Thesis--Copenhagen. / "English translation is by Einar Christensen." Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin, 1966. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

Thesis (M.S.)--University of Wisconsin--Madison, 1985. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 141-147).

Philosophiae Doctor - PhD / South Africa is undergoing a serious consideration of hydrogen economy in an effort to develop safe clean and reliable alternative energy sources for fossil fuels. Ammonia is one of the promising candidates due to its low production cost, ease in liquefaction at ambient temperatures, and high energy density as compared to methanol. Ammonia has a high content of hydrogen atoms per unit volume and can easily be cracked down into hydrogen and nitrogen. In the last four years carbon intensive coal dependent South Africa has become one of the leading global destinations for renewable energy investment. Another driving force behind the technology is the prevalence of platinum reserves found in South Africa. Platinum group metals are the key catalytic materials used in most fuel cells, and with more than 75 % of the world’s known platinum reserves found within South Africa. In this thesis, I have developed novel electrocatalysts that are highly specific and selective for production of hydrogen using ammonia as a fuel source. The electro-oxidation of ammonia on platinum electrode drop coated platinum nanoparticles (PtNP), platinum iridium nanoparticles (PtIrNP), platinum ruthenium nanoparticles (PtRuNP), platinum telluride nanoparticles (PtTeNP) and ternary nanoparticles (PtIrTeNP) finally (PtRuTeNP) was systematically studied in alkaline solution of potassium hydroxide (KOH) by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The electrocatalysts were synthesised using sodium borohydride as a reducing agent and polyvinylpyrrolidone (PVP) as a stabilising agent from aqueous solutions of H2PtCl6/IrCl3/RuCl3/NaHTe mixtures. XRD confirmed that the binary and ternary electro-catalyst displayed characteristic patterns which indicated that all catalysts have shown the Pt face-centred-cubic (fcc) crystal structure and that the nanoparticles were poly-orientated. The structural characterization was further confirmed with FTIR and UV-vis, FTIR showed the most striking evidence that the PVP stabilized Pt presented a broad peak between 1288 cm-1 and 1638 cm‐1 which corresponded to C‐N stretching motion and C=O stretching motion of monomer for PVP, respectively. The narrow absorption peak centered at 1420 cm‐1 and 2880 cm‐1 occurred in which was ascribed to the C–H bonding due to the presence of PVP. This was due to the formation of coordinate bond between the nitrogen atom of the PVP and the Pt2+, Ir3+, Ru3+ and Te2+ ions. UV-vis was able to show the oxidation state of the nanoparticles and obtained an exponential graph shape which indicated complete reduction because there was no peak observed. Morphological characterization in the form of high resolution scanning electron microscope (HRSEM) revealed the formation of poly-orientated nanoparticles with average particle size of 23- 46 nm with slightly aggregated crystalline materials. The elemental composition of the alloy nanoparticles measured using energy dispersive spectroscopy (EDS) showed the presence of the four elements; Pt, Ir, Ru and Te. High resolution transmission electron microscopy (HRTEM) revealed the formation of crystalline non-aggregated 0.6-5 nm sized nanoparticles. The elemental composition of the alloy nanoparticles measured using energy dispersive X-ray (EDX) showed the presence of the four elements; Pt, Ir, Ru and Te. Selected area electron diffraction pattern (SAED) nanoparticles showed characteristic electron diffraction rings of Pt, PtIr, PtRu, PtTe, PtIrTe and PtRuTe, confirmed the phase and crystallinity of the materials. The electrocatalytic behaviour of the PtIrTe and PtRuTe nanoparticles for ammonia oxidation in KOH solution showed reduced overpotential properties and an increased current density compared to the bare Pt nanoparticles electrode thus providing a promising alternative for development of low-cost and high-performance electrocatalyst for electro-oxidation of ammonia. In terms of minimising the ammonia oxidation overpotential, catalyst selection were ranked as follows PtTe > PtRuTe > PtIr > PtRu > PtIrTe > Pt, with regards to maximising the exchange current density, the ranking was PtTe > PtIrTe > Pt > PtRu > PtIr > PtRuTe. The results were further interrogated with EIS which revealed in terms of minimising charge transfer resistance (Rct) the nano catalysts selection were ranked as follows PtRuTe ˃ PtIrTe ˃ PtRu ˃ PtIr ˃ Pt ˃ Bare Pt electrode ˃ PtTe. That meant that the conductivity of the catalysts facilitated the flow of charge through the nanoalloys onto the surface of the electrode. The difference in charge transfer resistance revealed that PtRuTe and PtIrTe nanoalloys had an obvious advantage in reaction activity. The application of ternary metal nanoparticles had significantly enhanced the catalytic activity toward ammonia oxidation. The role of the third component (Te) had improved the catalysts in reducing Nads adsorption on Pt. The enhanced catalytic activity has been attributed by a number of factors including the change in Pt–Pt inter atomic distance, number of Pt nearest neighbours, Pt 5d band vacancy, and Pt metal content on particle surface.

xvi, 233 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / The coordination chemistry of iron with N 2 is becoming increasingly important as chemists try to find alternative routes to the production of ammonia. Current biological and industrial processes use iron to catalyze the formation of ammonia from N 2 ; however, huge amounts of energy are required for this conversion. Understanding how dinitrogen and other intermediates of dinitrogen reduction interact with iron could lead to energy efficient processes for the production of ammonia. This dissertation explores the synthesis and reactivity of an iron dinitrogen complex that reacts with acid to produce ammonia at room temperature and pressure. This dissertation also explores the progress toward determining the mechanism of this reaction in hopes of improving the yields of ammonia. Chapter I describes both the biological nitrogen fixation process and the industrial production of ammonia and provides an in-depth look at progress toward an alternative route to ammonia using iron complexes described in the literature thus far. Chapter II details the synthesis, characterization, and reactivity of dihydrogen and dinitrogen complexes of iron. These complexes are precursors to the active ammonia producing complex and are among a handful of dihydrogen and dinitrogen complexes that have been structurally characterized. Chapter III explores the synthesis and stability of Fe(DMeOPrPE) 2 N 2 . This complex produces ammonia and hydrazine upon protonation with a strong acid. Optimizing the yield of ammonia from this protonation is also described. Chapter IV discusses the synthesis and reactivity of several complexes of iron containing intermediates relevant to dinitrogen reduction, including diazene (N 2 H 2 ), hydrazine (N 2 H 4 ), and ammonia. By studying these intermediates, a mechanism of ammonia formation from the protonation of Fe(DMeOPrPE) 2 N 2 is proposed that may also provide insights into the mechanism of nitrogenase. Chapter V provides a summary of this research. This dissertation includes previously published and unpublished co-authored material. / Committee in charge: Darren Johnson, Chairperson, Chemistry; David Tyler, Advisor, Chemistry; Michael Haley, Member, Chemistry; Kenneth Doxsee, Member, Chemistry; Scott Bridgham, Outside Member, Biology

Excessive ammonia (NH3) emission, originating largely from agriculture, can affect water, air and soil quality, and through these, endanger ecosystem and human health. Since NH3 emission is strongly dependent on temperature and also influenced by other meteorological variables, the question arises: how will NH3 emission alter in a changing climate? A way to address this question and predict the subsequent environmental consequences is to construct meteorology-driven models of NH3 emission from every agricultural source. Furthermore, NH3 emission is a highly localised and dynamic process. The focus of this thesis is NH3 emission from grazing. In the first stage a new process-based model for NH3 emission from a urine patch was developed. The GAG model (Generation of Ammonia from Grazing) is capable of simulating the TAN (total ammoniacal nitrogen) and the water content of the soil under a urine patch and also soil pH dynamics. In the second stage, GAG was applied to the scale of a grazed field, combining multiple simulations of the patch-scale model including both urine-affected and unaffected (“clean”) areas. The modelled NH3 fluxes were found to be in good agreement with the observations for both model types. The sensitivity of NH3 flux was assessed to various soil physical and chemical parameters for both the patch and the field scale models. It was found that ammonia volatilization from a urine patch could be influenced by the possible restart of urea hydrolysis after a rain event as well as carbon-dioxide emissions from the soil. Over the field scale, it was shown that the temporal evolution of the NH3 exchange flux was dominated by the NH3 emission from the patches within the field. The results also suggested that NH3 fluxes over the field in a given day could be considerably affected by the NH3 emission from urine patches deposited several days earlier. In the last stage of the work, a comprehensive sensitivity analysis was carried out with a special focus on temperature, for both versions of the GAG model. It was shown that due to the different governing dynamics over the patch and the field scale, the temperature-dependence of NH3 exchange is stronger over the field scale. It was also concluded that the temperature-dependence of NH3 exchange is stronger if the sinks of NH3 are stronger within the system. Finally, it was found, that Q10, a widely-used metric to express the relative increase of trace gas emissions over a range of 10 °C, is influenced by the length of the period of investigation and the initial value of the temperature range.

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One problem of intensive fish culture systems is the progressive build-up of toxic wastes such as ammonia. The possibility of improving aquaculture water quality using two kinds of zeolite is discussed. Zeolites are alumino-silicates whose framework allows them to exchange cations. Ion exchange has been demonstrated to be competitive with other methods of ammonia removal due to the high selectivity for ammonia exhibited by zeolite materials. In this study an unknown Zambian zeolite (identified as laumontite by X-ray diffraction techniques) and Pratley clinoptilolite (a South African zeolite) were tested under laboratory conditions and in a fresh water recirculating system. Ammonia cation exchange capacities (CEC) and suitable application rates for efficient water treatment were determined using the batch and column ion exchange procedures. Estimated ammonia uptake, the most important criterion used to assess performance of zeolite filters was strongly influenced by zeolite type, particle size, pre-treatment, regeneration and ion exchange method used. Statistical analysis showed significant differences in average ammonia CEC values between clinoptilolite (14.94 mg g⁻¹) and laumontite (2.77 mg g⁻¹), with the former displaying a higher Na⁺ ® NH₄⁺ exchange rate especially in the early reaction stages. This difference accords with the higher purity of clinoptilolite, 47% as opposed to 4.7% for laumontite, which makes it a better zeolite for ammonium removal. CEC increased linearly as particle size of the clinoptilolite was reduced resulting in a linear regression model (y = 18.29 – 3.704 x; r² = 74%). Pre-treatment of clinoptilolite using 1N NaCl significantly improved the ammonia CEC of clinoptilolite. Overall performance of both the batch and column methods achieved after regeneration (18.3 mg g⁻¹) was 25% higher than the estimated CEC values (13.0 mg g⁻¹) for the unregenerated samples of clinoptilolite. Comparison of CEC estimates using Pratley clinoptilolite, showed that average batch CEC estimates were significantly lower than the column method estimates. The average ammonia CEC values estimated in a fresh water recirculating system (5.80 mg g⁻¹ and 4.12 mg g⁻¹ for the 0.7-1.0 and 1.0-1.4 mm particle sizes, respectively) were significantly lower than the column and batch estimates for the same particle sizes (P < 0.05). Some nitrite (NO₂) and nitrate (NO3) build up was experienced probably due to the growth of autotrophs in the filters. Mass balance of nitrogen (N) for the three treatments of the fish trial (0.7-1.0 mm, 1.0-1.4 mm and the control treatment that had no zeolite in the filter) indicated that less that 10% of the N was retained for growth. It was found that 60% of the NH₄-N present associated with the soluble N was available for absorption by the zeolite filter or biological nitrification and that a total of approximately 22% of NH₄-N available was absorbed by clinoptilolite. The results indicate that the rate of nitrification can be deductively estimated by allowing a zeolite filter to become a biological filter. It is concluded that water treatment by ion exchange using natural zeolites, provides a reliable and efficient method for ammonia removal and appears to be a viable supplementary water treatment method for fresh water systems.

The isothermal, endothermic, stepwise decomposition of ammonium metavanadate (AMV) in inert (argon or nitrogen), oxidising (air or oxygen) and reducing (ammonia) atmospheres as well as under high vacuum (pressure < IOn bar) conditions has been investigated. The reverse reaction, the isothermal recombination of V₂ 0₅ with ammonia and water vapour has also been investigated. The decomposition and recombination reactions were followed by continuously recording the mass loss of the sample with time using a Cahn R.G. Automatic Electrobalance. This enabled small samples ( ~ lOmg) to be used and consequently any self cooling of the sample during the decomposition was minimized. The intermediates and final products formed have been characterized by chemical analysis, X-ray powder diffraction studies, infrared spectroscopy and the mass loss involved in their formation. The changes in the physical properties of the samples during decomposition and recombination have been investigated by surface area measurements (using the BET method and krypton adsorption) and eIectron microscopy. Values for the enthalpy changes involved in the decomposition have been obtained by differential scanning calorimetry. The stoichiometry of the isothermal decomposition of ammonium metavanadate, under the various conditions of surrounding atmosphere has been discussed. Except for the later stages of the decomposition in ammonia, the results correspond well to the gradual reduction of the ratio of "(NH₄)₂ 0" to "V₂0₅" units from the original 1:1 ratio in ammonium metavanadate to pure "V₂0₅" with ammonia and water being evolved throughout the decomposition in the mole ratio of 2:1. The final product of the decomposition in vacuum, argon and air is "V₂0₅" and in ammonia, below 360°, V0₂. The kinetic parameters for each of the stages of the decomposition of AMV in each of the atmospheres studied have been determined. The mechanism of the first stage of the decomposition under the different conditions of surrounding atmosphere has been discussed from both the kinetic and the thermodynamic points of view. The absolute reaction rate theory has been applied to the decomposition in inert atmospheres enabling the formulae of the activated complexes formed during each stage to be calculated. It has also been shown that the detailed atomic movements occurring during the first stage of the decomposition in ammonia can be predicted from a knowledge of the stoichiometry of the reaction and of the detailed crystal structures of the starting and product materials. The kinetics and mechanism of the recombination of "V₂0₅" with ammonia and water vapour to form AMV have also been discussed in detail.