Phosphine complexes of nickel and palladium provide the best catalysts for the homogeneous catalysed carbon-carbon bond forming reaction between an organometallic nucleophile and an organic electrophile. Use of a homochiral ligand on the catalyst can lead to stereoselectivity in the cross-coupling reaction, with high ee's of coupled product being obtained. The processes of selectivity in the transmetalation step of the catalytic cycle have not been elucidated and the initial aim of the project was to study these processes. Initial experiments using organotin derivatives as the organometallic nucleophile highlighted the problems of selectivity and the forcing conditions needed in the attempted transfer of a benzyl group from the tin to the palladium catalyst. The compounds [8- (dimethylamino)-1-naphthyl]methyldiphenyltin (60) and [2-((dimethylamino)methyl) phenyl]methyldiphenyltin (70) were prepared and their reactivity in the palladium catalysed cross-coupling with 2-furoyl chloride, to give 2-benzoylfuran, was investigated. These molecules were found to undergo facilitated transfer of a phenyl group compared to transfer from control molecules. The effect was tested and attributed to the internal nucleophilic attack at the tin atom by the lone pair on the nitrogen atom. The compound [2- ((dimethylamino)methyl)-3-trimethylsilylphenyl]methyldiphenyltin (79) was prepared to test the effects of steric buttressing within the molecule, but was found to be of the same order of magnitude of reactivity as (60) and (70). All three molecules showed a reactivity of at least an order of magnitude greater than control compounds. The effect did not prove applicable to the transfer of a benzyl group or in other coupling reactions. The effect of palladium ligation was tested and the ligand triphenyl arsine found to increase the rate of the coupling reaction. The two facilitating processes were found to work in a co-operative fashion, giving a rate enhancement of ca. one hundredfold over control reactions. The nickel catalysed cross-coupling of α-substituted sp³ hybridised Grignard reagents with allylic esters was attempted, but proved unsuccessful. Stoichiometric reactions with nickel complexes were also found to be unsatisfactory in yielding coupled products. The synthesis of α-substituted diorganozinc reagents was attempted, but furnished only homocoupled products. The reaction of dibenzylzinc with aldehydes was found to proceed in the absence of catalyst, highlighting the reactivity of a benzylzinc moiety.

This research is concerned with identifying and characterizing four solid-state precipitation reactions in the W-Ni-Fe system that can be induced by appropriate heat treatments. Previous work in this area is reviewed, and a general overview of the research on this system that may, directly or indirectly, further the understanding of microstructure/mechanical property relationships in the W-Ni-Fe heavy alloy is presented. The many metallographic and analytical techniques that have been employed in the course of this investigation are also briefly reviewed. The specific precipitation reactions studied in the 90W-5Ni-5Fe heavy alloy are listed and briefly described. Interfacial precipitation - interfacial precipitates at the W-andgamma; and andgamma;-andgamma; boundaries were found to be andeta;-carbides. This morphology is expected to severely embrittle the alloy. Matrix-phase precipitation - discontinuous precipitation of W was observed in the matrix region. W-W grain boundary precipitation - W-W grain boundary allotriomorphs (andgamma;-phase) were identified and characterized. W-phase precipitation hardening - fine scale precipitation in the W-phase was found to strengthen the alloy. Deformation prior to aging significantly increased the rate of precipitate nucleation. TEM contrast analysis showed the precipitates to be plate-like with a {100} habit plane, and the strain in the W lattice normal to the precipitates was found to be tensile in nature. Matrix-composition alloys were manufactured to simulate the andgamma;-phase in the 90W-5Ni-5Fe alloy. Metallographic observations of these alloys furthered the understanding of reactions 1) and 2) above. These results are discussed in terms of (a) current theories of solid-state precipitation and (b) the influence of the various morphologies on mechanical properties.

No description available.

Production of hydrogen is primarily achieved via catalytic steam reforming, partial oxidation,and auto-thermal reforming of natural gas. Although these processes are mature technologies, they are somewhat complex and CO is formed as a by-product, therefore requiring a separation process if a pure or hydrogen-rich stream is needed. As an alternative method, supported metal catalysts can be used to catalytically decompose hydrocarbons to produce hydrogen. The process is known as catalytic cracking of hydrocarbons. Methane, the hydrocarbon containing the highest percentage of hydrogen, can be used in such a process to produce a hydrogen-rich stream. The decomposition of methane occurs on the surface of the active metal to produce hydrogen and filamentous carbon. As a result, only hydrogen is produced as a gaseous product, which eliminates the need of further separation processes to separate CO2 or CO. Nickel is commonly used in research as a catalyst for methane cracking in the 500-700C temperature range. To conduct methane catalytic cracking in a continuous manner, regeneration of the deactivated catalyst is required and circulation of the catalysts between cracking and regeneration cycles must be achieved. Different reactor designs have been successfully used in cyclic operation, such as a set of parallel fixed-bed reactors alternating between cracking and regeneration, but catalyst agglomeration due to carbon deposition may lead to blockage of the reactor and elevated pressure drop through the fixed bed. Also poor heat transfer in the fixed bed may lead to elevated temperature during the regeneration step when carbon is burned in air, which may cause catalyst sintering. A fluidized bed reactor appears as a viable option for methane catalytic cracking, since it would permit cyclic operation by moving the catalyst between a cracker and a regenerator. In addition, there is the possibility of using fine catalyst particles, which improves catalyst effectiveness. The aims of this project were 1) to develop and characterize a suitable nickel-based catalyst and 2) to develop a model for thermal catalytic decomposition of methane in a fluidized bed.

Fundamental studies on the mechanisms and kinetics of reduction of dense synthetic nickel oxide have been carried out in H2-N2 and H2-H2O mixtures. The influences of temperature, hydrogen partial pressure, and hydrogen-steam ratio on the reduction process were systematically investigated. The kinetics of the reduction process were followed metallographically by measuring the advance of the nickel product layer. The microstructures of the reduction products and their changes during heating were characterized using a high resolution scanning electron microscopy. In H2-N2 mixtures and H2-H2O mixtures with low steam content, it was found that the initial reduction rates were first order with respect to hydrogen partial pressure. In both sets of mixtures, it was found that the progress of NiO reduction was not a monotonic function of temperature. A minimum rate of advancement of NiO reduction was observed in the temperature range 700oC – 800oC depending on the hydrogen partial pressures and reduction time. A number of distinctly different nickel product microstructures, originating at the Ni-NiO interface were observed under various reduction conditions, namely coarse fibrous nickel with fissures, fine porous nickel-planar interface, large porous nickel-irregular interface and dense nickel product layer. The microstructures of reduction product were found to change with temperature and time. It was found that heating the coarse fibrous nickel structure resulted in a re-crystallization, grain growth and densification of nickel product. When the heat treatments were carried out on the porous nickel structures, the number of pores decreases with increasing temperature and time, which was accompanied by the increase in the pore sizes. The microstructures and kinetics of the reduction of nickel oxide were found to be a function of temperature, gas composition and reaction time. The study provides strong evidence for a link between the reduction kinetics and the changes in the reduction product microstructures. Mechanisms and kinetics of the reduction of nickel oxide have been discussed by considering reduction conditions, information on the structures and elementary processes involving in the reduction process.

Steam reforming is the most economical and widely-used route for the conversion of light hydrocarbon (such as natural gas) to various valued-added products. This process is commonly carried out over a low-cost alumina-supported nickel catalyst, which often suffers from carbon deposition resulting in loss of active sites, flow and thermal maldistribution, as well as excessive pressure drop. A bimetallic catalyst with improved anti-coking properties was formulated by incorporating the nickel-based system (15% loading) with cobalt metal (5% loading). Two-level factorial design was employed to investigate the effect of major preparation variables, namely impregnation pH value (2-8), calcination temperature (873-973 K), heating rate (5-20 K min-1) and time (1-5 h). The catalysts prepared were subjected to various characterisation techniques to determine key physicochemical properties (i.e. BET area, H2-chemisorption and NH3- TPD acidity). X-ray diffraction revealed that NiO, Co3O4, NiCo2O4 and a proportion of Ni(Co)Al2O4 aluminates were transformed during H2-reduction to active Co and Ni crystallites. TEM images showed an egg yolk profile in the low-pH catalyst suggesting that main deposition site was located in the particle centre, while metal deposition occurred primarily around the particle exterior for the high-pH catalyst. Temperature programmed experiments were carried out to examine the extent of conversion, type of surface species and solid-state kinetics (using the Avrami-Erofeev model) involved during various stages in catalyst life-cycle (calcination, reduction, oxidation and regeneration). Steam reforming analysis suggested that enhanced catalyst activity may be due to synergism in the Co-Ni catalyst. Specifically, the low-pH catalyst exhibited better resistance towards carbon-induced deactivation than the high-pH formulation. The study also provided the first attempt to develop a quantitative relation between catalyst preparation conditions and its performance (activity, product selectivity and deactivation) for steam reforming reaction. Deactivation and reforming kinetic coefficients were simultaneously evaluated from propane reforming conversion-time data under steam-to-carbon ratios of 0.8-1.6 and reaction temperatures between 773-873 K. The time-dependent optimum operational policy derived based on these rate parameters gave better conversion stability despite the heavy carbon deposit. Thermal runs further showed that the catalysts regenerated via two-stage reductive-oxidative coke burn-off exhibited superior surface properties compared to those rejuvenated by a single-step oxidation.

Doctor of Philosophy(PhD) / Soil contamination with heavy metal(loid)s is a major environmental problem that requires effective and affordable remediation technologies. The utilisation of plants to remediate heavy metal(loid)s contaminated soils has attracted considerable interest as a low cost green remediation technology. The process is referred to as phytoremediation, and this versatile technology utilises plants to phytostabilise and/or phytoextract heavy metal(loid)s from contaminated soils, thereby effectively minimising their threat to ecosystem, human and animal health. Plants that can accumulate exceptionally high concentrations of heavy metal(loid)s into above-ground biomass are referred to as hyperaccumulators, and may be exploited in phytoremediation, geobotanical prospecting and/or phytomining of low-grade ore bodies. Despite the apparent tangible benefits of utilising phytoremediation techniques, a greater understanding is required to comprehend the ecophysiological aspects of species suitable for phytoremediation purposes. A screening study was instigated to assess phytoremediation potential of several fern species for soils contaminated with cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn). Hyperaccumulation was not observed in any of the studied species, and in general, species excluded heavy metal uptake by restricting their translocation into aboveground biomass. Nephrolepis cordifolia and Hypolepis muelleri were identified as possible candidates in phytostabilisation of Cu-, Pb-, Ni- or Zn-contaminated soils and Dennstaedtia davallioides appeared favourable for use in phytostabilisation of Cu- and Zn-contaminated soils. Conversely, Blechnum nudum, B. cartilagineum, Doodia aspera and Calochlaena dubia were least tolerant to most heavy metals and were classified as being least suitable for phytoremediation purposes Ensuing studies addressed the physiology of arsenic (As) hyperaccumulation in a lesser known hyperaccumulator, Pityrogramma calomelanos var. austroamericana. The phytoremediation potential of this species was compared with that of the well known As hyperaccumulator Pteris vittata. Arsenic concentration of 3,008 mg kg–1 dry weight (DW) occurred in P. calomelanos var. austroamericana fronds when exposed to 50 mg kg–1 As without visual symptoms of phytotoxicities. Conversely, P. vittata was able to hyperaccumulate 10,753 mg As kg–1 DW when exposed to 100 mg kg–1 As without the onset of phytotoxicities. In P. calomelanos var. austroamericana, As was readily translocated to fronds with concentrations 75 times greater in fronds than in roots. This species has the potential for use in phytoremediation of soils with As levels up to 50 mg kg–1. Localisation and spatial distribution of As in P. calomelanos var. austroamericana pinnule and stipe tissues was investigated using micro-proton induced X-ray emission spectrometry (µ-PIXE). Freeze-drying and freeze-substitution protocols (using tetrahydrofuran [THF] as a freeze-substitution medium) were compared to ascertain their usefulness in tissue preservation. Micro-PIXE results indicated that pinnule sections prepared by freeze-drying adequately preserved the spatial elemental distribution and tissue structure of pinnule samples. In pinnules, µ-PIXE results indicated higher As concentration than in stipe tissues, with concentrations of 3,700 and 1,600 mg As kg–1 DW, respectively. In pinnules, a clear pattern of cellular localisation was not resolved whereas vascular bundles in stipe tissues contained the highest As concentration (2,000 mg As kg–1 DW). Building on these µ-PIXE results, the chemical speciation of As in P. calomelanos var. austroamericana was determined using micro-focused X-ray fluorescence (µ-XRF) spectroscopy in conjunction with micro-focused X-ray absorption near edge structure (µ-XANES) spectroscopy. The results suggested that arsenate (AsV) absorbed by roots was reduced to arsenite (AsIII) in roots prior to transport through vascular tissues as AsV and AsIII. In pinnules, AsIII was the predominant species, presumably as aqueous-oxygen coordinated compounds. Linear least-squares combination fits of µ-XANES spectra showed AsIII as the predominant component in all tissues sampled. The results also revealed that sulphur containing thiolates may, in part sequester accumulated As. The final aspect of this thesis examined several ecophysiological strategies of Ni hyperaccumulation in Hybanthus floribundus subsp. floribundus, a native Australian perennial shrub species and promising candidate in phytoremediation of Ni-contaminated soils. Micro-PIXE analysis revealed that cellular structure in leaf tissues prepared by freeze-drying was adequately preserved as compared to THF freeze-substituted tissues. Elemental distribution maps of leaves showed that Ni was preferentially localised in the adaxial epidermal tissues and leaf margin, with concentration of 10,000 kg–1 DW in both regions. Nickel concentrations in stem tissues obtained by µ-PIXE analysis were lower than in the leaf tissues (1,800 mg kg–1 vs. 7,800 mg kg–1 DW, respectively), and there was no clear pattern of compartmentalisation across different anatomical regions. It is possible that storage of accumulated Ni in epidermal tissues may provide Ni tolerance to this species, and may further act as a deterrent against herbivory and pathogenic attack. In H. floribundus subsp. floribundus seeds, µ-PIXE analysis did not resolve a clear pattern of Ni compartmentalisation and suggests that Ni was able to move apoplastically within the seed tissues. The role of organic acids and free amino acids (low molecular weight ligands [LMW]) in Ni detoxification in H. floribundus subsp. floribundus were quantified using high performance liquid chromatography (HPLC) and ultra performance liquid chromatography (UPLC). Nickel accumulation stimulated a significant increase in citric acid concentration in leaf extracts, and based on the molar ratios of Ni to citric acid (1.3:1–1.7:1), citric acid was sufficient to account for approximately 50% of the accumulated Ni. Glutamine, alanine and aspartic acid concentrations were also stimulated in response to Ni hyperaccumulation and accounted for up to 75% of the total free amino acid concentration in leaf extracts. Together, these LMW ligands may complex with accumulated Ni and contribute to its detoxification and storage in this hyperaccumulator species. Lastly, the hypothesis that hyperaccumulation of Ni in certain plants may act as an osmoticum under water stress (drought) was tested in context of H. floribundus subsp. floribundus. A 38% decline in water potential and a 68% decline in osmotic potential occurred between water stressed and unstressed plants, however, this was not matched by an increase in accumulated Ni. The results suggested that Ni was unlikely to play a role in osmotic adjustment in this species. Drought stressed plants exhibited a low water use efficiency which might be a conservative ecophysiological strategy enabling survival of this species in competitive water-limited environments.

Dissertation (Ph. D.)--University of Akron, Dept. of Chemical Engineering, 2007. / "December, 2007." Title from electronic dissertation title page (viewed 03/12/2008) Advisor, Steven S. C. Chuang; Committee members, Lu-Kwang Ju, Edward Evans, W. B. Arbuckle, Stephen Z. D. Cheng; Department Chair, Lu-Kwang Ju; Dean of the College, George K. Haritos; Dean of the Graduate School, George R. Newkome. Includes bibliographical references.

Zugl.: Karlsruhe, Univ., Diss.

Thesis (Ph.D.)--McMaster University, 2005. / Supervisor: Patrick S. Nicholson. Includes bibliographical references (leaves 162-181). Also available online.