In this thesis, the aim was to develop resins which are platinum and gold specific to be utilized for the early removal of these metals from the industrial feed. Efforts were therefore directed towards the synthesis of silica based resins with active centra which were designed for platinum and gold specificity respectively. The large chlorometallate ions in the feed stream were characterized in terms of physical parameters relevant to phase distribution namely distortability (RD), charge density, softness (σ) etc. Matching cations for each of the types were investigated. In order to attempt the design of platinum specific resins different structural amines were used to aminate the silicone precursor and subsequently to fix these onto the silica framework. Two different solvents i.e. alcohol and dmf were used for this process, resulting in two sets of resins with different properties. For gold specific resins, various polyethers were attached to a different type of silicone precursor, which was attached to the silica framework. The design was based on previous experience with these ions with reference to their behaviour towards different types of cations. The platinum species PtCl6 2- and PtCl4 2-, the gold species AuCl4 -, as well as the most important contaminants in the feed stream were typified bearing in mind size, charge, charge density and distortability. Different types of cationic centra having differences in charge density, stereochemical crowding and extent of hydrophobicity were synthesized and tested both as solvent extractants (where possible) and silica based resins. The results indicated that partly screened secondary ammonium cationic resin species, which could be regarded as “intermediate”, proved to be satisfactory both in their high percentage extraction for PtCl4 2- and rejection of contaminants like chlororhodates, chloroiridates(III) and FeCl4 -. It was, however, necessary to work at a redox potential where iridium(IV) in the form of IrCl6 2- is absent. Various 2-aminoalkane resins were prepared with variation in the length of alkane group and synthesized in the two different solvents. The latter resulted in two sets of resins with different compactness also having significantly different properties with reference to platinum specificity, HCl effect and stripping potential. The 2- aminobutane and 2-aminoheptane resins both proved to be very satisfactory platinum specific resins with respect to selectivity, platinum capacity and stripping potential. The various physical parameters could be utilized to accommodate the chemical behaviour. To obtain gold specific resins, experiments were performed with resins having oxygen-donor atoms which can readily be protonated to form onium type cations for example amides and ether oxygen atoms. In the case of the latter, various polyethers with a different number of ether groups (polyether groups linked by ethylene and propylene groups) and variations of hydrophobicity (by substitution) have also been studied. Linked to the polyether groups were alkane and aryl groups. Those having 8 to 10 ether groups and aromatic tail ends proved to be moderately successful in terms of gold capacity and sharp breakthrough curves of their columns, however, platinum could not be very effectively rejected.

This thesis considers the electrochemistry of platinum-iridium electrodes in both sulphate- and chloride-containing electrolytes at 20 - 25°C. Both wire electrodes of appropriate alloy compositions and titanium-substrate electrodes were employed. Polarization curves were obtained, and a technique for measuring the surface area of the electrodes was employed in order to determine the effect of potentiostatic electrolysis on the electrochemically active area. The wire alloy electrodes showed polarization behaviour in 1M NaCl; pH 2 identical to that of platinum electrodes, indicating that iridium is not effective in reducing the passivation of these electrodes even with up to 25% alloy content. The coated electrodes showed irreversible surface area losses in both sulphate and chloride electrolytes, with the latter producing significant reductions after very short polarization times. It is suggested that oxidation of the substrate leading to electrical isolation of coating plates is responsible for the area decay. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

No description available.

In recent years numerous complexes have been reported in which olefins were chelated to transition metals.Ever since the generally regarded first olefin complex, Zeise's salt (32) KPt(C2H43, the interest in this field of organometallic chemistry has expanded to several families of olefinic ligands and metals like palladium(II), platinum(II) copper(I), silver(I), and more recently vanadium and titanium The nature of the bonding of olefins to metal atoms seemed to involved the interaction between pi electrons in the unsaturated molecule and the hybrid orbitals of the metal rather than a localized sigma bonds between the metal atom and a particular carbon atom. The metal was complexed to a hydrocarbon which possessed a surplus of electrons. The direct overlap of a sigma orbital of the metal anad the p-orbital of the carbon atom formed a sigma type bond. The ligand carbon atom donated a surplus bonding pi-p electrons to a vacant sigma orbital of the metal while at the same time the excess negative charge was released back to the olefin from from a pi-d orbital of the metal to an empty antibonding pi-p orbital of the carbon atom. Dewar (9) illustrated this point by molecular orbital diagram. (See figure B) [see PDF file for Formula] The metal to olefin bond consisted of two parts: (a) overlap of the pi electron density of the olefin with sigma type acceptor orbital on the metal atom and (b) a "back-bonding" resulting from the flow of electron density from filled metal dxy or other dπ - pπ hybrid orbitals into antibonding orbital on the carbon atom. A schematic diagram of platinum olefin complexes can be shown as: [see PDF file for Formula] It was the intention of this research to increase our understanding of these stable diolefin complexes. In particular, the occurrence of rearrangement upon complexation of certain ligands to most likely a more stable configuration posed an interesting project. They syntheses of diolefin complexes provided an establishment of good technique and verification of reported data. The program of study was concentrated on the complexation of cyclic diolefins with primarily palladium(II) and platinum(II) chloride.

No description available.

Understanding the structure and kinetics of electrochemical oxidation of platinum single-crystal surfaces at the atomic level is important to understanding and improving the electrocatalysis of platinum in fuel cells. This thesis concerns the analysis of data from combined electrochemical and surface X-ray diffraction (SXRD) experiments on Pt(111) and Pt(100). In the early stages of oxidation, Pt atoms are extracted from their metal lattice sites and become part of a metal oxide. Their locations have been measured by collaborators using SXRD. The corresponding charges measured electrochemically are determined by integration of cyclic voltammetry, potential step and potential sweep-hold experiments, and used to propose reactions that are occurring in the oxidation. The measured charge consists of the wanted charge that passes in the electrochemical reactions and a capacitive charge associated with charging the electrical double-layer. Different ways of subtracting the double-layer charge were investigated. Reactions were proposed for optimally corrected charges, and for the worst case where no correction is made, in order to determine the reliability of the proposed reactions. From cyclic voltammetry experiments on Pt(111) surfaces, during oxidation 0.5 ML adsorbed oxygen and a few extracted PtO (less than 0.1 ML) are formed. Without baseline correction the data are consistent with 0.5 ML Oads and a few extracted PtO2. After fast scans, the Pt(111) surface is restructured as shown by the X-ray signal, but the oxide peaks in CV are nearly unchanged, which suggests that the electron transfer and Pt extraction do not need to be tightly coupled. From CV experiments on Pt(100) surfaces, during oxidation many more extracted Pt are formed than on Pt(111). These form long chains with PtO2 units (0.25 to 0.39 ML) together with Oads and a total coverage of 0.5 ML. If CV isn't baseline corrected, the data is not consistent with long chains with PtO2 units, but short Pt3O8 chains with equal numbers of independent PtO2 groups. From potential step experiments on Pt(100), there is an expectation from the literature that the charge will grow linearly with log t. However, this relationship was only found during the first second of each step, and then is unchanged after ~1 s. The slopes of the logarithmic plots are linearly related to potential. From sweep hold experiments on Pt(100), both charges and coverage of extracted Pt atoms are not very linear vs log t, and their slopes are also not linearly related to potential but change sharply during the potential range of Pt extraction. / Graduate

The use of heterogeneous catalysis is well established in chemical synthesis, energy, and environmental engineering applications. Supported Pt nanoparticles have been widely reported to act as catalysts in a vast number of chemical reactions. In this report, the performance of Pt/ZrO2 nanocatalyst for the decomposition of methanol, ethanol, 2-propanol, and 2-butanol is investigated. The potential of each alcohol for the production of H2 and other relevant products in the presence of a catalyst is studied. All the alcohols studied show some decomposition activity below 200°C which increased with increasing temperature. In all cases, high selectivity towards H2 formation is observed. With the exception of methanol, all alcohol conversion reactions lead to catalyst deactivation at high temperatures (T > 250°C for 2-propanol and 2- butanol, T > 325°C for ethanol) due to carbon poisoning. However, long-term catalyst deactivation can be avoided by optimizing reaction conditions such as operating temperature. In addition, the performance of Pt/γ-Al2O3 is evaluated in the oxidation of 2-propanol. Pt nanoclusters of similar size (~1 nm diameter) but different structure (shape) were found to display distinctively different catalytic properties. All the systems studied achieve high conversion (~ 90%) below 100°C. However, flatter particles display a lower reaction onset temperature, demonstrating superior catalytic performance. Acetone, CO2, and water are generated as products indicating that both partial and complete oxidation are taking place. A number of techniques including AFM, XPS, TEM, HAADF-TEM, XAFS as well as packed-bed reactor experiments were used for sample characterization and evaluation of catalytic performance.

Catalysis technologies are among the most important in the modern world. They are instrumental in the realization of a variety of products and processes including chemicals, polymers, foods, pharmaceuticals, fuels, and fuel cells. As such, interest in the catalysts that drive these processes is ongoing, and basic research has led to significant advances in the field, including the production of more environmentally friendly catalysts that can be tuned at the molecular/atomic level. However, there are many factors which influence the performance of a catalyst and many unanswered questions still remain. The first part of this work is concerned with the factors that influence the catalytic properties (activity, selectivity, and stability) of supported Pt and Pt-M nanoparticles (NPs). These factors are a synergistic combination of size, composition, support, oxidation state, and reaction environment (i.e. adsorbates, temperature, pressure, etc.). To probe the catalytic properties of complex and dynamic NP systems we have used MeOH decomposition and oxidation reactions, each of which has significant environmental and economic potential. We have given some emphasis to the state of NP oxidation, and with the aid of X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD), have followed the formation and temperature-dependent evolution of oxide species on Pt NPs. Further, we have explored how these species behave under the conditions of our probe reactions using a packed-bed mass flow reactor coupled to a quadrupole mass spectrometer (QMS). To carry out our investigations we exploit a NP synthesis method which is rather novel to nanocatalysis, micelle encapsulation. Since most available experimental techniques give information on ensemble averages, control over size distributions in NP samples is critical if unambiguous results are to be obtained. Micelle encapsulation allows us this control with several unique, inherent iv advantages. It is to this end that micelle encapsulation has allowed us to probe the detailed structure of small (~1 nm), supported, Pt NPs with extended X-ray absorption fine structure spectroscopy (EXAFS). Furthermore, we were able to explore experimentally, for the first time, the vibrational density of states (VDOS) of supported, isolated, monodispersed, mono and bimetallic NP systems via nuclear resonant inelastic X-ray scattering (NRIX). These synchrotron-based techniques (EXAFS, NRIXS) rely heavily on the monodispersity of the NP ensemble for reliable information

<p> Two isotopes of platinum, Pt192 and Pt194, have been investigated using Ge(Li) vs. NaI coincidence techniques. The following corrected angular distributions and mixing ratios in Pt192 were obtained: 468-316 keV A22 = 0.100(8) A44 = 0.011(8) 604-316 keV A22 = -0.410(15) A44 = -0.070(22) 308-612 keV A22 = -0.120(20) A44 = -0.027(20) 417-468 keV A22 = -0.120(26) A44 = -0.110(30) δ308 = -9.4(15) δ604 = + 3(1) |δ417|> 11 g factors for the following five levels of these nuclei were obtained using the method of perturbed angular correlations where the perturbing agent was the hyperfine field on platinum in an iron alloy: Pt192 316 keV g = 0.30(3) Pt192 612 keV g = 0.28(7) Pt192 785 keV g = 0.14(10) Pt194 329 keV g = 0.28(3) Pt194 622 keV g = 0.22(4) A comparison with the predictions of a microscopic collective model, the pairing-plus-quadrupole model, is made. / Thesis / Master of Science (MSc)

<p> The work describes the preparation and properties of some novel dibenzylideneacetone complexes of palladium and platinum. The structure and bonding in these complexes is discussed in view of their infrared and nuclear magnetic resonance spectra. The cyclotrimerization of acetylenes by zero-valent nickel complexes is discussed and the synthesis of a new cyclobutadiene-platinum complex is reported.</p> / Thesis / Master of Science (MSc)