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Direct alcohol fuel cells (DAFC) are attracting considerable interest to meet a variety of energy needs as they offer higher efficiency with less pollution compared to other conventional energy-conversion devices. However, the sluggish alcohol oxidation reaction kinetics and durability problems of the conventional Pt-Ru anode catalyst hamper the commercialization of the DAFC systems. With an aim to overcome these problems, there have been intensive efforts to alloy Pt-Ru with other metals. Although such strategies have led to some enhancement in activity, the durability problem caused by the instability of Ru could still not be alleviated. In this regard, this dissertation focuses on the development of non-Ru electrocatalysts with high activity and durability for DAFC applications. First, Ru-free, Pt-based bimetallic electrocatalysts for methanol oxidation reaction (MOR) were studied. Particularly, Pt-Sn and Pt-CeO₂ catalysts were synthesized, respectively, by a polyol method and a one-step reverse microemulsion (RME) method. The prepared samples are investigated for phase and morphological evaluations by various material-characterization techniques. Cyclic voltammetry and accelerated durability tests revealed that these alternative catalysts have much higher stability with a catalytic activity for MOR comparable to that of Pt-Ru. In the case of Pt-CeO₂, an improved particle morphology is obtained by the RME synthesis, and the advantage of the RME method is reflected by a higher catalytic activity in comparison to that of Pt-CeO₂ synthesized by the conventional synthesis method. It has been known that Pt-Sn is better than Pt-Ru for ethanol oxidation reaction (EOR), and the direct ethanol fuel cells (DEFC) employing Pt-Sn as the anode catalyst have better durability than the DMFC system employing a Pt-Ru anode catalyst. Therefore, this dissertation then focused on the enhancement of the catalytic activity for EOR by incorporating a third metal M to the Pt-Sn catalyst. Following the synthesis and characterization of the Pt-Sn-M (M = Mo and Pd) alloys, the effect of M on the enhanced catalytic activity of Pt-Sn-M is presented. The activity enhancement of the above catalysts is based on the promoting effect of the second or third elements added to Pt. However, in the final chapter of this dissertation, the activity enhancement of Pt nanoparticle itself through the formation of low energy surfaces is investigated. Carbon-supported Pt nanoparticles are synthesized in mixed water-ethylene glycol solvent, and the positive effect of the mixed solvent on both the morphology and surface structure of the Pt nanoparticles for COad oxidation is discussed. / text

L'objectif de cette thèse a été l'optimisation de la synthèse et des performances catalytiques des matériaux lamellaires au W et Mo dans les réactions d'oxydation de plusieurs composés organiques en présence d'H2O2. Le travail réalisé au cours de cette thèse est le développement de nouveaux catalyseurs hétérogènes pour la réaction d'oxydation qui est réalisée sélectivement en systèmes catalytiques homogènes, mais pour un développement durable, la catalyse hétérogène demeure beaucoup plus porteuse d'avenir au niveau industriel. La réaction d'oxydation de composés soufrés a un grand intérêt, en particulier dans l'élimination des composés organiques soufrés (thiophènes, sulfures) contenus dans les carburants et les coupes pétrolières, réalisée dans des conditions douces de température et pression, en présence de l'eau oxygénée. Les objectifs principaux de cette étude ont été les suivants: 1. élaboration des matériaux catalytiques : a) préparation des précurseurs de type hydrotalcites (HDL) à base de Mg-Al-NO3, Mg-Al-terephthalate et Ni-Mg-Al-NO3. b) préparation des matériaux hybrides par intercalation des espèces de Mo et W par deux voies de synthèse : réaction d'échange anionique et synthèse hydrothermale. 2. caractérisation de la structure, la texture et la nature des sites catalytique par différentes techniques : DRX, adsorption d'azote, ATG, spectroscopie Raman et UV-Vis, MEB etc. 3. applications de ces catalyseurs à la réaction d'oxydation des composes soufrés (sulfures, thiophènes, sulfoxydes), epoxydation de cyclooctene et oxydation d'anthracène. Les catalyseurs ont été stables au recyclage et aucun phénomène de leaching n'a été observé. / The objective of this thesis was the optimization of the synthesis and catalytic performances of nanocomposites materials containing W and Mo in the oxidation with H2O2 of a wide range of model organic compounds. The work achieved during this thesis is the development of new heterogeneous catalysts for the oxidation reaction who is carried out selectively in homogeneous catalytic systems, heterogeneous catalysis is still much more promising in future. The oxidation reaction of sulfur compounds has great interest, especially in the removal of organic sulfur compounds (thiophene, sulfide) contained in fuels and petroleum fractions, performed in mild conditions of temperature and pressure in the presence of H2O2. In this study were as follows : 1. elaboration of materials : a) preparation of precursors of type hydrotalcites (HDL) based on Mg-Al-NO3, Mg-Al-Ni-terephthalate and Mg-Al-NO3. b) preparation of hybrid materials by intercalation species of Mo and W by two synthetic routes : reaction of anion-exchange and hydrothermal synthesis. 2. characterization of the structure, texture and nature of catalytic sites by different techniques : XRD, nitrogen adsorption, TGA, Raman spectroscopy and UV-Vis, SEM, etc. 3. application of these catalysts in the reaction of oxidation of sulfur compounds (sulfides, thiophenes, sulfoxides), epoxidation of cyclooctene and oxidation of anthracene. The catalysts were stable under operating conditions.

This thesis is concerned with the reactions of sulfur-centred radicals and alkynes. The first objective of this work was to extend the scope of “self-terminating radical cyclisations” to sulfur-centred radicals, such as thiyl radicals. Preliminary experiments revealed that the reaction of thiyl radicals with alkynes was sensitive to residual oxygen. In the absence of oxygen, the reactions of photochemically generated phenylthiyl radicals with cyclodecyne (1) resulted in three isomeric sulfides, which were identified through a combination of techniques. (1S,6S)-2-phenylthiobicyclo[4.4.0]decane (trans-49a, unknown stereochemistry at C2) was identified by synthesis of an authentic sample, while the structure of (1S,2R,6S)-2-phenylthiobicyclo[4.4.0]decane (cis-49a1) was determined by X-ray analysis of the corresponding crystalline sulfone, cis-69. The third sulfide, (1S,2S,6S)-2-phenylthio-bicyclo[4.4.0]decane (cis-49a2), was assigned based on computational studies. / In addition, the reactions of benzylthiyl, tert-butylthiyl and allylthiyl radicals with cyclodecyne (1) were investigated. Various sources of thiyl radical generation were utilized, such as the photolysis of disulfides and thiols, hydrogen atom abstraction of thiols using radical initiators, as well as thiol autoxidation in the presence of oxygen. The radical cascade initiated by the addition of thiyl radicals to alkyne 1 was typically terminated by either reduction or disproportionation, whereas “self-termination” was only observed in one particular instance where the tert-butylthiyl radical was generated by autoxidation. However, this was only a minor pathway. / The second objective of this work was to investigate the reactions of thiyl radicals with alkynes in the presence of oxygen. For this purpose, phenylthiyl radicals were generated in the presence of diphenylacetylene (89) and molecular oxygen. Benzil (91), an α-diketone, and 1,2-diphenyl-2-(phenylthio)ethanone (93), an α-ketosulfide, were formed. The novel thiyl radical-mediated oxidation of diphenylacetylene to benzil mediated proceeds under mild and metal-free conditions, using various methods of thiyl radical generation. The product ratio of diketone to ketosulfide varied with the reaction conditions. Under photochemical conditions, benzil was formed but its photodegradation was also observed. Using autoxidation, moderate to good yields of both diketone 91 and ketosulfide 93 were obtained, although the product ratios varied with solvent and reaction conditions. Diketone 91 was the major product when the thiyl radical was generated electrochemically. Following investigation of the reaction mechanism using experimental and computational studies, the phenylthiyl peroxyl radical was identified as the key reactive intermediate. This represents the first synthetic application of thiyl peroxyl radicals. / Using autoxidation conditions, the oxidation was explored using substituted aromatic thiyl radicals, e.g. 2,6-dimethylbenzene, 2,4,6-tri-tert-butylbenzene, 4-methoxybenzene and 4-nitrobenzene thiyl radicals. Except for the case of 4-methoxybenzene thiyl radicals, where generation of the thiyl radicals was inefficient, diketone 91 was formed as the dominant product. This oxidation of alkynes to ketones, via thiyl radical-mediated activation of oxygen, was then applied to cyclodecyne (1). Bicyclic ketones 7/8 were found as the major products under photochemical conditions, while sulfides 152/trans-49a were the dominant products under autoxidation conditions. Bicyclic ketones 7/8 were formed due to the intramolecular radical processes directed by the transannular strain of the ten-membered carbon framework. Only trace amounts of the cyclic α-diketone 151 were detected under autoxidation conditions.

Thesis (Ph.D.)--University of Melbourne, School of Chemistry, 2009. / Typescript. Includes bibliographical references.

To prevent the global surface temperature from increasing past the 2 oC target, it is necessary to address CO2 emissions from small point sources. Within Canada’s heavy oil industry, SAGD facilities use natural gas combustion to produce the large amounts of steam required for the process, which produces approximately 0.5-2 Mtonnes of CO2 per annum. A suitable technology for CO2 mitigation from a SAGD facility is Pressurized Chemical Looping Combustion. PCLC is an oxy-combustion, carbon capture technology with a relatively low predicted energy penalty of 3-4%. The process requires a dual, interconnected fluidized bed reactor system with circulating solids. Natural gas is converted in the fuel reactor via a solid metal oxide, which is then circulated to the air reactor for reoxidation with air. As the cost of air compression is significant, the economical feasibility of the process is reliant on air reactor performance. The objective of this study is to investigate the oxidation reaction and derive a kinetic model for reactor design and performance assessment purposes. Ilmenite ore was chosen as the metal oxide, as it is low cost and has desirable oxygen transport properties for PCLC. Pressurized TGA tests were conducted to study the effects of oxygen concentration, temperature and pressure on the rate of the oxidation reaction. The total pressure was varied from 1-16 bara at 900 oC with air. The oxygen concentration was varied from 2.5-21 vol%, and the temperature from 800-1000 oC at 8 bar. Temperatures below 850 oC resulted in segregation of the Fe and Ti phase in the ilmenite ore, leading to a reduction in the overall oxygen carrying capacity. Crack formation was observed at higher oxygen partial pressures, resulting in increased surface area for reaction and a fast reaction rate. At lower oxygen partial pressures, a solid-state diffusion controlled regime was observed due to the absence of fissures. A dual mechanistic oxidation kinetic model was derived at 8 bar, with 2nd order random nucleation dominating at lower conversions, and Jander’s solid state diffusion model dominating at higher conversions. The transition from the nucleation and growth to the diffusion-controlled portion occurred at higher conversions with higher oxygen partial pressure. The activation energy was 16.6 kJ/mol and 48.7 kJ/mol while the order of reaction with respect to oxygen was 0.3 and 1.3 for respectively the nucleation and growth, and diffusion-controlled regimes. A preliminary air reactor model is constructed as a turbulent bed. The turbulent bed is modelled as an axial dispersion reactor for a basic performance assessment.

In this study the focus was on the electrochemical techniques and aspects behind the establishment of the better catalyst (platinum or gold) for the sulphur dioxide oxidation reaction (SDOR). One of the primary issues regarding the SDOR is the catalyst material, thus the comparative investigation of the performance of platinum and gold in the SDOR, as found in this study. Ultimately, the SDOR could lead to an effective way of producing hydrogen gas, which is an excellent energy carrier. The electrochemical application of the oxygen reduction reaction (ORR) and ethanol oxidation reaction (EOR) is an integral part of the catalytic process of water electrolysis, and by using fuel cell technology, it becomes even more relevant to this study and can therefore be used as a control, guide and introduction to the techniques required for electrochemical investigation of catalyst effectiveness. Subsequently, the EOR as well as the ORR was used as introduction into the different electrochemical quantification and qualification techniques used in the electrochemical analyses of the SDOR. Considering the ORR, gold showed no viable activity in acidic medium, contrarily in alkaline medium, it showed good competition to platinum. Gold also lacked activity towards the EOR in acidic medium compared to platinum, with platinum the best catalyst in both acidic and alkaline media. Ultimately, platinum was established to be the material with better activity for the ORR with gold a good competitor in alkaline medium, and platinum the better catalyst for the EOR in both acidic and alkaline media. With the main focus of this study being the SDOR, gold proved to be the best catalyst in salt and gaseous forms of SO2 administration compared to platinum when the onset potential, maximum current density, Tafel slope and number of electrons transferred are taken into consideration. The onset potential was determined as 0.52 V vs. NHE for both platinum and gold using SO2 gas and 0.54 V and 0.5 V for gold and platinum respectively, using Na2SO3 salt. The maximum current density using gaseous SO2 for platinum at 0 RPM was 400 mA/cm2 with a Tafel slope of 891 mV/decade whereas gold had a maximum current density of 300 mA/cm2 and a Tafel slope of 378 mV/decade. Using Na2SO3 salt, the maximum current density of gold was 25 mA/cm2 with a Tafel slope of 59 mV/decade whereas platinum only achieved 18 mA/cm2 with a Tafel slope of 172 mV/decade. Concerning the number of electrons transferred, gold achieves a transfer of 2 while platinum only 1 for both SO2 gas and Na2SO3 salt. Taking all these summarised determinations into account, gold was established to be a very competitive catalyst material for the SDOR, compared to platinum. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2015

In this study the focus was on the electrochemical techniques and aspects behind the establishment of the better catalyst (platinum or gold) for the sulphur dioxide oxidation reaction (SDOR). One of the primary issues regarding the SDOR is the catalyst material, thus the comparative investigation of the performance of platinum and gold in the SDOR, as found in this study. Ultimately, the SDOR could lead to an effective way of producing hydrogen gas, which is an excellent energy carrier. The electrochemical application of the oxygen reduction reaction (ORR) and ethanol oxidation reaction (EOR) is an integral part of the catalytic process of water electrolysis, and by using fuel cell technology, it becomes even more relevant to this study and can therefore be used as a control, guide and introduction to the techniques required for electrochemical investigation of catalyst effectiveness. Subsequently, the EOR as well as the ORR was used as introduction into the different electrochemical quantification and qualification techniques used in the electrochemical analyses of the SDOR. Considering the ORR, gold showed no viable activity in acidic medium, contrarily in alkaline medium, it showed good competition to platinum. Gold also lacked activity towards the EOR in acidic medium compared to platinum, with platinum the best catalyst in both acidic and alkaline media. Ultimately, platinum was established to be the material with better activity for the ORR with gold a good competitor in alkaline medium, and platinum the better catalyst for the EOR in both acidic and alkaline media. With the main focus of this study being the SDOR, gold proved to be the best catalyst in salt and gaseous forms of SO2 administration compared to platinum when the onset potential, maximum current density, Tafel slope and number of electrons transferred are taken into consideration. The onset potential was determined as 0.52 V vs. NHE for both platinum and gold using SO2 gas and 0.54 V and 0.5 V for gold and platinum respectively, using Na2SO3 salt. The maximum current density using gaseous SO2 for platinum at 0 RPM was 400 mA/cm2 with a Tafel slope of 891 mV/decade whereas gold had a maximum current density of 300 mA/cm2 and a Tafel slope of 378 mV/decade. Using Na2SO3 salt, the maximum current density of gold was 25 mA/cm2 with a Tafel slope of 59 mV/decade whereas platinum only achieved 18 mA/cm2 with a Tafel slope of 172 mV/decade. Concerning the number of electrons transferred, gold achieves a transfer of 2 while platinum only 1 for both SO2 gas and Na2SO3 salt. Taking all these summarised determinations into account, gold was established to be a very competitive catalyst material for the SDOR, compared to platinum. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2015

A reação de redução de oxigênio (RRO) e a reação de oxidação do borohidreto (ROB) foram estudadas em eletrólito alcalino em eletrodos formados por diversos tipos de óxidos de manganês dopados com Ni (II) dispersos sobre carbonos Monarch 1000, MM225 e E350. As técnicas de caracterização físico-química foram difração de raios X (DRX), microscopia eletrônica de transmissão de alta resolução (HR-TEM) equipado com espectrômetro de energia dispersiva de raios X (EDX). Já os estudos eletroquímicos compreenderam voltametria cíclica, curvas de polarização de estado quase estacionário além das técnicas de Espectroscopia de massas diferencial on line (DEMS) e Infravermelho com transformada de Fourier in situ (FTIR). Foi observada pequena inserção dos átomos de Ni na estrutura dos MnOx. A fase correspondente a NiMnOx/C está presente na forma de aglomerados nanocristalinos ou em forma de agulhas com tamanhos da ordem de 1,5 a 6,7 nm dependendo do tipo de carbono utilizado como substrato. Manganita (MnOOH) apresentou-se como fase preponderante para óxido de manganês disperso sobre carbono Monarch 1000 enquanto que para materiais dispersos sobre carbono MM225 e E350G a fase MnO2 esta presente em maior quantidade. Estudos eletroquímicos em camada fina utilizando eletrodo disco rotatório revelaram melhores atividade para a RRO e estabilidade para MnOx dopados com níquel. A RRO procede segundo o mecanismo peróxido, seguida pela reação de desproporcionação do íon HO2- formado. A extensão da reação de desproporcionação do íon HO2- aumenta com o aumento da quantidade de Ni. Sobre eletrocatalisadores suportados em carbonos MM225 e E350 a reação de desproporcionação é mais rápida e envolve um total de 4 e- por oxigênio molecular. As curvas de polarização para RRO obtidas na presença do íon BH4- mostraram que todos os materiais são tolerantes à presença do borohidreto. Resultados de DEMS on line e FTIR in situ mostraram que óxidos de manganês dopados com Ni além de serem ativos para RRO são também ativos para a ROB, porém há uma grande influência da composição e da morfologia dos materiais uma vez que, quando fases segregadas de Ni estão presentes nas amostras, a reação compete com a hidrólise heterogênea do BH4- levando a uma diminuição da eficiência faradaica. / The oxygen reduction reaction (ORR) and the borohydride oxidation reaction (BOR) were studied in alkaline medium on Ni (II) doped MnOx catalysts supported on different carbon powder substrates. Characterizations of physico chemical properties were made by X ray diffraction (XRD), high resolution transmition electronic microscopy (HR-TEM) equipped with X ray dispersive energy spectroscopy (EDS). Electrochemical studies involved cyclic voltammetry and oxygen reduction voltammograms. Also it was used Differential Electrochemical Mass Spectrometry on line (DEMS) and Fourier Transform Infra Red Spectrometry (FTIR) in situ. A small insertion of Ni atoms in the MnOx lattice was observed, this consisting of a true doping of the manganese oxide phase. The corresponding NiMnOx phase is present in the form of needles or agglomerates, with crystallite sizes in the order of 1.5-6.7 nm. Layered manganite (MnOOH) phase has been detected for the Monarch1000 supported NiMnOx material, while different species of MnOx phases are present at the E350G and MM225 carbons. Electrochemical studies in thin porous coating active layers in the rotating ring-disk electrode setup revealed that the MnOx catalysts present better ORR kinetics and electrochemical stability upon Ni doping. The ORR follows the so-called peroxide mechanism on MnOx/C catalysts, with the occurrence of minority HO2- disproportionation reaction. The HO2- disproportionation reaction progressively increases with the Ni content in NiMnOx materials. The catalysts supported on the MM225 and E350G carbons promote faster disproportionation reaction, thus leading to an overall four-electron ORR pathway. The results towards ORR in presence of sodium borohydride showed that all materials are tolerant to the presence of BH4- ion into some extent. DEMS on line and FTIR in situ showed that NiMnOx/C are also active toward the BOR, but there is a strong influence of the nature of the electrocatalysts with respect to the morphology, composition, the nature of the carbon substrate and the Ni load. Results indicate that the electrocatalysts containing segregate Ni phases, the bohohydride oxidation occurs together with the heterogeneous hydrolysis of the BH4- ion resulting in a decrease of the faradaic efficiency.

Eletrocatalisadores Pt/C, Pd/C, PtAu/C, PtIr/C, PdAu/C, PdIr/C, PtAuIr/C e PdAuIr/C foram preparados via redução por borohidreto de sódio em diferentes proporções atômicas, com 20% em massa de metal e suportados em carbono Vulcan XC72 de alta área superficial. Os materiais foram caracterizados pelas técnicas de espectroscopia de energia dispersiva de raios-X (EDX), análise de difração de raios-X (DRX) e microscopia eletrônica de transmissão (MET). A oxidação eletroquímica do etanol foi estudada por voltametria cíclica (VC) e cronoamperometria, utilizando a técnica do eletrodo de camada fina porosa e o estudo da oxidação eletroquímica de etanol \"in situ\" utilizando espectroscopia de infravermelho com transformada de Fourier (FTIR). Posteriormente os materiais foram testados em células à combustível alcalinas alimentadas diretamente com etanol. Os resultados demonstraram que houve formação de ligas, com tamanho médio de nanopartículas entre 4,0 - 10 nm. De acordo com os experimentos eletroquímicos os eletrocatalisadores ternários apresentaram maior atividade eletrocatalítica e os estudos em FTIR indicaram que o produto principal da oxidação eletroquímica de etanol em meio alcalino para todos eletrocatalisadores sintetizados foi o acetato, sugerindo que a oxidação ocorre de forma incompleta pelo mecanismo indireto. Os testes em célula mostraram os melhores resultados para PdAuIr/C (50:40:10) com o qual obteve-se potencial de circuito aberto de aproximadamente 0,78 V e densidade de potência máxima de aproximadamente 15 mW cm-2, cerca de 333% superior a Pd/C. / Pt/C, Pd/C, PtAu/C, PtIr/C, PdAu/C, PdIr/C, PtAuIr/C and PdAuIr/C electrocatalysts, were prepared by the sodium borohydride reduction process in different atomic proportions, with 20 wt.% of metal loading and supported on Vulcan XC72 carbon with high surface area. The materials were characterized by X-ray dispersive energy spectroscopy (EDX), X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). The ethanol electrochemical oxidation was studied by cyclic voltammetry (CV), chronoamperometry and in situ using Fourier Transform Infrared Spectroscopy (FTIR) using the thin porous coating technique, Afterwards the materials were tested on direct ethanol alkaline fuel cells. The results suggest alloys formation, with the mean nanoparticles sizes are from 4 - 10 nm. According to the electrochemical experiments the ternary electrocatalysts presented higher electrocatalytic activity, while that the FTIR studies indicated that the main product of the electrochemical oxidation of ethanol in alkaline medium for all synthesized electrocatalysts was acetate, also suggesting that the oxidation occurs incompletely by the indirect mechanism. The fuel cell experiments showed the best results for PdAuIr/C (50:40:10), where these materials had an open circuit potential of approximately 0,78 V and maximum power density of about 15 mW cm-2, about 333% higher than Pd/C.