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<p> Trimethylsilylstyrenes undergo protiodesilylation (Scheme 1, path A), via the β-silyl carbonium ion under acidic conditions. In contrast, the corresponding trichlorosilyl substituted compound was found to undergo an oligomerization reaction (Scheme 1, path B) with triflic acid as the catalyst. (See Diagram in Thesis)</p> <p> The β-effect [(σ-p)π overlap] may play a significant role in the weakening of the silicon-carbon bond and thus promote the cleavage process, as is observed in scheme 1, path A. Introduction of electronegative chloro groups on silicon weakens the β-effect and hence the silyl leaving group ability, resulting in oligomerization of the styrene (Scheme 1, path B).</p> <p> In this oligomerization reaction, chain termination by an internal Friedel-Crafts reaction competes with the chain propagation. As a result, indane terminated low moldecular weight oligomers are formed. The case is similar to β-methyldichlorosilylstyrene, with the only difference that here ca. 20% desilylation has occured, again reflecting the fact that subtle changes in the β-effect acan influence the course of electrophilic reactions.</p> / Thesis / Master of Science (MSc)

<p> The crystal structures of VOP2SiO8, VO(PO3)2, V(PO3)3, (VO)2P2O7 and VAsO5 have been determined with the help of x-rays, and are compared with the known structures in the V-P-As-O system. All the vanadium atoms in the mixed oxides are octahedrally coordinated and the V^+4 O6 and V^+5 O6 octahedra are all characterized by one short vanadyl bond. V^+3 O6 groups are nearly regular. The tetrahedral phosphorus is found in structural elements ranging from infinite metaphosphate chains (V(PO3)3, VO(PO3)2), to pyrophosphate groups ((VO)2P2O7) to isolated tetrahedra (VAsO5 and VOP2SiO8). Both structural and substitutional disordering is evident in the V-P-As-O system, and is discussed together with a detailed model for stacking faults in VAsO5.</p> <p> Some of the phases in the V-P-As-O system are known to catalyze the oxidation of butene to maleic anhydride, and certain structural features of the compounds are related to this catalytic activity. α-VPO5 can be related to (VO)2P2O7 through the formation of shears in a manner similar to shear formation in V2O5, and such a mechanism is proposed as a means whereby an α-VPO5 catalyst can change into (VO)2P2O7, the known composition of the spent catalyst.</p> / Thesis / Doctor of Philosophy (PhD)

<p> Reaction of the hydrated trichlorides of rhodium and Iridium with hexamethyldewarbenzene gave the complexes, (C5Me5MCl2)2 (M=Rh, Ir). A mechanism for this reaction is proposed.</p> <p> The dichloro complexes, (C5Me5MCl2)2, were reacted with a number of di- and tri-enes in ethanol in the presence of base and gave a variety of pentamethylcyclopentadienyl complexes of M(l) and M(lll). Evidence for a hydrido intermediate is presented and the hydrido- and deuterido- complexes, C5Me5IrH(D)ClPPh3, were isolated and characterised.</p> <p> The isomers endo-H and exo-H pentamethylcyclopentadiene(cyclopentadienyl) rhodium were isolated and showed significant differences in their properties. Cyclooctadienes reacted with (C5Me5MCl2)2 to give C5Me5M(1,5-C8H12) via the intermediacy of the π-2-cyclooctenyl complexes C5Me5MCl(C8H13); mechanisms are presented to account for the observed products. Cyclohexadienes gave the complexes, C5Me5M(1,3-C6H8). 1,4-Cyclohexadiene was isomerised to 1,3-C6H8; the rhodium complex, C5Me5Rh(1,3-C6H8), was a very active catalyst for the disproportionation of 1,3-C6H8 to cyclohexene and benzene, both ethanol and base were cocatalysts.</p> <p> Mass spectral data for these and other organo-metallic complexes are presented.</p> / Thesis / Doctor of Philosophy (PhD)

<p> This thesis presents an experimental study of the decomposition of the four isomers of butyl acetate over charcoal catalyst in a fixed bed reactor. The research attempts to determine the kinetics and mechanism of butyl acetate decomposition over a high surface area, non-selective catalyst, and to compare the catalyzed reactions of butyl acetates with their gas-phase reactions. When interpreting the experimental kinetic data it is hypothesized that each of the butyl acetates follows the same mechanism when reacting on charcoal. The best theoretical equation for expressing the rate of butyl acetate reaction was selected from the Langmuir-Hinshelwood equations.</p> / Thesis / Doctor of Philosophy (PhD)

<p> A continuous bubble reactor was used to study the transfer of oxygen into solutions of acetaldehyde. The reaction was catalysed by cobaltous acetate. The parameters investigated included temperature, catalyst concentration, air flow rate and column height.</p> <p> A mathematical model based on Houghton's work (36) was used to describe the absorption rate in the bubble column. The equation derived was solved numerically. The Sherwood numbers predicted by the theory were compared with those obtained experimentally.</p> / Thesis / Master of Engineering (MEngr)

The progress in fuel cell technology has resulted in an increased interest towards hydrogen fuel. Consequently, water gas shift reaction has found a renewed significance. Even though iron- and copper-based catalysts have been used for water gas shift reaction for decades, the catalysts are not strong enough to bring carbon monoxide concentration to a level tolerable for a fuel cell working at low temperatures. This study is focused on hydrogen production from water gas shift reaction using a nickel catalyst. Literature review revealed that nickel is one of the promising catalysts for water gas shift reaction. A thermodynamic analysis proved that exothermic water gas shift reaction is thermodynamically favorable at low temperatures but kinetically limited, and vice versa at higher temperatures. Initial experiments using 12 catalysts supported over monolith alumina revealed that nickel supported on ceria-promoted monolith alumina (Ni/CeO2-Al2O3) performed best, especially at 500oC. At this temperature and steam flowrates of 0.1-0.5 ml/min, the nickel catalyst had an activity of 94-99%, H2 yield of 55-61 vol.%, and H2 selectivity of 77-99%. A second set of experiments examined nine nickel based catalysts using different supports (mostly in powder form) which also demonstrated that Ni/CeO2-Al2O3 is the most promising catalyst for high temperature (450oC) water gas shift reaction. When nickel loading was varied from 1 to 8% (w/w), it was apparent that the catalyst performance increased with the nickel loading. Powder alumina resulted in better catalysis than monolith alumina. In this experiment, it was evident that the presence of minor amounts (1% (w/w) of the nickel loading) of a dopant material that included cobalt, chromium, molybdenum, or ruthenium affected the catalytic activity of the primary catalyst. The addition of cobalt or chromium resulted in positive effect on the performance of Ni/CeO2-Al2O3 catalyst. There was no appreciable effect due to the addition of ruthenium, and there was negative effect owing to the presence of molybdenum. Undoped, cobalt-doped, or chromium-doped Ni/CeO2-Al2O3 catalyst performed much better for water gas shift reaction at 450oC than that of a commercial (control) catalyst. A kinetic study revealed that the activation energy of water gas shift reaction over Ni/CeO2-Al2O3 was to be 104.5 kJ/mol.

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