Hydrogenation and hydrofunctionalisation reactions provide efficient, sustainable methodologies for the manipulation of synthetic handles and the formation of carbon-heteroatom bonds from readily available starting materials. Traditional hydrogenation methods typically require precious or semi-precious transition metal complexes or finely divided powders. Iron-based catalysts offer several advantages over more traditional ‘noble’ metal systems due to the high abundance, long-term availability, low cost and low toxicity of iron. To date, the most powerful iron-catalysed hydrogenation and hydrofunctionalisation reactions have required either highly air-sensitive iron(0) complexes or iron(II) complexes activated with an extremely reactive, pyrophoric organometallic reagent. An operationally simple and environmentally benign formal hydrogenation protocol has been developed using a simple iron(III) salt and NaBH4; an inexpensive, bench stable, stoichiometric reductant. This reaction has been applied to the reduction of terminal alkenes (22 examples, up to 95% yield) and nitro groups (26 examples, up to 95% yield) in ethanol, under ambient conditions (Scheme A1). Two novel series of structurally related alkoxy-tethered N-heterocyclic carbene (NHC) iron(II) complexes have been developed as catalysts for the regioselective hydroboration of alkenes. Significantly, Markovnikov selective alkene hydroboration with pinacolborane (HBpin) has been controllably achieved for the first time using an iron catalyst (11 examples, 35-90% isolated yield) with up to 37:1 branched:linear selectivity (Scheme A2). anti-Markovnikov selective alkene hydroboration was also achieved using catecholborane (HBcat) and modification of the ligand backbone (6 examples, 44-71% yield). In both cases, ligand design has enabled activator-free iron catalysis.

Orientador: Gustavo Paim Valença / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-20T14:34:27Z (GMT). No. of bitstreams: 1 CarrenoGonzalez_IvonMaritza_M.pdf: 7134932 bytes, checksum: acf616348074122010d96651cd1436a7 (MD5) Previous issue date: 2012 / Resumo: Sólidos monometálicos e bimetálicos de níquel e molibdênio suportado em alumina foram impregnados com 3% de teor metálico variando a ordem de impregnação até umidade incipiente, os quais podem ter efeitos significativos sobre o seu desempenho. As amostras foram calcinadas e caracterizadas, e utilizadas na desoxigenação catalítica do etilenoglicol. Esses materiais apresentaram áreas superficiais entre 177 e 160 m²g-¹. Os difratogramas de raios X de todos os sólidos obtidos exibiram a fase 'gama'-alumina e mediante o detector de energia dispersiva de raios X se confirmou a presença dos metais nos sólidos. Os testes catalíticos foram realizados em um reator de leito fixo, nas temperaturas de 533, 553, 573, 593 e 613 K e pressões de vapor do etilenoglicol de 13148 e 8662 Pa; a massa dos sólidos utilizada foi 35mg. Os compostos identificados foram a água, hidrogênio, metano, etano, éter etílico, acetaldeído e etanol. Foi realizado o balanço de mols do sistema e os valores dos graus de avanço de cada reação. Os cálculos dos efeitos difusivos demonstraram que as transferências de massa interna e externa e a transferência de energia externa não foram limitantes nas reações. Seis reações principais foram observadas e mediante os graus de avanço permitiu a avaliação de cada reação na formação dos determinados produtos de reação. Baseados na literatura se utilizaram expressões da taxa de reação para as reações propostas neste estudo. A seletividade aos produtos e conversão na desoxigenação do etilenoglicol apresentou mudanças baseadas na forma da ordem de impregnação dos sólidos. Igualmente foram realizados os cálculos das energias de ativação, fatores préexponenciais e as constantes da taxa / Abstract: Monometallic and bimetallic catalysts of nickel and molybdenum supported on alumina were prepared by incipient wetness with 3% metal content by varying the order of impregnation. The samples were calcined, characterized and used in the catalytic deoxygenation of ethylene glycol. The surface areas of the solids varied between 177 and 160 m²g-¹. The X-ray diffraction patterns of all solids had only 'gamma'-alumina phase. Analysis by X-ray dispersive energy confirmed the presence of both Ni and Mo in the solids. The catalytic tests were carried out in a fixed bed reactor and the reaction temperatures varied between 533 and 613 K while the vapor pressures of ethylene glycol were 8662 and 13148 Pa. The mass of the catalyst was kept constant at ca. 35mg. The identified compounds were water, hydrogen, methane, ethane, diethyl ether, acetaldehyde and ethanol. A mass balance for the reaction system was carried out and the extent of reaction was calculated for each reaction. The effect of diffusion was calculated and the results suggest that no internal or external mass transfer and external energy transfer were limiting in the reaction conditions used in this work. Rate expressions from the literature were used in this work. The results of conversion and selectivity to products in the deoxygenation of ethylene glycol reaction suggest that changes in the order of impregnation of the solid are important / Mestrado / Desenvolvimento de Processos Químicos / Mestre em Engenharia Química

Magister Scientiae - MSc / The objectives of this project were to synthesize and characterise pyridine carboxamide ligands and their palladium complexes and investigate their catalytic activity in the polymerization process of phenylactylene. / South Africa

Hydrogen, which is relatively inert at ordinary temperatures, was found to be, activated homogeneously in aqueous solution try dissolved cupric salts, as shown by their catalytic effect on the reactions between H₂ and reducible substrates such as Cr₂O₇⁼, IO₃⁻, and Ce⁺⁺⁺⁺. From kinetic studies of the Cu(ll)-catalyzed hydrogenation of Cr₂O₇⁼, it was shown that the catalytic activity of Cu⁺⁺ is greatly influenced by complex-forming reagents. The catalytic activities of cupric complexes were found to decrease in the order: butyrate, propionate > acetate > sulphate > chloride > H₂O (i.e. the uncomplexed Cu⁺⁺ ion) > glycine, ethylene-diamine . In all systems that were studied, the reaction was.found to be second order kinetically, the rate being proportional to the concentrations of Cu(ll) and H₂. The occurrence of an H⁺ ion as a product of the initial step of the reaction was postulated to account for the perchloric acid dependence of the rate. The promoting effect of various negative ions, which follows the order of their basicities, was thus explained by assigning to them the role of stabilizing the H⁺ ion. The following mechanism was postulated to account for the observed kinetics: Cu(ll) + H₂ [symbol omitted] CuH⁺ + H⁺ CuH⁺ + substrates [symbol omitted] Cu(ll) + products CuH⁺, the activated intermediate suggested by this mechanism, also seems on energetic grounds to be the most plausible of the possible intermediates having reasonable classical structures. It is suggested that the catalytic activity of Cu⁺⁺ is related to its electron affinity. An attempt is made to extend this interpretation to other homogeneous and heterogeneous hydrogenation catalysts. / Science, Faculty of / Chemistry, Department of / Graduate

The aim of this project was to investigate the use of iron porphyrin complexes as potential homogeneous catalysts for the decarbonylation of aldehydes. Complexes of the type Fe(TPP)L₂ (where L = n-Bu₃P, PPh₃ or piperidine) were prepared and reacted with CO gas, or with aldehydes as sources of CO. Since the loss of coordinated CO from the Fe(TPP)(CO)(n-Bu₃P) complex was more facile, the bis(n-Bu₃P) phosphine system was studied in more detail. The X-ray structure of FeTPP(n-Bu₃P)₂ Is described, and this includes the first determination of an FeII-P bond distance for a metalloporphyrin. The study using Fe(TPP)L₂ complexes as decarbonylation catalysts was somewhat hindered by the extreme air-sensitivity of the porphyrin complexes in solution. UV/visible spectroscopy and gas chromatography were used to monitor the decarbonylation reactions. The reaction mixtures were analysed by GC/MS. The decarbonylation reactions were characterised by inconsistent turnover numbers and lack of reproducibility; during the decarbonylation of phenylacetaldehyde, bibenzyl was detected. Such factors are indicative of a free radical mechanism, similar to that proposed earlier for related Ru(II) porphyrin systems. The carbonylation of FeTPP(n-Bu₃P)₂ by CO gas was of interest with respect to the catalytic reaction, which must involve formation of a carbonyl complex. The reaction, FeTPP(n-Bu₃P)₂ + CO K [mathematical formula omitted] FeTPP(n-Bu₃P)(CO) + n-Bu₃P was found to have a K value of 0.72 at 29°C, while the temperature dependence of K was studied to obtain the thermodynamic parameters ΔS and ΔH for the equilibrium. / Science, Faculty of / Chemistry, Department of / Graduate

Includes bibliographical references. / Polymer electrolyte membrane (PEM) fuel cells are promising clean energy alternatives to non - sustainable fossil fuels. During fuel cell operation, external humidification of reactant gases is typically required in order to increase PEM conductivity for improved performance. However, the use of external humidification is costly and increases system complexity. Recently it has been found that by including a cathode microporous layer (MPL) in the membrane electrode assembly (MEA) , performance under dry conditions (no external humidification) can be significantly improved . However, the precise function of the MPL is not well understood and therefore there is little theoretical basis to optimisation of physical properties. One possible reason for this lack of understanding is the absence of a well-established fabrication, characterization and electrochemical testing methodology for MPL research. In particular, current research places little emphasis on the effect of MEA variance on the uncertainty in MPL electrochemical performance results. In this study a methodology is developed for fabricating, characterizing and testing MPLs to accurately correlate physical properties with in-situ electrochemical performance. MPLs of two significantly different thicknesses (approximately 20 and 50 μm in the thickest regions) were fabricated in - house using a doctor blade method and varying the ink composition. The pore structure and thickness of MPLs were characterized by mercury intrusion porosimetry (MIP), scanning electron microscopy (SEM) and X-ray micro computed tomography (μCT).

Bibliography: leaves 77-81. / The ultimate objective of the study was to investigate the performance of suitably prepared gold catalysts for low temperature water gas shift (LTS) - and more specifically to investigate the performance of these catalysts at temperatures below those traditionally utilised. As opposed to the research undertaken to-date on gold catalysed water gas shift, the reaction was performed, as far as possible, under conditions resembling those found industrially, viz. conditions of temperature, pressure, WHSV and dry feed gas composition typical of those applicable to industrial LTS units. Important to this study was therefore the generation of a comprehensive performance benchmark for the commercially available LTS catalyst, a copper-based material, against which to compare the performance of the gold deposited catalysts. The gold catalysts were prepared by deposition-precipitation, a preparation procedure found to yield nano-sized gold particles, suggested in literature as being crucial for activity, on the metal oxide support. Using this procedure, gold promoted low (copper) and high (iron oxide) temperature shift catalysts and commercial zinc oxide supports were prepared and tested. A wide spectrum of Au particle sizes were prepared on the supports, ranging from approximately 3-500 nm. The gold promoted LTS catalyst was found to exhibit slightly higher activity than the commercially available catalyst at temperatures below the conventional LTS range. It would appear as if gold promotion is advantageous to the industrial catalyst and could impact greatly on LTS catalyst life. Even though substantially less active than the commercial copper catalyst was found, the gold promoted commercial zinc oxide catalyst exhibited significantly higher activity than that previously quoted in literature and better performance than the iron oxide supported catalysts of this study. Consequently, the Au/ZnO system exhibits good potential for further developments in terms of water gas shift conversion.

Despite the benefits of fuel cell technology its advancement to being commercially functional is hindered by a number of crucial factors. These factors are often associated with the lack of appropriate materials or manufacturing routes that would enable the cost of electricity per kWh to compete with existing technology. Whilst most research efforts have been directed towards developing more active catalysts, the amount of catalyst required in the fuel cell can be further reduced by improving the platinum utilisation in the membrane electrode assembly. The platinum utilisation is a strong function of the catalyst layer preparation step and there remains significant scope for optimisation of this step. Whereas significant work has been conducted into the different components of the catalyst ink there is limited work and understanding on the influence of the mixing method of the catalyst ink. This study will focus on the influence of the mixing technique on the catalyst ink properties and on the final fuel cell performance. Specifically, the study will investigate the effect of the three different mixing techniques on (i) catalyst ink quality (ii) the physical properties of the resultant catalyst layer and (iii) the in-situ electrochemical performance of the membrane electrode assembly. A large set of characterisation techniques were chosen to effectively study the step wise processing of the catalyst layer, and fuel cell performance. The results presented here include a comparison of the various mixing techniques and a comprehensive 2 x 2 factorial design into the individual techniques. The results suggest that high energy mixing is required for effective distribution of catalyst layer components, an even catalyst layer topography and a highly functional ionomer network which consequently, enhances performance. The mixing energy referred to involves prolonged mixing time, enhanced mixing intensity or a combination of the two. During bead milling of catalyst inks, high intensity mixing seems to be beneficial however, prolonged mixing time appears to be detrimental to the ionomer film structure. During high shear stirring and ultrasonic homogenisation of catalyst inks, the ink mixture significantly heats up. It has been observed that at higher temperatures, Nafion elongates and the contact with catalyst agglomerates is enhanced. High shear stirring of catalyst inks seems to be most effective at high agitation rates. High mixing energies result in high shear forces and in addition, high mixing temperatures which appear to be beneficial to establishing an effective catalyst/Nafion interface, enhancing the three phase boundary observed during in-situ testing. Ultrasonic homogenisation seems to be more effective at prolonged sonication times. Due to the erosive nature of ultrasonic dispersion, sufficient time is required to establish a well dispersed and distributed catalyst ink. However, the nature of particle size distribution resulting from ultrasonication shows that inks are unstable and is not recommended for high throughput processing. Overall, fuel cell performance is not significantly affected by the mixing step however; mixing does have an observable impact on catalyst layer formulation. Generally, when optimizing membrane electrode assembly fabrication, mixing parameters should be carefully chosen. This goes without saying that parameters need to be effectively studied before foregoing catalyst ink processing.

Bibliography: pages 225-233. / SAP0-34 and mordenite, catalysts with quite different pore structures, are known to be suitable for methanol conversion to light olefins and propene oligomerization to a distillate type product, respectively. In this study, these catalysts were modified in various ways and the effect of these modifications on the activity and selectivity of the above two reactions investigated. SAP0-34, a small-pore silicoaluminophosphate molecular sieve, is highly selective in the formation of ethene and propene from methanol, but deactivates rapidly due to coke formation. This catalyst was synthesized and modified in various ways in an attempt to increase the catalyst lifetime and selectivity to ethene. Mild hydrothermal conditions encountered during deep-bed calcination of SAP0-34 were found to increase the catalyst lifetime. A number of further modifications were made to this deep-bed calcined material in an attempt to increase further the lifetime of this material. These modifications were : (i) Silanization - in order to neutralize the acidity on the external surface of the crystallites and hence reduce pore-mouth blockage by coke species on the crystallite external surface; (ii) Steaming - to investigate the effect of more severe hydrothermal conditions than those encountered under deep-bed-calcination conditions; (iii) Acid site poisoning by ammonia - in an attempt to reduce the rate of coke formation which takes place readily on strong acid sites; (iv) Boron impregnation - in order to reduce the intercrystalline void volume and thereby sterically hinder the formation of bulky coke molecules within the SAP0-34 pores; (v) Acid and caustic treatments - in order to reduce the catalyst acidity and thereby limit the rate of the coke formation reaction.

Gallium/H-ZSM-5 zeolite catalysts have been extensively researched for the aromatization of liquified petroleum gas (LPG). In 1989 BP and UOP collaborated to commission a pilot plant in Grangemouth, Scotland, for the aromatization of propane and butane. This plant, based on a technology called the Cyclar process, used continuous catalyst regeneration (CCR) and a gallium impregnated ZSM-5 zeolite catalyst to achieve yields of ca. 65% aromatics, mainly benzene, toluene and xylenes (BTX) [Guisnet and Gnep, 1992]. As a result of the Fischer-Tropsch process used by SASOL Ltd., South Africa is in an internationally unique position, in that it has a surplus of long chain linear alkenes with carbon numbers in the range C6-C8 . There could be large economic incentives to convert these alkenes into more valuable products, like alcohols or aromatics. Thus the purpose of this project was to determine if gallium/H-ZSM-5 catalysts, similar to those used in the Cyclar process, would be suitable for the aromatization of long chain alkenes. Three methods were investigated for the introduction of gallium into ZSM-5: (i) physical mixing with gallium oxide; (ii) impregnation by incipient wetness with gallium nitrate; (iii) ion-exchange with gallium nitrate. The catalysts were. tested with regard to their catalytic activity for the aromatization of 1-hexene and 1-octene.