen to be supplied from renewable energy technology however, this type of technology is currently not mature enough to meet the continuous demand of the world's energy systems. Producing hydrogen from fossil fuels can be seen as a temporary solution while further advances are made in developing renewable hydrogen infrastructure. A fuel processing train, therefore, remains an important alternative to producing hydrogen. A fuel processing train converts fossil fuels into hydrogen for use in fuel cells and eliminates the need for hydrogen storage as hydrogen is produced on demand. Currently, the water-gas shift (WGS) reactor is one of the largest components in a fuel processing train and thus opportunity exists to reduce the size of this reactor. To design future WGS catalysts and an optimised fuel processor, the reaction kinetics taking place must be understood and quantified. In this study, kinetic measurements were conducted at 2 bar(a) and across a temperature range of 270 - 300 °C using 16 parallel fixed bed reactors (high throughput experimentation) over a 0.5 wt% Pt/CeO₂ catalyst. The feed composition was varied over the ranges 2 - 12 mol% CO, 20 - 45 mol% H₂O, 4 - 15 mol% CO₂ and 25 - 55 mol% H₂. An online micro gas chromatograph (μGC) was used to analyse the dry gas composition. Fitting of experimental data to various kinetic models was accomplished with the gPROMS software package. An initial evaluation of several Langmuir-Hinshelwood (LH) type mechanisms to two data sets obtained from literature was undertaken to evaluate the strengths and weaknesses of different kinetic expressions. The results of the initial evaluation indicate that a dual-site mechanism with an intermediate species results in the best fit for reducible supports, while a single site mechanism offers a better fit for non-reducible supports. For both kinetic models, the formation of the intermediate species is most likely to be the rate determining step. A power-rate law empirical rate expression and a LH type rate expression were both found to predict the WGS outlet composition well within 10 % error at 2bar(a). The apparent activation energy of the reaction was determined to be 110 kJ/mol. This value was confirmed to be constant, throughout the range of conditions evaluated, by means of a classical Arrhenius analysis. Simulations of increasing total system pressure, using both the empirical and "best fitting" LH model, indicate a significant pressure effect for the LH type equation, whereas the power-rate law empirical equation predicts a small, negative effect on the reaction rate with increaseing pressure. Consequently, further experiments were conducted to determine the true effect of pressure. It was found that increasing system pressure increased the WGS reaction rate, which has also been reported by Twigg (1989:288). Only the LH type rate expression was able to predict this. It is therefore recommended that either the power-rate law empirical rate expression or the LH type rate expression be used to predict the WGS outlet composition when operating below 2 bar(a). Furthermore, when predicting reaction rates outside of the window in which the rate equations were derived, it is recommended that the LH model be used as it is expected to give a better prediction as it is based on fundamental steps.
12
Jiang, Lin. "Novel catalysts by computational enzyme design /". Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/9248.
Testo completo
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Dekker, Nicholas John. "The Modern Catalyst: German Influences on the British Stage, 1890-1918". Columbus, Ohio : Ohio State University, 2007. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1180431503.
Testo completo
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PREDA, GLORIA. "Theoretical models of heterogeneous catalysts based on cerium oxide". Doctoral thesis, Università degli Studi di Milano-Bicocca, 2012. http://hdl.handle.net/10281/28402.
Testo completoAbstract (sommario):
In this Ph.D. thesis the reactivity of clean and silver precovered ceria surfaces is studied in the context of applications in catalysis of Diesel particulate soot abatement. In fact, ceria and in particular silver doped ceria show very good catalytic activity in decreasing the temperature of soot combustion. A key step in the mechanism of oxidation of the particulate, which is mainly amorphous carbon, is the activation of the oxygen molecule. In literature, experimental IR-Raman and EPR studies show the comparison of peroxo, O22-, and superoxo, O2-, species when O2 interacts with ceria.
With theoretical calculations we firstly investigate the interaction of O2 with regular CeO2(111) and defective CeO2-x (111) surfaces. While with the regular surface we find no interaction and no activation of the oxygen molecule, on the oxygen vacancy a peroxo strongly linked to the surface is observed. The formation of O22- is due to a charge transfer from the two Ce3+ centers that are located on the surface when an O is removed. The formation of a superoxo, thus, is not found when such an interaction is considered. The hypothesis is then that the interaction of O2 with isolated Ce3+ could generate O2- by charge transfer.
When O2- is studied, Electron Paramagnetic Resonance (EPR) properties can be evaluated. For superoxo formed on ceria the experimental spectra available in literature are not well resolved, so a comparison between calculated and experimental data is not trivial. Then, a model system is studied to validate the theoretical approach in reproducing EPR properties of superoxo. In fact, for O2- formed on Na precovered MgO surfaces, very well resolved EPR spectra are available. In this case we found that our theoretical approach can reproduce the EPR properties very well.
Subsequently, we studied the interaction of O2 with ceria clusters and nanoparticles. At first, we considered the model system Ce2O3, that has two Ce3+ ions. This species is modeled at different theoretical levels, and we always find the expected result, the formation of O2- by charge transfer from one low-coordinated Ce3+ center. The evidences of this are in the O-O bond length, in the IR frequency and in the EPR properties, that are in very good agreement with the experimental ones. This result is confirmed also on bigger defective nanoparticles, where the oxygen vacancy leaves two Ce3+ centers that stabilize on low-coordinated sites. The presence of low-coordinated and, more important, isolated Ce3+ centers is thus responsible of the formation of superoxo ions on ceria.
The role of silver in improving the catalytic activity of ceria is proved in literature by a decrease of the soot combustion temperature. Moreover, in literature, experimental EPR studies show a slightly increase of the signal due to the presence of superoxo ions. Experimental STM and XPS data of Ag nanoparticles deposited on stoichiometric and reduced thin CeO2 films grown on Pt(111) in UHV conditions show a reduction of ceria with comparison of Ce3+ centers. Theoretically, we studied the interaction of Ag atoms, Ag5 and Ag0 clusters and mono and bi-layers of silver adsorbed on CeO2(111) and CeO2-x(111) surfaces. We find a general tendency of silver to reduce ceria by charge transfer, with subsequent oxidation of the metal. However, the experimental data could also fit with an oxygen spillover mechanism. In this situation, oxygen atoms migrate from the surface to the metal particles, leaving a reduced support. Our calculations show that this mechanism is highly unfavourable from an energetic point of view. Therefore, both the experimental and the theoretical results agree with a reduction of ceria due to a charge transfer from silver.
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Díaz-Urrutia, Christian. "Vanadium-Catalyzed Aerobic Oxidation of Diols and Lignin Models/Extracts". Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35102.
Testo completoAbstract (sommario):
As the world moves forward to the development of biorefineries, the interest to replace chemicals and materials derived from petroleum is increasing exponentially. Lignin is a macromolecular by-product derived from the wood pulping industry, mainly used for heating purposes. The development of new processes to produce high value-added lignin products such as multifunctional aromatic chemicals and high-tech carbon materials are required to fulfill the needs for biorenewable feedstocks. Such processes are likely to include selective oxidation catalysis.
The aim of this Thesis is to advance the state-of-the-art for the oxidation of lignin models and lignin extracts using homogeneous catalysts based on vanadium, an inexpensive and abundant transition metal, using air as the only oxidant. Lignin models containing the most important features of lignin (e.g., β-O-4 and β-1 linkages) were initially used to assess the catalytic potential. Previously reported (HQ)2V(O)(OiPr) and (dipic)V(O)(OiPr) catalysts (dipic = dipicolinate and HQ = 8-oxyquinoline) displayed different selectivity for C-H, C-O and C-C bond cleavage upon varying of the solvent, the lignin model or the catalyst. Moreover, these catalysts cleave the C-H bond of secondary alcohols through a two-electron oxidation process and the C-C bond cleavage of the oxidation product ketone in the presence of exogenous base.
Several amine bis(phenolate) oxovanadium(V) catalysts were synthesized and fully characterized, and demonstrated very good activity for the oxidation of lignin models and the depolymerization of organosolv lignin. These new catalysts overcome the need for added base, display higher reaction rates of oxidation, and improve the selectivity for the disassembly of lignin models. The different selectivities involving C-H vs. C-O vs. C-C bond cleavage are discussed together with a novel redox-neutral C-C bond cleavage of lignin model 1,2-diphenyl-2-methoxyethanol.
The oxovanadium(V) catalysts, along with a metal-free variant and other transition metal catalysts, were employed to assess their performance for the oxidation and depolymerization of organosolv lignin. Although most catalysts oxidized the lignin extracts, the oxovanadium(V) complexes demonstrated the highest degree of lignin depolymerization as shown by Gel Permeation Chromatography (GPC), quantitative-Heteronuclear Single Quantum Correlation (q-HSQC) and quantitative 31P NMR spectroscopy of derived phosphite esters.
In a complementary study, oxovanadium(V) catalysts also established their utility for the valorization of cellulose-derived substrates (e.g., diols). Two trialkoxyamine oxovanadium(V) complexes bearing a triethoxyamine and tris[2-(3,5-di-tert-butyl-phenoxy)methyl]amine ligand respectively, selectively cleaved the C-C bond in 1,2-diols with excellent rates and using air as the only oxidant. In a stoichiometric investigation of this reaction, it was determined that the transformation proceeds through an unusual direct oxidative two-electron cleavage of diols, affording a non-oxo monometallic V(III) intermediate. DFT calculations support a single-site proton-coupled electron-transfer of the hydroxyl hydrogen to the V oxo orbital.
In summary, this Thesis describes new developments in vanadium catalysis such as mechanistic implications and catalyst optimization for the valorization of lignocellulosic biomass utilizing air as an oxidant.
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Fusion, Joe. "The Role of Environmental Dynamics in the Emergence of Autocatalytic Networks". PDXScholar, 2015. https://pdxscholar.library.pdx.edu/open_access_etds/2458.
Testo completoAbstract (sommario):
For life to arise from non-life, a metabolism must emerge and maintain itself, distinct from its environment. One line of research seeking to understand this emergence has focused on models of autocatalytic reaction networks (ARNs) and the conditions that allow them to approximate metabolic behavior. These models have identified reaction parameters from which a proto-metabolism might emerge given an adequate matter-energy flow through the system. This dissertation extends that research by answering the question: can dynamically structured interactions with the environment promote the emergence of ARNs? This question was inspired by theories that place the origin of life in contexts such as diurnal or tidal cycles. To answer it, an artificial chemistry system with ARN potential was implemented in the dissipative particle dynamics (DPD) modeling paradigm. Unlike differential equation (DE) models favored in prior ARN research, the DPD model is able to simulate environmental dynamics interacting with discrete particles, spatial heterogeneity, and rare events. This dissertation first presents a comparison of the DPD model to published DE results, showing qualitative similarity with some interesting differences. Multiple examples are then provided of dynamically changing flows from the environment that promote emergent ARNs more than constant flows. These include specific cycles of energy and mass flux that consistently increase metrics for ARN concentration and mass focusing. The results also demonstrate interesting nonlinear interactions between the system and cycle amplitude and period. These findings demonstrate the relevance that environmental dynamics has to ARN research and the potential for broader application as well.
17
Swann, Andrew Thomas. "Characterization of polymer-supported homogeneous catalysts by molecular modeling". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26702.
Testo completoAbstract (sommario):
Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2009.Committee Chair: Ludovice, Pete; Committee Member: Grover, Martha; Committee Member: Jones, Christopher; Committee Member: Realff, Matthew; Committee Member: Sherrill, David. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Nárovec, Jiří. "Moderní metody denitrifikace uhelných kotlů". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2015. http://www.nusl.cz/ntk/nusl-231795.
Testo completoAbstract (sommario):
V současnosti musí velké energetické podniky k dodržení emisních předpisů, zejména pak vyžadovaných limitů NOx, uplatňovat denitrifikační metody. Tématem předkládané diplomové práce jsou moderních denitrifikační metody a jejich praktické uplatnění v lokálních poměrech uhelného kotle s parním výkonem 640 t.h-1 v elektrárně Počerady. Práce obsahuje rešerši moderních denitrifikačních metod používaných velkými uhelnými kotli se zaměřením zejména na sekundární denitrifikační metody. Jsou uvažovány dvě možné varianty denitrifikace – varianta 1 využívá selektivní katalytickou redukci (SCR) a varianta 2 selektivní nekatalytickou redukci (SNCR) společně s nízkoemisními hořáky a stupňovaným přívodem spalovacího vzduchu. Pro výběr vhodné denitrifikační metody jsou studovány investiční náklady jednotlivých variant – nižší investiční náklady (o 19.4%) slibuje varianta 2. Při srovnávání SCR se SNCR vyšlo najevo, že investiční náklady metody SNCR jsou 5krát nižší než metody SCR. V souladu s investičními náklady, s dispozicí kotle a se složitostí jeho instalace je pro navazující studium problematiky využita varianta 2. Stěžejní část práce se zabývá stanovením optimálního tzv. teplotního okna pro konkrétní metodu SNCR. Těžištěm práce je tepelný výpočet ohniště a části deskového přehříváku pro stanovený rozsah paliv a výkon kotle v rozmezí 60-100%. S uvažováním výsledků z výpočtu jsou navrženy dvě vstřikovací roviny, které mají zaručit vysokou efektivitu denitrifikačního procesu při uvažovaných provozních podmínkách kotle. Diplomová práce rovněž diskutuje obecnou vhodnost instalace SNCR a SCR ve stávajících uhelných kotlích.
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Laher, Romain. "Synthèse de nouvelles molécules odorantes par catalyse à l’or (I) : L’or au service de la parfumerie moderne". Thesis, Université Côte d'Azur, 2020. http://www.theses.fr/2020COAZ4083.
Testo completoAbstract (sommario):
Ce manuscrit s’intéresse à la synthèse de composés olfactifs intéressants en vue d’une utilisation dans l’industrie de la parfumerie. Un premier chapitre bibliographique met en lumière l’utilisation de métaux de transition comme catalyseurs de réactions servant à la synthèse de composés commercialisés et utilisés dans des parfums. Le travail décrit dans ce manuscrit présente la mise au point et le développement de réactions de cycloisomérisation d’énynes-1,6 et d’additions de nucléophiles sur des substrats acétyléniques par catalyse à l’or (I) dans le but d’obtenir des molécules intéressantes pour l’industrie de la parfumerie. Le second chapitre de ce manuscrit s’intéresse à la synthèse de dérivés de 3-oxabicyclo[4.1.0]-hept-4-ènes. Ces composés ont pu être réalisés avec de très bons rendements à des charges catalytiques faibles, rendant possible l’industrialisation de telles structures. De manière remarquable, l’ensemble des composés synthétisés a présenté un intérêt olfactif, que ce soient les dérivés de départ ou bien les produits de cycloisomérisation. Il a été possible de mettre en évidence une induction de chiralité dans le cadre de la réaction de cycloisomérisation d’énynes-1,6 via l’utilisation de substrats énantiomériquement substitués en position -allylique. Le troisième chapitre met en avant des premiers exemples de réaction tandem de cycloisomérisation / réduction d’alcools acétyléniques ont été effectués conduisant à une nouvelle voie de synthèse de dérivés furaniques et pyraniques. L’emploi de catalyseur d’or permet la formation d’éther d’énol exocyclique puis la réduction de l’insaturation via l’utilisation d’un organosilane. L’ensemble des composés synthétisés évalués présente des notes remarquables permettant d’envisager des substitutions de produits à risque par de nouveaux ingrédients aux propriétés organoleptiques prochesThis manuscript is concerned with the synthesis of interesting olfactory compounds for use in the perfume industry. A first bibliographic chapter highlights the use of transition metals as reaction catalysts for the synthesis of compounds marketed and used in perfumes. The work described in this manuscript presents the optimization and development gold (I)-catalyzed cycloisomerization of 1,6-enynes and additions of nucleophiles on acetylenic substrates in order to obtain molecules of interest for the perfume industry. The second chapter of this manuscript deals with the synthesis of 3-oxabicyclo[4.1.0] -hept-4-enes derivatives. These compounds could be produced with very good yields at low catalytic loads, making the industrialization of such structures possible. Remarkably, all of the compounds synthesized were of olfactory interest, whether they were the starting derivatives or the products of cycloisomerization. It has been possible to demonstrate an induction of chirality within the framework of the cycloisomerization reaction of 1,6-enynes via the use of substrates enantiomerically substituted in the -allylic position. The third chapter highlights the first examples of tandem reaction of cycloisomerization / reduction of acetylenic alcohols have been carried out leading to a new route of synthesis of furanic and pyranic derivatives. The use of gold catalyst allows the formation of an exocyclic enol ether followed by the reduction of the unsaturation formed through the use of an organosilane as Et3SiH. All of the synthesized compounds evaluated present remarkable scores allowing to consider substitutions of risky products by new ingredients with similar organoleptic properties
20
Nicholls, Laura E. "Uranium silicate complexes as models for surface immobilised uranium catalysts". Thesis, University of Sussex, 2015. http://sro.sussex.ac.uk/id/eprint/58059/.
Testo completoAbstract (sommario):
Chapter 1 provides an insight into the current areas of research that could provide answers to the global energy problems outlined in Appendix A, namely the reductive functionalisation of carbon oxides and as an extension to this, the activation of other small molecules. The review predominantly concentrates on the chemistry of the 5f elements which already contain examples of reductive functionalisation of carbon oxides, albeit in homogeneous phase. In addition the chapter provides an overview of the current research in surface science and by extension, the development of molecular models that mimic such surfaces. This synopsis provides an insight into the difficulties involved in this area of research and why molecular mimics are of vital importance. Using ligating Si-O bonds to mimic a silica surface, Chapter 2 outlines the research which enabled the development of a series of uranium siloxides, centred on the previously unreported pentakis(triarylsiloxy) uranate(IV) ion. Characterisation data and full analysis are included within this chapter which provided the basis for the investigations discussed in the following chapters. This chapter also presents an interesting UV-Vis analysis of the uranium siloxides which will enable a wider understanding of the f -elements and the role f -orbitals have on the chemistry and geometry of f -element molecules. Chapter 2 develops a deeper understanding of these complexes by investigating the mechanisms of formation and the chemistry of the U(Ph3SiO)5 fragment using ESI techniques in conjunction with NMR analysis. Chapter 3 investigates the reactivities of the uranium siloxides previously developed and discusses a new dioxo species and a rare and novel UV monooxo complex which was synthesised and successfully isolated. An analysis of other dioxo and monooxo complexes is included which allows the reader to develop an appreciation of how few and far between monooxo products are. In addition, previous examples of monooxo's are lacking characterisation data and are mostly products of oxygen atom donor reactions, not as a result of small molecule activation as is presented here. There is currently one previous example of such a system resulting from small molecule activation which is also discussed in this chapter. Chapter 4 investigates a second ligand system which could be used to mimic a silica surface. Whilst the ligand, tris tertbutoxy has been investigated previously, at the time of this work, the ligand had not been successfully used in relation to a uranium complex. The U3.5 species, [(U(OSi(OtBu)3)3)2(μ-η6:η6-tol))] is presented here alongside the complexes [((tBuO)3SiO)3U]2(μ2-O)3 and U(OSi(OtBu)3)4. During the development of this species, very similar species were published by another group and these syntheses and characterisation data are presented here as a comparison to the species developed as part of this work. Chapter 5 investigates the reactivities of the uranium siloxides developed in Chapter 4 including decomposition analysis and reactions with small molecules such as O2, I2 and CO2 and presents the resulting complexes some of which were developed by a Masters student working in collaboration with the author.
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Kumar, Ankan. "Physical Models and Computational Algorithms for Simulation of Catalytic Monolithic Reactors". The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1230142666.
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22
劉毅廷 e Ngai-ting Lau. "An infected zone model for the deactivation of catalysts". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1990. http://hub.hku.hk/bib/B31209786.
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23
Hergueta, Santos-Olmo Cruz. "Modern fuels and catalytic technologies for low emissions in gasoline direct injection engines". Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8432/.
Testo completoAbstract (sommario):
The requirements for controlling Particulate Matter (PM) and gaseous emissions emitted from gasoline direct injection (GDI) engines, especially under cold start conditions, and the introduction of bio-alcohols fuels in the market demands the development of novel efficient aftertreatment technologies. Understanding the PM characteristics from the combustion of different fuels it is a key step in the design of next generation of catalysts and aftertreatment systems, including three-way catalyst (TWC) and catalyst coated or not gasoline particulate filters (GPFs). The research study presented in this thesis provides a detailed understanding of the synergies between bio-alcohols derived fuels combustion in GDI engines and novel aftertreatment technologies on the control of PM and gaseous emissions. The effect of the physico-chemical properties of bio-alcohol fuel blends on combustion and emissions at warm steady-state and cold start engine conditions has been investigated. Bio-butanol fuel blend has been further explored at different engine loads in combination with exhaust gas recirculation (EGR) technology. An extensive characterization of the PM emissions has been carried out using several methodologies and techniques such as high resolution transmission electron microscopy (HRTEM), thermogravimetric analysis (TGA), scanning mobility particle sizer (SMPS) and Raman spectroscopy. The combustion of bio-alcohols resulted in a significant reduction of 60% - 80% of PM emissions with the modification in their structural characteristics, leading to agglomerates with smaller primary particles (≈1-3 nm) and fractal dimensions and, soot with higher tortuosity (≈3.1 %) as TEM revealed. Under cold start event, bioalcohols emitted more reactive and less mature soot (i.e. higher organic content and impurities) as found from TGA and Raman analysis compared to soot emitted from gasoline fuel combustion. The TWC activity was improved between 4.3% and 1.5% in the exhaust stream from the bio-alcohols combustion. The aftertreatment architectures, including either coated GPFs or not and arrangement in the exhaust (i.e. upstream or downstream of the TWC) has shown a significantly impact on the TWC activity, reducing light-off temperatures up to 20°C. Catalytic GPF showed high performance to efficiently filter PM and removed gaseous emissions from GDI combustion with acceptable pressure drop.
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Ward, Jonathan Reid. "Housing through the wall: a study of catalytic architecture in the modern city". Thesis, Virginia Polytechnic Institute and State University, 1996. http://hdl.handle.net/10919/53429.
Testo completoAbstract (sommario):
The tangible occurrence filters into the life and path of the observers. Each view and place which one experiences should be seen and understood and pushed into the making of the built thing.Master of Architecture
25
Sander, Patrik. "Betydelsen av betydelse - Om identitet, mening och betydelse i det postmoderna samhället". Thesis, Malmö högskola, Lärarutbildningen (LUT), 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:mau:diva-30014.
Testo completoAbstract (sommario):
Syftet med detta arbete har varit att undersöka om berättelsen kan fungera som katalysator för elevernas reflektion över sig själva och deras situation i ett postmodernt samhälle. Väsentliga frågor i sammanhanget blev dels huruvida de själva kunde bli medvetna om och reflektera över sina egna och andras strategier i en sådan omfattande social omvandling. Ett sådant fenomen som kom i fokus var vårt behov av ytliga statussymboler.Det i grunden kvalitativa arbetet bygger på tre synvinklar och tillika källor. För det första, mig själv som oundvikligt subjektivt filter; för det andra eleverna och för det tredje, mediala källor som på olika sätt har kunnat användas i sammanhanget.Under arbetets lopp har jag kommit fram till att arbetets informativa, reflektiva och diskursiva processer i sig utgjorde ett lika intressant material som slutsatserna.The purpose of this work has been to examine the function of storytelling as an induct-ive way to develop self reflection and environmental awareness of the students. Key subjects have been if they could be attentive to the very reflective process itself and to the strategies we apply, when to cope with dynamic changes as those of the postmodern society. Also the possibility to find basic explanations, to specially one of these strategies – one that has been more and more frequently used – became a pursuit in this work. The phenomenon in mind is our seemingly growing demand for “superficial valuables”.This work is basically qualitative. Three perspectives – as well as sources of inform-ation – have been developed through the process of this work: firstly, the inevitably subjective experiences of my own; secondly, the students; and thirdly, different forms of applicable public media. Especially the contribution from the students can’t be overstated. Initially it was them who made me aware of the phenomenon, described above. Moreover they gave input, partly through the literature seminar and the related discussion, partly through a minor enquiry consisting of a few but fundamental questions connected to the matter of “wealth” and “ability”.Quite early during the progression of this work I came to an understanding that the informative, the introspective and the communicative processes of the work itself constituted a most interesting substance. Hence, I made a more careful attempt to describe this development and my thoughts connected to it, rather than giving too much focus on the aftermath. Retrospectively seen, it presents somewhat self-evident answers of the two initial questions above. Yes, storytelling might work as a complement to more radical experiences of the real life. It can be used as a key to existential reflection in an urban security-devoting postmodern society. Also obviously, there seem to be more profound explanations to our quest for superficial valuables – needs beyond the very appeal. They could be connected to the natural instinct of individual survival through real or “illusory” acceptance and irreplaceability within one or more collective social orders – in short, the importance of being important.
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Shanks, Brent Howard Bailey James E. "Reactor input manipulation for developing models for catalytic reactions /". Diss., Pasadena, Calif. : California Institute of Technology, 1988. http://resolver.caltech.edu/CaltechETD:etd-11092007-141214.
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Davies, Jonathan Conrad. "U.H.V. electrochemical transfer studies of modified platinum single crystal surfaces : models for fuel cell catalysis". Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310553.
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28
Illes-Smith, Peter C. "A study of the modelling, dynamic simulation and control of the modern fluid catalytic cracking process". Thesis, University of Leeds, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.330143.
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29
Li, Quinn. "Elucidating enzyme catalytic power and protein-ligand dynamics of human glucokinase: the role of modern allostery". Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6461.
Testo completoAbstract (sommario):
Glucokinase (GK) is an enzyme that catalyzes the ATP-dependent phosphorylation of glucose to form glucose-6-phosphate, and it is a tightly regulated checkpoint in glucose homeostasis. The monomeric enzyme possesses a highly exotic kinetic profile, with a sigmoidal dependence on glucose, which has been the source of vigorous investigation and debate in the last several decades. This unique regulatory behavior can be thought of as a remarkable glucose sensor, which may result in hyperglycemia when it is not active enough and hypoglycemia when it is too active. This interdisciplinary study, which draws on small angle X-ray scattering (SAXS) integrated with atomistic molecular dynamics simulations and experimental glucose binding thermodynamics, I reveal the critical regulation of the glucose sensor is due to a solvent controlled switch. Moreover, this solvent controlled switch manifests a regulatory mechanism of GK; a specific local conformational change that leads to an enzyme structure that has a much more favorable solvation energy than most of the protein ensemble. These findings have direct implications for the design of small molecule GK activators as anti- diabetes therapeutics as well as for understanding how proteins can be designed to have built-in regulatory functions via solvation energy dynamics.
30
Sears, John Steven. "Minimalistic Descriptions of Nondynamical Electron Correlation: From Bond-Breaking to Transition-Metal Catalysis". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19807.
Testo completoAbstract (sommario):
Thesis (Ph.D)--Chemistry and Biochemistry, Georgia Institute of Technology, 2008.Committee Chair: C. David Sherrill; Committee Member: Jean-Luc Bredas; Committee Member: Mostafa El-Sayed; Committee Member: Peter J. Ludovice; Committee Member: Thomas Orlando.
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Gonçalves, Larissa Martins. "Um modelo para detoxificação de organofosforados: efeito de micelas e vesículas na oximólise de p-nitrofenildifenilfosfato". Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/46/46131/tde-02022007-171907/.
Testo completoAbstract (sommario):
Oximas têm sido extensivamente usadas como antídoto para envenenamento por organofosforados e como desontaminante. Micelas e vesículas, utilizadas como catalisadores e transportadores de drogas, constituem agentes potenciais para tratamento e descontaminação. Neste trabalho descrevemos a reação de p-Nitrofenildifenilfosfato (PNPDPP), um substrato modelo para organofosforado, com: acetofenoxima (I); ácido 10- fenil-10-hidroxiiminodecanóico (II); 4-(9-carboxinonanil)-1-(9-carboxi-1-hidroiimino nonanil) benzeno (III); cloreto de N-dodecilpiridina (IV); cloreto N-metilpiridina 2-aldoxima (V), na presença de micelas catiônicas e zwitteriônicas de cloreto de hexadeciltrimetilamônio, CTAC e N-Hexadecil-N,N-dimetil-1-propano sulfonato, HPS, respectivamente, e vesículas catiônicas de dioctadecildimetilamônio, DODAC. O pKa aparente, pKap, das oximas em agregados de anfifilicos, a constante de velocidade de segunda ordem de oximólise em micelas ou vesículas, km, e as constantes de velocidade observadas para a oximólise de PNPDPP, kobs, foram determinadas espectrofotometricamente, a pH constante, variando-se a concentração dos anfifílicos. Os resultados foram analisados usando as teorias: modelo de pseudofase (PP) e modelo de pseudofase com considerações de troca iônica (PIE), descrita na literatura pelo nosso grupo. As constantes de segunda ordem para oximólise de PNPDPP em água, kox, determinadas foram 6,5 M^-1 min^-1 (I, II e III) e 2,8 M^-1 min^-1 (IV e V). O kobs máximo em micelas e vesículas, kobsmax, e o kobs em água, kw, no mesmo pH, foram utilizadas para calcular o fator de aceleração máxima, AF, para cada anfifílico (AF = kobsmax/kw). Os agregados catalisam a decomposição de PNPDPP e os valores de AF (e km) foram da ordem de 10^4 (32 min^-1), 10^4 (125 min^-1) e 10^6 (80 min^-1) para a reação da oxima IV com CTAC, HPS e DODAC, respectivamente. A análise quantitativa da dependência da concentração de agregados anfifílicos na oximólise mostrou um considerável aumento da constante de velocidade da reação produzido por micelas e vesículas (maior que 8 x 10^6 vezes). Esse efeito é parcialmente devido a: concentração local dos reagentes, efeitos nos pKas dos nucleófilos e, mais importante, mudança na reatividade intrínseca das oximas.Oximes have been extensively used as antidotes and decontaminants of organophosphates. Micelles and vesicles, catalysts and drug transport agents, constitute potential vehicles for Oxime treatment. Here we describe the reaction of p-nitrophenyldiphenylphosphate (PNPDPP) with: acetophenoxime (I); 10-phenyl-10-hydroxyiminodecanoic acid (II); 4-(9-carboxynonanyl)-1-(9-carboxy-1-hydroyiminononanyl) benzene (III); N-dodecylpyridinium chloride (IV); N-methylpyridinium 2-aldoxime chloride (V), in the presence of cationic and zwitterionic micelles, hexadecyltrimethylammonium chloride, CTAC and N-Hexadecyl-N,N-dimethyl-1-propanesulfate, HPS, respectively, and cationic vesicles of dioctadecyldimethylammonium, DODAC. The apparent pKa, pKap, of the oximes in the amphiphile aggregates, the second order rate constants of oximolysis in micelles and vesicles, km, and the observed rate constants for PNPDPP oximolysis, kobs, were determined spectrophotometrically at constant varying amphiphilic concentrations. The results were analyzed using the pseudo-phase theory (PP) and pseudo-phase / ion exchange (PIE). The second order rate constant for (uncatalyzed) oximolysis of PNPDPP were 6.5 M^-1 min^-1 (I, II and III) and 2.77 M^-1 min^-1 (IV and V). From the maximum value of kobs in micelles and vesicles, kobsmax, and the value of kobs in water, kox, at the same pH, the maximum acceleration factor, AF, were calculated (AF = kobsmax / kw). The amphiphiles catalyzed the oximolysis of PNPDPP and the values of AF (and km) were ca 10^4 (32 min^-1), 10^4 (125 min^-1) and 10^6 (80 min^-1) for the reactions of Oxime IV in CTAC, HPS and DODAC, respectively. Quantitative analysis of the amphiphile concentration-dependence of rates demonstrated that the considerable rate increase produced by micelles and vesicles on the rate of oximolysis (up to 8 x 10^6 fold) is partly due to reagent concentration in the aggregate, effects on the pKas of the nucleophiles and, more importantly, catalysis.
32
Seitsonen, Ari Paavo. "Theoretical investigations into adsorption and co-adsorption on transition metal surfaces as models to heterogeneous catalysis". [S.l.] : [s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=963831291.
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33
Lakhdar, Mahjoub. "Application de la reaction d'hydrodesazotation de la pyridine a la caracterisation de l'activite et de la selectivite de catalyseurs sulfures". Caen, 1987. http://www.theses.fr/1987CAEN2021.
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34
Khatmullin, Renat R. "Iminium Salts and Their Derivatives as Models for Catalytic Water Oxidation". Bowling Green State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1374795451.
Testo completo
35
Esteves, Larissa Cerrato. "Estudo cinético da hidrólise de betalaínas-modelo". Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/46/46136/tde-17082016-083643/.
Testo completoAbstract (sommario):
Betanina e indicaxantina foram obtidas e purificadas e a hidrólise térmica de betanina foi investigada em diferentes pHs, concentrações de tampão, temperaturas e com a adição de sais. Para a decomposição de indicaxantina, foi realizado um estudo em diferentes pHs. Tampões acetato e citrato se mostraram adequados para estudos com betanina, dentro de sua faixa de tamponamento. Os experimentos realizados com tampão fosfato indicaram a ocorrência de catálise geral pelo íon fosfato presente no tampão. O efeito dos sais sobre a hidrólise de betanina foi investigado em pHs 3 e 6,2, com a adição de sais de sódio, amônio e sais cloretos. p-Toluenosulfonato de sódio, cloreto de amônio e cloreto tetrabutilamônio foram os sais que apresentaram maior efeito sobre a constante cinética observada de hidrólise de betanina. A hidrólise das duas betalaínas apresentou um comportamento semelhante com a variação do pH e o ajuste multiparamétrico dos dados sugere que a catálise básica específica é a principal responsável pela hidrólise de betanina e indicaxantina. Um modelo que sugere a abertura do anel 1,2,3,4-tetrahidropiridínico das betalaínas é proposto para explicar o efeito do pH sobre a constante cinética de decomposição determinada em meio ácido.Betanin and indicaxanthin were obtained and purified and the thermal hydrolysis of betanin was investigated at different pH, buffer concentration, temperature and in the presence of different salts. For the decomposition of indicaxanthin, a study was conducted at different pHs. Acetate buffer and citrate buffer proved to be suitable for the study of betanin. The experiments carried out with phosphate buffer indicated the occurrence of general base catalysis by phosphate ion present in the buffer. The effect of salts on the betanin hydrolysis was investigated at pH 3 and 6.2 with the addition of sodium salts, ammonium salts and chlorides. Sodium p-toluenesulfonate, ammonium chloride and tetrabutylammonium chloride had the larger effects on the observed rate constant for the hydrolysis of betanin. The variation of pH resulted in similar hydrolysis profile for both betalains studied and multiparameter fitting of the data suggests that the specific base catalysis is primarily responsible for the hydrolysis of betanin and indicaxanthin. A model that suggests the opening of the 1,2,3,4-tetrahydropyridine ring of betalains is proposed to explain the effect of pH on the decomposition rate constant under acidic conditions.
36
Ved, V., e L. L. Tovazhnyansky. "Kinetics and mass transfer processes of thermal catalytic neutralization of gas emissions in modern waste processing complexes". Thesis, Львівська політехніка, 2017. http://repository.kpi.kharkov.ua/handle/KhPI-Press/36877.
Testo completoAbstract (sommario):
The method for calculation, design and manufacturing of the catalytic converters for waste processing complexes has been developed. The development of the method and mathematical model of heterogeneous catalytic process of harmful impurities are based on the experimental study of parameters of the process catalytic thermal purification.
37
Angueira, Ernesto J. "Novel Superacidic Ionic Liquid Catalysts for Arene Functionalization". Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7651.
Testo completoAbstract (sommario):
There is a continuing interest in the subject of arene carbonylation, especially in strong acids and environmentally-benign alternatives are sought to HF/BF3 and to AlCl3 as conversion agents. Ionic liquids offer a powerful solvent for useful conversion agents such as aluminum chloride. The ILs permit AlCl3 to be used at lower HCl partial pressures than with other solvents. The superior reactivity demonstrated by acidic, chloroaluminate ILs is probably due to their enhanced solvation power for HCl and CO. Addition of HCl gas increased reactivity of the system by forming Brnsted acids, and toluene carbonylation is a Brnsted demanding reaction. It was found that reaction is stoichiometric in Al species and only intrinsically acidic ILs are active for toluene carbonylation, therefore it was possible to correlate observed conversion with predicted amounts of Lewis + Brnsted acids. Molecular modeling provided information about the different species present in these ILs and predicted 1H NMR, and 27Al NMR spectrum. Predictions suggested that three types of HCl species are present; and these predictions were confirmed using data of 13C-labeled acetone and its 13C-NMR spectra. These data showed that only one of the three types of HCl in the IL were super acidic. Reactivity towards arene formylation can be tuned by adjusting the ligands R and R in the organic cation and by changing the anion. This reactivity tuning can be exploited in a process where high acidity is required for the conversion of substrate but where separation of product from IL is facilitated by low acidity.
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Benitez, Isa O. "Applications of Langmuir-Blodgett films and Langmuir monolayers supported catalysis and membrane models for urinary stone formation /". [Gainesville, Fla.] : University of Florida, 2004. http://purl.fcla.edu/fcla/etd/UFE0008242.
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Ullman, Andrew. "Polynuclear Cobalt Complexes as Models of a Cobalt Water Oxidation Catalyst". Thesis, Harvard University, 2015. http://nrs.harvard.edu/urn-3:HUL.InstRepos:23845429.
Testo completoAbstract (sommario):
The electrochemical oxidation of Co2+ ions in the presence of a buffering species such as phosphate (Pi), methyl phosphonate (MePi), and borate (Bi) leads to the formation of amorphous cobalt oxide thin films that are capable of catalyzing the four electron-four proton oxidation of water to dioxygen. These cobalt oxygen evolving catalysts (Co–OECs) have been extensively studied by electrochemical techniques; however, the amorphous nature of these films means that garnering insights at the molecular and atomic level is difficult because electronic and structural characterization methods rely on measurements of bulk material. To address this challenge, polynuclear cobalt hydroxide and cobalt oxide compounds have been employed as platforms for understanding Co–OECs at the molecular level.
In the first part of the thesis, we present the synthesis of a heptanuclear cobalt cluster in two different oxidation states, Co(II)7 and a mixed valence Co(III)Co(II)6. An anomalously slow self–exchange electron transfer rate as compared to that predicted from semiclassical Marcus theory was measured, supporting a charge transfer process that is accelerated by dissociation of the anion from the oxidized cluster. This mechanism sheds light on the inverse dependence of anions in the deposition mechanism of Co–OECs. Moreover, the results address a long-standing controversy surrounding the Co2+/3+ self–exchange electron transfer reaction of the hexaaqua complex.
In the second part of the thesis, we report the synthesis and characterization of a dinuclear cobalt complex, which we use as an edge sites mimic (ESM) of the Co-OEC. A comparative investigation of the Pi and Bi binding of buffers to this ESM is provided. We find that the binding to the boric acid component of borate buffer is rapid, while binding to K2HPO4 is much slower, taking days to equilibrate at room temperature. These studies are used to provide a model for the interaction of Pi and Bi species with the active site of the Co-OEC. An inverse dependence on [Bi] of the electrochemical driven water oxidation activity by Co-OECs is demonstrated, which provides validation for the model and indicates that dinuclear cobalt edge sites are necessary for water oxidation catalysis.
In the final chapter of the thesis, we use a series of spectroscopic and electrochemical methods to show that the observed water oxidation activity of the compound class Co4O4(OAc)4(py–X)4 emanates from a Co(II) impurity. This impurity is oxidized to produce Co-OEC, which is an active water oxidation catalyst. Differential electrochemical mass spectrometry (DEMS) is used to characterize the fate of glassy carbon at water oxidizing potentials, and demonstrate that such electrode materials should be used with caution for the study of water oxidation catalysis. We then investigate the electrochemical properties of Co4O4 cubanes in non-aqueous solvents, showing that the neutral cubanes may be oxidized by two electrons yielding a formal oxidation state of Co(IV)2Co(III)2. Finally, we show that these cubanes may be synthetically modified with tethered NMI photooxidants, which opens new avenues for exploring fixed-distance photoinduced ET using Co4O4 cubanes as the electron donor. Ultra-fast transient absorption experiments demonstrate that a charge separated state is formed following laser excitation.Chemistry and Chemical Biology
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Ganesan, Aravind. "Development of a modern catalytic system for the production of C3+ aliphatic alcohols by the Fischer-Tropsch method". Thesis, KTH, Energiteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-259958.
Testo completoAbstract (sommario):
This thesis deals with converting a mixture of H2 and CO, also referred to as syngas or producer gas, to higher or mixed alcohols and other fuels through a process called Fischer Tropsch Synthesis (FTS). It is a beneficial pathway that minimizes the dependence on oil and similar fossil fuels which contribute to rapid climate change by releasing harmful greenhouse gases. The syngas used in FTS, is generally obtained through gasification of biomass to make the entire process renewable and to make the resulting fuel carbon neutral. The products are pure due to prior cleaning of syngas mixture to remove oxides of nitrogen, sulphur and other particulate matter, before the process, thereby drastically reducing the net exhaust gas emissions. The major objective of this project is to design a novel catalyst system and subject it to a series of experimentation for testing its selectivity towards alcohols. This is because the present catalytic systems are either very expensive to assemble or confer to a low yield. Two cobalt (Co) based catalysts, one without a promoter and the other which is promoted by zirconium (Zr), are prepared. The activity and selectivity of Co catalysts are finally compared with the existing Swedish Biofuels AB’s Iron (Fe) based catalyst promoted by copper (Cu) and chromium (Cr) along with characterization of the optimum reaction parameters like temperature, pressure, GHSV and syngas ratio for FTS. Aqueous incipient impregnation approach was adopted wherein the Co active metal and Zr promoter (only in second catalyst) are introduced step-wise on a ϒ-alumina support to synthesize the catalyst after which it is heat treated through drying, calcination and reduction to obtain the active Co metal catalyst. A high temperature FTS, was employed for the yield of alcohols and other gasoline derivatives according to literature. Finally, the liquid and gaseous products are analyzed through GC or GC/MS analysis techniques. The unpromoted Co catalyst’s activity is regarded as a failure due to satisfactory results. There were a few problems associated with the catalyst alone like poor mechanical stability that could be attributed to the use of an incorrect binder. Other problems included methanation due to haphazard temperature variations and inefficient catalyst reduction. For the promoted Co catalyst, the yield of alcohols and hydrocarbons was significantly higher than the unpromoted Co catalyst. A temperature of 300 °C, a GHSV of 360 h-1 , a pressure of 10 bar and a H2:CO ratio of 1.3:1 were the optimal background conditions for FTS. Higher temperature caused methanation and reduced the chain growth probability factor, α, that resulted in the formation of lower hydrocarbons only. Any increase in gas ratio and GHSV, also increased the rate of methane formation and caused diffusion limitations. For a one-stage setup with the reversal of exhaust gases, the conversion rates of CO and H2 were quite promising. This success can be attributed to a higher calcination temperature that increased the degree of reduction of Co due to formation of promoter oxides thereby enabling CO hydrogenation and H2 insertion. It helped to reduce CO2 formation as well. Even for the Fe catalyst, a low temperature, a low GHSV and low syngas ratio were preferred. But unlike its Co counterpart, a higher pressure favored an increase in yield of alcohols and other long chain hydrocarbons. Fe’s ability to support WGS reaction disturbed the molar ratio of CO and also released more CO2 that could affect the rate of syngas conversion. But, on the whole, Fe catalyst was efficient than Co catalyst for alcohol synthesis. The overall yield of alcohols was just 5% of the liquid products. Nearly 86% of the alcohol fraction comprised of C1, C2 and C3 alcohols alone and very few C4, C5 and C6 alcohols were obtained.Denna avhandling behandlar omvandling av en blandning av H2 och CO, även kallad syngas eller producentgas, till högre eller blandade alkoholer och andra bränslen genom en process som kallas Fischer Tropsch Synthesis (FTS). Det är en bra väg som minimerar beroendet av olja och liknande fossila bränslen som bidrar till snabba klimatförändringar genom att släppa ut skadliga växthusgaser. Syngasen som används i FTS erhålls generellt genom förgasning av biomassa för att göra hela processen förnybar och för att göra det resulterande bränslet kolneutralt. Produkterna är rena på grund av föregående rengöring av syngasblandningen för att avlägsna kväveoxider, svavel och annat partikelformigt material före processen och därigenom drastiskt minska utsläppen av avgaserna. Huvudsyftet med detta projekt är att utforma ett nytt katalysatorsystem och utsätta det för en serie experiment för att testa dess selektivitet gentemot alkoholer. Detta beror på att de nuvarande katalytiska systemen antingen är mycket dyra att montera eller ge ett lågt utbyte. Två koboltbaserade (Co) -baserade katalysatorer, en utan en promotor och den andra som befordras av zirkonium (Zr), framställs. Aktiviteten och selektiviteten hos Co-katalysatorer jämförs slutligen med de befintliga Swedish Biofuels AB: s Iron (Fe) -baserade katalysator som främjas av koppar (Cu) och krom (Cr) tillsammans med karaktärisering av de optimala reaktionsparametrarna som temperatur, tryck, GHSV och syngasförhållande för FTS. Vattenhaltig begynnande impregneringsmetod användes där den Co-aktiva metallen och Zr-promotorn (endast i den andra katalysatorn) införs stegvis på ett ϒ-aluminiumoxidstöd för att syntetisera katalysatorn, varefter den värmebehandlas genom torkning, kalcering och reduktion för att erhålla aktiv Co-metallkatalysator. En hög temperatur FTS användes för utbytet av alkoholer och andra bensinderivat enligt litteratur. Slutligen analyseras de flytande och gasformiga produkterna genom GC- eller GC / MS-analystekniker. Den outpromoterade Co-katalysatorns aktivitet betraktas som ett misslyckande på grund av tillfredsställande resultat. Det fanns några problem associerade med katalysatorn ensam som dålig mekanisk stabilitet som kunde tillskrivas användningen av ett felaktigt bindemedel. Andra problem inkluderade metanering på grund av variationer i slumpmässiga temperaturer och ineffektiv katalysatorreduktion. För den befordrade Co-katalysatorn var utbytet av alkoholer och kolväten betydligt högre än den opromoterade Co-katalysatorn. En optimal temperatur på 300 ° C, en GHSV på 360 h-1, ett tryck av 10 bar och ett H2: CO-förhållande på 1,3: 1 var de optimala bakgrundsbetingelserna för FTS. Högre temperatur orsakade metanering och reducerade sannolikhetsfaktorn för kedjan tillväxt, a, vilket resulterade i bildandet av endast lägre kolväten. Varje ökning av gasförhållandet och GHSV, ökade också metanbildningshastigheten och orsakade diffusionsbegränsningar. För en inställning i ett steg med reversering av avgaser var omvandlingsgraden för CO och H2 ganska lovande. Denna framgång kan tillskrivas en högre kalcineringstemperatur som ökade graden av reduktion av Co på grund av bildning av promotoroxider och därigenom möjliggör CO-hydrering och H2-införing. Det hjälpte också till att minska koldioxidbildningen. Även för Fe-katalysatorn föredrog man en låg temperatur, ett lågt GHSV och lågt syngasförhållande. Men till skillnad från Co-motsvarigheten gynnade ett högre tryck en ökning av utbytet av alkoholer och andra långkedjiga kolväten. Fe: s förmåga att stödja WGS-reaktion störde det molära förhållandet CO och frigav också mer CO2 som kan påverka hastigheten på syngasomvandlingen. Men i stort sett var Fe-katalysator mer effektiv än Cokatalysator för alkoholsyntes. Det totala utbytet av alkoholer var bara 5% av de flytande produkterna. Nästan 86% av alkoholfraktionen bestod av C1-, C2- och C3-alkoholer enbart och mycket få C4-, C5- och C6-alkoholer erhölls.
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Hashim, Alaa Hassan. "Metallopeptides From Design to Catalysis: Structure, Oxidative Activities, And Inhibition Studies Of Designed And Naturally Occurring Metallopeptides". Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5626.
Testo completoAbstract (sommario):
Structural and mechanistic complexities of copper-dioxygen systems have attracted much attention in the field of bioinorganic chemistry, both in model systems and trapped protein intermediates. The research presented herein is focused on model and naturally occurring metallopeptide systems, from its design to catalysis. Copper is used as the coordinating metal ion, with cobalt and zinc as probes for metal binding. The bioinorganic chemistry of copper proteins and its coordination and spectroscopic properties are briefly discussed in chapter 1. The next two chapters are centered on the de novo design of a minimalistic metallopeptide system with an amino acid sequence of RHHPPHHE. Structural characterization of the peptide by means of CD and NMR spectroscopy techniques are presented in chapter 2, suggesting a characteristic beta-turn structure in its apo and di-metal bound form. The designed metallopeptide exhibits catecholase activity, which is presented in chapter 3. The data suggest the presence of two mononuclear copper active sites, exhibiting specificity towards the oxidation of catecholamine substrates. Similarly, the catecholase activity has been previously observed in copper complexes of Alzheimer's disease related peptide beta-amyloid, exhibiting metal-centered redox chemistry. The metallo-(beta-amyloid); complexes are the hallmark Alzheimer's disease and have been attributed to the generation of reactive oxygen species causing oxidative stress. Thus, inhibition of the observed oxidative activities was investigated. Probing the role of phosphate moieties in various compounds as potential inhibitors against the induced oxidative stress is presented in chapter 4. The phosphate analogs of the studied compounds exhibit more pronounced potency, where mutation of the beta amyloid peptide at Arg-5 and Lys-16 give insight into the interactions of the side chains of Arg and Lys with the phosphate moiety. 31P NMR relaxation studies further support the binding/interaction of phosphate with the Cu(II)-(beta-amyloid); complexes. The correlation of phosphate moiety binding/activity will allow for the design of more potent inhibitors toward the Cu(II)-(beta-amyloid); induced oxidative stress.
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Calvo, Sergio Rafael. "Reactivity and stability of platinum and platinum alloy catalysts toward the oxygen reduction reaction". [College Station, Tex. : Texas A&M University, 2007. http://hdl.handle.net/1969.1/ETD-TAMU-2457.
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Tholander, Fredrik Otto. "Catalytic mechanisms and evolution of leukotriene A₄ hydrolyse /". Stockholm, 2006. http://diss.kib.ki.se/2006/91-7140-952-1/.
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Bi, Wu. "PEM fuel cell catalyst degradation mechanism and mathematical modeling". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/29756.
Testo completoAbstract (sommario):
Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2008.Committee Chair: Fuller, Thomas; Committee Co-Chair: Deng, Yulin; Committee Member: Gallivan, Martha; Committee Member: Kohl, Paul; Committee Member: Singh, Preet. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Schall, Caroline Anja. "Chiral oxazoline and bis(oxazoline) ligands : new biomimetic models for iron containing nonheme proteins and their application in catalysis". kostenfrei, 2007. http://www.opus-bayern.de/uni-regensburg/volltexte/2008/891/.
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Lai, Jinfeng. "Models of chemical structure and dynamics via nuclear magnetic resonance and ab initio computational chemistry". Diss., [Riverside, Calif.] : University of California, Riverside, 2009. http://proquest.umi.com/pqdweb?index=0&did=1899476641&SrchMode=2&sid=1&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1269360290&clientId=48051.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--University of California, Riverside, 2009.Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed March 10, 2010). Includes bibliographical references. Also issued in print.
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Poliukh, К. "Modern state in the research and application of proteolytic enzymes of fungi". Thesis, National Aviation University, 2021. https://er.nau.edu.ua/handle/NAU/50640.
Testo completoAbstract (sommario):
1. Braga-Silva L.A., Santos A.L. Aspartic protease inhibitors as potential anti-Candida albicans drugs: impacts on fungal biology, virulence and pathogenesis. Curr Med Chem. 2011. Vol.18 (16). P. 2401-19.
2. Ghosh A.K., Osswald H.L., Prato G. Recent Progress in the developent of HIV-1 protease inhibitors for the treatment of HIV/AIDS. Journal of medicinal chemistry. 2016. Vol. 59 (11). P. 5172–5208.
3. Kim S.Y., Gunasekaran S., Olson N.F. Combined use of chymosin and protease from Cryphonectria parasitica for control of meltability and firmness of cheddar cheese. J Dairy Sci. 2004. Vol. 87(2). P. 274-83. URL: doi: 10.3168/jds.S0022-0302(04)73166-5.
4. Suwannarach N., Kumla J., Sujarit K. et al. Natural bioactive compounds from fungi as potential candidates for protease inhibitors and immunomodulators to apply for coronaviruses. Molecules. 2020. Vol. (25 (8). P.1800.
5. Варбанець Л.Д., Мацелюх О.В. Протеолітичні ферменти мікроорганізмів та методи їх дослідження: монографія. Київ. 2008. 108 с.Proteolytic enzymes are studied as tools for understanding protein structure and the mechanisms of enzymatic catalysis, or as well as bioactive substances applied in medicine, agriculture and industry. The growing needs of biotechnology, changes in environmental and radiation backgrounds, widespread usage of drugs encourages the search for a new, effective, safe species and strains of fungi which could be the base for new probiotics production and serve in biotransformations of food products.
Протеолітичні ферменти вивчаються як інструменти для розуміння білкової структури та механізмів ферментативного каталізу, або, а також біологічно активних речовин, застосовуваних у медицині, сільському господарстві та промисловості. Зростаючі потреби біотехнології, зміни в екологічних та умовах випромінювання, широке використання наркотиків сприяє пошуку нових, ефективних, безпечних видів та штамів грибів, які можуть бути базою для виробництва нових пробіотиків та служать у біотрансформаціях харчових продуктів.
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Ould, Hamou Cherif Aghiles. "Decomposition Mechanism of Lignin Models on Pt(111) : Combining Single Crystal Experiments and First-Principles Calculations". Thesis, Université d'Ottawa / University of Ottawa, 2019. http://hdl.handle.net/10393/38719.
Testo completoAbstract (sommario):
The world energy and product consumption keep increasing steadily over the years as the world population keeps growing and more countries become industrialized. As the world reserves deplete it becomes a necessity to find an alternative way to meet the population’s demand. Biomass conversion seems to be the future of a clean and sustainable world. Lignin is the second most abundant polymer in the biomass. Given the unique structure and chemical properties of lignin, a wide variety of bulk and fine chemicals can be obtained and be used for goods and biofuels production. Catalysis, with its selective bond cleavage and lower energy activation, is considered as a potential key solution in the process of lignin conversion into valuable chemicals. To gain insights into that catalytic system, we performed surface science experiments (X-ray Photoelectron Spectroscopy, Temperature Programmed Desorption and Reflection Absorption Infrared Spectroscopy) under Ultra-High Vacuum conditions (UHV). Due to lignin’s physical properties limitation under UHV conditions, lignin models with the same chemical structure such as phenol, anisole, 2-phenoxyethanol and veratrol were used to gain a better understanding of the reactivity of lignin itself.
Dosing anisole and 2-phenoxyethanol on Pt(111) surprisingly gave benzene, carbon monoxide and hydrogen as the main desorbing products of decomposition. With the help of Density Functional Theory (DFT), we successfully explain the unexpected selectivity. In the present work, we show in particular that phenoxy PhO stands as a key intermediate. Although the UHV conditions do not allow the hydrogenation of phenoxy into phenol, i.e. the catalytic product, they reveal the key role of both hydrogen and carbonaceous species. Under UHV conditions, anisole and 2-phenoxyethanol are extensively dehydrogenated: it results in the formation of carbonaceous fragments, which can actually perform the deoxygenation of phenoxy into benzene. The reactivity of veratrol on Pt(111) hindered the formation of benzene and only gave carbon monoxide and hydrogen as the main desorbing products of decomposition. Although carbonaceous fragments were formed on the surface, the deoxygenation of the two oxygenated arm moieties does not occur without the total decomposition of the aromatic ring, hence the formation of coke.
This detailed work opens the door to a rational design of metal-based catalysts and a route towards lignin valorization.
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Wu, Huei-Ru [Verfasser], Herbert [Akademischer Betreuer] Waldmann e Carsten [Gutachter] Strohmann. "Exploiting modern catalytic methods of C-glycosylation using the vinylogy concept / Huei-Ru Wu ; Gutachter: Carsten Strohmann ; Betreuer: Herbert Waldmann". Dortmund : Universitätsbibliothek Dortmund, 2019. http://d-nb.info/1201160847/34.
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González, Forero Danilo. "Automatized Nanoparticle Models Generation and Application to the Oxygen Evolution Reaction Catalyzed by IrO2. Slab vs Nanoparticle Models". Doctoral thesis, Universitat Autònoma de Barcelona, 2020. http://hdl.handle.net/10803/671127.
Testo completoAbstract (sommario):
Les nanopartícules tenen un gran impacte en múltiples camps científics principalment a causa d’i) la seva gran superfície específica i ii) la possibilitat d’ajustar l’estructura electrònica del material modificant la seva grandària i forma. Això és especialment rellevant en el camp de la catàlisi amb metalls de transició. Per a caracteritzar les propietats catalítiques de les nanopartícules s’han desenvolupat diverses tècniques experimentals i computacionals. No obstant això, la majoria dels esforços computacionals dedicats a comprendre l’activitat catalítica de les nanopartícules empren superfícies esteses per a representar el material. De fet, fins on sabem, hi ha pocs exemples de reaccions catalitzades per nanopartícules d’òxid metàl·lic utilitzant models de nanopartícules. Això limita l’exploració de llocs particulars sol presents en les superfícies de les nanopartícules i, per tant, és desitjable l’ús de models més realistes. Un dels colls d’ampolla en l’ús de models de nanopartícules realistes és el fet que la construcció del model no és senzilla, particularment per a materials multicomponent com els òxids de metalls de transició.
Aquesta tesi té dues parts principals. En primer lloc, desenvolupem una eina computacional capaç de construir models de nanopartícules per a compostos multicomponent amb estequiometria controlada i terminació de superfície de manera automatitzada, la qual cosa elimina la subjectivitat i el biaix humà. En segon lloc, utilitzem models de *slabs i nanopartícules per a avaluar els factors clau que determinen l’adsorció d’aigua i el rendiment catalític de *IrO2 per a la reacció d’evolució d’oxigen (*OER) mitjançant l’ús de simulacions DFT. El rendiment OER catalitzat per IrO2 s’ha explorat a través dels mecanismes d’atac nucleofílico d’aigua (WNA) i de oxoacoblament (I2M) tant per a superfícies com per a models de nanopartícules.
Hem trobat que la dissociació de l’aigua està controlada per les propietats intrínseques del material com l’acidesa de l’Anar, la basicitat Obr, la naturalesa del lloc vacant i els efectes cooperatius entre les molècules d’aigua adsorbidas. Respecte al mecanisme de la OER, els nostres resultats suggereixen que tant el mecanisme WNA com l’I2M requereixen intermediaris radicals per a ser factibles. A més, el mecanisme WNA sembla ser el més favorable per a gairebé tots els llocs estudiats en superfícies i nanopartícules. De fet, el mecanisme I2M només sembla ser el preferit en la superfície (011), on el caràcter oxil dels àtoms d’O en la superfície és major i la distància interatómica entre els grups oxil és bastant curta. A més, i de manera bastant notable, el lloc de la punta de la nanopartícula exhibeix un sobrepotencial lleugerament més gran que l’ideal, la qual cosa suggereix que els llocs tetracoordinats han d’explorar-se per a millorar el rendiment catalític del IrO2 per a la OER.Las nanopartículas tienen un gran impacto en múltiples campos científicos principalmente debido a i) su gran superficie específica y ii) la posibilidad de ajustar la estructura electrónica del material modificando su tamaño y forma. Esto es especialmente relevante en el campo de la catálisis con metales de transición. Para caracterizar las propiedades catalíticas de las nanopartículas se han desarrollado varias técnicas experimentales y computacionales. Sin embargo, la mayoría de los esfuerzos computacionales dedicados a comprender la actividad catalítica de las nanopartículas emplean superficies extendidas para representar el material. De hecho, hasta donde sabemos, hay pocos ejemplos de reacciones catalizadas por nanopartículas de óxido metálico utilizando modelos de nanopartículas. Esto limita la exploración de sitios particulares solo presentes en las superficies de las nanopartículas y, por lo tanto, es deseable el uso de modelos más realistas. Uno de los cuellos de botella en el uso de modelos de nanopartículas realistas es el hecho que la construcción del modelo no es sencilla, particularmente para materiales multicomponente como los óxidos de metales de transición. Esta tesis tiene dos partes principales. En primer lugar, desarrollamos una herramienta computacional capaz de construir modelos de nanopartículas para compuestos multicomponente con estequiometría controlada y terminación de superficie de manera automatizada, lo que elimina la subjetividad y el sesgo humano. En segundo lugar, utilizamos modelos de slabs y nanopartículas para evaluar los factores clave que determinan la adsorción de agua y el rendimiento catalítico de IrO2 para la reacción de evolución de oxígeno (OER) mediante el uso de simulaciones DFT. El rendimiento OER catalizado por IrO2 se ha explorado a través de los mecanismos de ataque nucleofílico de agua (WNA) y de oxoacoplamiento (I2M) tanto para superficies como para modelos de nanopartículas. Hemos encontrado que la disociación del agua está controlada por las propiedades intrínsecas del material como la acidez del Ir, la basicidad Obr, la naturaleza del sitio vacante y los efectos cooperativos entre las moléculas de agua adsorbidas. Con respecto al mecanismo de la OER, nuestros resultados sugieren que tanto el mecanismo WNA como el I2M requieren intermediarios radicales para ser factibles. Además, el mecanismo WNA parece ser el más favorable para casi todos los sitios estudiados en superficies y nanopartículas. De hecho, el mecanismo I2M solo parece ser el preferido en la superficie (011), donde el carácter oxil de los átomos de O en la superficie es mayor y la distancia interatómica entre los grupos oxil es bastante corta. Además, y de manera bastante notable, el sitio de la punta de la nanopartícula exhibe un sobrepotencial solo un poco más grande que el ideal, lo que sugiere que los sitios tetracoordinados deben explorarse para mejorar el rendimiento catalítico de IrO2 para la OER.
Nanoparticles have a large impact in multiple scientific fields mainly due to i) their large specific surface area and ii) the possibility of tuning the electronic structure of the material by modifying its size and shape. This has been particularly relevant in the field of catalysis with precious transition metals. To characterize the nanoparticle catalytic properties several experimental and computational techniques have been developed. Most of the computational efforts devoted to understand the catalytic activity of nanoparticles, however, employ extended surfaces to represent the material. Indeed, to the best of our knowledge, few examples of reactions catalyzed by metal oxide nanoparticles have been studied by using nanoparticles models. This limits the exploration of particular sites only present in the nanoparticle surfaces and thus, the use of more realistic models is desirable. One of the bottlenecks in the use of realistic nanoparticle models is the fact that model construction is not straightforward, particularly for multicomponent materials such as transition metal oxides. This thesis has two main parts. Firstly, we develop a computational tool able to construct nanoparticle models for multicomponent compounds with controlled stoichiometry and surface termination in an automatized manner, which removes human subjectivity and bias. Secondly, we use slab and nanoparticle models to evaluate the key factors that determine the water adsorption and the catalytic performance of IrO2 for the oxygen evolution reaction (OER) by using DFT simulations. The OER performance of IrO2 has been explored through the water nucleophilic attack (WNA) and oxo-coupling (I2M) mechanisms for both surfaces and nanoparticle models. We have found that the water dissociation is controlled by the intrinsic material properties like the Ir acidity, the Obr basicity, the nature of the vacant site and the cooperative effects between adsorbed water molecules. Concerning the OER mechanism, our results suggest that both the WNA and the I2M mechanisms require radical intermediates to be feasible. Moreover, the WNA mechanism seems to be the most favorable for almost all studied sites on surfaces and nanoparticles. Indeed, the I2M mechanism only seems to be the preferred one on the (011) surface, were the oxyl character of O atoms on the surface is larger and the interatomic distance between the oxyl groups is rather short. Furthermore, and quite remarkably, the tip site of the nanoparticle exhibits an OER potential that is only slightly larger than the ideal one, thereby suggesting that tetracoordinated sites should be explored to improve the catalytic performance of IrO2 for the OER.
Universitat Autònoma de Barcelona. Programa de Doctorat en Química