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Thesis (M. Sc.)(Chemical Eng.)--University of Pretoria, 2003. / Bibliography included.

Thesis (M. Sc.)--University of Hong Kong, 1968. / Typewritten.

Thesis (M. Phil.)--University of Hong Kong, 1975.

Thesis (Ph. D.)--Chemical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Dr. Christopher Jones; Committee Member: Dr. Dennis Hess; Committee Member: Dr. Hang Lu; Committee Member: Dr. Marcus Weck; Committee Member: Dr. Pradeep Agrawal. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Gold has been considered catalytically inert due to its resistance to oxidation and corrosion. However, decades ago, it was discovered that gold nano-particles (<5nm) on metal oxides demonstrate superior chemical activity towards many reactions. These seminal findings spurred considerable interest in investigations of the mechanistic details of oxidative reactions on gold-based catalysts. However, the active site and structure of supported Au nanoclusters as well as the active oxygen species remains elusive. Achieving high selectivity toward partial oxidation products also remains a challenge. In this dissertation, an oxygen-covered Au(111) crystal under ultra vacuum conditions was used as a model system to gain insights into oxidative reactions in gold-based catalysis. I have been able to demonstrate that (i) surface-bound oxygen atoms are metastable at low temperature; (ii) the oxygen atoms participate in surface reactions as a Brønsted base or a nucleophilic base; and (iii) the acid-base reactions that have been observed on silver and copper may also occur on gold. Low temperature CO oxidation and the associated mechanistic aspects are investigated. CO reacts with hydroxyls formed from water-oxygen interactions to produce CO₂ on Au(111) populated with atomic oxygen at low temperatures. Directing an ¹⁶O beam toward C¹⁸O₂ pre-adsorbed Au(111), the formation of carbonate is significantly enhanced. This reaction is suggested to follow a hot-precursor-mediated mechanism. The identification of reaction pathways in oxidation of N-containing molecules such as ammonia and propylamine is presented. Abstraction of hydrogen from ammonia or propylamine by O atoms is the initial step in the surface decomposition of NHx (or RNHx-1) on Au(111). Atomic oxygen or hydroxyl-assisted dehydrogenation steps have lower barriers than the recombination steps under relevant conditions. 100% selectivity of N₂ or propionitrile can be obtained if the oxygen coverage is below the stoichiometric value. The surface oxidative chemistry of alcohols on Au(111) is also investigated. Except for methanol that is fully oxidized, alcohols initially undergo O-H bond cleavage (producing alcoxides) followed by selective β-C-H bond activation to form aldehydes or ketones. This finding reveals that the interaction of Au with the metal oxide support might not be essential to facilitate the reactions if active oxygen species are readily present, particularly at low temperatures. / text

Recently, during the past10 years, with the intensified attention paid to the environment and industrial development, there has been growing interest in organocatalysis. One important area of the organocatalysis is the development of new designs of chiral catalysts for the synthesis of optically pure products. Another important area is to develop methods to simplify the purification of multi-component reactions. A chiral spirobiindane-based bisphosphine oxide catalyst was synthesized and employed in various reactions including Abramov-type phosphonylation reactions, reductive aldol reactions, direct aldol reactions, allylations, reductive cyclizations and C=N reduction reactions. The rigid and axially chiral spirobiindane skeleton of the bisphosphine oxide introduces steric hindrance and results in moderate to good enantioselectivity in Abramov phosphonylation and reductive cyclization reactions. However, the great steric hindrance of the catalyst also imposes negative effects on catalyst activity and yields of reactions. The observed slow reaction rates may possibly have led to the undesired, non-selective background reactions and therefore a lowered enantioselectivity. Secondly, the success of polymer-supported reagents in facilitating product purification prompted our attempt to prepare and examine two different types of polymer-supported benzothiazolines for hydrogen transfer reduction. An in situ generated self-supported polybenzothiazoline proved to be a rapidly formed polymer under mild conditions and could be applied to hydrogenation transfer reduction reactions with active alkenes. A rasta resin-supported benzothiazoline was also synthesized and examined in similar transformations. Both of the two polymer reagents afforded the desired reduction products, but further optimizations may be required to suppress the formation of byproducts and to improve their reactivity. / published_or_final_version / Chemistry / Master / Master of Philosophy

Not available / text

This dissertation describes the synthesis and characterization of nitrogen doped carbon nanotube (NCNT) supported nanoparticles for catalysis, specifically, the cathodic oxygen reduction reaction (ORR) in fuel cells. Strategies for synthesis of mono- and bimetallic nanoparticle catalysts through dendrimer based templating techniques and with the aid of metal organic chemical vapor deposition (MOCVD) precursors and efficient assembly protocols of the catalysts with the NCNTs are discussed in detail. Physicochemical properties of the NCNTs and NCNT supported catalysts were characterized using a host of tools including scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, x-ray photoelectron spectroscopy (XPS), thermo gravimetric analysis, BET surface area and pore size analysis and electrochemical techniques including cyclic voltammetry, chronocoulometry, chronoamperometry and rotating disk electrode voltammetry. Chapter 1 serves as a general introduction and provides a brief overview of challenges associated with the synthesis, characterization and utilization of graphitic carbons and graphitic carbon supported catalysts in heterogeneous catalysis. Chapter 2 provides an overview of the synthesis and characterization of systematically doped iron and nickel catalyzed NCNTs in an effort to understand the effect of nitrogen doping on ORR. Chapter 3 describes the use of NCNTs as supports for dendrimer templated nanoparticle catalysts for ORR. A facile synthetic strategy for the immersion based loading of catalysts onto NCNTs by spontaneous adsorption to achieve specific catalyst loadings is explored. Chapter 4 details the loading of monodisperse Pt, Pd and PtPd catalysts on the as synthesized NCNTs using MOCVD precursors. The MOCVD route offers promise for direct dispersion and activation of ORR catalysts on NCNT supports and eliminates a host of problems associated with traditional solvent based catalyst preparation schemes. Chapter 5 details future directions on a few topics of interest including efficient electrodeposition strategies for preparing NCNT supported catalysts, studies on PtCu catalysts for ORR and finally prospects of using NCNT supported catalysts in fuel cell applications.

As the recent environmental legislation highlights the risks associated with the use of gasoline additives such as octane enhancers, hydroisomerisation of n-alkanes in the gasoline feed to their corresponding isomers emerges as a key industrial alternative. Important catalysts have previously been tested and abandoned due to a number of problems including cost and poor resistance to catalyst poisons even in trace quantities. The current research evaluated the potentials of zirconia supported molybdenum carbide catalysts as replacements. The active carbided MoO3/ZrO2, MoO3/SO42- -ZrO2 and Rh/MoO3/ZrO2 have been prepared by in situ carburisation with CH4/H2 at 650oC and characterised by N2 adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, Diffuse Reflectance Fourier Transformed Infrared spectroscopy, and temperature programmed reduction and oxidation. The characterisation data showed the carburisation process to proceed in a stepwise manner, involving the participation of hydrogen and methane as reducing and carbiding agents, respectively. Low (0.5 wt %) Rh loading and pre-treatment cycle via reduction and reoxidation significantly reduced the carburisation temperature, with the extent of the effect been dependent on the MoO3 loading. All of the catalysts produced showed stable activity and selectivity. Over the carbided MoO3/ZrO2, the activity was generally low at 450oC, producing mainly hydrogenolysis products. However, the activity of carbided MoO3/SO42- -ZrO2 at 350-450oC showed strong dependence on the nature of the n-alkane with reaction rates being lower for the higher alkanes. n-Nonane and n-octane produced mainly hydrocracking products whereas n-hexane and n-heptane were converted to the corresponding isomers with a very high selectivity. The catalyst forms a potential material for hydroisomerisation of gasoline range light paraffins. The 10 wt% Rh/MoO3/ZrO2 catalyst was more active to hydrogenolysis than with 25 wt% Rh/MoO3/ZrO2 under similar conditions due to higher activity of Rh species. However, the hydroisomerisation selectivity was highly favoured at lower temperatures, especially with n-hexane.