Nanoparticles are involved in a broad range of applications, including heterogeneous catalysis. Nanoparticles tend to quickly lose their well-defined shapes and facets due to aggregation under duress such as heat. A series of highly studied materials are explored as support materials for nanoparticle supports. These supports include metal-organic frameworks (MOF), graphene oxide (GO), and a MOF-PRGO (partially reduced graphene oxide) hybrid. The inclusion of a support with the palladium increased lifespan of the catalyst by separation of nanoparticles. The choice of support material not only allowed for supporting of palladium nanoparticles, but allowed for rational catalyst synthesis in order to design catalysts with improved catalytic activity. CO oxidation, vanillin hydrogenation, and Suzuki cross coupling were studied. For the CO oxidation reaction, a cerium-based MOF, Ce-MOF, is shown to increase activity of palladium nanoparticles by capturing reactant gases and acting as an oxygen reservoir that cycles between (III) and (IV) states while transferring oxygen to palladium nanoparticles at the Pd/Ce-MOF interface. A hybrid Ce-MOF-PRGO was synthesized to increase the surface area and acidity of Ce-MOF materials and was shown to be active for vanillin hydrogenation. Smaller rod-like Ce-MOF crystals were observed, indicating intercalation of crystals on GO. Zirconium-based MOF UiO-66-NH2 was acidified via incorporation of tungstophosphoric acid (HPW), which increased the selectivity of products by adjusting the mechanistic pathway. GO was partially functionalized with aromatic amines to improve the coupling of bromobenzene and phenylboronic acid. Small amounts of aromatic amines increased the Pd(0) content and decreased nanoparticle size.

Thesis (M.Sc. (Physics)) --University of Limpopo, 2008 / We present first principles structural, electronic and optical properties investigation of PdS, which are carried out using density functional theory under plane wave pseudopotential method within the local density approximation. We used ultrasoft- pseudopotentials to carry out our calculations. Calculated lattice parameters of the system show excellent agreement with the experimental values. The lattice parameters were observed to decrease linearly with increasing pressure. The density of states and optical properties of PdS have been computed under hydrostatic pressure. The actual size of the band gap remains constant with increasing pressure, whilst the peaks just below and above the Fermi energy moves to the left and to the right respectively. We also investigated the effect of compositional variation on our reflectance by calculating the reflectivity of Pd4-xPtxS4 and Pd4-xNixS4. Since we have different positions for the same concentration, we used the heats of formation to determine the most stable structures and these structures were used to study the effect of compositional variation on our reflectance spectrum. We studied the equation of state (EOS), structure under hydrostatic pressure, and deduced the bulk modulus. It is important to study these properties under such extreme conditions of pressure and temperature as they tend to occur below the earth's surface. Investigation of stability and mechanical properties of binary and ternary compounds from PtS to PdS have been carried out, were the presence of the miscibility gap is still uncertain. We investigate stability of these compounds by studying the heats of formation, elasticity and electronic properties. Our results show no miscibility gap but continuum solid solution between these compounds. A shift of the Fermi energy towards the conduction band is observed at a 50% concentration of Pd and Pt. All the information obtained on PdS is intended to assist in fitting interatomic potentials to enable studies of systems with many atoms.

Doctor of Philosophy(PhD) / The present study deals with the synthesis and characterization of six tri-palladium complexes code named MH3, MH4, MH5, MH6, MH7 and MH8 that contained two planaramine ligands bound to the central or each of the terminal metal ions. The activity of the compounds against human cancer cell lines: A2780, A2780cisR and A2780ZD0473R, cell uptake, levels of DNA-binding and nature of interaction with salmon sperm and pBR322 plasmid DNA have also been determined. Whereas cisplatin binds with DNA forming mainly intrastrand GG adduct that causes local bending of a DNA strand, the tri-palladium complexes are expected to bind with DNA forming a number of long-range interstrand GG adducts that would cause a global change in DNA conformation. Among the designed complexes, MH6 that has two 2-hydroxypyridine ligands bound to each of the two terminal palladium ions is found to be most active. The compound also has the highest cell uptake and Pd-DNA binding levels. In contrast, MH8 which has two 4-hydroxypyridine ligands bound to each of the two terminal palladium ions is found to be least active. The results indicate that, as applied to the terminal metal centres, 2-hydroxypyridine would be more activating than 4-hydroxypyridine perhaps because of greater protection provided to the terminal centres from coming in contact with the solvent molecules. In contrast, when bound to the central metal centre, 4-hydroxypyridine appears to play a slightly greater activating role than 2-hydroxypyridine or 3-hydroxypyridine, suggesting that non-covalent interactions such as hydrogen bonding associated with the ligand rather than its steric effect may be a more important determinant of antitumour property. The results illustrate structure-activity relationships and suggest that the tri-palladium complex containing two 2-hydroxypyridine ligands bound to each of the three metal centres or the compound that contains two 2-hydroxypyridine ligands bound to each of the two terminal metal centres and two 4-hydroxypyridine ligands bound to the central metal centre, may be much more active than any of the designed complexes.

Thesis (Ph. D.)--University of Hong Kong, 2007. / Title proper from title frame. Also available in printed format.

No description available.

Les agrégats métalliques de taille nanométrique possèdent, par rapport aux matériaux massifs, des propriétés chimiques singulières, et constituent des modèles pour l'étude de la catalyse hétérogène. La réactivité d'agrégats de palladium, élaborés par croissance épitaxique sur MgO(100) et caractérisés par microscopie électronique en transmission, a été étudiée. Des expériences d'adsorption de NO et de réactions CO+NO et CO+O2 ont été réalisées sous ultravide par une technique de jet moléculaire pulsé. Avant de se chimisorber sur les agrégats, les molécules de monoxyde d'azote peuvent diffuser sur le support. Nous avons mesuré la probabilité de physisorption de NO sur MgO, et quantifié ce phénomène de diffusion-capture. Une fois adsorbé sur le palladium, le NO se dissocie, produisant de l'azote, ou se désorbe. L'énergie d'activation de désorption du NO est de 32 kcal/mol. Une influence de la température et de la morphologie des agrégats sur leur capacité à adsorber et dissocier le NO a été mise en évidence. La réaction de réduction de NO par CO produit essentiellement CO2 et N2. A pressions de réactifs égales, l'activité catalytique est maximale à environ 260°C. Les étapes limitantes de la réaction sont, à basse température, la dissociation du NO et, à haute température, l'adsorption du CO. La prise en compte de la diffusion des réactifs sur le support permet de déterminer précisément l'influence de la taille des agrégats sur leur activité catalytique, et révèle une corrélation avec les expériences d'adsorption de NO. Enfin, la cinétique de la réaction d'oxydation du CO a été analysée en régime transitoire, à l'aide de simulations simples. En deçà d'environ 200°C, la vitesse de la réaction est limitée par l'inhibition de l'adsorption de l'oxygène par le CO fortement chimisorbé sur les arêtes des agrégats. Au-delà de 200°C, c'est l'existence d'un état précurseur de la chimisorption de CO à fort recouvrement en oxygène qui réduit la vitesse de production de CO2.

Le palladium est couramment utilisé pour le stockage du tritium, isotope radioactif de l'hydrogène, car il forme un tritiure réversible, à basse pression d'équilibre. La décroissance du tritium en hélium-3 provoque un vieillissement du tritiure, caractérisé notamment par l'apparition de bulles d'hélium-3, qui est étudié ici. De précédents travaux de modélisation du vieillissement avaient abouti à la création de deux modèles traitant, d'une part, de la germination des bulles d'hélium-3 (utilisation d'un automate cellulaire) et, d'autre part, de la croissance des bulles (mécanique des milieux continus). Ces modèles étaient fonctionnels, mais leur utilisation était limitée par le manque de données expérimentales d'entrée et de recalage. Ce travail de thèse a donc consisté à acquérir les données expérimentales les plus pertinentes pour améliorer la modélisation du vieillissement du tritiure de palladium. La première partie de ce travail a consisté à estimer les propriétés mécaniques du tritiure de palladium (limite d'élasticité, contrainte maximale, loi de comportement...), déduites de celles de l'hydrure et du deutérure de palladium, mesurées à l'aide d'essais de traction in situ. En seconde partie, la caractérisation du vieillissement a été entreprise, focalisée sur des observations de bulles dans le tritiure de palladium par microscopie électronique en transmission, des mesures de pression à l'intérieur des bulles par résonance magnétique nucléaire et des mesures de gonflement macroscopique du matériau par pycnométrie. Ces travaux ont conduit à des avancées significatives quant à la compréhension du vieillissement et ont permis d'améliorer considérablement sa modélisation.

De nouvelle réactions multicomposants ont été mises au point. Une nouvelle ouverture de furane a par ailleurs été développée.

<p>The Heck reaction is one of the most appreciated methods for carbon-carbon bond formation. Due to its mildness and ability to be tuned by additives, it often leaves few alternative competitive reactions. It has also proven easy to develop the reaction conditions in an environmentally benign direction. Through the introduction of palladium chelating groups in olefinic precursors for the Heck reaction, it has been possible to direct the substitution in the following Heck arylation in favor of the terminal position with good regioselectivity. In this thesis, the concept has been utilized to produce a small array of drug-like compounds at useful yields under fast microwave-enhanced conditions utilizing the thermostable Herrmanns palladacycle. During the last decade, this, together with other palladacycles has become commonly employed as precatalyst for the Heck reaction. However, there have been conflicting opinions regarding the mechanisms governing its catalytic effect. A Pd^II-Pd^IV catalytic cycle has been suggested to be operative, in contrast to the classical Pd⁰-Pd^II cycle. In order to clarify the presence of such a mechanism, a set of Heck reactions was performed with the advent of different palladium precatalysts (classical and palladacycles), which revealed that the regiochemicαal substitution pattern is highly conserved, regardless of which precatalyst was employed, and thus, the same mechanism seems to be operative. This is also supported by data from ESI-MS investigations where all the reactions investigated gave rise to the same set of oxidative addition complexes. A crafted route to 3-aryl-1,2-cyclohexandiones has been developed in which 1,2-cyclohexandione is produced <i>is situ</i> from 2,3-epoxycyclohexanone, followed by Heck arylation. A diverse array of aryl bromides encompassing electron-rich, electron-poor, neutral and sterically hindered repressentatives has been successfully utilized to produce the corresponding products at useful yields.The intramolecular Heck reaction offers a route to quaternary carbonic centersand is being increasingly exploited in synthetic endeavors. However, the use of electron-rich olefinic precursors is only reported in a few cases. The implementation of one capto-dative and five electron-rich olefins has therefore been successfully subjected to Heck reaction conditions rendering the corresponding spiro compounds.</p>

Thesis (M. Ing.)--University of Stellenbosch, 1997. / Bibliography. Also available via the Internet.