Vid produktion av biodiesel produceras även råglycerol (10 vikt%) som biprodukt och utbudet av råglycerol har ökat över de senaste åren till följd av att biodieselproduktionen ökat. Marknadsvärdet för råglycerol är lågt, men det är en utmärkt föregångare till att producera mervärdesprodukter för exempelvis läkemedelsindustrin, kemikalieindustrin eller kosmetika. Genom att reformera glycerol till mervärdesprodukter ökar konkurrenskraftigheten för biodiesel och värdekedjans ekonomiska hållbarhet. Elektrokemisk reformering av glycerol är en lovande metod för att producera dess mervärdesprodukter, eftersom processen är justerbar och miljövänlig. En ytterligare fördel är att vätgas kan samproduceras med mervärdesprodukterna genom denna metod och energikonsumtionen för att producera vätgas genom denna metod är ungefär hälften av vad som krävs vid vattenelektrolys. Denna studie utvärderar hur masstransport påverkar selektiviteten och prestandan för elektrokemisk oxidation av glycerol, genom att utföra elektrokemiska experiment, karaktärisera processens katalysator och analysera produkter som produceras.  Den experimentella uppställningen innefattar en roterande diskelektrod med ett elektrodepositerat lager av Pd, på ett Ni-substrat, i varierande tjocklek. Elektroden undersöks i elektrolyter bestående av varierande koncentration av NaOH (1, 0.5 och 0.25 M) och 0.5 M glycerol vid 25 oC. Systemet konstrueras även som modell i Comsol Multiphysics 6.0 för att simulera experiment. Resultaten visar att masstransport av glycerol begränsar systemet genom att orsaka deaktiveringen av katalysatorn. Vid de lägre NaOH koncentrationerna begränsar även masstransport av OH- reaktionshastigheten genom att miljön omgärdande elektroden blir mindre oxidativ. Slutligen visas att reaktionsmekanismen vid alla tjocklekar av katalysatorn utgörs av två parallella reaktionsvägar. En ökande tjocklek hos katalysatorn ökar selektiviteten mot den ena reaktionsvägen framför den andra, samt ökar antal oxidationssteg som åstadkoms vid reaktionen. / Biodiesel production gives rise to 10 wt% crude glycerol as a byproduct, which is becoming increasingly available on the market owing to the increased biodiesel production over the last few years. Crude glycerol has a low market value, but it is an excellent precursor to producing value added products for the pharmaceutical industry, chemical industry or cosmetics to mention a few. By producing value added products with biodiesel derived glycerol, the ability of biodiesel to compete with fossil fuels is improved and its economical sustainability is promoted. One of the most promising methods to convert glycerol into its value added products is electrochemical reforming, as it poses high tunability and is an environmentally friendly process. Additionally, the process produces hydrogen concurrently and halves the energy consumption compared to producing hydrogen from water electrolysis. This study evaluates the impact of mass transport in the glycerol electrooxidation reaction (GEOR), as a parameter that can be used to finetune product selectivity and optimise the system performance. To do so, the study employs electrochemical experiments, catalyst characterisation and product analysis. The experimental setup consists of a rotating disk electrode (RDE) cell with electrodeposited Pd on Ni substrate at varying thicknesses, operating in 1, 0.5, 0.25 M NaOH and 0.5 M glycerol electrolyte at 25 oC. Additionally, the system is modelled in Comsol Multiphysics 6.0 which is used to perform simulations. It is found that mass transport of glycerol is limiting the system by causing the deactivation of the catalyst. At lower NaOH bulk concentrations for the thicker electrodes, the mass transport of OH- also limits the reaction rate by causing the formation of a locally less oxidative environment. Finally, it is found that all electrodes pose dual reaction mechanisms. Increasing the electrode thickness promotes one reaction mechanism over the other as well as it increases the number of oxidation steps achieved in the reaction.

Die Umsetzung von Kohlenwasserstoffen mit Wasserstoff auf Pd-Modellkatalysatoren wurde anhand von Molekularstrahlmethoden (MB) und IR-Spektroskopie mit Schwerpunkt auf dem Verständnis von mikroskopischen Faktoren, die die Aktivität und Selektivität bestimmen, studiert. Exemplarisch wurden die Reaktionen von cis-2-Buten mit H2(D2), cis-trans-Isomerisierung und Hydrierung, über einem geträgterten Pd/Fe3O4/Pt(1111)-Modellkatalysator und einem Pd(111)-Einkristall erforscht. Es wurde gezeigt, dass die Aktivität und Selektivität des Pd-Modellkatalysators stark von dessen Fähigkeit abhängt, ausreichend hohe Konzentrationen von H auf und in den Pd-Partikeln aufzubauen und aufrechtzuerhalten. Während Isomerisierung effektiv abläuft, wenn nur Oberflächen-H verfügbar ist, wird für die Hydrierung eine zweite Art von H-Spezies benötigt, welche mit Volumen-H assoziert ist. Kohlenstoffablagerungen auf niedrig-koordinierten Plätzen der Pd-Partikel induzieren anhaltende Hydrierung, was einer Begünstigung der H-Diffusion ins Pd-Volumen zugeschrieben wurde. Kohlenwasserstoffspezies hingegen inhibieren die Bildung von Oberflächen-H sowie noch stärker die von Volumen-H. Gepulste MB-Experimente zum H/D-Austausch zur Untersuchung der H-Verteilung zeigten, dass neben regulärem Oberflächen-H, eine zweite Art von H-Spezies, vermutlich Volumen-H, in die HD-Bildung involviert ist. C auf niedrig-koordinierten Plätzen beeinflusst die HD-Bildung vermutlich durch eine Erleichterung der H-Diffusion ins Pd-Volumen. Kohlenwasserstoffe hingegen inhibieren den H/D-Austausch. Die ersten Ergebnisse zur Adsorption und Reaktion von Isophoron, einem alpha,beta-ungesättigtem Keton, mit H2 auf einer Pd(111)-Oberfläche werden präsentiert. Veränderungen der Adsorptionsgeometrie wurden mit steigender Bedeckung und in Anwesenheit von H anhand von IRAS detektiert. In Übereinstimmung mit realistischen Katalysestudien wurde in TPR-Messungen eine deutliche Selektivität zur Hydrierung der C=C-Bindung festgestellt. / The conversion of hydrocarbons with hydrogen over well-defined Pd model catalysts has been studied using pulsed molecular beam (MB) techniques and IR spectroscopy with a special focus on the understanding of microscopic factors governing the activity and selectivity. Exemplarily, the conversion of cis-2-butene with H2(D2) toward cis-trans isomerization and hydrogenation was studied over a supported Pd/Fe3O4/Pt(111) model catalyst and a Pd(111) single crystal surface. It was found that the activity and selectivity of the Pd model catalyst depend strongly on its ability to build up and maintain a sufficiently high concentration of H on and in the Pd particles. While isomerization proceeds effectively when merely surface H is available, for hydrogenation a second hydrogen species is required that is associated with subsurface hydrogen. Carbonaceous deposits located on low-coordinated sites of the Pd particles were found to induce persisting hydrogenation activity which could be attributed to facilitation of H diffusion to subsurface sites. Hydrocarbon species, in contrast, were found to inhibit the formation of surface H and even more pronounced subsurface H. Pulsed MB experiments on the H/D exchange to probe the H distribution showed that - next to regular surface H - a second type of hydrogen species is involved in the formation of HD, most likely subsurface hydrogen. C deposited on low-coordinated sites was shown to affect the HD formation presumably by facilitating subsurface H diffusion. Hydrocarbons strongly inhibit the H/D exchange. The first results on the adsorption and reaction of isophorone, an alpha,beta-unsaturated ketone, with hydrogen over a Pd(111) single crystal surface are presented. Changes in the adsorption geometry with increasing coverage and due to co-adsorbed H were detected using IRAS. In line with realistic catalytic studies, a strong chemoselectivity toward the hydrogenation of the C=C double bond was found in TPR measurements.

Doctor of Philosophy / Department of Chemistry / Stefan Bossmann / My thesis is divided into two parts. The first part is focused on studies of N-heterocyclic carbene (NHC) palladium(IV) intermediates, which are involved in oxidative addition mediated C-C, and C-O bond formation processes as well as in C-Cl bond forming reactions via a reductive elimination process. Bis-NHC-Pd(II) complexes have been reported as effective catalysts to mediate direct conversion of methane into methanol. However, a H-D exchange study revealed that the bis-NHC-Pd(II) complexes are not the active species responsible for the C-H bond activation reaction. This unexpected result implies that the high oxidation state bis- NHC-Pd(IV) species may be the real catalyst! The oxidative addition of methyl iodide to the bis- NHC-Pd(II)-Me2 complex led to the successful observation of the formation of a transient trimethyl bis-NHC-Pd(IV) intermediate by both 1H-NMR and 13C-NMR spectroscopy. Different oxidants such as O2, PhI(OAc)2, PhI(OTFA)2 and Cl2 reacted with the bis-NHC-Pd(II)-Me2 complex, and competitive C-C and C-O bond formations, as well as C-C and C-Cl bond formations were observed. Dioxygen triggered C-C bond formation under dry condition and both C-C and C-O bond formation in the presence of H2O gave strong indications that the bis-NHCPd( II)-Me2 complex can be oxidized to a bis-NHC-Pd(IV) intermediate by dioxygen. The reaction between the hypervalent iodine regents PhI(OAc)2 and PhI(OTFA)2 and the bis-NHCPd( II)-Me2 complex gave only reductive elimination products. Therefore, this system can act as a model system, which is able to providing valuable information of the product forming (functionalization) step of the C-H bond activation system. The reaction between chlorine and the bis-NHC-Pd(II)-Me2 complex resulted in a relatively stable bis-NHC-Pd(IV)-Cl4 complex, which was characterized by 1H-NMR spectroscopy and mass spectroscopy. The structure of bis- NHC-Pd(IV)-Cl4 was unambiguously established by X-ray crystallography. The second part of this thesis describes the synthesis of functionalized bimagnetic core/shell iron/iron oxide nanoparticles for the treatment of cancer. Biocompatible dopamineoligoethylene glycol functionalized bimagnetic core/shell Fe/Fe3O4 nanoparticles were prepared via ligand exchange, and purified by repeated dispersion/magneto-precipitation cycles. A porphyrin (TCPP) has been tethered to the stealth nanoparticles to enhance their uptake by tumor cells and (neural) stem cells. The stealth nanoparticles have been delivered in a mouse model to tumor sites intravenously by using the EPR (enhanced permeation and retention) effect. Magnetic hyperthermia proved to be very effective against B16-F10 mouse melanomas in Charles River black mice. After hyperthermia, the nanoparticles have shown a significant effect on the growth of tumor (up to 78% growth inhibition).

The aim of this work was to investigate palladium-catalysed cyclisations of bromoenynamides in the synthesis of amidodienes, which on further reaction or oxidation can lead to a diverse range of heteroaromatic systems. Building upon work within the Anderson group on the palladium-catalysed cyclisations of bromoenynes, we have been able to successfully apply a palladium-catalysed carbopalladation/Stille coupling/electrocyclisation cascade to bromoenynamides and then further develop this to incorporate a Suzuki coupling, leading to bicyclic amidodienes which can undergo selective oxidation to a range of heteroaromatics including indolines, indoles, tetrahydroquinolines and benzazepines. During the investigations into the cascade cyclisation, a reductive cyclisation was discovered which enabled access to a range of monocyclic amidodienes. These could subsequently be subjected to a series of Diels-Alder cycloadditions (thermal, Lewis acid-catalysed, arynes) and oxidations to afford a complimentary range of heteroaromatic systems. Whilst this methodology was successful with bromoenynamides, extension of its application to bromoenynhydrazides, with the hope of accessing a relatively unusual range of heteroaromatic structures including indazoles, cinnolines and diazepines, proved to be more problematic. Finally, expansion of the cascade methodology into a fully intramolecular cyclisation, enabled studies towards the synthesis of the trikentrin family of natural products to be conducted.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 1997. / This study focuses on the preparation and characterization of palladium-silver-nickel composite membranes. Electroless plating was used to deposit thin metal films on aluminazirconia membrane supports. Palladium conversion, in the electroless palladium plating process, was optimized with the aim of minimizing expensive palladium losses. The effect of deposition order on alloy composition and heat treatment on structural characteristics of the composite membrane was investigated. The inorganic support membranes were thoroughly cleaned and pretreated prior to plating to catalyze the surface. Factorial designs were used to obtain the maximum palladium conversion. Tetra amine palladium nitrate gave better solution stability and resulted in higher conversions than tetra amine palladium chloride. Buffer pH values of 9 to 11 caused little variation in palladium conversion. Moving outside this range resulted in a sharp decline in palladium conversion. At a pH of 9 to 11 the stabilizer is in the correct ionic form (EDTA3 and EDTA4,) to best stabilize the palladium ions, and hydrazine acts as a proper reducing agent. Significant interactions existed between the EDTA concentration (stabilizer) and hydrazine concentration (reducing agent) and between EDTA and temperature. The EDTA concentration was the most sensitive variable. A 27.5 g 10% tetra amine palladium nitrate solution per liter plating solution was used. Conversions exceeding 80% were obtained after three hours plating with 20 ml plating solution at the following conditions: temperatures from 71 to 77 DC, 40-60% molar excess hydrazine, EDTA:Pd-salt molar ratios between 30:1 and 40: 1 and buffer pH = 11. Silver plating rates for two hours plating of up to 2 mg/cm2 were obtained using a dilute silver nitrate solution with hydrazine as reducing agent. Electroless nickel plating was performed in a low temperature bath (40 DC) with nickel sulphate as source of metal ions and sodium hypophosphite as reducing agent. Metal films were fully characterized before and after heat treatment for 5 hours in a hydrogen atmosphere at 650 dc. Scanning electron microscopy (SEM) was used to analyze the surface structure. X-ray diffraction (XRD) patterns were taken to examine alloying and detect changes in the crystal structure .after heating. Energy dispersive X-ray maps (EDS) were used to visualize the diffusion process and particle induced X-ray emission (PIXE) was used to construct concentration profiles across the thickness of the metal films. Palladium deposits were dense, but columnlike, with a purity of 99.75%. Silver deposits were non-homogeneous, in other words it did not cover the entire substrate. The purity of the silver films was 99.5%. The nickel films were about 97% pure, very dense and defect free. When silver was deposited on palladium, the alloy penetrated more than 3 microns into the support and the palladium and silver concentrations varied across the thickness of the film after heating. By depositing palladium on silver, there was very little penetration into the support membrane pores (about 1 micron) and the palladium to silver ratio remained constant across the thickness of the film after heating. Silver-palladium-nickel alloy films call be prepared by first depositing silver, then palladium and finally nickel. During heat treatment, a counter diffusion process took place and the smaller nickel atoms penetrated into pores and defects that might be present in the palladium-silver solid solution. By adding more than 3% nickel, dense defect free films can be prepared, which is much thinner than conventional palladium-silver films. This method makes it possible to reduce the film thickness of dense, non-porous films to less than 5 microns, reducing fabrication cost and increasing the hydrogen flux through the film. Dense, non-porous palladium-silver films are usually in the range of 10-15 microns.

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: In this thesis we describe the synthesis of several new N-(n-propyl)-1-(2-pyridyl and quinolyl)-imine ligands (ML1-ML4) as well as peripheral functionalised iminopyridyl and iminoquinolyl poly(propylene-imine) dendrimeric ligands (DL1-DL8) with a 1,4- diaminobutane core. The dendrimeric ligands were obtained by modification of the peripheral groups of Generation 1 and Generation 2 poly(propylene-imine) dendrimers, (DAB-(NH2)n which are commercially available, with a series of aldehydes. All the ligands were fully characterised by ESI-mass spectrometry, elemental analysis, 1H&13C{1H}-NMR, FT-IR and UV/Vis spectroscopies. These ligands were utilised to synthesise Pd(II) and Cu(I) complexes using appropriate metal precursors. Some of mononuclear complexes, [N-(n-propyl)-(2-pyridyl and quinolyl) methanimine] dichloro Pd(II) complexes (C1-C4) and bis[N-(n-propyl)-(2-pyridyl and quinolyl) methanimine] copper(I) tetrafluoroborate complexes (C14) were structurally characterised. Pd(II) complexes adopted a distorted square-planar geometry around the metal centre while Cu(I) complex exhibit a distorted tetrahedral arrangement around the metal centre. Both Pd(II) and Cu(I) multinuclear complexes (metallodendrimers) were characterised using a range of analytical techniques. / AFRIKAANSE OPSOMMING: In hierdie tesis word die sintese van verskeie nuwe N-(n-propiel)-1-(2-piridiel) en kinolielimien ligande (ML1-ML4) sowel as gefunksioneerde imienopiridiel en imienokinoliel poli(propilien-imien) dendrimeriese ligande (DL1-DL8) beskryf. Die dendrimeriese ligande was behaal deur die modifikasie van perifere groepe van Generasie 1 en Generasie 2 poli(propilien-imien) dendrimere met ‘n reeks aldehiede. Alle ligande was volledig deur ESI-massaspektrometrie, elementele analiese, 1H en 13C{1H} – KMR, FT-IR en UV/Sigbare spektroskopie gekarakteriseerd. Hierdie ligande was gebruik om Pd(II) en Cu(I) komplekse te berei om van die gepaste metaal voorlopers te gebruik te maak. Sommige van die mono-kern komplekse, [N-(npropiel)-( 2-piridiel) en kinoliel metanimien] dikloor Pd(II), komplekse (C1-C4) en bis[N-(npropiel)-( 2-piridiel) metanimien] koper(I) tetrafloorboraat, kompleks (C14) was struktureël gekarakteriseerd. Pd(II) komplekse neem ‘n versteurde vierkant valk geometrie om die metaal senter aan, terwyl die Cu(I) kompleks, ‘n versteurde tetrahedriese opset rondom die metaal toon. Beide Pd(II) en Cu(I) multikern komplekse (metaaldendrimere) was deur ‘n verskeidenheid van analitiese tegnieke gekarakteriseerd.

Thesis (MSc)--University of Stellenbosch, 2011. / Please refer to full text for abstract.

Thesis (PhD)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: Please refer to fulltext for abstract / AFRIKAANSE OPSOMMING: Sien asb volteks vir opsomming.

The development and optimisation of conditions for oxidative Wacker-type cyclisations followed by establishing the reaction scope are reported. Building upon the achievements in the field of oxidative Wacker-type reactions that has recently gathered interest, hydroxylamines and hydrazines were converted to isoxazolidines and pyrazolidines respectively. Secondary hydroxylamines cyclised yielding syn-isoxazolidines with excellent diastereoselectivities, whereas secondary hydrazines cyclised yielding anti-pyrazolidines but still maintained a high level of diastereoselectivity. Additionally, an enantioselective variant was explored. Isoxazolidines were successfully transformed to the corresponding 1,3-amino alcohols, which were further converted to amino sugar derivatives.

Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: The determination of the platinum group metals (PGMs), platinum, palladium, rhodium, iridium, ruthenium and osmium, remains a problem for the low-grade ore samples, and the analysis of these samples in a routine laboratory relies entirely on the fire assay technique. The use of large sample masses to overcome sub-sampling errors has been the greatest advantage of this technique. The increased economic value of PGMs and recent developments in instrumentation such as inductively coupled plasma-mass spectrometry (ICP-MS) which is capable of trace element detection as low as part per billion (Ppb) levels, have led to a search for complementary methods to ensure the accuracy of fire assay results. This work investigates the feasibility of direct dissolution of ore samples using microwave-assisted dissolution followed by ICP-MS as the measurement technique. Due to the limited sample mass that can be used, a thorough consideration had to be given to sampling errors and analytical errors to assess the overall precision achievable. Most PGM-bearing minerals occur as sulphides and these are highly resistant to acid dissolution. It was found that roasting the Merensky type samples in air, prior to dissolution gives quantitative recoveries for platinum. Recoveries up to 100% were obtained for platinum, palladium, rhodium and gold for a Merensky flotation concentrate with excellent precision (about 4%) except for gold which had poorer precision (16%). However, ore samples presented a problem due to their lower PGM content and smaller sample masses being used. Precision for all elements improved significantly (from about 20% to about 8%), with the use of l g-sample aliquot compared to that ofO.25 g-sample. Acid dissolution, even after roasting proved to be insufficient for the UG-2 chromitite samples. When roasting was followed with reduction under hydrogen flame the solubility of the UG-2 flotation concentrate improved remarkably. The recoveries obtained were approximately 95 ± 5% for platinum, 99 ± 5% palladium, 104 ± 12% gold and 102 ± 5% for rhodium with good precision (comparable to that of Merensky concentrate). The accuracy and precision of the results depended very much on the sample mass and air-flow in the furnace during the roasting procedure. For this method to be used successfully, the air flow is very critical, and should lead to a better furnace design which can rotate the crucibles to enable an even flow of air over all the samples during roasting. / AFRIKAANSE OPSOMMING: Die bepaling van platinumgroep metale (PGM'e), platinum, palladium, rhodium, iridium, ruthenium en osmium is 'n voortdurende probleem vir die lae-graad erts monsters. Die analise van hierdie monsters in 'n roetine laboratorium is geheel afhanklik van die klassieke "fire assay"-tegnieke. Die groot voordeel van hierdie tegniek is die voorkoming van monsternemingsfoute deur die gebruik van groter monster massas. Die ekonomiese waarde van PGM'e saam met die onlangse ontwikkeling van instrumentasie soos die induktief-gekoppelde plasma-massaspektrometrie (IGP-MS) wat in staat is om spoorelemente in konsentrasies so laag soos dele per biljoen (ppb) te meet, het daartoe gelei na soeke vir komplementêre metodes om die akkuraatheid van klassieke "fire assay" -tegnieke te verseker. Hierdie werk ondersoek die waarskynlikheid van direkte oplossing van ertsmonsters deur gebruik te maak van mikrogolf-ondersteunde oplossing gevolg deur IGP-MS as opmetingstegniek. As gevolg van die beperkte monster massa wat gebruik kan word, moes deeglike oorweging gegee word aan monsternemingsfoute en analitiese foute, om die oorkoepelende presiesheid te bepaal. Meeste PGM-draende minerale bestaan in die vorm van sulfiede en bied groot weerstand teen oplossing in 'n suur. Die gloei van Merensky-tipe monsters in lug voor oplossing gee kwantitatiewe herwinning van platinum Herwinning tot 100% is behaal vir platinum, palladium, rhodium en goud vir 'n Merensky-flotasie-konsentraat met uitstekende akkuraatheid (4%) behalwe vir goud met 'n swak (16%) akkuraatheid. Die erts monsters was problematies as gevolg van die laer PGM inhoud en kleiner monstermassas wat gebruik is. Presiesheid vir al die elemente het beduidend verbeter (van 20% tot 8%) met die gebruik van 1 g- monster massas vergelyk met 0.25 g-monsters. Ten spyte van die gloei van die monster is suur oplossing onvoldoende vir die UG-2 chromatiet-houdende monsters. Wanneer die monster gegloei is onder 'n waterstof vlam (reduksie) het die oplossbaarheid van UG-2 flotasie-konsentraat aansienlik verbeter. Die herwinbaarheid wat behaal is, is 95 +/- 5% vir platinum, 99 +/- 5% vir palladium, 104 +/- 12% vir goud en 102 +/- 5% rhodium met goeie relatiewe presiesheid vergeleke met Merensky-konsentrate. Die akkuraatheid en presiesheid van resultate hang meerendeels af van monster massa en lugvloei in die oond gedurende gloei. Die lugvloei is krities vir die sukses van hierdie metode en sal moet lei tot beter oond ontwerp wat kroesies kan roteer en 'n gelyke vloei van lug oor die monsters gedurende verbranding toelaat.