The global oil refining industry with its present shift inproduct distribution towards fuels such as gasoline and dieselwill most likely hold the fort for many years to come. However,times will change and survival will very much depend onprocessing flexibility and being at the frontiers of refiningtechnology, a technology where catalysts play leading roles.Today oil refiners are faced with the challenge to producefuels that meet increasingly tight environmentalspecifications, in particular with respect to maximum sulphurcontent. At the same time, the quality of crude oil is becomingworse with higher amounts of polyaromatics, heteroatoms(sulphur and nitrogen) and heavy metals. In order to staycompetitive, it is desirable to upgrade dense streams withinthe refinery to value-added products. For example, upgradingthe fluid catalytic cracking (FCC) by-product light cycle oil(LCO) into a high quality diesel blending component is a veryattractive route and might involve a two-step catalyticprocess. In the first step the LCO is hydrotreated andheteroatoms are removed and polyaromatics are saturated, in thesecond step naphthenic rings are selectively opened to improvethe cetane number of the final product. The present research is devoted to the second catalytic stepof LCO upgrading and was carried out within the framework of aEuropean Union project entitled RESCATS. From the patent literature it is evident that iridium-basedcatalysts seem to be good candidates for ring-opening purposes.A literature survey covering ring opening of naphthenicmolecules shows the need for extending investigations toheavier model substances, more representative of the dieselfraction than model compounds such as alkylated mono C5 and C6-naphthenic rings frequently employed in academic studies. Ring-opening catalysts, mainly Pt-Ir based, were synthesisedat KTH by two different methods: the microemulsion and theincipient wetness methods. Characterization of the catalystswas performed using a number of techniques including TPR,TEM-EDX, AFM and XPS etc. Catalytic screening at atmosphericpressure using pure indan as model substance was utilized todetect ring-opening activity and the magnitude of selectivityto desired cetane-boosting products. The development of suchring-opening catalysts is the topic of Paper I. When designing a catalytic system aimed at refiningpetroleum, it is crucial to monitor the evolution of thesulphur distribution throughout the different stages of theprocess so that catalyst properties and reaction parameters canbe optimised. The final section of this thesis and Paper II arethus devoted to high-resolution sulphur distribution analysisby means of a sulphur chemiluminescence detector (SCD). Keywords:ring opening, naphthenes, cetane numberimprovement, indan, light cycle oil (LCO), Pt-Ir catalyst,catalyst characterization, aromatic sulphur compounds, GC-SCD,distribution, analysis.

<div>Thermochemical processing using fast-pyrolysis technology has been used to upgrade feedstocks like biomass and natural gas and more recently studied for plastic recycling. This work aims to improve the selectivity to desired products from a pyrolysis process through better catalysts and reactor design.</div><div>Fast-pyrolysis of biomass to fuels is considered a promising technology due to the higher yields to liquid fuel products. However, the process suffers from low carbon efficiency to hydrocarbon products due to carbon losses to biochar, accounting for 25-40 wt.% of the product stream depending on the biomass type. Using a combination of inorganic free-model compounds, biomass pretreatments and mass spectrometric analyses coupled with lab-scale reactor experiments, the char contribution from the lignocellulosic components (cellulose, hemicellulose, and lignin) and mineral content was investigated. The lignocellulosic components were found to follow the order: Lignin > Hemicellulose > Cellulose. Addition of inorganic salts (K, Na and Ca) to cellobiose, a model compound for cellulose, was found to catalyze additional dehydration reactions on primary pyrolysis products (e.g., levoglucosan) to yield secondary products (e.g., 5-HMF), and produce more char. This knowledge of char formation contributors can enable optimization of the bio-refining process sequencing using process system engineering tools and thus achieve higher carbon efficiency for biomass conversion.</div><div>While biomass has been viewed as a future energy source, there is a need for a transition fuel with the lowest possible greenhouse gas (GHG) footprint. Shale gas, consisting primarily of methane, is a potential candidate due to its large availability and high hydrogen to carbon ratio. Recently, single-atom catalysts have been studied as stable and non-coking catalysts for the non-oxidative coupling of methane (NOCM) to higher hydrocarbons (like ethylene). However, lack of post reaction catalyst characterization and rigorous kinetic testing have raised questions on the stability of these materials. This work combines homogenous (Chemkin simulations, gas phase kinetics) and heterogeneous reaction kinetic studies (reaction orders, steady state kinetics), coupled with microscopy (Scanning and Transmission Electron Microscopy (SEM, TEM)) and surface characterization tools (BET, TGA, Raman spectroscopy, CO-IR spectroscopy) to understand the role of the solid materials during NOCM. Post reaction catalyst characterization using transmission electron microscopy (TEM) analysis on the spent samples (CH4 treated at 975 deg C for 3 hours) reveals that the materials containing Pt single atoms (SA) and Pt nanoparticles (NP) are found to sinter to particles approximately 5-7 nm in size. Ethylene hydrogenation experiments, a kinetic probe for surface Pt, shows initial ethane formation rates that are four orders of magnitude lower on the isolated Pt+2 sites, found on Pt SAs, when compared to the rates obtained if all the surface Pt were assumed to be metallic. These results suggest that single atoms are not the active sites. However, under same reaction conditions (50 mL min-1 CH4 flow and 975 deg C), the ethylene formation rates (in mol h-1) on the solid materials are 2-7 times higher than the empty tube rates, indicating that the surface plays a role during NOCM. Addition of incremental amounts of the solid material increases methane conversion, extrapolating to the bare tube conversion at zero loading. This indicates that the solid materials improve the NOCM performance.</div><div>Experiments with pure methane feeds indicate that the solid materials are found to deactivate due to coking on the surface, evidenced by the coke buildup observed using thermogravimetric analysis (TGA) and the initial time-on-stream kinetic results showing rapid methane deactivation. Raman spectroscopy on the spent catalysts indicate at the development of a similar graphite-like surface intermediate under steady state conditions on all the materials. When compared under the same reaction conditions (975 deg C, 60 mL min-1 Pure CH4 with 10% UHP N2 feed, space velocity = 39.6 L h-1 gcat-1), these coked surfaces show a linear dependence for the ethylene formation rate (in mol h-1 gcat-1) with the spent surface area of the material (in m2 gcat-1). This observation is irrespective of the type of the material studied (alpha Al2O3, Davisil SiO2, 1 wt.% Pt/CeO2, Graphene, Graphite, etc.). In conclusion, these results prove that the spent surface area is critical for NOCM.</div><div>Similar experimental setup was used to study the dehydrogenation of methane, ethane, and propane mixture in the gas phase. Initial experiments at 1 bar pressure and reaction temperatures ranging from 650-850 deg C revealed that ethylene and hydrogen are the main gas phase products, with methane acting as a diluting agent under these reaction conditions. These results could enable direct processing of the shale gas without the use of a conventional ethane/propane separation step. These results were further studied by the system engineers using ANSYS ChemkinPro. For practical applications, these experiments were suggested to be performed at much higher operating pressures (~30 bar) and low residence time (~0.2 s), with a quick quenching step added after the reactor to prevent change in the exit stream compositions. A new reaction system was built to experimentally validate these recommendations.</div>

No description available.

Alkenes can undergo a variety of chemical reactions to form more complex molecules with a range of functional groups. This makes them useful starting materials for synthesizing a wide range of organic compounds. Chapter I provided an overview of the development history of alkenyl C−H bond activation. The early reactions of C−H compounds with metal complexes, as well as stoichiometric activation of the transition metal-activated C–H bond, were discussed. Then the first successful and efficient organometallic-catalyzed transformations of a C−H bond, the first transition metal-catalyzed vinylic C–H functionalization, and the first transition metal-catalyzed olefinic C–H functionalization under mild conditions were demonstrated. Finally, enantioselective vinylic C–H functionalization was discussed. In Chapter II, a method for enantioselective vinylic C(sp2)−H bond activation using a Ru(II) catalyst and a chiral transient directing group was developed. Chiral amine was also utilized to control the Z/E stereoselectivity. The method demonstrated a broad substrate scope with good yield, high Z/E ratio stereoselectivity, and excellent enantioselectivity. Its synthetic utility was demonstrated by the synthesis of key structural motifs of particularly useful natural products and pharmaceutical compounds. Additionally, a rare vinylic C−H bond activated ruthenic complex was isolated and determined by single-crystal X-ray diffraction. The methodology suggested in this work is expected to facilitate the further development of asymmetric vinylic C−H functionalization reactions. In Chapter III, a practical and efficient methodology for Ru(II)-catalyzed enantioselective alkenyl C–H bond functionalization of indole-substituted acrylaldehyde derivatives via the chiral transient directing group (CTDG) strategy to obtain optically active pyrrolo[1,2-a]indole derivatives was suggested. The methodology resulted in a series of optically active products with good yields (up to 80%), good stereoselectivity (up to 25.0:1 Z/E), and excellent enantioselectivity (up to 95% ee). Furthermore, synthetic transformations were explored. Chapter IV presented the first demonstration of a sequentially composed catalytic substitution reaction of alkenes for building multi-amido methylated derivatives while reserving the π- components. The process involved a simple Fe (III)-catalyst and bisamidomethane reagent, which directly and selectively transformed α-substituted styrenes into several biologically and pharmaceutically relevant N-heterocycles through tandem processes.

M.Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology / Water contaminated with non-biodegradable organics is becoming increasing problematic as it has a hazardous effect on human health and the aquatic environment. Therefore, the removal of organic contaminants is of importance and an active heterogeneous Fenton catalyst is thus required. The literature indicates that a bimetallic oxide Fenton catalyst is more active than an iron oxide catalyst. This study focused on increasing the activity of iron-based Fenton catalysts with the addition of transition metals such as manganese, cobalt and copper and optimizing the preparation method. In this study, bimetallic oxide (Fe-Cu, Fe-Mn, Fe-Co) and monometallic oxide (Fe, Cu, Mn,Co) catalysts supported on silica SiO2 where prepared by incipient wetness impregnation. The total metal oxide contents were kept constant. The catalysts where calcined in two different ways, in a conventional oven and in a microwave. These catalysts were characterized with XRD, XPS and CV and were tested for the degradation of methylene blue dye at 27°C. The catalysts calcined in a microwave oven had a higher catalytic activity than those prepared in a conventional oven. The bimetallic oxide catalysts outperformed the mono- metallic oxide catalysts in the degradation of methylene blue. The Fe2MnOx prepared by microwave energy were the most active catalyst yielding the highest percentage of degradation of methylene blue dye (89.6%) after 60 minutes. The relative amounts of manganese and iron oxide were varied while keeping the total metal content in the catalyst the same. The optimum ratio of Fe to Mn was 1:7.5 since it yielded the most active catalyst. A 96.6 % removal of methylene blue was achieved after 1 hour of degradation. Lastly this ratio 1Fe:7.5Mn was prepared by varying different microwave power (600, 700 and 800 W) and irradiation time (10, 20 and 30 min). The optimum microwave power and irradiation time was 800W and 10 min with the methylene blue percentage removal of 96.6 % after 1 hour of degradation.

<p>  </p> <p>A historically important reaction, the Ueno-Stork reaction promotes, through the use of toxic organotin species, the cyclization of a haloacetal onto an alkene generating bicyclic acetals. This reaction has been used over the years in several total syntheses of biologically relevant natural products, especially the prostaglandin class of natural products. Herein, will be described the development of a novel nickel-catalyzed Ueno-Stork cyclization reaction, which no toxic organotin and radical promoters are used, and instead a greener, operationally friendly, and non-toxic earth abundant nickel catalyst is applied. Optimization studies, substrate scope, scalability, relative stereochemistry of the bicyclic acetals, as well as derivatization of the products were studied. Furthermore, the newly developed reaction was applied on the total synthesis of tricyclic-PGDM Methyl ester, a prostaglandin D2 metabolite of important clinical relevance that currently suffers from material supply issues.</p> <p>Cyclopropanol ring opening reactions have different reactivity modes. Either a metal homoenolate species or a b-keto radical species can be formed after ring opening depending on the reaction conditions applied. More specifically, hydroxycyclopropanols have been studied to access several important motifs present in an array of natural products and medicinally important molecules. The Dai group has used this strategy to access several motifs through intramolecular trapping of the homoenolate species with and without the presence of carbon monoxide to generate oxaspirolactones, THF/THP-fused bicyclic lactones, and disubstituted THF/THP heterocycles. Herein, it will be discussed the application of similar concepts to access new classes of heterocycles 4-ketovalerolactones and 3-furanones. The optimization of two reaction conditions to selectively synthesize each product starting from the same starting material was studied. Furthermore, the substrate scope, scale-up, and derivatization studies of each motif will be disclosed. </p>

No description available.

The two main requirements for ceria-zirconia hydrodeoxygenation (HDO) catalysts are the presence of defect sites to bind oxygenates and the ability to adsorb and dissociate hydrogen. Two types of sites were identified for exchange of hydrogen and deuterium. The activation energy for one type of site was associated with H2-D2 exchange through oxygen defect sites. The activation energy for the second type of site was associated with H2-D2 exchange through hydroxyl groups and correlated with crystallite size. Ceria-zirconia can convert guaiacol, a model pyrolysis oil compound, with a high selectivity to phenol, an HDO product. Ceria-zirconia catalysts had a higher conversion of guaiacol to deoxygenated products as well as a higher selectivity towards phenol than pure ceria. They did not deactivate over the course of 72 hours on stream, whereas coking or the presence of water in the feed can cause serious decay of common HDO catalysts HDO. Therefore, ceria-zirconia catalysts are promising HDO catalysts for the first step of deoxygenation. The stability of supported Ru on ZrO2 in acidic or basic environments at reaction temperature is examined. In this study, the ruthenium dispersion is greatly increased by hydrothermal treatment in acidic and basic pH without alterations to the surface area, pore volume, pore size or crystal structure. An increase in Ru dispersion showed an increase in the selectivity to propylene glycol relative to ethylene glycol. A decrease in total Lewis acid site concentration was correlated with a decrease in the ethylene glycol yield. The conclusions of this study indicate that stability of catalysts in realistic industrial environments is crucial to the design of catalysts for a reaction.

Doctor of Philosophy / Department of Chemical Engineering / Keith L. Hohn / Superparamagnetic iron oxide nanoparticle functionalization is an area of intensely active research, with applications across disciplines such as biomedical science and heterogeneous catalysis. This work demonstrates the functionalization of iron oxide nanoparticles with a quasi-monolayer of 11-sulfoundecanoic acid, 10-phosphono-1-decanesulfonic acid, and 11-aminoundecanoic acid. The carboxylic and phosphonic moieties form bonds to the iron oxide particle core, while the sulfonic acid groups face outward where they are available for catalysis. The particles were characterized by thermogravimetric analysis (TGA), transmission electron microscopy (TEM), potentiometric titration, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray photoelectron spectrometry (XPS), and dynamic light scattering (DLS). The sulfonic acid functionalized particles were used to catalyze the hydrolysis of sucrose at 80˚C and starch at 130˚C, showing a higher activity per acid site than the traditional solid acid catalyst Amberlyst-15, and comparing well against results reported in the literature for sulfonic acid functionalized mesoporous silicas. In sucrose catalysis reactions, the phosphonic-sulfonic nanoparticles (PSNPs) were seen to be incompletely recovered by an external magnetic field, while the carboxylic-sulfonic nanoparticles (CSNPs) showed a trend of increasing activity over the first four recycle runs. Between the two sulfonic ligands, the phosphonates produced a more tightly packed monolayer, which corresponded to a higher sulfonic acid loading, lower agglomeration, lower recoverability through application of an external magnetic field, and higher activity per acid site for the hydrolysis of starch. Functionalizations with 11-aminoundecanoic acid resulted in some amine groups binding to the surfaces of iron oxide nanoparticles. This amine binding is commonly ignored in iron oxide nanoparticle syntheses and functionalizations for biomedical and catalytic applications, affecting understandings of surface charge and other material properties.

In recent years an emphasis has been placed on the development of alternative and clean energy sources to reduce the global use of fossil fuels. One of these alternatives entails the use of H2 as an energy carrier, which can be obtained amongst others using thermochemical processes, for example the hybrid sulphur process (HyS). The HyS process is based on the thermal decomposition of sulphuric acid into water, sulphur dioxide and oxygen. The subsequent chemical conversion of the sulphur dioxide saturated water back to sulphuric acid and hydrogen is achieved in an electrolyser using a platinum coated proton exchange membrane. This depolarised electrolysis requires a theoretical voltage of only 0.158 V compared to water electrolysis requiring approximately 1.23 V. One of the steps in the development of this technology at the North-West University, entailed the establishment of the platinum coating technology which entailed two steps; firstly using newly obtained equipment to manufacture the membrane electro catalyst assemblies (MEA’s) and gas diffusion electrodes (GDE’s) and secondly to test these MEA’s and GDE’s using sulphur dioxide depolarized electrolysis by comparing the manufactured MEA’s and GDE’s to commercially available MEA’s and GDE’s. Different MEA’s and GDE’s were manufactured using both a screen printing (for the microporous layer deposition) and a spraying technique. The catalyst loadings were varied as well as the type and thickness of the proton exchange membranes used. The proton exchange membranes that were included in this study were Nafion 117®, sPSU-PBIOO and SfS-PBIOO membranes whereas the gas diffusion layer consisted of carbon paper with varying thicknesses (EC-TP01-030 – 0.11 mm and EC-TP01-060 – 0.19mm). MEA and GDE were prepared by first preparing an ink that was used both for MEA and GDE spraying. The MEA’s were prepared by spraying various catalyst coatings onto the proton exchange membranes containing 0.3, 0.6 and 0.9 mg/cm2 platinum respectively. The GDE’s were first coated by a micro porous carbon layer using the screen printing technique in order to attain a suitable surface for catalyst deposition. Using the spraying technique GDE’s containing 0.3, 0.6, 0.9 mg/cm2 platinum were prepared. After SEM analysis, the MEA’s and GDE’s performance was measured using SO2 depolarized electrolysis. From the electrolysis experiments, the voltage vs. current density generated during operation, the hydrogen production, the sulphuric acid generation and the hydrogen production efficiency was obtained. From the results it became clear that while the catalyst loading had little effect on performance there were a number of factors that did have a significant influence. These included the type of proton exchange membrane, the membrane thickness and whether the catalyst coating was applied to the proton exchange membrane (MEA) or to the gas diffusion layer (GDE). During SO2 depolarized electrolysis VI curves were generated which gave an indication of the performance of the GDE’s and MEA’s. The best preforming GDE was GDE-3 (0.46V @ 320 mA/cm2), which included a GDE EC-TP01-060, while the best preforming MEA’s were NAF-4 (0.69V @ 320mA/cm2) consisting of a Nafion117 based MEA and PBI-1 (0.43V @ 320mA/cm2) made from a sPSU-PBIOO blended membrane. During hydrogen production it became clear that the GDE’s produced the most hydrogen (best was GDE-02 a in house manufactured GDE yielding 67.3 mL/min @ 0.8V), followed by the Nafion® MEA’s (best was NAF-4 a commercial MEA yielding 57.61 mL/min @ 0.74V) and the PBI based MEA’s. , (best was PBI-2 with 67.11 mL/min @ 0.88V). Due to the small amounts of acid produced and the SO2 crossover, a significant error margin was observed when measuring the amount of sulphuric acid produced. Nonetheless, a direct correlation could still be seen between the acid and the hydrogen production as had been expected from literature. The highest sulphuric acid concentrations produced using the tested GDE’s and MEA’s from this study were the in-house manufactured GDE-01 (3.572mol/L @ 0.8V), the commercial NAF-4 (4.456mol/L @ 0.64V) and the in-house manufactured PBI-2 (3.344mol/L @ 0.8V). The overall efficiency of the GDE’s were similar, ranging from less than 10% at low voltages (± 0.6V) increasing to approximately 60% at ± 0.8V. For the MEA’s larger variation was observed with NAF-4 reaching efficiencies of nearly 80% at 0.7V. In terms of consistency of performance it was shown that the Nafion MEA’s preformed most consistently followed by the GDE’s and lastly the PBI based MEA’s which for the PBI based membranes can probably be ascribed to the significant difference in thickness of the thin PBI vs. the Nafion based membranes. In summary the study has shown the results between the commercially obtained and the in-house manufactured GDE’s and MEA’s were comparable confirming the suitability of the coating techniques evaluated in this study. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2014