Dissertations / Theses on the topic 'Hydrogen peroxide direct synthesis'

Hydrogen peroxide (H2O2) is a versatile environmentally friendly oxidizing agent that has many practical applications. H2O2 has countless qualities and it is one of the world’s most important bulk inorganic chemicals. Most of the world’s H2O2 is produced by auto-oxidation process (AO). The AO process involves indirect oxidation of H2 to yield H2O2. The first commercial anthraquinone (AQ) process was operated by I.G. Farbeinindustrie in Germany during the second world war. The AO process is successfully used to produce most of the world’s H2O2 because it avoids explosive H2/O2 gas mixture. However AO process suffers from several drawbacks, such as the use of a complex and toxic solvent system, the periodic replacement of costly quinone-derivative due to non-selective hydrogenation, the deactivation of the hydrogenation catalyst, high requirements of energy and intensive process steps for the removal of organic impurities. Also, it is known to have high capital and operating costs, thus it economically viable only for large scale productions (>4*104 tons per year). Therefore, H2O2 is produced in few locations and then transported to the customers. Transportation of H2O2 creates additional safety concerns since concentrated H2O2 can decompose explosively. A process where H2O2 forms from the direct combination of its elements (H2 and O2) could be preferred, especially for small scale productions at the end-user site, if control of the sequential hydrogenation can be achieved, but none of the presently available processes has solved the productivity vs. safety dilemma. Traditionally, the attention of the scientists focused on the identification of an active and particularly selective catalyst, overlooking the impact of safety and multiphase issues. Both aspects may benefit from continuous operations and suitable feeding policies, along with kinetics studies as we are currently investigating. Three reactor set-ups were developed and realized for hydrogen peroxide direct synthesis: two of them are based on batch reactors of different volumes to perform catalytic tests and kinetics studies, and one is based on a novel trickle bed reactor (TBR). Most of the work presented here is focused on the continuous reactor, far more attractive from an industrial perspective. In the TBR set up different catalysts were chosen to investigate H2O2 direct synthesis. A systematic study on operative conditions was performed, varying liquid and gas flow rates (contact time between liquid,gas and solid phases), changing H2/O2 ratio, investigating conditions for H2O2 decomposition and the effect of pressure. With this work very high values of selectivity were achieved (up to 90%), improving catalytic performances compared to those previously obtained in batch reactor set-ups. The best results were accomplished with a Pd and Au catalyst supported on sulfated zirconia. Despite an extensive body of research on the direct synthesis process, very little has been published about kinetic rate expressions of the full reaction network, and in this study experimental kinetics in a batch reactor and their relative modeling are treated for the first time.
Il perossido di idrogeno è un ossidante “verde” e non tossico, che non genera sottoprodotti inquinanti per l’ambiente, poiché si decompone a dare solamente acqua ed ossigeno. Il perossido di idrogeno viene utilizzato principalmente nelle cartiere come sbiancante, nell’industria tessile e metallurgica, come intermedio nella sintesi chimica, come disinfettante e additivo per detergenti, e molto altro. L’H2O2 viene attualmente prodotto con il processo dell’antrachinone, il quale necessita di numerose operazioni per la produzione e la purificazione del prodotto finale, con il conseguente elevato consumo energetico, a cui sono associati notevoli costi di esercizio, e la formazione di sottoprodotti inquinanti. La sintesi diretta di H2O2 è un’alternativa interessante, che si propone di eliminare i sottoprodotti inquinanti e ridurre drasticamente i costi di impianto e di esercizio, per produzioni su piccola scala direttamente in situ presso l’utilizzatore finale (che non è Berlusconi). In questo modo sarebbe possibile abbattere anche i costi di trasporto e i rischi ad esso connessi. Negli ultimi anni particolare attenzione è stata data al processo di sintesi diretta di acqua ossigenata, tuttavia i lavori pubblicati e brevettati vertevano per lo più sullo sviluppo di un catalizzatore che potesse avere delle caratteristiche tali da favorire la formazione di perossido di idrogeno a dispetto delle reazioni di decomposizione e idrogenazione dello stesso, anch’esse facenti parte del network di reazione. Scarso interesse è invece stato rivolto allo studio sistematico delle condizioni operative e allo sviluppo di un processo continuo. Ad esempio, lo studio in reattori batch non è stato mai approfondito con cinetiche di reazione e con lo studio degli equilibri liquido-vapore che si instaurano all’interno del sistema di reazione. In questo lavoro sono stati sviluppati e realizzati due reattori di tipo batch (di due volumi differenti) e un reattore in continuo: dei due reattori batch, uno è stato utilizzato per testare i catalizzatori e condurre studi preliminari, mentre nell’altro si sono svolti studi di cinetiche di reazione, che sono stati successivamente utilizzati per sviluppare un modello cinetico relativo all’intero network di reazioni. Il reattore continuo, invece, è un reattore a letto fisso (trickle bed reactor) in cui viene caricato il catalizzatore. Un notevole interesse dalle realtà industriali è rivolto all’operazione in continuo, per cui in questo progetto particolare attenzione è stata data allo sviluppo di un tale processo, ottimizzandone le condizioni operative per massimizzare la produzione di acqua ossigenata. Numerosi catalizzatori mono- e bi- metallici sono stati studiati, supportati su diversi materiali, sia inorganici che organici, e per ognuno di essi sono state studiate le migliori condizioni operative. Nel Capitolo 1 è presentato lo stato dell’arte della ricerca sulla sintesi diretta del perossido di idrogeno, e viene spiegato come la ricerca effettuata fin d’ora abbia posto l’attenzione sullo studio di un catalizzatore che potesse essere adatto alla sintesi diretta, trascurando però lo studio reattoristico del sistema impiegato. Nel Capitolo 2 è descritto lo sviluppo dei reattori in seguito utilizzati nella sperimentazione, ed i sistemi di analisi implementati. Vengono presentati gli schemi di impianto e gli studi preliminari condotti sia sui reattori batch, che sul reattore continuo. Il Capitolo 3 affronta temi di cinetica con la relativa modellazione. Sono stati condotti esperimenti di sintesi diretta in un reattore batch ad alta pressione, e da questi dati è stato ricavato un primo approccio di modello cinetico ancora assente in letteratura. Nel Capitolo 4 si è studiato un catalizzatore al palladio su un supporto di ceria sulfatata, con il quale sono stati condotti esperimenti di decomposizione e idrogenazione del perossido di idrogeno. Partendo da questi risultati si è svolto uno studio teso ad identificare le migliori portate di gas e di liquido per ottenere la massima produttività e la massima selettività. Un’altra condizione operativa indagata è stata la pressione ed il suo effetto sulla produzione di acqua ossigenata. Nel Capitolo 5 sono stati scelti 4 catalizzatori a base di palladio, supportati su diversi materiali inorganici. Variando le condizioni operative di sistema si è studiato il comportamento di questi catalizzatori in relazione alla produzione di H2O2 e alla loro selettività. I vari catalizzatori, a seconda del supporto, hanno proprietà differenti e le condizioni operative devono essere ottimizzate di conseguenza per ottenere il massimo rendimento sulla sintesi diretta. Il Capitolo 6 tratta lo studio di catalizzatori bimetallici a base di palladio e oro e catalizzatori a base di solo palladio. Diversi supporti inorganici sono stati utilizzati ed è stato introdotto un nuovo supporto organico. I catalizzatori sono stati confrontati tra di loro variando le condizioni operative di sistema. È stato inoltre studiato l’effetto della concentrazione di idrogeno immesso come reagente e il suo effetto sulla sintesi diretta di H2O2. Il Capitolo 7 riassume i migliori risultati ottenuti e fornisce indicazioni relativamente agli sviluppi futuri. In Appendice è fornito un approccio per la modellazione termodinamica del sistema.

The direct synthesis of hydrogen peroxide from hydrogen and oxygen over supported gold, palladium and gold palladium catalysts was studied in a high-pressure stirred autoclave containing a stabiliser-free solvent system. The rate of H2O2 synthesis for supported Au catalysts was found to be lower than that of the Pd only catalysts. However, carbon, titania, iron oxide and alumina supported Au-Pd catalysts are significantly more active and selective for H2O2 synthesis than the monometallic catalysts. For silica supported gold-palladium catalysts, the activity was found to scale directly with palladium content and no synergy was observed with gold-palladium catalysts. Gold-palladium catalysts prepared on iron oxide, alumina and titania were all found to form core-shell structures on calcination consisting of a gold core surrounded by a palladium shell. However, on silica and activated carbon the bimetallic catalysts formed homogenous alloys. The activity and selectivity of the catalyst was found to be highly dependant on the reaction conditions employed factors such as catalyst mass, solvent composition, catalyst composition and reaction length had significant effects on the catalyst activity. Modification of the support with a dilute acid prior to metal deposition led to gold-palladium catalysts with >98% selectivity to H2O2 when compared to catalysts prepared on the unmodified support. This increase in catalytic performance corresponded to an increase in metal particle size - indicating that smaller gold-palladium catalysts are highly active and selective for the direct synthesis of hydrogen peroxide. Acid pre-treatment of silica prior to metal deposition led to bimetallic catalysts where the activity did not scale with the palladium content.

In this thesis the direct synthesis of hydrogen peroxide from hydrogen and oxygen using gold-palladium supported catalysts is described. The direct route presents a greener and sustainable alternative to the current industrial manufacture process. This work aims to meet industrial requirements set by Solvay® which would make the direct process industrially viable. The drawback preventing the requirements being met is the reaction of hydrogen and oxygen over a catalyst can yield water as well as hydrogen peroxide. Once H2O2 is formed, it can be consumed by either reduction or decomposition. Thus, the rates of the subsequent reactions must be minimized to increase the selectivity and therefore H2O2 concentration to a desirable level. Aspects of the catalyst design and reaction variables have been studied over three results chapters. Firstly, the thermal treatment conditions have been altered, ultimately producing a catalyst with no activity to the H2O2 consumption under standard conditions. Switching off H2O2 hydrogenation was concluded to be due to an increase in Pd2+, isolating active Pd0 species. Secondly, active catalysts to both the synthesis and hydrogenation of H2O2 have been produced with no halide; the addition of halide has been shown to decrease hydrogenation activity while maintaining synthesis activity. Finally, a biphasic solvent system and a constant flow of gases through the reaction medium have been examined in order to produce higher H2O2 concentrations. In the former case H2O2 is extracted in-situ from an immiscible organic phase. The production of a 3 wt% H2O2 solution highlights the potential of such a system. In the latter case a semi-continuous flow reactor is utilised increasing the H2O2 concentration up to ca. 1 wt% (from ca. 0.2 wt%). The reactor allowed H2 selectivity and H2O concentration to be measured as a function of time, thus providing greater insight into catalyst activity.

The research presented in this thesis describes the direct synthesis of hydrogen peroxide from H2 and O2 using supported palladium based catalysts. The direct synthesis of hydrogen peroxide offers a more straightforward and sustainable alternative to the current industrial anthraquinone autoxidation (AO) process. Au-Pd bimetallic catalysts have been proved to be highly active for the direct synthesis process. The work presented in this thesis attempted to produce less expensive catalysts through adding cheap secondary metal to Pd as an effective substitute to Au or using an effective preparation for a low metal loading of Au-Pd nanoparticles. In addition, a comprehension of the actual active sites over bimetallic and Pd monometallic particles for H2O2 direct synthesis was also attempted. The first part of this work aims to explain an interesting phenomenon – an increase of activity for H2O2 direct synthesis and a decrease of hydrogenation of H2O2 over carbon supported Ni-Pd bimetallic and Pd only catalysts after both hydrogen peroxide synthesis and storage under ambient conditions. Based on the results of XPS, XRD and CO-chemisorption integrated with previous publications, it was concluded that (i) both the reaction of hydrogen peroxide direct synthesis and catalyst storage led to an decrease of particle dispersion; (ii) relative to the active sites on high energy surfaces/small particles of Pd (0), those on low energy surfaces/large particles are more selective for H2O2 synthesis, as the latter demonstrates lower activity of dissociative adsorption of O2 and H2O2. The role of secondary metal-Ni added to Pd was also investigated for H2O2 direct synthesis in the thesis. For carbon supported Ni/Pd catalysts (including Ni monometallic, Pd monometallic and Ni-Pd bimetallic catalysts), the addition of Ni to Pd enhanced catalytic activity and selectivity for H2O2 synthesis. The results of MP-AES, XPS, XRD and TPR implied that metallic Pd may sit on the top of Ni oxides with a dissolution of metallic Ni in Pd to some degree. Electron transfer from Ni to Pd probably also occurred which was inferred by XPS analysis. The role of Ni in Pd for H2O2 direct synthesis was Preface III also investigated over TiO2 supported catalysts which led to an enhancement of H2O2 productivity, H2 conversion rate and H2O2 selectivity relative to Pd only catalyst. Based on the results of XPS, TPR and STEM, it was concluded that inactive Ni species diluted Pd sites as individual Pd atoms which are the selective active sites for H2O2 direct formation. The next part of the study addressed a modified impregnation method (MIm) for the preparation of Au-Pd nanoparticles. These nanoparticles have been proved previously by STEM which are well dispersed homogeneous particles because of excess amount of Cl- ions in the preparation. As a consequence, the resulted catalyst demonstrated a superior activity than conventional impregnation method (CIm) analogues even the latter loaded with a quintuple metal loading. Through tuning Pd metal loading in 1 wt% Au-Pd and Pd only catalysts for H2O2 direct synthesis, two typical phenomena were observed in general: (i) an enhanced synergistic effect of Au and Pd by MIm than CIm and (ii) a rise of H2O2 productivity based on the mass of Pd loading with the addition of Au in 1 wt% Au-Pd MIm catalysts. As the possible formation of homogeneous Au-Pd alloy, an increase of H2O2 productivity based on Pd with the increase of Au content is probably out of the ensemble effect from the secondary metal.

In this thesis the direct synthesis of hydrogen peroxide (H2O2) from hydrogen and oxygen using gold-palladium supported catalysts was investigated. The direct route represents a greener and sustainable alternative to the current industrial manufacturing process. The main objective of this study was to achieve the industrial requirements of H2O2 yields and selectivity, which would make the direct process industrially viable. In order to reach the required target, two innovative approaches for the direct synthesis of H2O2 were examined. The first part of this thesis was dedicated to the development of a biphasic solvent system comprising an organic alcohol and water. The advantages of this system was highlighted and the effect of reaction variables (such as solvent composition, pressure, reagent ratio, temperature and reaction time) were evaluated using two different catalysts. The identification of two optimum conditions resulted in an important enhancement in the H2O2 yield for the two catalysts examined. By finely tuning the reaction conditions and using two different solvent systems ((i) decan-1-o1-water (ii) diisobutyl carbinol-water) H2O2 concentrations between ~ 0.30 and 28 wt. % were achieved. The second part of this thesis was dedicated to studying the direct gas phase synthesis of H2O2 in a continuous gas flow reactor. Two lab scale flow reactors were designed and built in situ: The first was for studying the direct gas phase synthesis of H2O2 at atmospheric pressure and the second for studying the reaction at pressures above atmospheric. The results demonstrate the direct gas phase synthesis of H2O2 was challenging and the absence of solvent seriously compromises the stability of the H2O2. Despite this, the results demonstrate by using gold-palladium nanoparticles and a mixture of hydrogen and oxygen it is possible to not only oxidise organic molecules in the gas phase but the synthesis rates were high enough to detect H2O2 as a product in a fixed bed gas phase reactor and a temporal analysis of products (TAP) reactor. This observation opens up the possibility of synthesising H2O2 directly in a gas phase reaction.

The direct synthesis of hydrogen peroxide from molecular hydrogen and oxygen represents an attractive atom efficient alternative to the current industrial auto-oxidation process which relies on the sequential oxidation and reduction of an anthraquinone. The first and most widely studied catalysts for this reaction were palladium based however over-hydrogenation of the synthesised hydrogen peroxide is a problem. Recent advances demonstrate that the addition of gold to the catalyst has been shown to significantly improve the productivity of the catalysts by suppressing the hydrogenation and decomposition activity. The work in this thesis shows that tin can be used as a catalyst additive as a direct replacement for gold by a simple impregnation method. By tuning the heat treatments of these bimetallic tin-palladium catalysts it was possible to switch off the competing hydrogenation and decomposition reactions. The construction of a small scale flow system has allowed the independent study of reaction variables and the determination of global kinetics and rate constants for the synthesis and subsequent reactions. It was shown that in a flow system it was the decomposition reaction that had a greater limiting effect on the production of hydrogen peroxide than the hydrogenation reaction. A study was also carried out into CO oxidation using gold / iron oxide catalyst prepared in Cardiff and by Prof. Haruta’s group in Tokyo. These catalysts underwent extensive tests to try and identify the active species of the catalyst. Detailed testing and STEM characterisation of the samples identified the possibility of different mechanisms operating at different temperatures and no correlation between the nanoparticle population and activity at sub ambient temperature could be made which challenges the hypothesis that nanoparticles are the most active species and that sub nanometer clusters may be the active species at low temperatures.

The research program developed during the Ph.D. School is focused on the study of metal catalysts supported on cross-linked functional polymers (CFPs) for the direct synthesis of hydrogen peroxide. In the last twenty years this compound has become a commodity with a constant increasing demand because of its strong oxidant properties and the formation of water as the reduction byproduct. In particular, H2O2 is widely employed as environmentally-friendly bleaching and cleaning agent. The best alternative to the current process, in particular for the small-scale production, is certainly the synthesis of H2O2 from the elements (direct synthesis). This is generally carried out with a heterogeneous catalyst under triphase condition. For safety reasons, the hydrogen-oxygen mixtures, according to the wide explosion range, are properly diluted with an inert gas, usually nitrogen or carbon dioxide. The catalyst is generally composed by one or more nanostructured noble metals, supported on an inorganic solid, carbon or organic materials. It is well known in literature that the presence in solution of additives, like halides (bromide and chloride) and mineral acids, dramatically improves the catalytic performances, in particular the selectivity towards H2O2. However, the use of these additives presents some process drawbacks, such as corrosion, leaching of catalyst, etc, which do not allow the straightforward use of the H2O2 solutions obtained from the direct synthesis. It is therefore mandatory a further step of purification to remove the additives. As a consequence, in order to evaluate the effective performance of the catalysts,the research activity during this PhD thesis aim at the investigation of catalytic systems free of selectivity enhancers. In particular, their presence has been avoided not only in the reaction mixture, but also during the preparation of the catalysts. In the frame of this PhD Thesis, a few sets of mono- and bimetallic catalysts, supported on the commercially available macroreticular resin, Laxness Lewatit K2621, have been studied in detail. This work has been performed in a research group with a long standing experience in the investigation of polymer-based metal catalysts for industrially relevant reactions and, for a few months, in the Laboratory of Industrial Chemistry and Reaction Engineering of Akademi Prof. Tapio Salmi (Department of Chemical Engineering, Process Chemistry Centre, Åbo Akademi University, Turku, Finland) for the detailed study of the catalysts performances. The research program is based on the synthesis, the characterisation and the investigation of the catalytic behaviour of the catalysts, obtained by carefully controlling a few essential parameters during the synthesis, such as the nature of the precursor, the reducing agent and the experimental conditions. These three key-points remarkably affect the features of metal nanoparticles (size distribution, difective structure, etc...) and, hence, the behaviour of the catalysts. In particular, the use of tetraaminepalladium (II) sulfate as the metal precursor and the reductive treatment with hydrogen under mild condition lead to a catalyst with noteworthy catalytic performances, specially a remarkable selectivity (70%). The investigation has also included four libraries of bimetallic materials, Au/Pd and Pt/Pd catalysts based on K2621, obtained as followed: - by keeping constant the content of palladium (1 wt.%) and changing the one of the second metal (0.1, 0.25, 0.5, 1 wt.% of Pt or Au); - by treating the material with two different reduction protocols (formaldehyde under reflux temperature and hydrogen (5 bar) under 60°C ). The catalytic results clearly show that the addition of platinum and gold to palladium improves the catalytic performances, although apparently with different mechanisms. The best catalysts are consistent with the empiric trends so far reported in literature. Finally a new class of mesoporous cross-linked polymers, featured by high surface area at the dry state, has been studied. This non-commercial polymer, quite promising as catalytic support, has been investigated in details and used for the preparation of palladium nanoparticles. This material, in view of its peculiar morphology, shows unique catalytic properties, exhibiting simultaneously a modest activity and a remarkable (70 – 80) and constant H2O2 selectivity: this unique features makes this catalyst a good candidate for a mechanistic study of the direct synthesis of hydrogen peroxide.
Il programma di ricerca sviluppato durante il triennio della Scuola di Dottorato si focalizza sullo studio di catalizzatori metallici supportati su polimeri reticolati funzionali per la sintesi diretta di perossido di idrogeno. Questa sostanza, diventata negli ultimi anni una commodity con un mercato in costante crescita, è massicciamente utilizzata come forte ossidante e, in particolare, come sbiancante , in quanto è compatibile con l'ambiente. Il processo di sintesi di H2O2 che in prospettiva può diventare alternativo all'attuale per produzioni su piccola scala è la sintesi a partire dagli elementi (sintesi diretta). Questa reazione viene normalmente condotta con un catalizzatore eterogeneo in condizioni trifasiche. Inoltre le miscele idrogeno-ossigeno vengono debitamente diluite con un gas inerte, a causa dell'ampio intervallo di esplosività dei due gas. Il catalizzatore è normalmente costituito da uno o più metalli nobili nanostrutturati, supportati su un solido inorganico, carbone o matrici organiche. È noto in letteratura che l'uso di additivi in soluzione, come alogenuri (bromuri e cloruri) e di acidi minerali, migliora drasticamente le prestazioni catalitiche, in particolare la selettività verso H2O2. Queste stesse sostanze sono però indesiderate, in quanto non consentono l'uso diretto della soluzione di H2O2 ottenuta, se non previa rimozione degli additivi e in aggiunta creano problemi dal punto di vista impiantistico (corrosione, leaching, ecc). L'intero studio è stato concepito con lo scopo di indagare i sistemi catalitici, in modo da evitare qualsiasi interferenza dovuta a questi additivi, evitandone quindi la presenza, non solo durante le prove catalitiche, ma anche in fase di sintesi, attraverso l'accurata scelta dei precursori metallici. In questo triennio, sono stati studiati alcuni materiali mono- e bimetallici supportati su una resina macroreticolare commerciale, Laxness Lewatit K2621. Il lavoro è stato svolto nell'ambito di un gruppo di ricerca già attivo da anni nello studio di catalizzatori metallici supportati su polimeri per reazioni di interesse industriale e per alcuni mesi presso i laboratori di ricerca del Prof. Tapio Salmi (Department of Chemical Engineering, Process Chemistry Centre, Laboratory of Industrial Chemistry and Reaction Engineering Åbo Akademi University, Turku, Finland) per la realizzazione delle prove catalitiche. L'indagine si è incentrata sulla sintesi, sulla caratterizzazione e sullo studio delle prestazioni catalitiche di materiali preparati variando alcuni importanti parametri di sintesi, quali il tipo di precursore, l'agente riducente e le condizioni sperimentali. Questi hanno una grande ripercussione sulle caratteristiche delle nanoparticelle metalliche (distribuzione dimensionale, difettività, ecc), le quali incidono a loro volta pesantemente sulle proprietà catalitiche. In particolar modo, l'uso di un complesso tetraamminico di palladio (II) e la riduzione in condizioni blande con idrogeno impartiscono al materiale notevoli proprietà catalitiche, caratterizzate da una rimarchevole selettività (70%), inedita in letteratura. Lo studio ha preso in considerazione anche quattro librerie di catalizzatori bimetallici Au/Pd a Pt/Pd supportate sulla stessa resina usata in precedenza, ottenute sia mantenendo fissa la quantità in peso di palladio e variando quella del secondo metallo, che utilizzando due distinti protocolli di riduzione. I risultati catalitici portano a supporre che platino e oro aumentino le prestazioni catalitiche con meccanismi tra loro molto differenti. Inoltre, la composizione dei migliori catalizzatori bimetallici preparati nell'ambito di questo lavoro di Tesi risulta in linea con le indagini fenomenologiche riportate in letteratura. Durante il periodo di dottorato, è stato preparato e studiato un polimero reticolato non commerciale ad elevata porosità e successivamente utilizzato come supporto per il catalizzatore. Il materiale risultante ha mostrato peculiari proprietà catalitiche esibisce una bassa conversione di idrogeno ma un'elevata selettività in H2O2 con valori nell'intervallo tra 70 e 80%. Queste caratteristiche lo pongono come un buon candidato per uno studio meccanicistico più approfondito della reazione.

I The research presented in this thesis describes the direct synthesis of hydrogen peroxide from H2 and O2 using supported gold-palladium based catalysts. The direct synthesis process offers a green and sustainable approach compared to the anthraquinone autoxidation (AO) process, which is currently used on an industrial scale to produce >95% H2O2 worldwide. The work presented in this thesis is an attempt to examine the direct synthesis process in terms of determining optimum catalyst compositions for potential scale-up in the near-future. The primary aim of this investigation is centred on catalyst design and characterisation. The first part of this work is a catalyst optimisation study for 2.5 wt% Au-2.5 wt% Pd/TiO2, and involved changing the amount of water used in the catalyst preparation, in this case wet impregnation. It was found that the addition of small amounts of water resulted in approximately 100% enhancement in activity for TiO2-supported catalysts but not for carbonsupported Au-Pd catalysts. The rate of Au/Pd uptake was contrasted and it was determined that the isoelectric point of the support was highly influential. While the activity can be enhanced for TiO2-supported catalysts, both catalyst nanostructure and stability were detrimentally affected by the addition of water during the impregnation step. The second part of this work is focussed on understanding the precise nature of the acid pre-treatment effect, where treatment of a carbon support in dilute nitric acid prior to the impregnation of Au and Pd precursors can result in the complete switching-off of sequential H2O2 hydrogenation activity over the catalyst. Characterisation and heat treatment studies gave an improved understanding of the relationship between Au/Pd and the carbon support. The next part of the study addresses the use of a colloidal immobilisation method to pre-fabricate Au-Pd ‘designer’ nanoparticles onto supports and is accompanied by extensive advanced aberration corrected electron microscopy studies. The effect of acid pre-treating silica based supports is then considered for catalysts prepared by wet-impregnation, specifically the fact that acid pre-treatment of silica is required to induce synergy between Au and Pd metals for the direct synthesis of hydrogen peroxide. The final part of this work considers the effect of introducing a third metal into the catalyst design, specifically the addition of Pt to Au/Pd compositions. An extensive catalyst screening study is undertaken for Au-Pd-Pt/CeO2 catalysts.

The research presented in this thesis focuses on the process of direct synthesis of hydrogen peroxide from molecular hydrogen and oxygen. This reaction potentially offers an approach which is greener and more sustainable when compared to the current industrial indirect auto-oxidation process. The work presented herein examines some of the key factors in determining the viability of the process in a water solvent at ambient temperature, conditions which would represent a very economically and environmentally attractive option, if feasible. The first part of this thesis investigates the ways in which changing reaction conditions affects the fundamental reaction processes of the direct synthesis reaction – synthesis of hydrogen peroxide and its subsequent degradation by decomposition and hydrogenation. It was found that moving to a water solvent and ambient temperature results in significantly lower yields and greater degradation comparative to previously used water/methanol solvents and 2°C reactions. The second part of this thesis explores the design of catalysts which are active for the direct synthesis of hydrogen peroxide while limiting degradation activity, to increase the yield in water at ambient temperature. A series of supported metal catalysts of the nominal formulation 0.5 wt. % Pd - 4.5 wt. % ‘base metal’ were prepared and treated with a cyclic oxidative-reductive-oxidative heat treatment. This produced highly stable catalysts with activity for the synthesis of hydrogen peroxide, but low to no activity for both decomposition and hydrogenation pathways. These catalysts also fulfilled a secondary aim of producing economically attractive catalysts due to the low loadings of precious metals used. The third and final part of this thesis studies the implementation of these highly selective catalysts in both gas and gas/liquid phase flow reactors. The production of hydrogen peroxide in a gas phase flow system is shown to be attainable although most likely not a commercially viable option. The direct synthesis of hydrogen peroxide in a gas/liquid flow system is shown to proceed with selectivities greater than those previously reported for different catalysts under similar conditions. Tests also show that hydrogen peroxide can be produced under ‘real world’ conditions of high flow rates, a hard water solvent and a dilute hydrogen in air gas mix. These studies could be used to inform future work on high throughput water cleaning technologies.

Hydrogen peroxide, which annual world production is estimated in 3.5 mil tons/year, is prevalently used in paper industry, chemical synthesis and textile industry. The use of the green oxidant H2O2 is strongly recommended because of the high content of active oxygen and the formation of water as the only oxidation by-product. However, H2O2 is rather expensive, and today its wide employment is unfortunately far. The reaction of direct synthesis of hydrogen peroxide is know from 1914 and it can be considered as a possible strategic solution to obtain in an economic way diluite hydrogen peroxide solution. The Research Group where I carry out this Thesis work has a long experience in the activation of molecular hydrogen and oxygen upon using size controlled metal nanoclusters supported on cross-linked functional polymers. These type of catalysts, were synthesized, characterized by TEM, EXAFS, a-XRD and tested in the direct synthesis of hydrogen peroxide. With Pd°/K2621 catalysts, yields greater than 50% (respect the limiting reagent H2) after 90 minutes were obtained. A very promising catalyst was obtain upon generation of Pd° nanoclusters inside Nafion Sac-13. The support is a super acidic commercial material, obtained by dispersion of the perfluorinated polymer Nafion (13% w/w) on silica. This catalyst showed in the direct synthesis of hydrogen peroxide a very high selectivity (higher than 90%), respect to the limiting reagent H2.

Hydrogen peroxide is a versatile oxidizing agent with several industrial applications. It is also one of “greenest”, since its oxidation by-product is only water. The global demand of the peroxide is increasing, due to its recent usage in new large scale oxidation processes, such as the epoxidation of propylene to propylene oxide and the synthesis of caprolactam. Nowadays most of the world production of H2O2 is carried out by the anthraquinone autoxidation process. Though very safe (H2 and O2 are never in direct contact), the costs related to the high energy consumption for the extraction and purification of the peroxide produced, together with the usage and periodic replacement of toxic and expensive solvents, stimulated the interest in new production paths. Among the several alternatives proposed, the most fascinating one is the direct synthesis (DS) from H2 and O2. It is a environmentally friendly process that would be economically profitable for an in-situ production, requiring lower investments and operating costs. During the last thirty years this system has been under intensive study both by industries as well as academia. However, it has not been commercialized yet, mainly because of poor selectivity and safety concerns. While most of the efforts on improving DS must address the catalyst, there are reaction engineering aspects that deserve attention. DS is frequently carried out in solvents other than water, both to improve H2 solubility and isolate the undesired product (H2O). Further, CO2 is used for safety, H2 solubility and H2O2 stability. However, the lack of information about the solubility of the reagents makes it difficult to develop a realistic kinetic description of the reactions involved in the DS process. Hence, the first step of the research presented herein dealt with solubility measurements, at temperatures in the range 268-288 K and pressures between 0.37 and 3.5 MPa. Measurements were focused on H2, i.e. the limiting reagent during the reaction. At all conditions investigated a linear relation between hydrogen partial pressure and concentration was observed. Increasing the temperature resulted in an enhanced H2 solubility at the same H2 partial pressure. At constant H2 fugacity, the presence of CO2 favored the dissolution of hydrogen in the liquid phase. Correlation and generalization of the measurements were provided through an EoS-based thermodynamic model for the estimation of H2 solubility at reaction conditions. A batch apparatus for the direct synthesis of hydrogen peroxide was developed, to carry out activity measurements on new catalysts and develop a quantitative model of the kinetics. Hydrogenation, disproportionation and direct synthesis reactions were studied on a commercial 5 wt.% Pd/C catalysts at temperatures in the range 258-313 K and pressure up to 2 MPa. Separate experiments were performed to highlight the role of each reaction. An enhanced H2O2 production was obtained adopting different H2 feeding policies, although selectivity did not exceeded 30%. A model of the gas bubbling, batch slurry reactor for H2O2 direct synthesis was developed. A sensitivity analysis on the mass transfer coefficients excluded any limitations occurring at experimental conditions. Comparable temperature dependence was observed for H2O production, hydrogenation and disproportionation (activation energies close to 45 kJ mol-1), while H2O2 synthesis had a much lower activation energy (close to 24 kJ mol-1), suggesting that a higher selectivity is achievable at low temperature. Disproportionation reaction had a very limited influence on the overall peroxide production rate, while hydrogenation was the most rapid side reaction. Water formation was significant, prevailing at higher temperatures. Following these results, Pd and PdAu catalysts supported on SBA15 were prepared and investigated for H2O2 direct synthesis. Catalysts were doped with bromine, a promoter in the H2O2 direct synthesis. Productivity and selectivity decreased when bromine was incorporated in the catalysts, suggesting a possible poisoning due to the grafting process. A synergetic effect between Pd and Au was observed both in presence and absence of bromopropylsilane grafting on the catalyst. Three modifiers of the SBA15 support (Al, CeO2 and Ti) were chosen to elucidate the influence of the surface properties on metal dispersion and catalytic performance. Higher productivity and selectivity were achieved incorporating Al into the SBA15 framework, whereas neither Ti nor CeO2 improved H2O2 yields. The enhanced performance observed for the PdAu/Al-SBA15 catalysts was attributed to the increased number of Brønsted acid sites. Supported catalysts were also synthesized depositing Pd on a highly acidic, macroporous PS-DVB resin (Lewtit K2621). Catalysts with active metal content in the range 0.3-5 wt.% were tested batchwise for the direct synthesis of H2O2. Preliminary H2O2 measurements and X-ray photoelectron spectroscopy (XPS) analysis revealed that the reduced form of Pd was more selective than PdO towards the peroxide. Transmission electron microscopy (TEM) images showed that smaller nanoclusters favored the production of H2O, likely due to their O-O bond breaking aptitude
Il perossido di idrogeno è un potente agente ossidante, molto usato nella pratica industriale. E’ uno dei meno tossici, dal momento che l’unico sottoprodotto della sua ossidazione è l’acqua. A livello mondiale, la domanda di H2O2 è in costante aumento, non da ultimo grazie a recenti usi in nuovi processi ossidativi, quali l’epossidazione del propilene e la sintesi del caprolattame. Attualmente l’acqua ossigenata viene prodotta quasi esclusivamente attraverso l’auto-ossidazione dell’antrachinone. Sebbene molto sicuro (non vi è mai contatto diretto tra idrogeno ed ossigeno), questo processo presenta alcuni svantaggi, quali ad esempio gli alti costi di esercizio, dovuti in particolare all’alta richiesta energetica per la separazione e la purificazione del perossido prodotto. Si tratta inoltre di un processo potenzialmente inquinante, in quanto fa uso di costosi solventi tossici, e dagli alti costi d’investimento, essendo economicamente vantaggioso solo per grandi produzioni (>4*104 tonnellate all’anno). Pertanto l’H2O2 è attualmente prodotta in pochi grandi impianti e trasferita per grandi distanze all’utente finale. Il trasporto aggiunge costi e rischi, in quanto soluzioni concentrate di H2O2 possono decomporre violentemente. Nelle ultime decadi vi è stato un notevole interesse nella ricerca di nuovi processi di produzione del perossido di idrogeno, che fossero contemporaneamente meno costosi ed inquinanti. Tra le varie alternative proposte, la più affascinante è sicuramente la sintesi diretta a partire da H2 ed O2. Si tratta di un processo “verde”, che si propone di eliminare i sottoprodotti inquinanti e, allo stesso tempo, ridurre i costi di produzione, rendendo economicamente vantaggiosa la produzione in situ presso l’utilizzatore finale. Nonostante il grande interesse sia industriale che accademico suscitato da tale processo negli ultimi trent’anni, a tutt’oggi non vi è nessuna applicazione industriale. Il motivo di ciò è da ricercarsi principalmente nei problemi di sicurezza e selettività che a tutt’ora restano irrisolti. La mancanza di informazioni sulla solubilità dei reagenti alle condizioni di reazione rende difficoltoso ottenere una descrizione cinetica precisa delle reazioni coinvolte nella sintesi diretta. Pertanto i primi passi della ricerca qui presentata sono stati mossi con l’obiettivo di raccogliere dati di solubilità alle condizioni di reazione (temperatura compresa tra i 268 e i 288 K e pressione tra 0.37 e 3.5 MPa). In particolare, si era interessati all’H2, in quanto reagente limitante del processo. A tutte le condizioni indagate, è stata riscontrata una relazione lineare tra la pressione parziale e la concentrazione di H2. Contrariamente a quanto normalmente avviene, l’incremento di temperatura ha avuto l’effetto di aumentare la solubilità nella fase liquida (a parità di pressione parziale). Inoltre, a parità di fugacità di H2, la presenza di CO2 ha favorito la concentrazione dell’H2 nel liquido. I risultati ottenuti sono stati generalizzati sviluppando un modello per stimare la solubilità dell’H2 alle condizioni di reazione. E’ stato poi realizzato un apparato batch per la sintesi diretta di acqua ossigenata. Un catalizzatore commerciale a base di Pd (5 wt.%) su carbone è stato utilizzato per studiare le reazioni di idrogenazioni, dismutazione e sintesi a temperature comprese tra 258 e 313 K e pressioni fino a 2.0 MPa. Il ruolo di ciascuna reazione è stato studiato attraverso esperimenti specifici. Appropriate politiche di alimentazione dell’H2 hanno permesso di realizzare un aumento di produzione rispetto a condizioni tipicamente batch. Tuttavia il catalizzatore testato ha rivelato limiti di selettività, non superando valori del 30% ca. Per studiare le cinetiche di reazione, è stato sviluppato un modello per il reattore batch. Un’analisi di sensitività sui coefficienti di trasporto di materia (sia dalla fase gassosa alla liquida che dalla liquida al catalizzatore) ha permesso di escludere ogni limitazione tra le fasi coinvolte nelle reazioni. Le reazioni indesiderate (formazione di H2O, dismutazione ed idrogenazione) hanno rivelato una simile dipendenza dalla temperatura (con un’energia di attivazione di circa 45 kJ mol-1). Una minore energia di attivazione è stata ottenuta per la reazione di sintesi diretta di H2O2 (24 kJ mol-1), il che suggerisce che la selettività è favorita alle basse temperature. Un confronto tra le velocità delle reazioni coinvolte ha permesso di identificare la dismutazione come la reazione più lenta di distruzione del perossido. Inoltre, la formazione di acqua era sempre significativa, compromettendo la selettività. A seguito di questi risultati, si è deciso di focalizzare l’attenzione sul catalizzatore. Catalizzatori mono e bi-metallici sono stati realizzati depositando Pd e PdAu su SBA15, una silice macroporosa e strutturata. Tali catalizzatori sono stati anche dopati con l’aggiunta di bromo, un noto promotore della reazione di sintesi diretta. Sia la selettività che la produttività sono diminuite modificando i catalizzatori con l’alogenio, probabilmente a causa di un avvelenamento durante la procedura di innesto del bromo. Una sinergia tra i metalli Pd e Au è stata osservata sia nei catalizzatori con e che senza bromo. Tre modifiche sono state apportate al miglior catalizzatore sviluppato (PdAu/SBA15) per evidenziare l’influenza delle proprietà superficiali sulla reazione di sintesi diretta. Tre modificatori sono stati incorporati nel supporto: Al, CeO2 e Ti. Un aumento sia di selettività che di produttività è stato riscontrato solo con l’aggiunta di Al. Tale risultato è stato attribuito al maggior numero di siti acidi di Brønsted riscontrati su questo catalizzatore. Un'altra famiglia di catalizzatori, con un contenuto di metallo attivo variabile tra lo 0.3 ed il 5 wt.%, è stata sintetizzata depositando del Pd su una resina acida e macroporosa, miscela di PS e DVB. I risultati preliminari dei test catalitici e delle analisi di spettroscopia fotoelettronica a raggi X (XPS) hanno rivelato che lo stato di ossidazione del palladio più selettivo verso il perossido è quello ridotto, mentre il PdO porta più facilmente alla formazione di H2O. Le immagini al microscopio elettronico a trasmissione (TEM) hanno mostrato che i nanocluster di Pd più piccoli portato alla formazione preferenziale di H2O, il che è probabilmente legato alla loro propensione alla rottura del legame O-O

The work presented within this thesis can be separated into two distinct parts. The first investigates the direct synthesis of hydrogen peroxide from molecular hydrogen and oxygen using gold-palladium supported catalysts and caesium exchanged tungstophosphoric acid as an acidic additive. The direct synthesis of H2O2 presents an environmentally friendly alternative to the current industrial, anthraquinone process. However for the direct route to be viable a variety of issues must be addressed. Primarily catalytic selectivity towards H2O2 is a major concern for the majority of catalysts active for H2O2 synthesis, with the degradation of H2O2 through hydrogenation or decomposition reported for a number of catalysts within the literature. The use of acid either during catalyst preparation or as part of the reaction solution has previously been shown to improve selectivity towards H2O2. Furthermore acidic supports, including heteropolyacid, have been observed to produce catalysts with greater selectivity than those with a higher isoelectric point and in turn provide higher yields of H2O2. This work investigates the ability of caesium exchanged heteropolyacids to improve catalytic activity towards H2O2 when used in addition to Au-Pd supported catalysts, in particular 2.5 wt. % Au - 2.5 wt. Pd/TiO2. The second part of this work is concerned with the ammoximation of cyclohexanone to cyclohexanone oxime via the in-situ formation of H2O2, in a one-pot style process. The conditions associated with ammoximation of cyclohexanone that is the presence of elevated temperatures and basic conditions, are considered extremely harsh for H2O2 stability. The in-situ generation of H2O2 during the ammoximation of cyclohexanone to cyclohexanone oxime would yield significant reductions in overall costs of the ammoximation reaction. Primarily these costs are associated with the purchasing, transport, storage and dilution of H2O2. This work determines the feasibility of a one-pot ammoximation process via in-situ H2O2 formation. Firstly, reaction conditions are established for this process and following this the role of catalyst design in improving selectivity towards cyclohexanone oxime as well as cyclohexanone conversion for this reaction is studied.

The aim of this study is the synthesis of hydrogen storage compounds by electrodeoxidation technique which offers an inexpensive and rapid route to synthesize compounds from oxide mixtures. Within the scope of this study, two hydrogen storage compounds, FeTi and Mg2Ni, are aimed to be produced by this technique. In the first part, effect of sintering conditions on synthesis of FeTi was studied. For this purpose, oxide pellets made out of Fe2O3-TiO2 powders were sintered at temperatures between 900 °
C &ndash
1300 °
C. Experiments showed that by sintering at 1100 °
C, Fe2TiO5 forms and particle size remains comparatively small, which improve the reducibility of the oxide pellet. Experimental studies showed that the reduction of MgO rich MgO-NiO oxide pellet to synthesize Mg2Ni occurs only at extreme deoxidation conditions. Pure MgO remains intact after deoxidation. In contrast to these, pure NiO and NiO rich MgO-NiO mixtures were deoxidized successfully to Ni and MgNi2, respectively. Conductivity measurements address the low conductivity of MgO-rich systems as one of the reasons behind those difficulties in reduction. In the last part, a study was carried out to elucidate the low reducibility of oxides. It is considered that the oxygen permeability becomes important when the reduction-induced volumetric change does not yield fragmentation into solid-state. The approach successfully explains why MgO particles could not be reduced at ordinary deoxidation conditions. The study addresses that Mg layer formed at the surface of MgO particles blocks the oxygen transport between MgO and electrolyte as Mg has low oxygen permeability.

The work in this thesis describes the synthesis and characterisation of direct and indirect hydrogen storage materials. The main experimental techniques used have been Powder X-ray Diffraction (PXD), Powder Neutron Diffraction (PND) and Temperature Programmed Desorption (TPD). The Magnesium ammines, Mg(NH3)6X2 (where X= Cl, Br, I) are interesting materials for use as an indirect H2 storage material (by the splitting of NH3) due to their high H2 gravimetric capacities. These ammines have been synthesised at room temperature through the reaction of the starting salt with NH3 and are cubic (Fm3m). TPD investigations have revealed that the ammines deammoniate in a three step process, with the chloride ammine possessing the most favourable deammoniation temperatures. Ex-situ PND has been used to refine the structure and in-situ PND has been employed to study the deammoniation processes in more detail. ‘H2 release’ systems have been examined as a potential solution for H2 storage. Mg(NH3)6Cl2 has been mixed with LiH or MgH2 at room temperature and studied using TPD with the LiH system the most encouraging in terms of the H2 release temperature. In-Situ PND has also been employed to understand the mechanism of H2 release. The Mg(OH)2 –LiH ‘H2 release’ system has also been studied using both bulk starting materials and microstructured materials. Microplates of Mg(OH)2 have been synthesised by a new MW (microwave) heating process in 6 mins. The employment of microstructured materials has reduced the onset reaction temperature from 147 oC in the bulk materials to 79oC when the starting materials are mixed for 10 mins.

Epoxy resins are thermosetting resins with excellent mechanical properties, high adhesiveness to many substrates, good thermal stability and chemical resistances, high tensile strength and modulus, and ease of handling and processability. Currently epoxy resins are very popular as fiber-reinforced materials, general-purpose adhesives, high-performance coatings, paints and encapsulating materials. During the last decades, demand for material systems with precise control over multiple properties has increased, as well as the necessity to find new sustainable processes for their manufactory. Thanks to a collaboration between the German company Rutgers and professor Raveendran of the University of Amsterdam, the work presented here was focused on a novel, environmentally friendly path for the achievement of epoxy functionalized poly-DCPD. Reaction of epoxidation of DCPD with hydrogen peroxide, catalyzed by various metal oxides, was studied and optimized in view of a future polymerization of the functionalized monomers. Direct epoxidation of poly-DCPD was also attempted.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

Vanadium haloperoxidases (VHPOs) are enzymes that catalyse the oxidation of halide ions to hypohalous acids by hydrogen peroxide. There are many unanswered questions on the mechanism by which the oxidation reaction occurs. In this work, is reported the synthesis of [VO(O2)H2EDTA], studies of the effect of acid concentration on the decomposition of [VO(O2)HEDTA]-2, and mechanistic studies of the rate law. The decomposition reaction was found to be first order with respect to acid concentration and also [VO(O2)HEDTA]-2 concentration. The reaction of [VOHEDTA]-1 and hydrogen peroxide progressed via a free radical path way. In addition, the vanadium(V) complex [VO(O2)H2EDTA] was synthesized and characterised by FT-IR, UV-VIS and GC-MS. The catalytic properties of [VO(O2)H2EDTA] were investigated for an oxibromination reaction. It was found that the catalysed, and the control reaction showed no major differences except for the fact that the reaction with the catalyst gave a dibrominated product without a carbonyl group.

This thesis describes the catalytic asymmetric epoxidation of olefins mediated by chiral iminum salts. The first chapter introduces some of the most novel and effective catalytic asymmetric methods for preparing chiral oxiranes. The second chapter is divided into three sections. The first section of chapter two is dedicated to our efforts to develop new aqueous oxidative conditions using both hydrogen peroxide and sodium hypochlorite as efficient, green oxidants that remove the temperature boundaries observed with the use of Oxone® as the stoichiometric oxidant. A wider range of available temperatures was examined allowing optimization of both oxidative systems. Ethereal hydrogen peroxide was observed to mediate asymmetric epoxidation within an acetonitrile monophasic co-solvent system giving enantioselectivities of up to 56%. When sodium hypochlorite was used in a biphasic solvent system in conjunction with dichloromethane; it was observed to mediate oxidation of the substrate alkenes in up to 71% ee. The second and third sections of chapter two are dedicated to our efforts to synthesize chiral iminium salts as catalysts for asymmetric epoxidation based on a biphenyl azepinium salt catalyst structure. From previous work within the Page group, the asymmetric synthesis and subsequent defined stereochemistry of a chiral carbon atom α to the iminium nitrogen atom was shown to have significant effect on the enantiocontrol of epoxidation using the iminium salt catalyst. Work was completed on biphenyl azepinium salt catalysts, inserting an alkyl or aryl Grignard reagent into the iminium bond using a pre-defined dioxane unit as a chiral auxiliary. Oxidation of the subsequent azepine gave a single diastereoisomerically pure azepinium salt. The methyl analogue of this sub-family of azepinium catalysts has been shown to give up to 81% ee for epoxidation of 1-phenylcyclohexene, furthermore, the binaphthalene azepinium salt with an additional methyl group was also synthesized and was shown to give up to 93% for epoxidation of 1-phenylcyclohexene. Continuation of the substitution α to the nitrogen atom gave rise to an interesting tetracyclic (biphenyl) azepinum salt catalyst. Construction of an asymmetric oxazolidine ring unit encapsulating the azepinium nitrogen and one of the methylene carbon atoms was achieved. In doing so two chiral centres α to the nitrogen atom were generated. The azepinium chiral carbon atom was populated by an addition methyl group with variation in the substitution on the oxazolidine chiral carbon atom. The benzyl analogue of this sub-family of tetracyclic azepinium catalysts has shown to give up to 79% ee for epoxidation 1-phenylcyclohexene. The third chapter is the experimental section and is dedicated to the methods of synthesis and characterization of the compounds mentioned in the previous chapter. X-ray reports regarding the crystallographic analysis of the structures presented in chapter two are provided in appendix A. Appendix B contains the analytical spectra for the determination of enantiomeric excess of the epoxides.

Iron-mediated oxidative cyclisation provides an efficient approach to pyrano[3,2-a]carbazole alkaloids. Thus, improved routes to girinimbine and murrayacine as well as the first total syntheses of O-methylmurrayamine A and 7-methoxymurrayacine are reported. Asymmetric epoxidation of girinimbine led to (−)-trans-dihydroxygirinimbine and the assignment of its absolute configuration
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich

Iron-mediated oxidative cyclisation provides an efficient approach to pyrano[3,2-a]carbazole alkaloids. Thus, improved routes to girinimbine and murrayacine as well as the first total syntheses of O-methylmurrayamine A and 7-methoxymurrayacine are reported. Asymmetric epoxidation of girinimbine led to (−)-trans-dihydroxygirinimbine and the assignment of its absolute configuration.
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

A tecnologia de células a combustível associada à crescente exigência de baixo impacto ambiental tornou-se bastante promissora no cenário mundial de energia. As células a combustível são, em princípio, dispositivos que convertem energia química diretamente em energia elétrica e térmica, possuindo, entretanto, uma operação contínua, graças à alimentação constante de um combustível. Particularmente, o negro de fumo Vulcan XC72 é usualmente empregado como suporte dos eletrocatalisadores, e alguns fatores como uma superfície acessível e área superficial suficientemente grande para uma máxima dispersão dos cristalitos dos eletrocatalisadores, além de tamanho dos poros, distribuição dos poros adequada e a presença de grupos funcionais na superfície do negro de fumo são considerados fundamentais para o desenvolvimento de materiais inovadores. Entretanto, o material denominado Vulcan XC72 ainda revela condições insuficientes para este fim. Este estudo consiste na preparação e caracterização físico-química de carbono funcionalizado por peróxido de hidrogênio e com cadeias poliméricas do tipo poliestireno sulfonado condutoras de prótons, visando sua posterior utilização como suporte de eletrocatalisadores para células a combustível tipo PEMFC e DMFC. Após a funcionalização do carbono, obteve-se uma melhora da dispersibilidade do negro de fumo em solução aquosa, efeito este benéfico para a preparação dos eletrocatalisadores. Observou-se também que os grupos funcionais e as cadeias poliméricas funcionaram como estabilizadores do crescimento dos cristalitos produzindo catalisadores mais homogêneos e com menor diâmetro médio dos cristalitos; e especialmente, no caso da funcionalização com cadeias poliméricas, obteve-se uma diminuição da queda ôhmica do sistema, referente à melhoria da transferência protônica.
The fuel cell technology associated with the growing exigency of low environmental impact energy became prosperous in the world energy scenery. The fuel cell is basically a device that converts directly the chemical energy of a fuel into electrical and thermal energy with a continuous operation by the constant feed of a fuel. Especially, the carbon black Vulcan XC72 is usually employed as an electrocatalyst support, and some factors as an accessible and high surface area in order to get maximum particles dispersion, pore size, adequate pore distribution and the presence of functional groups in the carbon black surface are considered fundamental characteristics for an innovative materials development. However, the Vulcan XC72 still reveals insufficient conditions for these purposes. This study consists in the preparation and in the physical chemical characterization of functionalized carbon black by hydrogen peroxide and by polymeric chains with proton conduction properties, and its posterior utilization as electrocatalyst support for PEMFC and DMFC application. After the carbon functionalization, an improvement in the carbon black dispersibility in water media was observed, a beneficial effect for electrocatalyst preparation. It was also observed, that the functional groups and the polymeric chains worked as stabilizers in the particle growing, producing much more homogeneous electrocatalysts, exhibiting smaller average particle size. Especially, in the case of polymeric chains functionalization, a decrease in the ohmic drop was observed for this system, attributed to an improvement in the proton transference.

Os desafios atuais no desenvolvimento de biossensores abrangem diversos aspectos, tais como a necessidade de se aperfeiçoar a interface de contato entre o substrato e o material biológico, a eficiência de transdução do sinal químico em um sinal mensurável, o tempo de resposta, a compatibilidade dos biossensores com matrizes biológicas e a integração de diferentes elementos de reconhecimento biológico em um único dispositivo, visando a detecção de distintos analitos. Nesse contexto, o desenvolvimento da nanociência tem criado recursos bastante atraentes para otimizar os aspectos descritos acima. O presente trabalho apresenta, portanto, estudos realizados para a construção de mediadores nanoestruturados que possam operar de maneira mais eficiente que os correspondentes materiais maciços (sistemas não-nanoestruturados). Em uma das abordagens utilizadas, um mediador híbrido de hexacianoferrato de cobre/polipirrol (CuHCNFe/Ppy) teve suas propriedades eletroquímicas aliadas às propriedades morfológicas e eletrônicas de um feltro revestido com nanotubos de carbono do tipo \"cup-stacked\" (feltro/NTCCS) para o desenvolvimento de um sensor de H2O2. O feltro/NTCCS é uma malha hidrofílica condutora que permite uma dispersão bastante uniforme do mediador híbrido. Essa característica, aliada ao aumento da área eletroativa e à interação eletrônica existente entre o CuHCNFe/PPy e os nanotubos de carbono criaram uma plataforma favorável para a construção de um biossensor de glicose. Em uma segunda estratégia, esferas de poliestireno com diâmetros de 300, 460, 600 e 800 nm foram utilizadas como molde para a formação de filmes de CuHCNFe/PPy macroporosos. Os distintos mediadores foram aplicados na detecção de H2O2 com o intuito de se correlacionar a importância do tamanho do poro com o desempenho analítico obtido. Diferentemente do esperado, os mediadores maciços e porosos apresentaram desempenhos analíticos bastante similares, o que levou a uma consideração das propriedades termodinâmicas de superfícies curvas, da molhabilidade de materiais porosos e da influência da cinética eletroquímica na utilização de sistemas porosos. Tais plataformas também foram aplicadas com sucesso na construção de biossensores de glicose e de colina. Por fim, foi possível sintetizar mediadores nanoestruturados através da imobilização de camadas de azul da Prússia e de CuHCNFe dentro das cavidades de filmes de TiO2 mesoporosos (13, 20 e 40 nm de diâmetro). Os resultados obtidos demonstraram a possibilidade de se modular o desempenho dos sensores de H2O2 em função do diâmetro dos poros e da quantidade de mediador imobilizado. A união dos resultados analíticos obtidos com os dados de microscopia eletrônica de varredura possibilitou observar a importância do efeito de confinamento no desempenho dos mediadores. Além disso, dados espectroscópicos na região do visível foram fundamentais para relacionar a presença de defeitos estruturais com a reatividade do material. No fim, tais plataformas foram utilizadas para a formulação de biossensores de colina.
Nowadays, the challenges in the development of biosensors cover various aspects such as the need to improve the interface between the substrate and the biological material, the efficiency of the chemical signal transduction in a measurable one, the response time, the compatibility with biological matrices and the integration of different biological recognition elements in a single device, in order to perform detections of different analytes. In this context, the development of nanoscience has created very attractive features to optimize the aspects described above. Consequently, the present work studies the build up of nanostructured transducers that can operate more efficiently than the corresponding bulk materials (systems non-nanostructured). In one of the approaches used, a hybrid transducer consisting of copper hexacyanoferrate/polypyrrole (CuHCNFe/Ppy) had its electrochemical properties combined with the morphological and electronic properties of a felt decorated with cup-stacked type carbon nanotubes (felt/CSCNT) for development of a H2O2 sensor. Felt/CSCNT is a hydrophilic conductive mesh that allows a uniform dispersion of the hybrid transducer. This feature, coupled with the improvement of electroactive surface and with the electronic interaction among the CuHCNFe/Ppy and carbon nanotubes have created a favorable platform for the construction of a glucose biosensor. In a second strategy, polystyrene spheres with diameters of 300, 460, 600 and 800 nm were used as templates for the formation of macroporous CuHCNFe/Ppy films. The transducers were used to detect H2O2 in order to correlate the importance of pore size with the obtained analytical performance. Unlike expected, porous and bulk transducers presented very similar analytical performances, which led to a consideration of the thermodynamic properties of curved surfaces, the wettability of porous materials and the influence of electrochemical kinetics during the use of porous systems. Such platforms have also been successfully applied in the preparation of glucose and choline biosensors. Finally, it was possible to synthesize nanostructured transducers through the immobilization of Prussian blue layers and CuHCNFe inside the cavities of mesoporous TiO2 films (pore diameters of 13, 20 and 40 nm). The obtained results demonstrated the possibility of modulating the performance of H2O2 sensors according to the pore diameter and the amount of immobilized transducer. The union of the obtained analytical results with scanning electron microscopy data showed the importance of confinement effect on the transducers performances. In addition, spectroscopic data in the visible region were essential to correlate the presence of structural defects with the material reactivity. In the end, these platforms were used for the formulation of choline biosensors.

My diploma thesis is focused on a comparison of direct-current and high frequency (15-80 kHz) electric discharge, which generates non-thermal plasma in water solution of sodium chloride. Mainly current-voltage and Lissajous charts are discussed in the first part of this thesis. These charts describe different discharge phases: electrolysis, bubble formation, discharge breakdown and discharge regular operation in a pin-hole of a dielectric barrier. Influence of frequency, electrolyte conductivity, thickness of the diaphragm (or length of the capillary) and pin-hole diameter on discharge breakdown and bubble generation was studied, too. Measurements were realized in a polycarbonate reactor with total volume of 110 ml, which was divided by a changeable polyacetal insulating wall. This wall divided the reactor into two approximately equal spaces with one stainless steel planar electrode in each part. The Shapal-MTM ceramic discs (thickness of 0.3–1.5 mm and diameter of the central pin-hole of 0.3-0.9 mm) were mounted in the centre of the insulating wall. Initial conductivity of sodium chloride solution was chosen within the interval of 100900 S/cm. The second part of my thesis compares an influence of the direct-current (DC) and high frequency (HF) power sources on physical solution properties (conductivity, pH and temperature) and generation of hydrogen peroxide. A plasma reactor with total volume of 4 l and with mixing set up was divided into two equal spaces with one planar platinum electrode in each part. Diaphragm with thickness of 0.6 mm and pin-hole diameter of 0.6 mm was installed in the middle of the separating wall. Experiment was held at discharge operation of 45 W for 40 minutes with both power sources. Detection of hydrogen peroxide was realised by using a titanium reagent forming a yellow complex, which was analysed by absorption spectroscopy. If HF discharge power is plotted as a function of applied frequency, exponential decrease of frequency with increasing power can be observed. Higher breakdown voltage is necessary for thicker dielectric barriers, on the other hand for bigger diameter of the pin-hole lower breakdown voltage and higher power is needed in DC as well as in HF regime. Breakdown voltage is decreased by the increasing conductivity in both regimes; due to more charge carriers in the higher conductivity lower breakdown voltage is needed. However frequency in HF regime and DC discharge power increases. HF discharge power is decreased by the increasing conductivity. Solution conductivity and temperature are increased by initial conductivity value in both discharge regimes. Solution pH drops to acidic conditions when HF or DC positive regime is applied due to the generation of reactive species and electrolysis (in DC regime). However solution becomes alkaline when DC negative regime is applied. Concentration of hydrogen peroxide is produced linearly when HF or DC negative regime is applied and it depends on initial solution conductivity.

博士
國立臺灣科技大學
化學工程系
107
Hydrogen peroxide (H2O2) is an important chemical for human life since it has been used in various industries. The global need for this chemical is increasing due to increased population and wealth. Therefore, the research topics associated with this material, especially regarding how to produce H2O2 by considering cost and environment issues, become important. Among all, the direct synthesis of hydrogen peroxide (DSHP) is proposed to replace the indirect one. In DSHP, the chosen catalyst plays the key role. Being able to understand the reaction mechanism is the key to improve the productivity and to design a better catalyst. In view of this, the dissertation concerns the study of alloy catalyst for DHSP and the development of novel theoretical approach in assessing the catalytic mechanism, as well as finding suitable catalysts. The thesis consists of four main topics. All topics have been done using computational approaches, and the results are referred to or validated by experimental results in previous literature. Firstly, DFT study reveals the geometric and electronic synergisms of palladium mercury alloy catalyst used for hydrogen peroxide formation. One of the main obstacles confronting the DSHP is how to maintain the unbroken O-O bonding of the intermediate species on the catalytic surface. To address this challenge Pd-Hg alloys have been used with initial reports suggesting their performance offers advantages when compared to monometallic Pd and Pd-Au alloys; however, the interactions of O2 with Pd-Hg alloys are not well characterized. In this study, density functional theory (DFT) calculations, employed to investigate O2 adsorption on the Pd and Pd-Hg alloy surfaces, suggested O2 adsorption can occur via either a superoxo or a peroxo pathway and that when Hg is alloyed to Pd there are more adsorbed superoxo groups compared to adsorption on a monometallic Pd surface. The Hg in Pd6Hg3/Pd(111) results in an electronic surface structure different to that of Pd(111) and a reduced O2 adsorption energy. The stronger O2 surface interactions, when combined with weaker O-O bonding (of the adsorbed O2), which result from the presence of Hg on the Pd-Hg surface leads to synergistic geometric and electronic effects that result in an increased selectivity during of the synthesis of H2O2. Secondly, descriptor study by density functional theory analysis for the direct synthesis of hydrogen peroxide using palladium–gold and palladium–mercury alloy catalysts. It is well-known that the chosen catalyst used in DSHP affects the productivity of DSHP. Pd-based catalysts with various compositions of transition metal (TM) alloys have been often considered for the direct synthesis of H2O2. In particular, PdAu and PdHg alloys are known catalysts for their good catalytic activity. However, finding a suitable catalyst with designed composition is not easy, and fundamental understanding of the mechanism behind the enhanced activity is often lacking. To facilitate the quest, descriptor sets are proposed based on Density Functional Theory to represent the whole reaction steps on Pd, PdAu and PdHg surfaces in direct H2O2 synthesis. By considering surface electronic effect caused by surface alloying compositions, descriptor sets consisting of the adsorption energy for the reaction intermediate such as O2, O and OOH and activation energy barriers are derived from elementary reaction steps. The geometric factors of adsorbed species are also considered, though they are found less prominent. The adsorption energy of O2 versus O (Eb.O2/O) is performed to determine that the presence of surface adsorbed O2* is seen as the required intermediate species to form desired product. The selectivity is assessed by comparing the adsorption energy of OOH versus O (Eb.OOH/O). Considering main thermodynamic and kinetic characteristics, the results show that PdHg alloy with the surface composition in the atomic ratio of 6:3 (namely 2:1) gives the best selectivity among others. Based on the results of the descriptor analysis, it is suggested that the alloyed Pd surface with less active metals, such as Hg and Au, can be the key to designing catalysts for better catalytic activity and selectivity. Thirdly, descriptor study by density functional theory analysis for the direct synthesis of hydrogen peroxide using palladium–base core-shell catalyst. This study is intended to expand the descriptor use found in the second approach. The calculated model M6@Pd32 has truncated octahedron (TO) structure, where M can be Pd, Ag, Cd, Pt, Au, Hg, Ni, Cu, or Zn. In this work, the structure of the model has been proven to be the most stable of the other structures with 38 atoms core-shell model. Based on this work, a selectivity descriptor is the comparison of the adsorption energy of OOH with O (Eb.OOH/O) on the various core M on M6@Pd32. The higher catalyst selectivity indicates the higher OOH adsorption and the lower O adsorption energy. The selectivity of the catalyst is confirmed using the reaction rate which is a comparison of adsorption energy of O2 versus O (Eb.O2/O). By calculating the adsorption energy of OOH, O2, and O on M6@Pd32, the catalyst selectivity can be determined. Based on the calculation, the Ni6@Pd32 and Zn6@Pd32 showed the good selectivity catalyst for DSHP. I also introduce the catalyst selectivity related to the flexibility, while the stability connected to the surface distortion. Surface flexibility and distortion represent the geometric descriptors which calculated based on the root mean square dislocation (RMSD) of the adsorbed O-catalyst structure. The result showed that the Ni6@Pd32 catalyst is more stable than Zn6@Pd32 for direct synthesis of hydrogen peroxide. The overall study with 38 atoms core-shell configuration shows that Ni@Pd outperforms other catalysts. Fourthly, a study of the high spin Ni role in the core-shell PdNi@Pd(111) catalyst for the DSHP by DFT. Based on my previous work, the O adsorption energy has the same trend with the O2 adsorption energy in DSHP mechanism on the various surfaces. By investigating the adsorbed O on the surface of Pd(111), Pd3Ni@Pd(111), PdNi@Pd(111), and PdNi3@Pd(111) using DFT approach, the trend of adsorption energy of O (Eb.O) has been captured based on the varied Ni composition. Once the trend of O adsorption energy (Eb.O) has been known, the O2 adsorption energy also can be predicted. The presence of Ni on the Pd(111) lowering the O adsorption energy (Eb.O) compared with that on Pd(111). The higher composition Ni leads to the lower Eb.O. The varied composition Ni affects the geometrical structure of the core-shell, even when the ratio of Pd:Ni is 1:1, the structure is able to (or will) change from fcc to fct. The surfaces of Pd3Ni@Pd(111) and PdNi@Pd(111) lowered 14% of Eb.O on Pd(111). The lower Eb.O, the lower Eb.O2. The result indicated the reason of why the core-shell Ni@Pd can be better catalyst than Pd(111) for DSHP. However, Eb.O is the weakest on the PdNi3@Pd(111) which is possible to release the adsorbed O2 to the gas state. The density of state (DOS) is investigated to study the electronic effect, while the lattice change of varied Ni composition is calculated for investigating the geometry effect. From the comparison of d-band center versus Eb.O and lattice distance versus Eb.O on varied Ni composition, both electronic and geometric effect showed the linear effect to the Eb.O. However, the electronic effect which is represented by DOS showed the more sensitive factor to the Eb.O change. By this work, the wet experiment activity is offered to realize the catalyst finding such as PdNi alloy used for DSHP.

Este trabalho consiste no estudo de um catalisador novel para a síntese electroquímica de peróxido de hidrogénio, adequado para o uso de uma célula de combustível de membrana trocadora de protões (PEM). Métodos de caracterização electroquímicos (numa célula de três eléctrodos) e a actual tecnologia PEM bem como os materiais necessários para as mesmas foram utilizados. O conhecido catalisador de platina foi analisado e usado como referência. Os métodos de caracterização electroquímicos usados foram a voltametria cíclica (para caracterização da superfície do metal), o eléctrodo rotativo de disco - RDE (para calcular a actividade do catalisador, as correntes limite associadas à cinética da reacção, o número de electrões trocados, etc.) e o eléctrodo rotativo de disco e anel - RRDE (para quantificar a densidade de corrente relativa à produção de peróxido de hidrogénio). A tecnologia PEM foi igualmente usada para a caracterização electroquímica. Alguns dos factores interferentes na concentração de peróxido de hidrogénio produzido foram estudados. Por exemplo, a dependência da temperatura dos humidificadores, da pressão e do gás reagente usado no cátodo (ar ou oxigénio). Curvas de polarização foram determinadas e usadas para determinar a densidade de corrente obtida na célula de combustível, a resistência da membrana e outros parâmetros relacionados. Durante a mesma, o peróxido de hidrogénio foi recolhido e analisado. A sua quantificação foi feita por análise volumétrica. A eficácia do catalisador foi calculada. Estes estudos revelaram que o catalisador patenteado representa uma melhoria significativa para a produção de peróxido de hidrogénio. A produção do mesmo por via da tecnologia PEM verificou-se possível

碩士
國立成功大學
航空太空工程學系碩博士班
101
Subject：Metal Foams as Flow Field in Direct Sodium Borohydride-Hydrogen Peroxide Fuel Cell Student：Jain-Ming Chen Advisor：Chin-Hsiang Cheng(chcheng@mail.ncku.edu.tw) Chih-Yung Wen(chihyung.wen@polyu.edu.hk) The main purpose of this study is to investigate the metal foams as a flow passage in the direct sodium borohydride – hydrogen peroxide fuel cell (DBFC) based on the pressure drop and the performance of the single cell. First, the measurement of the pressure drop of different flow channels was performed. Second, we set the experimental parametric values for the different flow channels and different concentrations of borohydride in anode, and tried to find the best performance of a single cell. The result reveals that the performance is improved by using the metal foam as the flow passage. The performance of metal foams are better than that for the serpentine one. In the study of the effect of different sizes of metal foams, it is found that a larger pore size results in a lower pressure drop because of less resistance moreover. A smaller pore size results in a uniform flow distribution in the reaction area. In the study of the effect of metal foams coated with /without PTFE, a larger pore size is appropriate for coating PTFE on metal foam. It can enhance the removal of the hydrogen production and produce the uniform flow distribution in the reaction area. A smaller pore size is not appropriate for this way. It will greatly reduce the average of pore size after coating PTFE. Experimental result indicated that the maximum power achieved 18 W respectively.

碩士
國立成功大學
化學工程學系碩博士班
96
The first part of the the dissertation is on the characterization of the nanocomposite comprising gold nanoparticles and polyaniline nanofibers. Au nanoparticles were generated along with the simultaneous formation of polyaniline（PANI）nanofibers using interfacial polymerization route. Scanning electron microscopic（SEM）revealed that PANI possesses nanofiber structure. The nanofiber structure of PANI acts as not only reducing agent but also matrix to prevent the aggregation of gold nanoparticles. Transmission electron microscopic（TEM）results revealed that particle size of gold nanoparticles is at ca. 10-30 nm which is consistent with the result from the calculation by x-ray diffraction pattern （XRD）. X-ray photoelectron spectroscopy（XPS）and Fourier transform infrared spectroscopy（FTIR）results showed that there were more side products and higher oxidized states for the nanocomposite synthesized by using HAuCl4 as oxidant. On the second part of the dissertation, we extended our work to study the electrochemical sensing properties of the prepared nanocomposite for hydrogen peroxide. The nanocomposite comprising gold nanoparticles and PANI nanofibers possess the sensing ability for hydrogen peroxide. Furthermore, the optimal operation of the nanocomposite for sensing hydrogen peroxide is at pH 7.5. The hydrogen peroxide sensor shows a linear calibration curve over the range from 2.5×10-7 to 2×10-3 M, with a slope and detection limit（S/N=3）of 9.53 μA/mM and 2.5×10-7 M, respectively. In addition, the hydrogen peroxide sensor possesses a fast response time（6 sec）for sensing hydrogen peroxide.

碩士
淡江大學
化學學系碩士班
102
In current study, a cobalt oxide based uric acid biosensor is fabricated through a drop coating of glutaraldehyde, and uricase onto a BSA coated Co3O4 based rotating disc graphite electrode (RGDE). Uric acid is measured via an uricase based Co3O4 modified biosensor cathodicly. The amperometric signal of this sensor is measured based on the uricase converts uric acid into hydrogen peroxide and reduces by Co3O4. The homemade cobalt oxide fabricated by hydrothermal synthesis is better than the commercial one. Qualitative analysis and morphology of cobalt oxide was characterized by High resolution X-ray diffractmeter (HRXRD) and scanning electron microscopic (SEM). The results show that homemade cobalt oxide is Co3O4 and exhibits rectangular sheets with pore and piled the nanosheets of each other. The uric acid biosensor was simply fabricated with mixing carbon ink and 70% Co3O4 then placed on RDGE and dried in the oven at 80℃ for an hour. Followed drop coated 5 μL 0.5 % BSA, 5 μL 0.1% glutaraldehyde, and 5 μL 0.5 units uricase onto electrode till dried in 4℃ refrigerator. The biosensor showed optimum conditions for the analysis of uric acid are in 0.05 M pH 9.5 Clark & Lubs buffer, when applied at 0.05 V (vs. Ag/AgCl) with rotating rate of 400rpm. The linear range of this scheme covers from 2 μM to 102 μM (R=0.999), with sensitivity is 18.24 μA/mM and a detection limit of 0.6 μM. The relative standard deviation (RSD) for 20 times successive measurement of 25 μM UA is 1.38%, and the response time (t90%/10%) is 27.34 s. These metabolites have interference except acetaminophen, creatine, and dopamine. Others ratio of interference were between -556.56 % and 5.8%. Among these metabolites, ascorbic acid has -556.56 % interference. Therefore, the removal of AA interference could be eliminated by pretreatment of 10 units ascorbate oxidase with sample for one hour in advance. This sensor has good stability during 83 days study with 4.12% of RSD.

博士
長庚大學
化工與材料工程學系
99
Nano-channeled alumina was made from high purity aluminum foil via anodizing process in 0.3 M oxalic acid aqueous solution. The pore diameter of the channel was varied with the applied oxidation voltage. The optimal oxidation voltage of the preparation of nano-channeled alumina was 40 V which exhibited the good symmetry and uniformity of pore shape and size. Thus obtained pore diameter was 82.7 nm and its density was 9.45 × 109 pores/cm2. We used this nano-channeled alumina as template to synthesis polyaniline (PAn) by electrochemical process. The electron microscopic images presented the PAn with fibrous shape because of the confinement of pore space. The diameter of the PAn nano-fiber was close to the pore size of 80 nm. The cytotoxicity of PAn nano-fiber was assayed in-vitro with HEK293 and U87 cell lines and rat cerebellum normal cell. The results showed that the PAn nano-fiber has the biocompatibility with the cells and has the potential to be used as biomaterial applications. In addition, the doping type polyaniline-polyacrylic acid (PAn-PAA) composite films with porous structure were prepared and developed as an enzyme-free hydrogen peroxide (H2O2) sensor. The carboxyl group of the PAA could react with H2O2 to form peroxy acid groups, and the formed peroxy acid further oxidized the imine structure of PAn to form N-oxides. The N-oxides could be reverted to their original form by electrochemical reduction and caused the increase of the reduction current. Based on this result, PAn-PAA was used to modify the gold (PAn-PAA/Au) electrode as a working electrode for the nonenzymatic detection of H2O2. The characteristics of the proposed sensors could be tuned by the PAA/PAn molar ratio. The reduction current of the PAn-PAA/Au electrode obviously increased when H2O2 was added. At the optimal condition, the linear concentration range of the H2O2 sensor was from 0.04 to 12 mM with a sensitivity of 417.5 μA/mM-cm2. The enzyme-free H2O2 sensor also showed a rapid response time, excellent stability and high selectivity.

碩士
東海大學
應用化學系
84
Abstract one-step synthesis of methyl isobutyl ketone (MIBK) from acetone and hydrogen over metal modified solid base catalysts has been studied at atmospheric pressure and 175~250℃by using a fixed-bed , integral-flow reactor . Two types of catalysts have been used : (1) metal oxides modified with sodium and palladium (Pd/Na/MgO , Pd/Na/NaOH/γ- Al2O3) ; (2) zeolites modified with palladium (Pd/KZSM-5 , Pd/Kβ) . The catalyst properties , i.e., the composition , the basicity , the surface area and the structure are characterized by the methods of atomic absorption , temperature- programmed desorption , surface adsorption and scanning electron microscopy . Sodium vapor deposition on magnesia followed by impregnation with tetraamine palladium(Π) chloride apparently enhances the catalyst basicity as compared with that of magnesia supported palladium ; Pd/0.47wt.-%Na/MgO exhibits the largest base amount . For catalysts of different supports , the base amount decreases in the order of Pd/Na/MgO > Pd/Na/NaOH/γ-Al2O3 > Pd/KZSM-5 > Pd/Kβ , in accordance with the catalyst activities . As the amount of palladium in Pd/Na/MgO increases , both acetone conversion and MIBK selectivity also increase but then decrease . Better acetone conversion and MIBK selectivity are obtained at higher pretreating temperature of hydrogen . The catalyst activity of Pd/Na/MgO increases with the reaction temperature but the decay rate also increases . The acetone/hydrogen molar ratio of 1 gives the highest acetone conversion . Increasing contact time causes an increase in the selectivity of diisobutyl ketone due to further reaction of MIBK with acetone and hydrogen . Based on the above results , the optimum reaction conditions are 0.5wt.-%Pd/0.47wt.-%Na/MgO , reaction temperature 200℃ , acetone /hydrogen molar ratio 1, W/FA 6g.h/mol and the pretreatment temperature of hydrogen 400℃ . According to the FT-IR results of acetone adsorption on Pd/Na/MgO , the following reaction mechanism is proposed : self condensation of acetone on catalyst base sites followed by dehydration on acid sites and then hydrogenation to yield MIBK .

M. Tech. Chemical Engineering.
Discusses the scope of this research study composes of three interactive steps. The first step involves the design of the specific zeolite system (ZSM-5) and the set-up of an autoclave reactor for the hydrothermal synthesis of this and other zeolites and nano materials, then the oxidation catalyst (TS-1) development, i.e. the substitution of aluminium with titanium in the zeolite framework, and finally the formulation and preparation of the isomorphous Silicalite zeolite by omitting the aluminium in the synthesis. And further, set-up of suitable equipments and apparatus for the catalytic testing of the Titanium Silicalite-1 in the oxidation reaction of phenol as the test reaction. Therefore, the overall objectives of this research are: set up an autoclave reactor for the hydrothermal synthesis, formulation of a synthesis recipe for MFI family of catalysts in the laboratory, synthesis of ZSM-5, Silicalite-1, and TS-1 zeolites catalysts in the laboratory, characterization and optimization of the of catalysts listed above, testing the Ti-Silicalite catalyst in the oxidation reaction of phenol with hydrogen peroxide, as the oxidant, set up analytical system (Gas Chromatography, ASS) for analysis of catalyst performance in the oxidation reaction, Evaluate the conversion of the reaction and the selectivity of the individual catalysts reaction Evaluate the conversion of the reaction and the selectivity of the individual catalysts reaction and verify results obtained and compare with systems described in the literature.

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Ultrasmall semiconductor particles (diameters 1-10 nm) of CdS, ZnO, and TiO2 have been synthesized. These particles exhibit the quantum-size effect, which is characterized by a shift of the absorption onset (i.e., bandgap energy) from the visible region for the bulk material to the UV for ultrasmall diameters. The ability of these colloids to photocatalyze various chemical transformations was investigated. Semiconductors were found to be efficient photoinitiators of polymerization of vinylic monomers. Q-sized colloids demonstrated significantly higher rates of photopolymerization than their bulk-sized counterparts. The semiconductor photoinitiation efficiencies were correlated to the reduction potentials of the conduction band electrons. The rates of polymerization were found to depend upon the solvent nature, the monomer and initiator concentrations, and the incident light intensity. The polymerization reaction proceeds via a mechanism involving anionic initiation by conduction band electrons. The valence band holes, which are formed upon illumination, are scavenged by the solvent. The observed rate of polymerization increased proportionally to the square root of the incident light intensity; this functional dependence arises from the second-order termination reactions of the free-radical intermediates. Aqueous, oxygenated suspensions of quantum-sized ZnO particles with added hole scavengers produced steady-state H2O2 concentrations as high as 2 mM upon bandgap illumination. Isotopic labeling experiments demonstrated that H2O2 was produced via the reduction of adsorbed oxygen by conduction band electrons. The quantum yields followed an inverse square-root dependency on absorbed light intensity. Quantum yields as high as 30% were obtained. The quantum yield of H2O2 production increased as the Q-sized particle diameter decreased. Q-sized ZnO particles also photocatalyzed the oxidation of acetate, formate, and glyoxylate. The observed product distributions were discussed regarding direct oxidation by the valence band holes or indirect oxidation by surface-bound hydroxyl radical intermediates. In illuminated semiconductor suspensions, radical intermediates react with the semiconductor surface, forming trapped species which are further oxidized either by semiconductor holes or by self-injection of a second electron into the conduction band. In the final investigation of semiconductor photocatalyzed reactions, humic-like substances were formed in illuminated aqueous Q-sized suspensions containing catechol or gallic acid. Their formation was attributed to polymerization-type reactions initiated by [...] radicals.

Głównym przedsięwzięciem niniejszej rozprawy doktorskiej jest opracowanie metod unieruchamiania enzymów na wybranych podłożach, biorąc szczególnie pod uwagę kontrolowanie orientacji przestrzennej cząsteczek enzymów na powierzchni oraz określenie jej wpływu na aktywność bioelektrokatalityczną, strukturę oraz stabilność biokatalizatorów. Tematyka badawcza skupia się na opracowaniu efektywnych powierzchni katalitycznych, które mają kluczowe znaczenie dla rozwoju technologii biopaliwowych i biosensorów trzeciej generacji. Ponadto praca obejmuje charakterystykę fizykochemiczną układów nanostrukturalnych, których oddziaływanie na biomolekuły jest niezwykle ważne z punktu widzenia zastosowań biomedycznych. W pracy wykorzystywane są trzy wybrane enzymy: lakaza, peroksydaza chrzanowa (HRP) oraz katalaza (CAT). Stanowią one główny element otrzymywanych, a następnie badanych układów elektrodowych. Aktywność elektrokatalityczna biokatalizatorów sprawdzana jest na kilku podłożach modyfikowanych chemicznie bądź elektrochemicznie np. tioalkoholami, solami diazoniowymi, lipidami, tlenkiem grafenu (GO), makro- oraz nanostrukturalną polianiliną lub poprzez chropowacenie złota. Realizację poszczególnych zadań badawczych umożliwiła duża różnorodność dostępnych technik pomiarowych np.: woltamperometria cykliczna (CV), chronoamperometria (CA), technika Langmuira - Blodgett (LB), mikroskopia kąta Brewstera (BAM), skaningowa mikroskopia elektronowa (SEM), mikroskopia optyczna i mikroskopia w podczerwieni, spektroskopia UV-Vis, Ramana oraz absorpcyjna spektroskopia odbiciowa w podczerwieni z modulacją polaryzacji światła (PMIRRAS). Na efektywne działanie badanych układów wpływa wiele parametrów. Szczególnie ważne jest odpowiednie zorientowanie się cząsteczek enzymów względem powierzchni elektrody, a także ich oddziaływanie z warstwą pośredniczącą w transporcie elektronów, pamiętając że modyfikacje podłoża powinny charakteryzować się dużym przewodnictwem elektrycznym.
The main goal of this thesis is to develop methods of enzymes immobilization on selected substrates, considering controlling of the spatial orientation of the enzymes molecules and to determine this effect of immobilization on bioelectrocatalytical activity and stability of biocatalysts. Research focuses on developing of efficient catalytic surfaces which are crucial for biofuel technolgies and third-generation biosensors. In addition, the work involves physicochemical characteristics of nanostructured systems, being extremely important for biomedical applications. In this PhD thesis three selected enzymes are used: laccase, horseradish peroxidase (HRP) and catalase. They are the main component of obtained and studied electrode systems. The electrocatalytic activity of biocatalysts is checked on several, chemically or electrochemically modified substrates eg. tioles, diazonium salts, lipids, graphene oxide (GO), macro- and nanostructured polyaniline or on roughened gold. The implementation of individual research tasks enabled the wide variety of available measurement techniques such as: cyclic voltammetry (CV), chronoamperometry (CA), the Langmuir-Blodgett technique (LB), Brewster angle microscopy (BAM), scanning electron microscopy (SEM), optical microscopy and infrared microscopy, UV-Vis spectroscopy, Raman spectroscopy and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). Many parameters influence the performance of studied systems. Particularly important is the appropriate orientation of the enzyme molecules with respect to the surface of the electrode and their interaction with the intermediate layer, which influence the electron transport. Apart from the orientation, the electrical conductivity of intermediary layer plays an important role.

The utilization of in vitro tests with a tiered testing strategy for detection of mild ocular irritants can reduce the use of animals for testing, provide mechanistic data on toxic effects, and reduce the uncertainty associated with dose selection for clinical trials. The first section of this thesis describes how in vitro methods can be used to improve the prediction of the toxicity of chemicals and ophthalmic products. The proper utilization of in vitro methods can accurately predict toxic threshold levels and reduce animal use in product development. Sections two, three and four describe the development of new sensitive in vitro methods for predicting ocular toxicity. Maintaining the barrier function of the cornea is critical for the prevention of the penetration of infections microorganisms and irritating chemicals into the eye. Chapter 2 describes the development of a method for assessing the effects of chemicals on tight junctions using a human corneal epithelial and canine kidney epithelial cell line. In Chapter 3 a method that uses a primary organ culture for assessing single instillation and multiple instillation toxic effects is described. The ScanTox system was shown to be an ideal system to monitor the toxic effects over time as multiple readings can be taken of treated bovine lenses using the nondestructive method of assessing for the lens optical quality. Confirmations of toxic effects were made with the utilization of the viability dye alamarBlue. Chapter 4 describes the development of sensitive in vitro assays for detecting ocular toxicity by measuring the effects of chemicals on the mitochondrial integrity of bovine cornea, bovine lens epithelium and corneal epithelial cells, using fluorescent dyes. The goal of this research was to develop an in vitro test battery that can be used to accurately predict the ocular toxicity of new chemicals and ophthalmic formulations. By comparing the toxicity seen in vivo animals and humans with the toxicity response in these new in vitro methods, it was demonstrated that these in vitro methods can be utilized in a tiered testing strategy in the development of new chemicals and ophthalmic formulations.