Thesis (Ph. D.)--Ohio state University, 1917.

Graduation date: 1995

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 142-144) Also available in print.

Protonation and hydrogen bonding effects on the redox properties of verdazyl radicals were investigated. Verdazyls with various substituents at the C3 position were synthesized, including species with no basic site, a basic site distant from the verdazyl heterocycle, a basic site proximal to the verdazyl heterocycle but with strained hydrogen bonding geometry, and a basic site proximal to the verdazyl heterocycle with favourable hydrogen bonding geometry. Treatment of these verdazyls with trifluoroacetic acid resulted in several general changes to their cyclic voltammograms: the oxidation and reduction potentials shifted to higher potentials, with concurrent loss of reversibility of the reduction process due to protonation of the verdazylate anion. These changes were likely a result of intermolecular interactions between the substrate and acidic medium rather than specific protonation or intramolecular hydrogen bonding effects. Acid treatment of the verdazyl with favourable hydrogen bonding geometry resulted in emergence of a new reversible process in the CV that was found to match the oxidation process of the corresponding leuco verdazyl. Attempts to synthesize this leuco verdazyl were successful, however purification was not completed. Spectroscopy of the crude product suggests that it may be stable to air, an uncommon feature in leuco species due to their propensity to be easily oxidized by O2. Preliminary investigations of the potential of verdazyls as alcohol oxidation catalysts were made. Several previously reported and novel species were investigated as stoichiometric and catalytic oxidants akin to nitroxides and phenoxyls. It was found that the verdazyls, verdazylium cations and verdazyl-metal complexes tested did not stoichiometrically or catalytically oxidize alcohols. / Graduate

The focus of this thesis was on the synthesis, characterization and application of ceria nanocubes. This thesis is divided into two main sections; the first section investigates the electronic properties of ceria nanocubes, and the second explores their catalytic applications towards alcohol oxidation reactions. The first project of this thesis consisted of the X-ray characterization of hydrothermally synthesized ceria nanocubes of various sizes. For the first time, the electronic properties of such nanocubes were systematically studied using high resolution XPS and XANES. It was found that the concentration of Ce3+ present within the nanocubes was independent of the particle size, as well as the Ce precursor used during synthesis. Throughout the analysis of the Ce 3d and 4d XPS spectra, it was observed that the surface of the ceria nanocube samples was undergoing photoreduction/damage over time. This damage was attributed to the samples’ exposure to high intensity X-ray radiation. This was confirmed through examination of the Ce M4,5- and N4,5-edge XANES spectra. From these results, it was clear that the concentration of Ce3+ on the surface of the ceria nanocubes was independent of particle size. This fact may become important when investigating their potential catalytic activity. The second project of this thesis concentrated on the analysis of the catalytic activity of a variety of CeO2, Au and Au/CeO2 catalysts towards the oxidation of benzyl alcohol. The low temperature oxidation reactions were studied using 1H NMR spectroscopy. It was observed that Au NPs, Au/bulk CeO2, and Au/CeO2 nanocubes in water and K2CO3 were active catalysts for this oxidation reaction at 60°C in both air and O2 (g) atmospheres. Surprisingly, however, the Au/bulk CeO2 and Au/CeO2 nanocube catalysts showed very similar activities. It was also found that ceria nanocubes alone, and Au25(SR)18/bulk CeO2 showed no activity for this reaction under similar conditions. It was determined that below a substrate to catalyst ratio of ~ 1500:1, the Au/CeO2 catalysts, which showed the highest activities, were mass-transport limited with respect to the O2 in the system. The turnover frequencies of the supported catalysts were approximately double those of the unsupported NPs. Furthermore, these reactions have indicated that activating Au25(SR)18/CeO2 for catalysis is a non-trivial task, and more work needs to be done to understand the activation of such clusters.

Thesis (Ph. D.)--University of Hong Kong, 1990.

It is ideal to theoretically predict the activity of a catalyst. It has been recognized that not only the type of metal, but also its atomic size plays an important role in catalysis. In the past, atomic clusters have been created by sputtering from a sacrificial metal plate and then using a mass selector to choose cluster sizes from 1-233 atoms of gold. This approach has practical limitations. In this thesis, I describe a procedure by which atomic clusters of gold containing 1-8 atoms are deposited in polyaniline as an isolation matrix. My atomic deposition follows a cyclic pathway. Atomic clusters of palladium and atomic alloys of gold and palladium are also deposited in polyaniline using the same process. It is to show that this method will also work for other metals. These composite materials are characterized, and the catalytic activity for alcohol oxidation is evaluated. This thesis is divided into seven chapters. The first chapter discusses the chemistry of polyaniline for using gold and palladium as catalysts. The technique developed to deposit the atomic clusters is discussed in the second chapter. This technique deposits one atom of metal per imine site on polyaniline, per cycle. The cycle is repeated n-times until a cluster of specified size, Mn, and composition has been synthesized. It is known that polyaniline plays an important role in stabilization of the formed clusters which prevents their aggregation. The optimization of this technique is the topic of the third chapter along with the description of how these composite films are produced. To end this chapter, the composite films are characterized by cyclic voltammetry, Kelvin probe, and X-ray photoelectron spectroscopy. In chapters 4 and 5, the catalytic activity of the polyaniline/gold composites for the oxidation of alcohols in alkaline media using cyclic voltammetry is evaluated. In chapter 4, the correlation of the electrochemical activity for the oxidation of n-PrOH with the odd-even pattern from the calculated HOMO-LUMO gap energies for the same size clusters is shown. It is shown that the infrared spectrum of polyaniline with different sizes of atomic gold clusters also follows the odd-even pattern. Chapter 5 expands on the discussion of the catalytic oxidation of alcohols. The oxidation of methanol, ethanol, propanol, and butanol is surveyed. The peak currents are again dominated by the odd-even pattern. In chapter 6, the versatility of the atomic deposition cycle is shown by depositing atomic palladium clusters. The peak currents for the oxidation of n-PrOH by these palladium composite films again follows the predicted pattern of the calculated HOMO-LUMO gap energies for atomic palladium clusters. This chapter also explores bimetallic atomic clusters of gold and palladium. The results indicate that the catalytic activity depends on the orientation of the cluster in the polyaniline matrix. Chapter 7 discusses the oxidation of methanol, ethanol, and isopropanol on AunPd1 bimetallic atomic clusters. The addition of palladium in the cluster increases the peak current densities for the oxidation of both alcohols except for the most stable of the atomic gold clusters, while it inactivated the electrodes for isopropanol. The possible future work for this project is discussed in chapter 8. Overall, this thesis has developed a novel and unique technique for depositing atomic metal clusters into a polyaniline matrix. The technique is versatile enough to deposit atomic metal clusters other than gold, as shown by creating atomic palladium clusters and atomic bimetallic clusters of gold and palladium. This is extremely useful, since this single technique can produce many different types of atomic catalysts. The composite materials have been shown to be catalytically active for the oxidation of alcohols in alkaline media. This indicates a significant improvement to conserve precious metals while still retaining a high catalytic activity.

Thesis (MSc)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: In this thesis the synthesis of a wide range of model and siloxane functionalized N-(n-propyl)-1-(2-pyridyl and quinolyl)-imine ligands (L1-L6) are described. Functionalized ligands (L4-L6) were obtained by the reaction of the pyridyl and quinolyl aldehydes with 3-aminopropyltriethoxysilane. Model ligands were characterized by FT-IR and 1H NMR spectroscopy while 13C{1H} NMR spectroscopy was additionally used for functional ligand characterization. Functionalized complexes of both Pd(II) and Cu(I) were found to be more thermally stable than their model counterparts. Overall the model Pd(II) complexes showed a higher thermal stability than the model Cu(I) complexes. Ligands (L1-L6) were reacted with either Pd(II) or Cu(I) metal precursors to produce both the model and functionalized Pd(II) (C1-C6) and Cu(I) (C7-C12) metal complexes. These metal complexes were all characterized by FT-IR spectroscopy, 1H NMR and UV/Vis spectroscopy for the model Cu(I) complexes. Functionalized complexes were additionally characterized with 13C{1H} NMR spectroscopy. Siloxane functionalized complexes of Pd(II) and Cu(I) were immobilized on MCM-41 and SBA-15 silica materials to produce heterogenized immobilized catalysts. These immobilized catalysts were characterized by a wide range of solid state techniques including: BET nitrogen adsorption/desorption, scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), ICP-AES, FT-IR spectroscopy, powder XRD and solid state 13C{1H} NMR spectroscopy. ICP-AES and BET surface analysis showed that better complex immobilization occurred for SBA-15 supported materials despite SBA-15 having a significantly lower surface area than MCM-41. This higher immobilization was ascribed to the larger pore sizes of SBA-15 (50 Å) vs. that of MCM-41 (26 Å). Immobilized catalysts were tested for the oxidation of benzyl alcohol to benzaldehyde. Immobilization had a positive effect on the catalytic activity of the Pd(II) complexes with higher conversions being observed for immobilized Pd(II) catalysts when compared to their model analogues. Overall the MCM-41 immobilized Pd(II) catalysts showed a higher increase in activity than SBA-15 immobilized catalysts. For Ti-doped supports a generally higher activity was seen for the Ti-SBA-15 system. The Cu(I) systems however were not as effective in the oxidation reactions. / AFRIKAANSE OPSOMMING: In hierdie tesis word die sintese van `n wye reeks model sowel as gefunksioneerde N-(n-propiel)-1-(2-piridiel en kinoliel)-imien ligande (L1-L6) beskryf. Gefunksioneerde ligande (L4-L6) is gevorm deur die reaksie van piridiel en kinoliel aldehied met 3-amniopropieltriëtoksiesilaan. Model ligande is gekaraktariseer deur FT-IR en 1H KMR spektroskopie terwyl 13C{1H} KMR spektroskopie addisioneel gebruik is vir die karaktarisering van die gefunksioneerde ligande. Ligande (L1-L6) is gereageer met Pd(II) of Cu(I) metaal voorgangers om beide model sowel as gefunksioneerde Pd(II) (C1-C6) en Cu(I) (C7-C12) metaal komplekse op te lewer. Hierdie metaal komplekse is almal gekaraktariseer deur FT-IR, 1H KMR en UV/Vis spektroskopie vir die model Cu(I) komplekse. Gefunksionalseerde komplekse is addisioneel gekaraktariseer deur gebruik te maak van 13C{1H} KMR spektroskopie. Dit is gevind dat gefunksionaliseerde komplekse van beide Pd(II) sowel as Cu(I) termies meer stabiel was as hulle ooreenstemmende model komplekse. Oor die algemeen het die Pd(II) komplekse hoër termiese stabiliteit as die Cu(I) komplekse getoon. Siloksaan gefunksioneerde komplekse van Pd(II) en Cu(I) is geimmobiliseer op MCM-41 en SBA-15 silika materiale om heterogene geimmobiliseerde katalisatore op te lewer. Hierdie geimmobiliseerde katalisatore is gekaraktariseer deur van `n wye reeks vaste toestand tegnieke gebruik te maak. Hierdie suit in: SEM, TGA, ICP-AES, FT-IR, poeier XRD en vaste toestand 13C{1H} KMR spektroskopie. ICP-AES en BET oppervlak analieses het getoon dat beter kompleks immobilisering vir die SBA-15 silika material plaas gevind het, ondanks die feit dat SBA-15 `n laer oppervlak area beskik. Hierdie hoër graad van immobilisering is toegeskryf aan die groter poriegrootte van SBA-15 (50 Å) teenoor die van MCM-41 (26 Å). Geimmobiliseerde katalisatore is getoets in die oksidasie van bensielalkohol na bensaldehied. Dit is gevind dat die immobilisering van die Pd(II) komplekse op die silika materiaal `n positiewe uitwerking op die aktiwiteit van die katalitiese van die komplekse gehad het. Die hoogste toename in aktiwiteit is gesien vir geimmobiliseerde Pd(II) katalisatore wanneer hulle met hul ooreenstemmende model komplekse vergelyk is. Oor die algemeen is gevind dat MCM-41 geimmobiliseerde Pd(II) katalisatore n hoër toename in aktiwiteit getoon het as die van SBA-15. Vir die Ti-gedokterde silika materiale het die Ti-SBA-15 sisteem oor die algemeen `n hoër aktiviteit getoon as die Ti-MCM-41 sisteem. Die Cu(I) sisteme was egter nie so effektief in oksidasie reaksies nie.

Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: In this thesis we describe various attempts at incorporating macrocycles into dendritic architectures to form macrocycle-dendrimer conjugates with the aim of preparing materials that would exhibit properties that are more than the sum of the constituent parts, in this case macrocycles and dendrimers. A further aim was the synthesis and characterization of metallodendrimers based on such scaffolds and to test these as catalyst precursors in the catalytic oxidation of alcohols. The synthesis of two different types of conjugate systems was attempted; viz. dendrimers functionalized with macrocycles on the peripheries and dendrimers with macrocyclic cores. The synthesis of conjugate systems based on cyclam as the macrocycle was attempted. This required the mono functionalization of cyclam with a linker molecule capable of further reaction with the functional groups at the periphery of commercially available N,N,N,N-tetrakis(3-aminopropyl)-1,4-butanediamine dendrimer. Several approaches were taken in trying to make such conjugate systems but they were not entirely successful. One of the major issues was the final deprotection step, of the Boc-protected cyclam units which proved difficult in our hands. Another approach to prepare the target conjugates involved the use of click chemistry in order to synthesize a dendrimer with an aromatic core and cyclam peripheries. A dendrimer with Boc-protected cyclam peripheries that are bonded through triazole groups to the aromatic core was synthesized. However, subsequent attempts at de-protection of the cyclam functionalities of this conjugate failed to yield the pure de-protected dendrimer. Greater success was achieved with the preparation of a dendrimer with a macrocyclic core. A cyclam cored dendrimer with salicylaldimine peripheries was successfully synthesized and characterized. This dendritic ligand was complexed to Cu(II), Ni(II) and Zn(II) metal ions respectively to form a series of new metallodendrimers. These metallodendrimers were fully characterized using a range of analytical techniques including FT-IR spectroscopy, mass spectrometry, elemental analysis, thermogravimetric analysis, magnetic susceptibility measurements and NMR spectroscopy where appropriate. The Cu(II) and Ni(II) metallodendrimers were tested as catalyst precursors in the catalytic oxidation of benzyl alcohol to benzaldehyde. The catalytic system consisted of the appropriate metallodendrimer, the free radical, 2,2,6,6-tetramethylpiperidinyl- 1-oxyl (TEMPO) and O2 as the oxidant. The reaction parameters, namely the nature of the solvent, catalyst loading, substrate concentration and reaction temperature were sequentially optimized to achieve the best catalytic efficiency. The Cu(II) catalyst precursor exhibited relatively high catalytic activity and achieved TOF’s between 40 and 30 when operating under the optimized conditions, while the Ni(II) catalytic system showed very poor catalytic activity. / AFRIKAANSE OPSOMMING: In hierdie tesis beskryf ons pogings om makroringe in die dendritiese argitektuur te inkorporeer om makroring-dendrimeer gekonjugeerdes te vorm met die hoop dat sulke molekules eienskappe sal toon wat meer is as die somtotaal van die afsonderlike eenhede. ‘n Verdere doel was die sintese en karakterisering van metallodendrimere gebaseer op sulke draers sowel as die toetsing van hierdie molekules as pre-katalisore in die katalitiese oksidasie van alkohole. Pogings tot die sintese van twee verskillende tipes makroring-dendrimeer gekonjugeerdes word beskryf naamlik, dendritiese ligande met makroringe by die buiterand sowel as dendritiese ligande met ‘n makroring as kern word bespreek. Die sintese van makroring-dendrimeer gekonjugeerdes gebasseer op die makroring cyclam word beskryf. Hierdie sintese vereis die gebruik van ‘n monogefunksioneerde cyclam wat ‘n gepaste koppelingsgroep besit. Hierdie koppelingsgroep kan dan verder met funksionele groepe op die oppervlak van die kommersieel beskikbare DAB-dendrimeer reageer. Verskeie pogings is aangewend om sulke gekonjugeerde stelsels te sintetiseer maar hierdie pogings was nie volkome suksesvol nie. ‘n Groot uitdaging was die gebruik en gevolglike latere verwydering van beskermende groepe soos Boc. ‘n Ander benadering het gebruik gemaak van “click” chemie met die doel om ‘n dendrimeer bestaande uit ‘n aromatiese kern en cyclam periferie te vorm. ‘n Dendrimeer met Boc beskermde cyclam eenhede op die buiterand geheg aan ‘n aromatiese kern deur triasool groepe is gesintetiseer. Die verwydering van die beskermende groepe geheg aan die cyclam eenhede was egter weereens ‘n probleem en hierdie metode kon nie die suiwer dendrimeer lewer nie. Groter sukses is behaal met die sintese van ‘n dendrimeer met ‘n cyclam kern en salisielaldimien periferieë. Die dendritiese ligand is vervolgens met metaalsoute van Cu(II), Ni(II) en Zn(II) gereageer om verskeie multikern metaalkomplekse te vorm. Die metaalkomplekse is volledig gekarakteriseer deur verskeie analitiese tegnieke insluitende infrarooi spektroskopie, massa spektrometrie, termografiese analiese, mikroanaliese asook KMR spektroskopie waar moontlik. Die Cu(II) en Ni(II) metaalkomplekse is geëvalueer as pre-katalisatore in die katalitiese oksidasie van alkohole. Hierdie katalitiese sisteem bestaan uit die metaalkompleks, die radikaal TEMPO en molekulêre suurstof. Die invloed van verskeie reaksie- parameters soos die tipe oplosmiddel, die hoeveelheid katalisator, die konsentrasie van die alkohol asook die temperatuur is ondersoek. Gevolglik is die optimale kondisies bepaal om die hoogste opbrengs van bensaldehied te lewer. Die Cu(II) kompleks het ‘n relatief hoë omset van bensielalkohol na bensaldehied getoon met omset frekwensie waardes tussen 30 en 40 onder die optimale kondisies. Die Ni(II) kompleks het egter swak aktiwiteit getoon vir hierdie transformasie.

O ouro foi considerado um metal pouco interessante do ponto de vista catalítico por muito tempo, devido ao fato de não quimiossorver moléculas como hidrogênio e oxigênio. Entretanto, suas propriedades catalíticas são reveladas quando suas dimensões são reduzidas a poucos nanômetros, particularmente menores do que 10 nm. Assim, nanocatalisadores de ouro vêm recebendo atenção devido as suas excelentes propriedades catalíticas e alta seletividade em reações de oxidação e redução. O presente trabalho descreve a síntese e caracterização de nanopartículas de ouro suportadas e sua aplicação em reações de oxidação de alcoóis para produção de aldeídos, cetonas e ésteres. Para facilitar a separação do catalisador, um suporte magnético composto de magnetita revestida com sílica foi desenvolvido. A síntese das nanopartículas de ouro suportadas foi realizada de duas maneiras: (I) pela impregnação do suporte com espécies aniônicas de ouro seguido de redução e (II) pela impregnação de nanopartículas de ouro pré-sintetizadas. Em todos os casos nanopartículas de ouro na faixa de 5 nm foram obtidas. A etapa de redução do metal impregnado no suporte foi investigada em detalhe através de duas estratégias: a redução térmica e a redução por hidrogênio. Os testes catalíticos para as reações de oxidação de alcoóis mostraram que os catalisadores sintetizados apresentam altas taxas de conversão e seletividade, porém dependentes do método de preparação utilizado / Gold in the bulk form has been regarded to be an uninteresting metal from the point of view of catalysis, as it is chemically inert towards chemisorption of reactive molecules such as oxygen and hydrogen. However, the catalytic properties of gold are revealed when the size is reduced to few nanometers, particularly with dimension less than 10 nm. Therefore, gold nanocatalysts have received great attention due to the excellent catalytic properties and high selectivity in oxidation and reduction reactions. This master thesis describes the synthesis and characterization of supported gold nanoparticles and their application in alcohol oxidation reaction to produce aldehydes, ketones and esters. In order to improve the catalyst separation and recovery, a magnetic support comprised of magnetite coated by silica was developed. The supported gold nanoparticles were synthesized in two different ways: (I) by impregnation of anionic gold species on silica surface followed by metal reduction, and (II) by impregnation of pre-synthesized gold nanoparticles on the support. In all examples supported gold nanoparticles of about 5 nm were obtained. The reduction step (of the metal impreganted on the support) was investigated in detail by two different strategies: thermal reduction and reduction by hydrogen. The synthesized catalysts showed high conversion rates and selectivity in the catalytic reactions of alcohol oxidation, but those are dependent on the preparation method