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do, Nascimento Daniel Luis. "Olefin Metathesis Catalysts: From Decomposition to Redesign." Thesis, Université d'Ottawa / University of Ottawa, 2021. http://hdl.handle.net/10393/42541.
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Olefin metathesis is arguably the most versatile catalytic route yet developed for the assembly of carbon-carbon bonds. Metathesis methodologies are attractive from both synthetic and ecological standpoints, because they employ unactivated double bonds. This reduces the total number of synthetic steps, and the associated generation of chemical wastes. The drive to deploy olefin metathesis in highly demanding contexts, including pharmaceutical manufacturing and chemical biology, puts severe pressure on catalyst lifetime and productivity. Understanding the relevant decomposition pathways is critical to achieve essential performance goals, and to enable informed catalyst redesign. This thesis work expands on significant prior advances that identified and quantified critical decomposition pathways for ruthenium catalysts stabilized by N-heterocyclic carbene (NHC) ligands. Because pristine catalyst materials are essential for mechanistic study, it focuses first on methods aimed at improving efficiency and purity in catalyst synthesis. Merrifield iodide resins were shown to function as efficient, selective phosphine scavengers in the production of clean second-generation catalysts from PCy3- stabilized precursors.
The thesis then turns to mechanistic examination of decomposition pathways that underlie success and failure for leading NHC catalysts, for comparison with a new family of catalysts stabilized by cyclic (alkyl)(amino) carbene (CAAC) ligands. These represent the first in-depth mechanistic studies of the CAAC catalysts, which have attracted much attention for their breakthrough productivities in challenging metathesis reactions. The remarkable productivity of the CAAC catalysts is shown to originate in their resistance to decomposition of the key metallacyclobutane intermediate via b-elimination, and (to a lesser extent) in their resistance to attack by nucleophiles and Bronsted bases. Importantly, however, they are more susceptible to bimolecular decomposition. The latter behaviour, as well as their resistance to b-elimination, is traced to the strong trans influence of the CAACs relative to NHC ligands. This insight significantly advances our understanding of the fundamental properties governing both productivity and decomposition.
Finally, two new catalysts are developed, building on the principle that nucleophilic stabilizing ligands should be avoided in the precatalysts. In the first of these complexes, an o-dianiline ligand is employed to stabilize the precatalyst. This flexible, H-bonding chelate serves the further purpose of accelerating macrocyclization of flexible dienes that bear polar functionalities. As its H-bonding capacity also increases its sensitivity to trace water, however, an alternative catalyst architecture was pursued. The latter consists of a dimer bearing bulky Ru-indenylidene centers, in which a dative bond from a bridging chloride affords the fifth ligand essential to stabilize the precatalyst.
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Norooz, Oliaee Shirin. "Catalyst Development and the Structure-Dependent Properties for Hydrazine Decomposition." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1468618168.
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Malich, Ashley M. "Decomposition of Novel Diazosugars: Effects on Regioselectivity." Youngstown State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ysu1222195006.
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Chai, Wai Siong. "Characterization & analysis on electrolytic decomposition of hydroxylammonium nitrate (HAN) ternary mixtures in microreactors." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/40544/.
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Rapid development of micropropulsion systems arose from growing interest on micro- and nanosatellites. Utilization of liquid energetic materials such as hydrazine and hydrogen peroxide as propellant in propulsion yielded promising results. However, safety issue remains a great concern as hydrazine is highly toxic. This drives the development of propellants towards lower toxicity and more environmental friendly, namely green propellants. Hydroxylammonium nitrate (HAN) was selected among three green propellants due to its high energy density in addition to ease in storage and handling properties. In order to understand the effect of addition of fuel into HAN binary solution, electrolytic decomposition of zero oxygen balance HAN ternary mixture in thermal isolated beaker was performed at macroscale. Addition of a fuel to binary HAN solution generally has more stages of decomposition, as opposed to single stage in binary HAN solution. Rate of temperature increase in the first stage of decomposition (Ṫ1) was found to be directly proportional to electrical resistivity of the HAN ternary mixture, while maximum electrolytic decomposition temperature (Tmax) of HAN ternary mixture obtained was dependent on fuel added. Visualization of HAN decomposition was demonstrated using transparent PDMS microreactors. A novel DPST integration in triggering the power supply and high speed camera was proposed. Such integration greatly reduced the cost of using a DAQ system, and was shown to capture the decomposition successfully at 5000 fps. Parametric optimization was also carried out in PDMS microreactors. Usage of 3 pairs of electrodes has increased overall reaction rate as high as 225 %, as compared to 1 pair counterpart. The overall reaction rate is proportional to flowrate and applied voltage. 3 pairs of electrodes can initiate decomposition in low voltage region. Applied voltage is the most significant parameter affecting the overall reaction rate. HAN-dextrose has lower decomposition performance compared to binary HAN solution in PDMS microreactor, using the optimized parameters carried out on binary HAN solution. This work has demonstrated both effect of fuel addition in binary HAN solution and parametric optimization in binary HAN solution towards their decomposition phenomena at macroscale and microscale,respectively. Several recommendations were made in future work section, including using screen-printing technology on the microreactor and adding a catalytic reactor after HAN was electrolyzed, to further improve decomposition efficiency.
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Bailey, Gwendolyn Anne. "Inside the Cycle: Understanding and Overcoming Decomposition of Key Intermediates in Olefin Metathesis." Thesis, Université d'Ottawa / University of Ottawa, 2018. http://hdl.handle.net/10393/37501.
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Ru-catalyzed olefin metathesis is an exceptionally powerful, versatile methodology for the assembly of carbon–carbon bonds. The N-heterocyclic carbene (NHC)-stabilized, “second-generation” Ru catalysts have enabled groundbreaking recent advances, ranging from the RCM assembly of cyclic peptides as hepatitis C virus therapeutics, to the elaboration of renewable seed oils and phenylpropanoids into value-added products and chemicals. However, key limitations arise from facile catalyst decomposition. Despite a plethora of studies on the synthesis of new catalysts, and on the decomposition processes accessible to the precatalyst and resting-state species, the underlying principles that govern decomposition of the active intermediates have been surprisingly little examined. One important reason for this is their incredible reactivity: the four-coordinate methylidene intermediate RuCl2(H2IMes)(=CH2) is too short-lived to be observed, while the metallacyclobutane (MCB) intermediate RuCl2(H2IMes)(2-C3H6) can only be observed below –40 °C. This makes them extremely challenging, but also fascinating targets for study. Understanding the underlying chemistry that dictates their reactivity and decomposition is essential for informed catalyst and process redesign, and is thus of fundamental interest, but also considerable practical importance.
This thesis work thus aims at understanding the decomposition of active intermediates relevant to the highly-active, second-generation class of catalysts. Emphasis is placed on examining a variety of metathesis contexts, as well as providing solutions. Treated first are the decomposition pathways that arise during metathesis of electron-deficient olefins, a frontier area in organic synthesis, and in the utilization of renewable resources. An unexpected correlation is revealed between rapid catalyst decomposition, and the presence of a stabilizing PCy3 ligand in the standard catalyst for this reaction. The nucleophilic phosphine ligand is shown to attack an acrylate olefin, forming enolates that function as potent Brønsted bases. Literature evidence suggests that such strong bases are innocuous towards the precatalyst, pointing towards a key role for the active intermediates in Brønsted base-induced catalyst decomposition.
Precisely which intermediate is involved, as well as the site of deprotonation, is elucidated next. Prior to this work, the NHC ligand was widely believed to be the target for attack. However, through labelling experiments, analysis of the Ru and organic byproducts, and computational studies, deprotonation is shown to occur at the MCB ring. Moreover, MCB deprotonation is revealed to be unexpectedly general, and not contingent on the presence of either an exceptionally strong base, or an electron-deficient substrate. This understanding is key, given recent reports from pharma highlighting the adverse impact of base contaminants, as well as current interest in metathesis of amine-containing substrates.
Next examined are the intrinsic decomposition pathways operative for the MCB and four-coordinate methylidene. Prior to this work, the only reported pathway for decomposition of these two species involved beta-elimination of the MCB ring as propene. However, beta-elimination is shown to play an unexpectedly minor role in catalyst decomposition: less than 40% propenes are observed, even under conditions expected to favour MCB elimination. Bimolecular coupling of the methylidene, with loss of the methylidene moiety as ethylene, is proposed to account for the difference. Thus, transiently-stabilized adducts RuCl2(H2IMes)(=CH2)(L)n (L = o-dianiline or pyridine) are synthesized at temperatures down to –120 °C. On warming, these adducts lose Ln and rapidly decompose via bimolecular coupling, with loss of the methylidene moiety as ethylene. These experiments provide the first unambiguous evidence for bimolecular coupling in the important "second-generation" Ru systems, nearly two decades after which this pathway was dismissed in leading papers and reviews.
The last two sections focus on solutions. First, a powerful, straightforward solution to the “enolate problem” is developed, whereby the acrylate enolates are quenched and sequestered via reaction with a polyphenol resin. Then, methods for preventing catalyst decomposition during matrix-assisted laser desorption / ionization mass spectrometry (MALDI-MS) are developed, via elucidation of the instrumental and experimental factors that promote successful analysis. As one of the only MS methods capable of affording insight into neutral metal complexes and catalysts, MALDI has unique potential to enable routine analysis of catalyst speciation and decomposition in situ, under real catalytic conditions, for a wide range of catalytic reactions.
Collectively, the findings in this thesis offer a much more complete understanding of the fundamental pathways accessible to the important, highly-active metathesis intermediates, and offer strategies likely to inform practice in both academic and industrial settings. This understanding is key to harnessing the full potential of metathesis methodologies.
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Rico, Pérez Verónica. "Optimization of N2O decomposition RhOx/ceria catalysts and design of a high N2-selective deNOx system for diesel vehicles." Doctoral thesis, Universidad de Alicante, 2013. http://hdl.handle.net/10045/35739.
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Okura, Kaname. "Studies on Ammonia Decomposition for Hydrogen Production over Ni Catalysts." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225614.
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Harada(Onishi), Chie. "Direct Decomposition of Nitrous Oxide over Alkali-doped Co3O4 Catalyst in the Presence of Oxygen." 京都大学 (Kyoto University), 2009. http://hdl.handle.net/2433/124545.
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Petty, Renee Lynn. "Catalytic Decomposition of Nitric Oxide and Carbon Monoxide Gases Using Nanofiber Based Filter Media of Varying Diameters." University of Akron / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=akron1279505229.
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Ireland, Benjamin. "Amines in Olefin Metathesis: Ligands and Poisons." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/34342.
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Olefin metathesis is a powerful tool for assembly of carbon-carbon bonds. Amines and related N-donors are problematic functional groups in Ru-catalyzed olefin metathesis - a well- documented, but poorly understood problem.
The first part of this thesis focuses on amine-induced deactivation pathways; two of which are described in depth. Alkylidene abstraction, a previously unknown reaction for nitrogen nucleophiles, was observed for smaller and less Bronsted-basic amines. Deprotonation of the metallacyclobutane intermediate formed during catalysis is prominent for highly Bronsted basic or sterically bulky N-donors. Monosubstituted (and, by extension unsubstituted) metallacyclobutanes are particularly vulnerable to deprotonation.
For each pathway, the fate of the alkylidene Ru=CHR functional group proved key in determining the nature of deactivation. Both pathways have been detected during catalysis, as evidenced by formation of diagnostic amine (RCH2NR2’) or substituted propene products. A combination of quantitative NMR and GC-MS analysis was used to identify these species on loss of the Ru-alkylidene functional group.
The second part of this thesis focuses on incorporating amines into catalyst design – an under-utilized strategy in the context of Ru-catalyzed olefin metathesis. A modified Grubbs-type catalyst was developed featuring a bulky, relatively non-basic biaryldiamine ligand. Metathesis activity for this catalyst was comparable, and in some cases superior to the most widely-used homogeneous catalysts currently available. Several new, related Ru-benzylidenes were also prepared and fully characterized in conjunction with the mechanistic studies described above.
Progress toward development of N-anion-containing metathesis catalysts is also discussed. Synthesis of Ru-hydride complexes originally intended for this purpose allowed for a fundamental study of the coordination chemistry and reductive elimination chemistry of the NPh2– anion.
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Brandt, Bjoern. "Selectivity in hydrocarbon conversions and methanol decomposition on a Pd/Fe 3 O 4 model catalyst." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2008. http://dx.doi.org/10.18452/15854.
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Selektivität zu erreichen ist eines der Hauptziele der Chemie. In der Katalyse wird allgemein von einem engen Zusammenhang zwischen der Selektivität und der Katalysatorstruktur ausgegangen - allerdings erschwert die komplexe mikroskopische Struktur realer Katalysatoren ein tiefergehendes Verständnis; daher wird versucht, weitergehende Erkenntnisse an strukturell vereinfachten Materialien zu gewinnen. Für diese Arbeit wurde hierzu ein Pd/Fe3O4-Modellkatalysator verwendet. Auf diesem System wurde die Selektivität in zwei katalytische Modellreaktionen untersucht. Die Reaktantenexposition erfolgte dabei über Molekularstrahlen im Hochvakuum, und die Reaktionsraten wurden massenspektrometrisch gemessen; Adsorbate wurden IR-spektroskopisch detektiert. - Zersetzung von Methanol: Es wird gezeigt, dass Methanol auf dem Oxid Fe3O4 sehr selektiv durch Reaktion mit Oberflächensauerstoff (Mars-van-Krevelen-Mechanismus) zu Formaldehyd und Wasser dehydrogeniert wird. Auf Pd-Metall zersetzt sich Methanol im wesentlichen sehr schnell zu Kohlenstoffmonoxid und Wasserstoff (bzw. zu Kohlenstoffablagerungen in einer Nebenreaktion). Es werden Experimente gezeigt, die darauf hindeuten, dass Diffusion von oxidgebundenem Methanol/Methoxy auf die Pd-Metallpartikel signifikant zur Gesamtaktivität des Modellkatalysators beiträgt. - Umsetzung von 2-Buten mit Deuterium: Zunächst wird gezeigt, dass die Erzielung katalytischer Aktivität kritisch von der dissoziativen Adsorption des Reaktanden Deuterium abhängt, die durch Kohlenwasserstoffadsorbate stark inhibiert wird; es war allerdings möglich, diese Limitierung experimentell zu umgehen. Darüberhinaus wird gezeigt, dass die Hydrierungsreaktion durch die Anwesenheit stark zersetzter Kohlenwasserstoffablagerungen selektiv induziert werden kann, während die alternative Reaktion (H/D-Austausch/Isomerisierung) auch in Abwesenheit dieser Spezies abläuft; mögliche Erklärungsmodelle werden diskutiert. Schließlich wird die mögliche Ursache für die unter bestimmten Reaktionsbedingungen beobachteten unterschiedlichen Reaktionsraten mit cis- und trans-2-Buten als Reaktanten diskutiert.The achievement of selectivity is one of the main objectives in chemistry. For catalysis, selectivity is generally seen to be closely linked with catalyst structure; the complex microscopic structure of real catalysts, however, obstructs to obtain a deeper understanding; for this reason, structurally simplified materials are studied. For the current work, studies have been conducted on a Pd/Fe3O4 model catayst. On this system, the selectivity in two catalytic reactions has been examined. The exposure of the reactants was effected by molecular beams in high vacuum, and the reaction rates have been measured mass spectrometrically; additionally, adsorbates were detected by IR-spectroscopy. - Decomposition of Methanol: It is shown that on the oxide Fe3O4 methanol is dehydrogenated very selectively to formaldehyde and water by reaction with surface oxygen of the oxide (Mars-van-Krevelen mechanism). On Pd metal it is mainly decomposed very quickly to carbon monoxide and hydrogen (and, in a side reaction, to carbonaceous deposits). Experiments are shown indicating that the diffusion of oxide-related methanol and methoxy to the Pd metal-particles contributes significantly to the overall activity of the model catalyst. - Conversion of 2-Butene with Deuterium: At first it is shown that the catalytic activity depends critically on the dissociative adsorption of the reactant deuterium, which is strongly inhibited by hydrocarbon adsorbates; it was, however, possible to overcome this limitation experimentally. In addition, it is shown that the hydrogenation reaction can be selectively induced in the presence of strongly dehydrogenated carbonaceous deposits, whereas the alternative reaction (H/D-exchange/isomerisation) can proceed also without the presence of those species; possible models for explanation are discussed. Finally, the possible origin of the different reaction rates with cis- and trans-2-butene that were observed only under certain reaction conditions is discussed.
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MONTEIRO, FELIPE ZANONE RIBEIRO. "STUDY OF THE THERMAL DECOMPOSITION OF GREEN COCONUT FIBER IN THE PRESENCE OF A NANO STRUCTURED CATALYST." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2017. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=32928@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Com aumento da preocupação político-ambiental, torna-se imperativo desenvolver processos eficientes em termos econômicos e energéticos para a produção sustentável de combustíveis e produtos químicos. A liquefação hidrotérmica (HTL) é um processo para a transformação de materiais orgânicos, tais como bio-resíduos ou biomassa, em óleo bruto, em temperaturas usualmente inferiores a 400 graus Celsius sob altas pressões na presença de água, e, dependendo do processo, de um catalisador. Nesse contexto, é importante entender o comportamento de degradação térmica do material em atmosfera inerte, no sentido de se investigar a possibilidade de quebra das cadeias poliméricas inicias em moléculas menores, que, mediante pressão, poderão ser convertidas em novos produtos. Assim sendo, os objetivos do presente trabalho estão associados ao estudo termogravimétrico (TG) da degradação térmica da fibra do coco verde na presença de ferrita de cobalto (Fe2CoO4), utilizada no intuito de gerar um efeito catalítico, acelerando a degradação térmica das estruturas poliméricas presentes, e, que possa ser usada posteriormente em uma rota HTL. Os catalisadores foram produzidos a 1000 graus Celsius em diferentes tempos de calcinação (3h, 6h e 9h), sendo, nas misturas com a fibra, a fração mássica de óxido igual a 50 por cento. As amostras de interesse para a pesquisa foram caracterizadas mediante diferentes técnicas, tais como, a microscopia eletrônica de varredura, para o estudo da morfologia e composição elementar, difração de raios X, para a quantificação das fases presentes nas amostras de ferrita, e espectroscopia de infravermelho, visando à identificação das principais ligações químicas nas fibras, tanto antes quanto durante o tratamento térmico. Dentre todos os ensaios de TG realizados, os experimentos com o catalisador calcinado durante 9h homogeneizado com gral de ágata foi o que mostrou uma melhor resposta com relação à degradação térmica das fibras. Os resultados sugerem ainda que, tanto o tempo de calcinação, quanto a natureza do processo de mistura apresentam efeitos significativos sobre a cinética de degradação.
With increasing political-environmental concern, it becomes imperative to develop efficient processes in economic and energy terms for the sustainable production of fuels and chemical products. Hydrothermal liquefaction (HTL) is a process for the transformation of organic materials such as bio-waste or biomass into crude oil at temperatures usually below 400 degrees Celsius under high pressures in the presence of water and, depending on the process, of a catalyst. In this context, it is important to understand the behavior of thermal degradation of the material under inert atmosphere, in order to investigate the possibility of breaking the initial polymer chains into smaller molecules, which, under pressure, can be converted into new products. The objectives of the present work are associated to the thermogravimetric study (TG) in the thermal degradation of the green coconut fiber in the presence of a cobalt ferrite (Fe2CoO4), used to generate a catalytic effect, accelerating the thermal degradation of the polymeric structures present, and which can be used later on an HTL route. The catalysts were produced at 1000 degrees Celsius at different calcination times (3h, 6h and 9h) and in the fiber mixtures, the oxide mass fraction was equal to 50 percent. The samples of interest for the research were characterized by different techniques, such as scanning electron microscopy, for the study of the morphology and elemental composition, X-ray diffraction, for the quantification of the phases present in the ferrite samples, and spectroscopy of Infrared, in order to identify the main chemical bonds in the fibers, both before and during the heat treatment. Among all the TG assays performed, the experiments with the catalyst calcined for 9h homogenized with mortar and pestle showed the best to the thermal degradation of the fibers. The results further suggest that both the calcination time and the nature of the blending process have significant effects on the degradation kinetics.
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Reinicker, Aaron D. "High Throughput Study of the Structure Sensitive Decomposition of Tartaric and Aspartic Acid on Surfaces Vicinal to Cu(111) and Cu(100)." Research Showcase @ CMU, 2015. http://repository.cmu.edu/dissertations/572.
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There are many reactions that are sensitive to the surface structure of a catalyst. In order to obtain a comprehensive understanding of structure sensitive surface chemistry we use Surface Structure Spread Single Crystals (S4Cs) that expose a continuous distribution of crystal planes across their surfaces. Those crystal planes that lack mirror symmetry contain terraces, monatomic steps, and kinks and can be described as chiral with an R or an S orientation. When coupled with spatially resolved surface analysis techniques, S4Cs can be used to study the effects of surface structure and chirality on surface chemistry across a continuous distribution of crystal planes. A set of six Cu S4Cs has been created that spans all possible crystal planes of Cu. The Cu(111) S4C was used to study the structure sensitivity of L- and D-tartaric acid (TA) decomposition and the Cu(100) S4C was used to study the structure sensitivity of L-4-13C and D-aspartic acid (AA) decomposition. Isothermal Temperature Programmed Reaction Spectroscopy (TPRS) was implemented in which the S4Cs with monolayers of TA and AA were held at a temperature below the temperature of peak decomposition observed in a standard TPR experiment (heating at 1 K/s). At various times during isothermal heating, the surface was cooled to quench the reaction. Spatially resolved X-ray Photoelectron Spectroscopy (XPS) was performed to identify those regions on the surface in which the adsorbates had decomposed and those in which they were still intact. On the Cu(111) S4C which exposes both (100) and (110) step edges, TA decomposition is most sensitive to the density of (100) steps. AA decomposition on the Cu(100) S4C was enantioselective: L-AA-4-13C decomposed on S surfaces before R surfaces while D-AA decomposed on R surfaces before S surfaces. The decomposition of CH3CH2OH, CD3CD2OD, and CF3CH2OH on Zn was studied using temperature programmed reaction spectroscopy (TPRS). The decomposition products of each reaction were determined and a reaction mechanism was proposed for CH3CH2OH decomposition based on the product ratios and peak temperature locations. The CH3CH2OH decomposition mechanism includes the formation of two intermediate species on the surface: CH3CH2- to form CH2=CH2 and CH3CH2O- to form CH3CH=O.
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Goudreault, Alexandre. "Roles for Nucleophiles and Hydrogen-Bonding Agents in the Decomposition of Phosphine-Free Ruthenium Metathesis Catalysts." Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/40042.
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With its unrivaled versatility and atom economy, olefin metathesis is arguably the most powerful catalyst methodology now known for the construction of carbon-carbon bonds. When compared to palladium-catalyzed cross-coupling methodologies, however, catalyst productivity lags far behind, even for the “robust” ruthenium metathesis catalysts. Unexpected limitations to the robustness of these catalysts were first widely publicized by reports describing the implementation of metathesis in pharmaceutical manufacturing. Recurring discussion centered on low catalyst productivity resulting from decomposition of the Ru catalysts by impurities, including ppm-level contaminants in the technical-grade solvent. Over the past 7 years, a series of mechanistic studies from the Fogg group has uncovered the pathways by which common contaminants (or indeed reagents) trigger catalyst decomposition. Two principal pathways were identified: abstraction of the alkylidene or methylidene ligand by nucleophiles, and deprotonation of the metallacyclobutane intermediate by Bronsted base. Emerging applications, however, notably in chemical biology, highlight new challenges to catalyst productivity.
The first part of this thesis emphasizes the need for informed mechanistic insight as a guide to catalyst redesign. The widespread observation of a cyclometallated N-heterocyclic carbene (NHC) motif in crystal structures of catalyst decomposition products led to the presumption that activation of a C-H bond in the NHC ligand initiates catalyst decomposition. Reducing NHC bulk has therefore been proposed as critical to catalyst redesign. In experiments designed to probe the viability of this solution, the small NHC ligand IMe4 (tetramethylimidazol-2-ylidene) was added to the resting-state methylidene complexes formed in metathesis by the first- and second-generation Grubbs catalysts (RuCl2(PCy3)2(=CH2) GIm or RuCl2(H2IMes)(PCy3)(=CH2) GIIm, respectively). The intended product, a resting-state methylidene species bearing a truncated NHC, was not formed, owing to immediate loss of the methylidene ligand. Methylidene loss is now shown to result from nucleophilic attack by the NHC – a small, highly potent nucleophile – on the methylidene. Density functional calculations indicate that IMe4 abstracts the methylidene, generating the N-heterocyclic olefin H2C=IMe4. The latter is an even more potent nucleophile, which attacks a second methylidene, resulting in liberation of [EtIMe4]Cl. These findings report indirectly on the original question concerning the impact of ligand truncation. The ease with which a small, potent nucleophile can abstract the key methylidene ligand from GIm and GIIm underscores the importance of increasing steric protection at the [Ru]=CH2 site. This chemistry also suggests intriguing possibilities for efficient, selective, controlled methylidene abstraction to terminate metathesis activity while leaving the “RuCl2(H2IMes)(PCy3)” core intact. This could prove an enabling strategy for tandem catalysis applications in which metathesis is the first step.
The second part of this thesis, inspired by the potential of olefin metathesis in chemical biology, focuses on the impact of hydroxide ion and water on the productivity of phosphine-free metathesis catalysts. In reactions with the important second-generation Hoveyda catalyst HII, hydroxide anion is found to engage in salt metathesis with the chloride ligands, rather than nucleophilic attack. The resulting Ru-hydroxide complex is unreactive toward any olefins larger than ethylene, while ethylene itself causes rapid decomposition. Proposed as the decomposition pathway is bimolecular coupling promoted by the strong H-bonding character of the hydroxide ligands.
Lastly, the impact of the water on Ru-catalyzed olefin metathesis is examined. In a survey of normally facile metathesis reactions using state-of-the-art catalysts, even trace water (0.1% v/v) is found to be highly detrimental. The impact of water is shown to be greater at room temperature than previously established at 60 °C. Preliminary evidence strongly suggests that the mechanism by which water induces decomposition is temperature-dependent. Thus, at high temperature, decomposition of the metallacyclobutane intermediate appears to dominate, but this pathway is ruled out at ambient temperatures. Instead, water is proposed to promote bimolecular decomposition. Polyphenol resin, which can sequester water by H-bonding, is shown to offer an interim solution to the presence of trace water in organic media. These findings suggest that major avenues of investigation aimed at reducing intrinsic catalyst decomposition may likewise be relevant to the development of water-tolerant catalysts.
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Zhu, Zhaoxuan Zhu. "Control-oriented Modeling of Three-Way Catalyst Temperature via Projection-based Model Order Reduction." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1534271429299604.
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Jones, Simon Philip. "Influence of modifiers on Palladium based nanoparticles for room temperature formic acid decomposition." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:873277f2-c4f7-45b7-a16d-bba064e24bee.
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Heterogeneous catalysts form a highly important part of everyday life, ranging from the production of fertiliser enabling the growth of crops that sustain much of the world's population to the production of synthetic fuels. They constitute a key part of the chemical industry and contribute towards substantial economic and environmental benefits. Heterogeneous catalysts are also believed to have an important role to play in a future hydrogen economy, reducing our requirements for fossil fuels. To this end, formic acid has been proposed as a potential hydrogen storage material for small portable devices. Additionally, formic acid has historically been used as a probe molecule to study catalyst materials and recent developments in the knowledge of its decomposition pathways and the preferred sites of these reactions, establish a good foundation for further study. This work explores a range of novel modification techniques that alter the activity of Pd nanoparticles to decompose formic acid to H2 and CO2. The methods used are the addition of polymers, attaching various functional groups to the surface of the catalyst support and decoration of nanoparticles with sub-monolayer coverages of another metal. Using a range of characterisation methods including FTIR of an adsorbed CO probe, XRD and XPS coupled with computational modelling, it is found that these methods result in some significant electronic and/or geometric alterations to the Pd nanoparticles. For polymer modification, the nature of the pendent group is highly important in determining the effects of the polymer on the Pd particles, with all the tested polymers resulting in varying degrees of electronic donation to the Pd surface. The geometric modifications caused by the polymers also varied with pendent groups; with amine containing pendent groups found to selectively block low coordinate sites, preventing the undesired dehydration of formic acid which results in poisoning of the Pd catalyst by the resulting CO. Attachment of amine groups to the surface of metal oxide catalyst supports, is demonstrated to result in dramatic electronic promotional effects to the supported Pd nanoparticles, and when an amine polymer is attached to the support surface the geometric modification is again observed. Finally decoration of Pd nanoparticles with a sub-monolayer coverage of a second metal is examined, resulting in some similar electronic and geometric effects on Pd nanoparticle surfaces to those observed with polymer modification with corresponding changes in formic acid decomposition activity. Overall, a number of methods are displayed to tune the catalytic activity and selectivity of Pd nanoparticles for formic acid decomposition, resulting in catalysts with some of the highest reported TOF's at room temperature. These modification methods are believed to be potentially applicable to a wide range of other catalytic reactions that operate under mild conditions.
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Slosky, Lauren M. "Targeting the Cystine/Glutamate Antiporter System xc⁻ in Cancer-Induced Bone Pain." Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/594941.
Full textAbstract:
Many common cancers, including breast, prostate and lung cancers, have a propensity to metastasize to bone. Although these cancers go undetected in their native tissues, bone metastases often produce excruciating pain, the etiology of which is poorly understood. Cancer-induced bone pain (CIBP) is not well-controlled with existing medications, severely compromising patient quality of life. While CIBP is multifaceted, increased level of the excitatory neurotransmitter glutamate in the bone-tumor microenvironment may contribute to the pain state. Here, we demonstrate for the first time a relationship between reactive oxygen/nitrogen species, glutamate in the bone-tumor microenvironment and pain behaviors. The murine mammary adenocarcinoma cell line 66.1 is found to release glutamate via the cystine/glutamate antiporter system xc⁻. In a syngeneic model of breast CIBP in which 66.1 cells are inoculated into the femur intramedullary space, administration of sulfasalazine, an established system xc⁻ inhibitor and anti-inflammatory agent, reduces femur glutamate level and attenuates CIBP-related behaviors. Peroxynitrite, a reactive nitrogen species known to be generated in breast tumors, is shown to drive 66.1 system xc⁻ functional expression and tumor cell glutamate release. The elimination of peroxynitrite with the redox modulators FeTMPyP or SRI10 not only modulates tumor cell system xc⁻ functional expression in vitro and in vivo, significantly altering glutamate levels, but also assuages CIBP. In sum, we demonstrate that pharmacological inhibition of system xc⁻ transport attenuates CIBP-related behaviors. These data support a role for tumor-derived glutamate in CIBP and validate system xc⁻ an analgesic target in this pain state.
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Davis, John D. Jr. "Spectroscopic Examination of the Catalytic Decomposition of hydrogen Peroxide by a Copper (II) Complex of a Dissymmetric Schiff Base and an Imidazole Derivative." Digital Commons @ East Tennessee State University, 2003. https://dc.etsu.edu/etd/801.
Full textAbstract:
Previous studies involving copper (II) complexed with a dissymmetric Schiff base and imidazole derivatives had identified catalase activity of these complexes towards H2O2. Reactions such as this are of great interest due to the important role of copper-based complexes in biological systems. Our research has been conducted to add to the base of knowledge regarding the efforts of other researchers to investigate copper complexes that exhibit similar reactivity as copper-based proteins towards dioxygen. The copper complex chosen for this study contained a tri-dentate Schiff base adduct which, when complexed with an imidazole derivative, limited the manner in which peroxo adducts could bind while providing distinct spectral peaks which were used to conduct kinetic studies. Our results indicate a reaction mechanism by which the role of the complexed copper (II) ion is to activate the peroxo adduct for decomposition through reactions with other peroxide molecules, dioxygen, and water.
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Johar, Jasmeet Singh. "An experimental investigation of the urea-water decomposition and selective catalytic reduction (SCR) of nitric oxides with urea using V2O5-WO3-TiO2 catalyst." Texas A&M University, 2005. http://hdl.handle.net/1969.1/2595.
Full textAbstract:
Two flow reactor studies, using an electrically heated laminar flow reactor over
Vanadia based (V2O5-WO3/TiO2) honeycomb catalyst, were performed at 1 atm pressure
and various temperatures. The experiments were conducted using simulated exhaust gas
compositions for different exhaust gases. A quartz tube was used in order to establish
inert conditions inside the reactor. The experiments utilized a Fourier transform infrared
(FTIR) spectrometer in order to perform both qualitative and quantitative analysis of the
reaction products.
Urea-water solution decomposition was investigated over V2O5-WO3/TiO2 catalyst
over the entire SCR temperature range using the temperature controlled flow reactor.
The solution was preheated and then injected into pure nitrogen (N2) stream. The decomposition
experiments were conducted with a number of oxygen (O2) compositions (0,
1, 10, and 15%) over the temperature range of 227oC to 477oC. The study showed ammonia
(NH3), carbon-dioxide (CO2) and nitric oxide (NO) as the major products of decomposition
along with other products such as nitrous oxide (N2O) and nitrogen dioxide
(NO2).
The selective catalytic reduction (SCR) of nitric oxide (NO) with urea-water solution
over V2O5-WO3/TiO2 catalyst using a laboratory laminar-flow reactor was investigated.
Urea-water solution was injected at a temperature higher than the vaporization
temperature of water and the flow reactor temperature was varied from 127oC to 477oC.
A FTIR spectrometer was used to determine the concentrations of the product species. The major products of SCR reduction were NH3, NO and CO2 along with the presence
of other minor products NO2 and N2O. NO removal of up to 87% was observed.
The aim of the urea-water decomposition experiments was to study the decomposition
process as close to the SCR configuration as possible. The aim of the SCR experiments
was to delineate the effect of various parameters including reaction temperature
and O2 concentration on the reduction process. The SCR investigation showed that
changing parameter values significantly affected the NO removal, the residual NH3 concentration,
the temperature of the maximum NO reduction, and the temperature of complete
NH3 conversion. In the presence of O2, the reaction temperature for maximum NO
reduction was 377?C for ratio of 1.0.
20
Peyrovi, Mohammad-Hassan. "Etude de la destruction du coke et de ses précurseurs en presence d'hydrogène sur catalyseurs à base de platine." Poitiers, 1987. http://www.theses.fr/1987POIT2038.
Full textAbstract:
L'etude de la reaction et de la cinetique de decomposition du coke est realisee sur des catalyseurs bifonctionnels. L'influence de l'aire metallique ou d'addition de rhenium ou d'iridium sur la reaction de cokage est determinee. La formation, uniquement de methane, montre que l'elimination des precurseurs de coke est le resultat de l'hydrogenolyse
21
Machado, Taís Espíndola. "Decomposição catalítica do metano sobre catalisador Cu-Ni-Al : taxa da reação e regeneração do catalisador." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2007. http://hdl.handle.net/10183/10051.
Full textAbstract:
O hidrogênio é considerado uma fonte ideal de energia, pois sua combustão não gera contaminantes, apenas água. Dentre os processos disponíveis para produção de hidrogênio, destaca-se a decomposição catalítica do metano, pois, ao contrário do que ocorre na reforma a vapor e na oxidação parcial, nesta rota não há produção de CO. O objetivo deste trabalho é o estudo cinético e a determinação da taxa da reação de decomposição do metano sobre catalisador tipo óxido misto (Cu-Ni-Al) para obtenção de hidrogênio de alta pureza. O catalisador foi separado em quatro faixas de granulometria a fim de se determinar a influência da difusão interna à partícula na velocidade da reação, e o critério de Mears foi utilizado para avaliar o efeito da difusão externa. Os resultados obtidos mostram que, nas condições estudadas, os efeitos difusivos não influenciam significativamente a velocidade da reação. A seguir, a reação foi realizada sob diferentes temperaturas (500 a 600°C) e concentrações de metano (0,5 a 1,2 mol m-3), para determinação da equação da taxa. Observou-se que a reação é de primeira ordem, com uma energia de ativação de 50655 J mol-1. Além do hidrogênio, a reação forma carbono que se deposita na superfície do catalisador causando sua desativação. Os efeitos da regeneração do catalisador por oxidação deste carbono também foram investigados. Repetidos ciclos de reaçãoregeneração foram executados, sendo a regeneração realizada por oxidação do carbono com ar sintético ou por oxidação e redução. A oxidação foi conduzida a diferentes temperaturas (500 a 600°C) e intervalos de duração (20 a 75 min), com a reação ocorrendo em condições severas (600°C e 1,2 mol m-3 de metano). A melhor condição de regeneração, ou seja, aquela que permite um maior número de ciclos com baixa perda de atividade, foi determinada. Observou-se, também, que o carbono depositado apresenta a forma de nanotubos, os quais têm se tornado um dos campos mais ativos da nanociência e da nanotecnologia, devido a suas propriedades excepcionais. Os nanotubos de carbono formados durante a reação foram analisados, quanto a sua estrutura, por Microscopia Eletrônica de Varredura (MEV).Hydrogen is considered the ideal source of energy, because its combustion doesn't generate pollutants, just water. The catalytic decomposition of methane stands out among the available processes for hydrogen production because, unlike steam reform and partial oxidation, in this route there is not production of CO. The objective of this work is the kinetic study and the reaction rate determination of methane catalytic decomposition over Cu-Ni-Al catalyst for pure hydrogen production. In order to determinate the limiting step, reaction was conducted using four catalyst particle size ranges and the Mears criterion was applied. The external diffusion effects and diffusion in porous catalysts step do not influence significantly the reaction rate in the studied conditions. The reaction was carried out in a thermobalance with different temperatures (500 to 600°C) and methane concentrations (0.5 to 1.2 mol m-3) to determining the reaction rate. It was observed that the reaction is of first order, with activation energy of 50655 J mol-1. The reaction also forms carbon, which is deposited on the catalyst surface causing deactivation. The carbon oxidation for catalyst regeneration was also investigated. Repeated reaction-regeneration cycles were carried out, being the regeneration composed by oxidation or by oxidation and reduction. The oxidation was carried out at different temperatures (500 to 600°C) and times (20 to 75min), with the reaction happening in severe conditions (600°C and methane concentration of 1.2 mol m-3). The best regeneration condition, that is, the condition that allows a larger number of cycles with low activity loss, it was determined. It was also observed that the deposited carbon is in the nanotubes form, which has exceptional properties. The structure of carbon nanotubes formed during the reaction was analyzed by Scanning Electron Microscopy (SEM).
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Montagne, Xavier. "Caracterisation et reactivite des intermediaires reactionnels dans la decomposition du methanol a pression atmospherique." Paris 6, 1987. http://www.theses.fr/1987PA066020.
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Brunet, Sylvette. "Mode d'action des catalyseurs d'hydrodesazotation des coupes petrolieres : decomposition de quinoleines et d'anilines sur catalyseurs a base de sulfures de nickel et de molybdene." Poitiers, 1987. http://www.theses.fr/1987POIT2287.
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Pane, Flavia. "Kinetic analysis of Phenol Steam Reforming over Rh and Ni-Co based catalysts: identification of reaction’s pathway." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2022.
Find full textAbstract:
Great research efforts have been made during the last decades for the development and production of sustainable energy through renewable sources.Hydrogen has been considered a clean fuel and it can be produced from biomass,whose pyrolysis leads to the production of bio-oil that contains many components,which are the most renewable energy carriers.Phenol is the major component of the bio-oil and its catalytic steam reforming provides a promising technique for hydrogen production.The present work provides an extensive kinetic study of the mechanisms that occurs in the PSR,where the effect of temperature,space-time and partial pressure of the reactants(phenol and water)is investigated using two different catalysts over the same support.Due to the good metal-support interaction,Rh and Ni-Co active metals and γ-Al2O3 support have been selected and they were found to be appropriate catalysts with long-term stability for the hydrogen production via PSR,with Rh presenting the better performance in respect to transient metal-based catalysts.Identification of primary and secondary products revealed the reaction mechanism to be affected by the metal.On Rh, phenol is adsorbed with its aromatic ring in parallel with Rh,suggesting that the C-C bond activation is leading the reaction mechanism;on Ni-Co is observed the phenol dissociative adsorption producing phenoxyl and benzene species,suggesting the O-H and C-O bond activation happens first,followed by decomposition and reforming reactions.At lower temperatures,phenol dehydrogenation,dehydroxylation and decomposition were found to be the main reaction pathways,whereas at higher temperatures reforming and water gas shift reactions became enhanced.The excess of water was able to promote the WGS reaction.Time-on-stream studies at 500°C revealed Rh/γ-Al2O3 to have a good balance between stability,activity and selectivity.Oxidation of spent catalysts were also performed,in order to identify the type of carbonaceous deposits.
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SHIH, TUNG-PENG, and 石宗鵬. "Decomposition of Diisopropyl ether on CeO2/ZrO2 catalyst." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/82940275012654285977.
Full textAbstract:
碩士國立臺灣科技大學
化學工程系
97
In this study CeO2/ZrO2 catalysts were prepared by coprecipitation. The effects of Ce/Zr ratio and calcination temperature on catalyst activity were examined. The prepared catalysts were characterized by the use of XRD, N2-adsorption (BET), FTIR, TGA/DTA, NH3-TPD and ESCA. The activities of the catalysts were tested in a continuous flow micro reactor. The reaction was carried out at atmospheric pressure. The mass of the catalysts used in each reaction is fixed at 0.2 g. Diisopropyl ether (DIPE) is fed to the reactor accompanied by Ar as the balance gas. The Ar:DIPE mole ratio was fixed at 1:1.2 for each reaction. The product from the reactor were analyzed by a gas chromatograph and then using the data to calculated the conversion of DIPE and selectivity of isopropyl alcohol. The results showed that among the catalysts with Ce/Zr mole ratio of 1:9, 3:7 and 5:5 the 1:9 catalyst exhibited the highest activity. Between the catalysts calcined at 500℃ and 800℃. The 500℃ one displayed a higher DIPE conversion but lower IPA selectivity. The effects of reaction condition were investigated through the changes of reaction temperature, the introduction of water in the feed and the partial pressure of DIPE. For reaction between 140℃ and 190℃, low temperature resulted in low conversion and high selectivity. Incorporating water steam in the feed could yield a higher DIPE conversion but a lower product selectivity. Under a constant total pressure, decreasing the partial pressure of the reactant would decrease the DIPE conversion but increase the product selectivity. Severe deactivation of the catalysts was observed during the reaction. Carbon deposit was believed to be one of the causes for the deactivation. Comparing the catalyst calcined at 800 ℃ with that at 500 ℃, the former was more stable.
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Chen, Jia-Hao, and 陳家豪. "Decomposition of Naphthalene Using Catalyst in Gas Phase." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/21751905590970215028.
Full textAbstract:
碩士國立臺灣大學
環境工程學研究所
92
The purpose of this study is to investigate the feasibility of the application of the catalytic incineration using Pt/γ-Al2O3 to decompose polycyclic aromatic hydrocarbons (PAHs) (taking naphthalene which is the simplest and least toxic PAH, as a target compound) generated from the waste gaseous stream or diesel engine emission to atmosphere. The relationships between conversion efficiency, operating parameters and influential factors, such as treatment temperatures, catalyst sizes, space velocities and ozone inlet concentrations have been examined. Also, the related kinetic model is proposed to describe the reaction mechanism. The results indicate that the catalyst of Pt/γ-Al2O3 used accelerates the reaction rate of decomposition of naphthalene, and decreases the reaction temperature. A high conversion (over 95%) can be achieved at the moderate reaction temperature of 480 K and space velocity below 35,000 hr-1. At the same operation condition, the reaction temperature needed is as high as over 1000 K to achieve conversion over 95% for the case without Pt/γ-Al2O3 catalyst. Therefore, the reaction temperature is a determining factor in the catalytic decomposition. CO2 is the major product obtained from the catalytic decomposition of naphthalene. When the conversion of naphthalene is higher than 95%, over 92% mineralization can be achieved at the reaction temperature of 505 K. Also, the results indicate that Rideal-Eley mechanism and Arrhenius equation can be reasonably applied to describe the data by using the pseudo-fist-order reaction kinetic equation. The activation energy (35.4 kcal/mol) and frequency factor (3.26 × 1017 s-1) are obtained therefore.
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Khare, Prashant Yang Vigor. "Decomposition and ignition of han-based monopropellants by electrolysis." 2009. http://etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-3475/index.html.
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Chen, Mei-chun, and 陳玫君. "Perovskite-type oxides prepared as the catalyst for NO decomposition." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/91894568150296760160.
Full textAbstract:
碩士國立中央大學
環境工程研究所
100
Perovskite-type oxides including La2NiO4, LaSrNiO4, and La0.7Ce0.3SrNiO4 were prepared by the citric acid complexation and used as catalysts for direct decomposition of NO. Moreover, non-thermal plasma technology was applied after calcinations of La0.7Ce0.3SrNiO4. In this study, i.e., citric acid complexation (without plasma treatment), N2-plasma-treated, and air-plasma-treated catalysts were tested for NO decomposition to understand the effect of plasma treatment on the catalytic performance. The catalysts before and after plasma treatment were characterized, respectively, to discern the effects. The activities of La2NiO4, LaSrNiO4, and La0.7Ce0.3SrNiO4 for NO decomposition were tested and the results indicate that in the same experimental parameters, La0.7Ce0.3SrNiO4 catalyst is of the highest NO decomposition with Ar, with the efficiency up to 49.89%. The inlet NO concentration was controlled at 1000 ppm, and the reaction temperature ranged from 600℃ to 900 ℃, while the space velocity was fixed at 8,000h-1. The influences of oxygen content and water vapor content on NO decomposition were also explored. In the absence of O2, NO decomposition achieved is much higher as N2 is used as carrier gas compared with Ar. With 1% oxygen content in the gas stream, NO decomposition decreased slightly to 99.12% and 44.97%, respectively, as N2 and Ar are used as the carrier gases. The results indicate that the activation of catalyst was slightly suppressed with 1% O2 content. On the other hand, NO decomposition decreases rapidly as the oxygen content is increased to 3% and 6%. Non-thermal plasma is applied to modify the performance of perovskite-type oxides catalyst. The operating parameters are as following：gas flow rate is 1000 sccm, space velocity is 1241 h-1, the applied voltage is 16.5kV, and the discharge frequency is 100 Hz with either nitrogen or air as carieer gas. At 900℃, NO decomposition achieved with La0.7Ce0.3SrNiO4 catalyst before plasma treatment as N2 is used as carrier gas is much higher than that the catalyst after plasma treatment in the presence of 0% or 1% O2, however, as the oxygen content is increased to 3% and 6%, the La0.7Ce0.3SrNiO4 catalyst before plasma treatment activity is significantly decreased to 24.66% and 6.54%, respectively, as N2 is used as the carrier gas. The results lower than the La0.7Ce0.3SrNiO4 catalyst after plasma treatment with N2 as the carrier gas. As the oxygen content is increased to 3% and 6%, the N2-plasma-treatment catalyst activity is 36.45% and 17.81%, respectively, and air-plasma-treatment catalyst activity is 28.55% and 12.27%, respectively. The results indicate that the the catalysts after plasma treatment possess strong tolerance in the presence of 3% and 6% oxygen content.
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Lee, Chun-Yuan, and 李俊淵. "Cu-YDC/Al2O3 CATALYST FOR METHANOL STEAM REFORMING AND METHANOL DECOMPOSITION." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/69270731760382644352.
Full textAbstract:
碩士大同大學
化學工程研究所
88
The objective of this research was to investigate the catalyst applied in methanol steam reforming and methanol decomposition, such that methanol would react to form hydrogen and monoxide. This experiment was based on copper catalyst to investigate the effects of oxygen-ionic conducting material (Yttria doped Ceria, simple called YDC) addition onγ-Al2O3 and various methanol/steam ratio for methanol steam reforming and decomposition reaction. The characteristics of catalyst were detected by TPR to observe the composition and the Cu surface area and dispersion; XRD to identify the crystal phase and crystalline size of catalyst; BET to detect the total surface area and pore size. The reaction was carried out in fixed-bed reactor, with the addition of proper glass beads at designed temperature and ambient pressure. And the products were sent by the way on-line method into GC for analysis. BET surface area analysis showed that the total surface area of γ-Al2O3 would be decreased by the addition of metals such as Cu, Y and Ce, and that was due to blockage of partial small pores resulting in larger pores occurred and smaller BET surface area than γ-Al2O3 support. For methanol steam reforming reaction, the oxygen-ionic conducting (YDC) support showed more apparent improvement on activities, but worse in decomposition reaction by decreasing of Cu+ amount. Methanol decomposition reaction produce lots of methyl formate in lower temperature, and reaction produce lots of dimethyl ether in higher temperature by acid property of carrier Al2O3.
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(8774588), Spencer A. Fehlberg. "Decomposition of ammonium perchlorate encapsulated nanoscale and micron-scale catalyst particles." Thesis, 2020.
Find full textAbstract:
Iron oxide is the most common catalyst in solid rocket propellant. We have previously demonstrated increased performance of propellant by encapsulating iron oxide particles within ammonium perchlorate (AP), but only nanoscale particles were used, and encapsulation was only accomplished in fine AP (~20 microns in diameter). In this study, we extended the size of particle inclusions to micron-scale within the AP particles as well the particle sizes of the AP-encapsulated catalyst particles (100s of microns) using fractional crystallization techniques with the AP-encapsulated particles as nucleation sites for precipitation. Here we report catalyst particle inclusions of micron-scale, as well as nanoscale, within AP and present characterization of this encapsulation. Encapsulating micron-sized particles and growing these composite particles could pave the way for numerous possible applications. A study of the thermal degradation of these AP-encapsulated particles compared against a standard mixture of iron oxide and AP showed that AP-encapsulated micron-scale catalyst particles exhibited similar behavior to AP-encapsulated nanoscale particles. Using computed tomography, we found that catalyst particles were dispersed throughout the interior of coarse AP-encapsulated micron-scale catalyst particles and decomposition was induced within these particles around catalyst-rich regions.
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Yeh, Chun-hung, and 葉俊宏. "Cesium, Barium Promoted Ru/Carbon Catalyst for Hydrogenation from Ammonia Decomposition." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/18558955079317210629.
Full textAbstract:
碩士國立聯合大學
化學工程學系碩士班
98
The purpose of this research was to observe Ruthenium /Carbon (Ru/C) promoted with Cesium (Cs), Barium (Ba) single ion promoter and Cs with Ba double ions promoter for hydrogenation from ammonia decomposition. This research added 1mol~8mol Cs, Ba single ion promoter to Ru/C catalyst and prepared three different molar ratios (Ba: Cs: Ru=0.5:4.5:1, 1:4:1, and 3:2:1) of Ba-Cs-Ru/C catalyst for the ammonia decomposition experiment at reaction temperature of 300℃~450℃ and ammonia input rate of 3.0 ml/min, 7.5 ml/min. The results of the experiment with ammonia decomposition indicated the higher reaction temperature could get better ammonia conversion and hydrogen formation. The hydrogen formation could be enhanced by a high ammonia input rate but the ammonia conversion would be lower than the low ammonia input rate. A Cs-Ru/C catalyst with higher Cs ion molar ratio had a better ammonia conversion and hydrogen formation, but Ba-Ru/C with a higher Ba ion molar ratio (Ba: Ru > 1mol) had an opposite result. Compare with Ru/C catalyst, the hydrogen formation of Cs-Ru/C (Cs: Ru=4:1 molar ratio) catalyst increased by 38.06% at the reaction temperature of 350℃ and the ammonia input rate of 3.0 ml/min. At 450℃ and 7.5 ml/min, the hydrogen formation of Ba-Cs-Ru/C (Ba: Cs: Ru=1:4:1 molar ratio) increased by 3.77% than Cs-Ru/C (Cs: Ru=4:1 molar ratio) catalyst. Additionally, the cannelure-plate structure of the Ru/C catalyst with particle size of 100μm was observed from FE-SEM. A crystal structure of Ba promoted Ru/C (Ba: Ru=1:1 molar ratio) catalyst was observed from XRD. The addition of Cs ion promoter to Ru/C decreased the specific surface area obviously based on BET analysis.
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Hsieh, Cheng-Hsien, and 謝政憲. "Supported Pt catalyst for catalytic decomposition of formaldehyde at ambient temperature." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/11097122942773047787.
Full textAbstract:
碩士國立雲林科技大學
化學工程與材料工程系碩士班
100
Nowadays, people stay indoors longer and longer. Long-term exposure to indoor air containing volatile organic compounds may damage human health. An attempt was made to prepare platinum/titanium dioxide catalyst (Pt/TiO2) for the removal of formaldehyde at ambient temperature. This study was divided into two parts: The part one: we used the improved impregnation method and the chemical reduction method to prepare the catalysts with various Pt contents. Observing from XRD patterns and TEM images, Pt formed nanoparticles of ~1 nm in diameter and well dispersed deposited in the surface of the as-prepared catalysts. Because GC analysis was limited to low-concentration detection formaldehyde due to the sensitivity of a TCD detector, we changed to use the derivative method and HPLC analyses (measured at 360 nm) to quantify formaldehyde in this study. The experimental results showed that the conversion of formaldehyde could be near 100% for the 1.0-wt% Pt loading. The corresponding decomposition rate formaldehyde''s was 8.5784 mg/min．g cat. (GHSV = 49931.0 h-1). The part two: we used the functional silane to modify the 0.1wt% Pt/TiO2 and evaluated its activity. The experimental results showed that the conversion reached 25.6% while the ratio of catalyst and APTES was 1:1. The corresponding decomposition rate formaldehyde''s was 2.56 mg/min．g cat. (GHSV = 83000 h-1).
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Chang, Hong Yih, and 張弘毅. "The promoter effect on the decomposition reaction of acetophenone over Pd catalyst." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/82393292163536695806.
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Liou, Jia-Yi, and 劉加毅. "Decomposition of sick house gas by catalyst embedded in cellulose nanofiber film." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/08986110647512382234.
Full textAbstract:
碩士國立臺灣科技大學
化學工程系
103
In this work, we have successfully prepared the TEMPO-oxidized cellulose nanofiber (TOCNF). Platinum nanoparticles stabilized by an NH2-terminated fourth generation poly(amido amine) dendrimer (DEN(PtNP)s) were covalently immobilized on 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose nanofiber (TOCNF) by using a condensing agent for amide bond formation between TOCNF and DEN(PtNP)s. Subsequently, the films with different concentrations of DEN(PtNP)s were prepared by filtrating TOCNF/DEN(PtNP)s suspensions on filter membranes, and the dried films were characterized. As-prepared TOCNF/DEN(PtNP)s film possessed the high catalytic efficiency to decomposition of formaldehyde (HCHO). The detection of formaldehyde is based on the Hantzsch reaction. This reaction involves the cyclization of 2,4-pentanedione and the formation of 3,5-diacetyl-1,4-dihydrolutidine (DDL), which can be detected by UV-vis absorption spectra. The relationship between absorbance of DDL at 413 nm and concentration of formaldehyde were determined on calibration curve, which was followed Beer–Lambert law. The results indicate that the DEN(PtNP)s prepared at the mixing ratio of [Pt-precursor] : [NH2 group in dendrimer] = 0.5 : 1 was adequate. Then the Pt nanoparticles could decompose successfully the HCHO molecules.
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Yang, Chu-chun, and 楊筑鈞. "Optimize the non-precious metal catalyst for ammonia decomposition with Taguchi method." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/q7ugft.
Full textAbstract:
碩士國立臺北科技大學
資源工程研究所
107
The rare earth polishing powder usually contains 50% cerium oxide, 20% lanthanum oxide and other elements. A large amount of waste polishing powder was mostly treated by burial or incineration. If the lanthanum and cerium compounds in the wasted polishing powder could be recycled that will greatly reduce enterprise cost and implement waste circulation. Most of the catalysts for NH3 decomposition usually rely on copper-based catalysts. It has the advantages of low price, high catalytic ability, high stability and recyclability. Therefore, copper-based catalysts have become one of the materials intensively researched by industry and academia in recent years. In this study, we recycled the wasted glass polishing powder by acid-solution method, and mix different non-precious metal oxides to synthesize the catalysts with combustion synthesis method. Through Taguchi orthogonal array L18(21x37) planned the copper-based catalysis to add ten elements such as La, Sr, Co, Fe, Mg, Mn, Ni, Ce, Gd and Mo for NH3 decomposition. The catalysts effect of NH3 decomposition was detected by gas sensor. In result, the catalysts showed the average NH3 conversion and N2 selectivity. At 200℃, NH3 conversion and N2 selectivity was respectively at 73% and 97%. At 250℃, NH3 conversion and N2 selectivity was respectively at 77.8% and 67%. The NH3 conversion increased with the increase of reaction temperature. By the optimization analysis of Taguchi quality characteristics and change calcination time, it’s showed that the optimized catalyst of the NH3 conversion could rise to 84%, the N2 selectivity could rise to 99% at 200℃. At 250℃, the optimized catalyst of the NH3 conversion and N2 selectivity was respectively at 93% and 83%. Compared with the other sample in this study, the conversion and selectivity of optimized catalyst could be found the catalytic effect is more effective.
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Yeh, Chi-Wei, and 葉智偉. "Evaluation of PCDD/F Decomposition over SCR Catalyst and Activated Carbon-Supported Catalysts." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/10511364482298981699.
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碩士國立中央大學
環境工程研究所
93
SCR was mainly applied to removal of NOx as initially developed and now it has been used to abate dioxin emissions as well. Presently, abatement of dioxin using catalysis has become the mainstream technology. This study can be divided into two parts including field tests and pilot-scale system tests. The former focuses on sampling and investigating the control of dioxin emissions for existing SCR devices. The latter utilized several kinds of activated carbon-supported catalysts (Cu/C, Fe/C and Cu-Fe/C) to evaluate the feasibility of removing dioxins. Regarding the tests conducted in field, the results showed that removal efficiency of gas-phase dioxin achieved with SCR at metal smelting factory was 66% while that of PCDD and PCDF were 67.6% and 65.4%, respectively. For the MSWI, the SCR could remove 95% of gas-phase dioxin, in which 96% of PCDD and 97% of PCDF were removed. The surface area of the honeycomb-type V2O5/WO3/TiO2 catalyst (870m2/m3) adopted by MSWI is much higher than that of plate-type V2O5/WO3/TiO2 catalyst (320 m2/m3) utilized by metal smelting factory, resulting in the higher removal efficiency obtained in MSWI. The source of pilot-scale system sampling in metal smelting factory conducted the removal efficiencies achieved by utilizing Cu/C, Fe/C and Cu-Fe/C catalysts were as high as 95%. As for source of pilot-scale system sampling in the MSWI, the removal efficiencies achieved with Cu/C and Fe/C catalysts were more than 90%. In the metal smelting factory, the destruction efficiencies of three catalysts at 150℃ were about 20-30%. However, the destruction efficiencies obtained with Fe/C and Cu-Fe/C catalysts increased with increasing temperature. At 250℃, the destruction efficiency achieved with Fe/C catalyst was 78%. In the MSWI, the destruction efficiencies obtained with activated carbon-supported catalysts (Cu/C and Fe/C) were 30-40% when the temperature was kept at 150℃. For the Fe/C catalyst, the obtained destruction efficiency at 200℃ was 66%; however, once the temperature is increased to 250℃, the destruction efficiency was reduced to 57%. For the results of metal smelting factory, dioxin were generated through catalysis when the temperature of the Cu/C catalyst was 200℃ or 250℃ and that of the Cu-Fe/C catalyst was 250℃. In the MSWI, dioxin were generated through catalysis while the temperature of the Cu/C catalyst was 250℃. Compared with the results obtained with Cu/C and Fe/C catalysts in the metal smelting factory, it can be concluded that dioxin would be more easily produced when Cu/C catalyst is applied. Although the Cu-Fe/C contained Cu as well, no dioxin was generated at 200℃, which might be relevant to the Cu content and operating temperature.
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Li, Chia-Wen, and 李嘉文. "The effects of catalyst fillings on reactor performance for hydrogen production from ammonia decomposition." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/79631831706872076977.
Full textAbstract:
碩士國立聯合大學
機械工程學系碩士班
100
In this study, we investigate the effects of catalyst fillings on reactor performance for hydrogen production from ammonia decomposition. These different catalyst fillings ways are: (1) packed bed、(2) wall coated、(3) stainless steel mesh coated、(4)metal foam coated. The (1) and (2) are in common used. We propose (3) and (4) can easy to replace catalyst when it didn’t effect. We use the size is 10mm*6mm*2mm small flatbed reactor, 5wt%Ru/C is catalyst, CsNO3 is promoter, and sugar is adhesives. The ammonia decomposition temperature’s rage is 320~400oC. We also investigate the effects of carbonization temperature and Cs fillings for hydrogen production from ammonia decomposition. The results showed that the carbonization temperature for hydrogen production from ammonia decomposition is effect, and the best carbonization temperature is 800 oC. The results also showed that the decomposition efficiency of NH3 would increase with increasing the molar ratio of Cs/Ru when is 3.5 ratio, decreasing the flow rate of NH3 and increasing the temperature of reaction. If the Cs/Ru ratio is more than 3.5, the NH3 conversion would be low. It’s mean the Cs/Ru ratio have the best proportion. In addition, these four different ways on small flatbed reactor efficacy the best is packed bed, second is metal foam coated, next are wall coated and stainless steel mesh coated.
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Van, der Merwe Abraham Frederik. "Reaction kinetics of the iron-catalysed decomposition of SO3 / Abraham Frederik van der Merwe." Thesis, 2014. http://hdl.handle.net/10394/13491.
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In this study the performance of pure, very fine iron (III) oxide powder was investigated as catalyst for the decomposition of sulphur trioxide into sulphur dioxide and oxygen. This highly endothermic reaction requires a catalyst to lower the reaction temperature. This reaction forms part of the HyS (Hybrid Sulphur) cycle, a proposed thermochemical process for the industrial scale production of hydrogen and oxygen from water.
The study aimed at obtaining reaction kinetics for this reaction employing pure, unsupported iron (III) oxide as catalyst as a cheaper alternative compared to supported iron catalysts.
It was found that the SO3 conversion was carried out in the absence of diffusion limitations and that the reverse reaction did not play a significant role. By assuming plug flow conditions in the reactor and 1st order kinetics, the kinetic parameters of the reaction were obtained.
These parameters that form part of the Arrhenius law in describing the reaction rate constant, were determined to be 118(±23) kj / mol for the activation energy ( Ea ), and a value of 3(±0.5) x 108hr-1 was obtained for the Arrhenius frequency factor ( A ). Both values correspond to literature, although in general larger activation energies were published for iron (III) oxide derived supported catalysts.
A comparison of the performance of the pure, unsupported iron (III) oxide catalyst with other iron (III) oxide derived supported catalysts (or pellets) has shown that the pure iron (III) oxide catalyst exhibit similar activities. Avoiding expensive catalyst preparation will be an initial step in the direction of developing a cost effective catalyst for the decomposition of sulphur trioxide. It is, however, recommended to investigate different particle sizes as well as purity levels of the unsupported iron (III) oxide to find an optimum cost to performance ratio, as the degree of fineness and the degree of purity will largely influence the final catalyst cost.
A qualitative investigation with various reaction product species as well as water in the reactor feed was conducted to assess the influence of these species on the reaction rate. The addition of these species seems to have a larger influence on the reaction rate at low reaction temperatures around 700°C than at higher reaction temperatures (i.e. 750°C and 825°C). This can be attributed to adsorption rates of such species that reduce at higher temperatures. Observations at higher reaction temperatures also suggest that the reaction is of a first-order nature.MIng (Chemical Engineering), North-West University, Potchefstroom Campus, 2014
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You, Shih-Wei, and 游世暐. "Decomposition of Reactive Black 5 in Aqueous Solution by Ozone/H2O2 Process in the Presence of a Magnetic Catalyst." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/62970506797730188229.
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碩士國立宜蘭大學
環境工程學系碩士班
98
Particles are often too small to be separated from a reaction system and recycled, especially in wastewater treatment via a catalytic ozonation process. Thus, the objective of this study was to prepare a magnetic catalyst (SiO2/Fe3O4) that can be recycled by magnetic force. The effects of the characteristics of the magnetic catalyst, pH values, catalyst dosage, and initial concentration of Reactive Black 5 (RB5) on mineralization efficiency of the magnetic catalyst/H2O2/O3 process were also investigated. The mineralization efficiency of RB5 under various conditions followed the sequence: SiO2/Fe3O4/H2O2/O3 > SiO2/Fe3O4/O3 >Fe3O4/O3 ≈H2O2/O3 >O3 > SiO2/Fe3O4/H2O2. The recovery efficiency of the suspension SiO2/Fe3O4 by magnetic force was still > 90% for reuse. Given the results of our reuse and recovery experiments, the magnetic catalyst shows considerable promise for use in water treatment.
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Brandt, Björn [Verfasser]. "Selectivity in hydrocarbon conversions and methanol decomposition on a Pd-Fe3O4 model catalyst : a molecular beam study / von Björn Brandt." 2008. http://d-nb.info/992390052/34.
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Huang, Yu-Wen, and 黃昱文. "Synthesis of Magnetic Binary Metal Oxide Catalyst and Its Application on Wet Air Oxidation Process for Decomposition of 2,4-Diaminotoluene." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/80670677855610720893.
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碩士國立臺灣大學
環境工程學研究所
98
This study focuses on the synthesis of magnetic binary metal oxide catalyst (Pt/TiO2-ZrO2/SiO2/Fe3O4, Pt/T-ZSM) and the modified of magnetic catalyst (Pt/ZrO2/Fe3O4, Pt/ZM). These magnetic particles are used in the catalytic wet air oxidation process (CWAO) for the decomposition of 2,4-diaminotoluene (TDA). The performances for the treatment of TDA via WAO and CWAO systems are investigated. The characteristics of Pt/ZM and Pt/T-ZSM prepared in this work are with BET specific surface areas of 86.04 and 111.32 m2 g-1, saturation magnetizations of 13.14 and 6.08 emu g-1 respectively, contents of platinum on the catalyst surface of 2.59 and 1.75 wt.%, diameters of particles are smaller than 100 nm. Further, the superparamagnetic properties of these catalyst are still held after the use in CWAO process. In WAO system, the dominant operating parameter is temperature (T). The energy supply for the decomposition of contaminants increases with the increasing temperature. To ensure efficient oxidation, of course, the pressure of oxidant (PO2) should be sufficient for the reaction. After three hours reaction time (t) in WAO, as T = 523 K, PO2 = 1.38 MPa, stirring speed Nr = 500 rpm and initial concentration of TDA (CTDAo) = 500 mg L-1,the decomposition efficiency of TDA (ηTDA) and mineralization efficiency of TOC (ηTOC) are 99 and 75%, respectively. It shows that TDA is nearly decomposed at the condition of high temperature with enough oxidant. For the case with 0.5 g Pt/T-ZSM in CWAO, at the same conditions as above,ηTDA and ηTOC are 99 and 83%, respectively. In the same reaction conditions with 0.5 g Pt/ZM, ηTDA and ηTOC are 99 and 95%, respectively. Thus, as the magnetic catalysts are employed in the WAO system, the CWAO process can lower the activation energy of reaction, promoting the reaction rate and giving a higher ηTOC at the same reaction time. Comparing the performances per mass of Pt for the two catalysts, the ratio of values of ηTOC of Pt/T-ZSM to Pt/ZM is 1.29, indicating the oxidation ability of binary metal oxide catalysts Pt/T-ZSM is better than that of single metal oxide catalyst of Pt/ZM.
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Stander, Barend Frederik. "Evaluation of a catalytic fixed bed reactor for sulphur trioxide decomposition / Barend Frederik Stander." Thesis, 2014. http://hdl.handle.net/10394/13946.
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The world energy supply and demand, together with limited available resources have resulted in the need to develop alternative energy sources to ensure sustainable and expanding economies. Hydrogen is being considered a viable option with particular application to fuel cells. The Hybrid Sulphur cycle has been identified as a process to produce clean hydrogen (carbon free process) and can have economic benefits when coupled to nuclear reactors (High Temperature Gas Reactor) or solar heaters for the supply of the required process energy. The sulphur trioxide decomposition reactor producing sulphur dioxide for the electrolytic cells in a closed loop system has been examined, but it is clear that development with respect to a more durable active catalyst in a reactor operating under severe conditions needs to be investigated. A suitable sulphur trioxide reactor needs to operate at a high temperature with efficient heating in view of the endothermic reaction, and has to consist of special materials of construction to handle the very corrosive reactants and products. This investigation was undertaken to address (1) the synthesis, characterisation, reactivity and stability of a suitable catalyst (2), determination the reaction rate of the chosen catalyst with a suitable micro reactor (3) construction and evaluation of a packed bed reactor for the required reaction, and (4) the development and validation of a reactor model using computational fluid dynamics with associated chemical reactions.
A supported catalyst consisting of 0.5 wt% platinum and 0.5 wt% palladium on rutile (TiO2, titania) was prepared by the sintering of an anatase/rutile supported catalyst with the same noble metal composition, synthesized according to an incipient impregnation procedure using cylindrical porous pellets (±1.7 mm diameter and ±5 mm long). Characterization involving: surface area, porosity, metal composition, - dispersion, - particle size, support phase and sulphur content was carried out and it was found from reactivity determinations that the sintered catalyst, which was very different from the synthesized catalyst, had an acceptable activity and stability which was suitable for further evaluation.
A micro pellet reactor was constructed and operated and consisted of a small number of pellets (five) placed apart from each other in a two-stage quartz reactor with sulphur trioxide generated from sulphuric acid in the first stage and the conversion of sulphur trioxide in the second stage, respectively. Attention was only confined to the second stage involving the conversion of sulphur trioxide with the supported catalyst. The overall reaction kinetics of the pellets involving momentum, heat and mass transfer and chemical reaction was evaluated and validated with constants obtained from literature and with an unknown reaction rate equation for which constants were obtained by regression. As result of the complexity of the flow, mass and heat transfer fields in the micro pellet reactor it was necessary to use a CFD model with chemical reactions which was accomplished with a commercial code COMSOL MultiPhysics® 4.3b. A reversible reaction rate equation was used and a least squares regression procedure was used to evaluate the activation energy and pre-exponential factor. The activation energy obtained for the first order forward reaction was higher than values obtained from literature for a first order reaction rate (irreversible reaction) for the platinum group metals on titania catalysts. Detailed analyses of the velocity, temperature and concentration profile revealed the importance of using a complex model for determination of the reaction parameters.
A fixed bed reactor system consisting of a sulphuric acid vaporizer, a single reactor tube (1 m length, 25 mm OD) heated with a surrounding electrical furnace followed, by a series of condensers for the analysis of the products was constructed and operated. Three process variables were investigated, which included the inlet temperature, the weight hourly velocity and the residence time in order to assess the performance of the reactor and generate results for developing a model. The results obtained included the wall and reactor centreline temperature profiles together with average conversion. As a result of the complexity of the chemistry and the phases present containing the products from the reactor a detailed calculation was done using vapour/liquid equilibrium with the accompanying mass balance (Aspen-Plus®) to determine the distribution of sulphur trioxide, sulphur dioxide, oxygen and steam. A mass balance was successfully completed with analyses including SO2 with a GC, O2 with a paramagnetic cell analyser, acid/base titrations with sodium hydroxide, SO2 titrations with iodine and measurement of condensables (mass and volume). The results obtained showed that a steady state (constant conversion) was obtained after approximately six hours and that it was possible to obtain sulphur trioxide conversion approaching equilibrium conditions for bed lengths of 100 mm with very low weight hourly space velocities.
A heterogeneous 2D model consisting of the relevant continuity, momentum, heat transfer and mass transfer and the reaction rate equation determined in this investigation was developed and solved with the use of the commercial code COMSOL MultiPhysics® 4.3b with an appropriate mesh structure. The geometry of the packed bed (geometry) was accomplished by generating a randomly packed bed with a commercial package DigiPac™. The model predicted results that agreed with experimental results with conversions up to 56%, obtained over the following ranges: weight hourly space velocity equal to 15 h-1, temperatures between 903 K and 1053 K and residence times between 0.1 and 0.07 seconds. The post-processing results were most useful for assessing the effect of the controlling mechanisms and associated parameters.PhD (Chemical Engineering), North-West University, Potchefstroom Campus, 2014
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Saad, Sarra Ahmed Mohamed. "Processes and balance of organic matter turnover and transformation of mineral compounds during decomposition of biogenic material in the presence of soil material." Doctoral thesis, 2002. http://hdl.handle.net/11858/00-1735-0000-0006-AEC0-3.
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Ciura, Klaudia. "Nośnikowe katalizatory rozkładu $N_{2}O$ : nanospinel kobaltowy rozproszony na podłożach tlenkowych." Praca doktorska, 2020. https://ruj.uj.edu.pl/xmlui/handle/item/269529.
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Gudyka, Sylwia. "Opracowanie strukturalnego katalizatora do rozkładu $N_{2}O$ na podstawie funkcjonalnej korelacji : skład - morfologia - działanie." Praca doktorska, 2020. https://ruj.uj.edu.pl/xmlui/handle/item/276481.
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(5929820), Shourya Jain. "Burning Behaviors of Solid Propellants using Graphene-based Micro-structures: Experiments and Simulations." Thesis, 2018.
Find full textAbstract:
Enhancing the burn rates of solid propellants and energetics is a crucial step towards improving the performance of several solid propellant based micro-propulsion systems. In addition to increasing thrust, high burn rates also help simplify the propellant grain geometry and increase the volumetric loading of the rocket motor, which in turn reduces the overall size and weight. Thus, in this work, burn rate enhancement of solid propellants when coupled to highly conductive graphene-based micro-structures was studied using both experiments and molecular dynamic (MD) simulations.
The experiments were performed using three different types of graphene-structures i.e. graphite sheet (GS), graphene nano-pellets (GNPs) and graphene foam (GF), with nitrocellulose (NC) as the solid propellant.
For the NC-GS samples, propellant layers ranging from 25 µm to 170 µm were deposited on the top of a 20 µm thick graphite sheet. Self-propagating combustion waves were observed, with burn rate enhancements up to 3.3 times the bulk NC burn rate (0.7 cm/s). The burn rates were measured as a function of the ratio of fuel to graphite layer thickness and an optimum thickness ratio was found corresponding to the maximum enhancement. Moreover, the ratio of fuel to graphite layer thickness was also found to affect the period and amplitude of the combustion wave oscillations. Thus, to identify the important non-dimensional parameters that govern the burn rate enhancement and the oscillatory nature of the combustion waves, a numerical model using 1-D energy conservation equations along with simple first-order Arrhenius kinetics was also developed.
For the GNP-doped NC lms, propellant layers, 500 30 µm thick, were deposited on the top of a thermally insulating glass slide with the doping concentrations of GNPs being varied from 1-5% by mass. An optimum doping concentration of 3% was obtained for which the burn rate enhancement was 2.7 times. In addition, the effective thermal conductivities of GNP-doped NC lms were also measured experimentally using a steady state, controlled, heat flux method and a linear increase in the thermal conductivity value as a function of the doping concentration was obtained.
The third type of graphene structure used was the GF - synthesized using a chemical vapor deposition (CVD) technique. The effects of both the fuel loading ratio and GF density were studied. Similar to the GNPs, there existed an optimum fuel loading ratio that maximized the burn rates. However, as a function of the GF density, a monotonic decreasing trend in the burn rate was obtained. Overall, burn rate enhancement up to 7.6 times was observed, which was attributed to the GF's unique thermal properties resulting from its 3D interconnected network, high thermal conductivity, low thermal boundary resistance and low thermal mass. Moreover, the thermal conductivity of GF strut walls as a function of the GF density was also measured experimentally.
Then as a next step, the GF structures were functionalized with a transition metal oxide (MnO2). The use of GF-supported catalyst combined the physical eect of enhanced thermal transport due to the GF structure with the chemical effect of increased chemical reactivity (decomposition) due to the MnO2 catalyst, and thus, resulted in even further burn rate enhancements (up to 9 times). The burn rates as a function of both the NC-GF and MnO2-NC loadings were studied. An optimum MnO2-NC loading corresponding to the maximum burn rate was obtained for each NC-GF loading. In addition, thermogravimetric (TG) and differential scanning
calorimetry (DSC) analysis were also conducted to determine the effect of NC-GF and MnO2-NC loadings on the activation energy (E) and peak thermal decomposition (PTD) temperatures of the propellant NC.
In addition to the experimental work, molecular dynamics simulations were also conducted to investigate the thermal transport and the reactivity of these coupled solidpropellant/graphene-structures. A solid monopropellant, Pentaerythritol Tetranitrate (PETN), when coupled to highly conductive multi-walled carbon nanotubes (MWCNTs) was considered. The thickness of the PETN layer and the diameter of the MWCNTs were varied to determine the effect of PETN-MWCNT loading on the burn rates obtained. Burn rate enhancement up to 3 times was observed and an optimal PETN-MWCNT loading of 45% was obtained. The enhancement was attributed to the faster heat conduction in CNTs and to the layering of PETN molecules around the MWCNTs surface. Moreover, the CNTs remained unburned after the combustion process, conrming that these graphene-structures do not take part in the chemical reactions but act only as thermal conduits, transferring heat from the burned to the unburned portions of the fuel.
A long-pursued goal, which is also a grand challenge, in nanoscience and nanotechnology is to create nanoscale devices, machines and motors that can do useful work. However, loyal to the scaling law, combustion would be impossible at nanoscale because the heat loss would profoundly dominate the chemical reactions. Thus, in addition to the solid propellant work, a preliminary study was also conducted to understand as how does the heat transfer and combustion couple together at nano-scales.
First, an experimental study was performed to understand the feasibility of combustion at nano-scales for which a nano-scale combustion device called "nanobubbles" was designed. These nanobubbles were produced from short-time (< 2000 µs) water electrolysis by applying high-frequency alternating sign square voltage pulses (1-500 kHz), which resulted in H2 and O2 gas production above the same electrode. Moreover, a 10 nm thick Pt thermal sensor (based on resistance thermometry) was also fabricated underneath the combustion electrodes to measure the temperature changes obtained. A signicant amount of bubble production was seen up to 30 kHz but after that the bubble production decreased drastically, although the amount of faradaic current measured remained unchanged, signifying combustion. The temperature changes measured were also found to increase above this threshold frequency of 30 kHz.
Next, non-reactive molecular dynamic simulations were performed to determine as how does the surface tension of water surrounding the electrodes is affected by the presence of dissolved external gases, which would in turn help to predict the pressures inside nanobubbles. Knowing the bubble pressure is a perquisite towards understanding the combustion process. The surface tension of water was found to decrease with an increase in the supersaturation ratio (or an increase in the external gas concentration), thus, the internal pressure inside a nanobubble is much smaller than what would have been predicted using the planar-interface surface tension value of water. Once the pressure behavior as a function of external gas supersaturation was understood, then as a next step, reactive molecular dynamic simulations were performed to study the effects of surface-assisted dissociation of H2 and O2 gases and initial system pressure on the ignition and reaction kinetics of the H2/O2 system at nano-scales. A signicant amount of hydrogen peroxide (H2O2), 6-140 times water (H2O), was observed in the combustion products. This was attributed to the low temperature(~300 K) and high pressure (2-80 atm) conditions at which the chemical reactions were taking place. Moreover, the rate at which heat was being lost from the combustion chamber (nanobubble) was also compared to the rate at which heat was being released from the chemical reactions and only a slight rise in the reaction temperature was observed (~68 K), signifying that, at such small-scales, heat losses dominate.