C3H6 oxidation over a Pt/Al2O3 catalyst with or without NOx present was investigated. In particular, its reaction mechanism was studied using diffuse reflectance infrared spectroscopy (DRIFTS), a reactor system designed for monolith-supported catalysts and a micro-reactor system designed for powder catalysts referred to as CATLAB. These experiments reveal that C3H6 oxidation is inhibited by the presence of NO, NO oxidation is inhibited by the presence of CeH6, and that adsorbed NOx can react with gas phase C3H6. DRIFTS and CATLAB results confirm the reaction between C3H6 and nitrates, which are formed during NOx adsorption, with linear nitrites observed as reaction products. Therefore, a reaction route is proposed for C3H6 oxidation in the presence of NOx, namely, nitrates acting as oxidants. Using NO2 instead of NO, or using a high NOx/C3H6 ratio, which is beneficial for nitrate formation, favors this reaction pathway. Data also showed that Pt is required for this reaction, which suggests the nitrates in proximity to the Pt particles are affected/relevant. Reaction kinetics studies of C3H6 oxidation over Pt/Al2O3 and Pt/SiO2 catalysts were performed in CATLAB using a temperature-programmed oxidation method with different oxidants: O2, NO2 and nitrates. The reaction kinetics of these possible reactions were compared in order to determine which reaction is more important. NOx adsorption does not occur on the SiO2 surface so the reaction between C3H6 and NO2 could be isolated and the effect of nitrates could be observed as well when compared to the results from Pt/Al2O3. The Pt dispersions were determined using H2 chemisorption and were 1.3 and 1.6% for Pt/Al2O3 and Pt/SiO2, respectively. C3H6 oxidation starts at a lower temperature with O2 than with NO2 but the activation energy was lower with NO2. This gives indication that hydrocarbons must be activated first for NO2 to be favored in hydrocarbon oxidation. When the experiment was done with C3H6 and nitrates, the reaction did not occur until NOx started to desorb from the catalyst at higher temperatures, when nitrates become unstable and decompose. Therefore, O2 was added to the system and the reaction began at even lower temperature than with just C3H6 and O2. This proved that hydrocarbons need to be activated in order for surface nitrates to affect C3H6 oxidation and this reaction also resulted in a lower activation energy than with just C3H6 and O2. Nitrate consumption was also observed as less NOx desorbed from the catalyst at the later stage of the temperature ramp compared to the amount desorbed when the catalyst was not exposed to C3H6.

In this thesis, a combination of laboratory experimentation under well defined conditions coupled with a kinetic modelling approach is used to verify the existence and respective kinetic rates of previously unconfirmed or postulated mechanisms that drive and limit dark Fenton (Fe(II)/H2O2) - mediated As(III) oxidation at pH 3 and 8 and dark Cu(II) - H2O2 - mediated As(III) oxidation at pH 8. Dark Fenton - mediated oxidation of As(III) at pH 3 is first examined and the effects of the variation in the concentration of reactants (As(III), Fe(II) and H2O2), oxygen, phosphate and organics (2 - propanol, formate, and citrate) are reported and analysed. The kinetic models developed for these systems show high applicability to full scale water treatment application and key mechanistic findings include the significance of the cycling of Fe(II) / Fe(III) via HO2 ???/O2 ??????, the effects of As(IV) termination reactions in the absence of oxygen and the retarding effects of phosphate due to the postulated formation of a Fe(III) - phosphate complex (at a derived rate constant of 2.2 x 106 M-1s-1, that also appears to have negligible kinetic activity in terms of reduction to Fe(II) by HO2 ???/O2 ??????). The work also demonstrates the significance of the free radical by products of formate and citrate oxidation by ???OH (HCOO???/CO2 ?????? and 3HGA???2???). The examination of the dark Cu(II) - H2O2 - mediated oxidation of As(III) at pH 8 with variation in the concentration of reactants (As(III), Fe(II) and H2O2), carbonate and organics (2 - propanol, formate and citrate) demonstrated for the first time the high applicability of this system to the pre - oxidation of As(III) in water treatment and mechanistically that ???OH and CO3 ?????? are the dominant As(III) oxidants in this system. The As(III) oxidant CO3 ??????, is suggested to be generated by the interaction of ???OH and O2 ?????? with the carbonate matrix, at the respective rate constants of 4.9 x 107 M-1s-1 and 5.5 x 106 M-1s-1. Examination of the dark Fenton - mediated oxidation of As(III) at pH 8 and the effects of variation in the concentration of reactants (As(III), Fe(II) and H2O2), carbonate, organics (2 - propanol, formate and citrate) and Cu(II) demonstrates the varied potential mechanistic pathways in relation to the generation of As(III) oxidants from the Fenton reaction, Fe(II) + H2O2 such as Fe(IV) and CO3 ?????? and the previously dismissed ???OH, due to the presence of Fe(II) - citrate complexes. This work also demonstrates and models the enhancement of As(III) oxidation in the presence of an additional transitional metal ion, Cu(II).

The physiologically important free radicals, nitrogen monoxide and superoxide, can combine to form the reactive intermediate peroxynitrite. Peroxynitrite can react with proteins and their constituent amino acids, such as tyrosine, resulting in protein peroxidation, oxidation and nitration. The nitration of proteins, assessed by the analysis of 3-nitrotyrosine, is a proposed index of pathophysiological activity of peroxynitrite. The aim of the work was to investigate the reaction products between peroxynitrite and protein, develop an assay for 3-nitrotyrosine and measure its levels in biological samples. To study the amino acid products arising from the reaction of peroxynitrite and protein, both liquid chromatography (LC) and gas chromatography (GC) combined with mass spectrometry (MS) were adopted. Approaches to 3-nitrotyrosine assay development were first, to take advantage of the intrinsic sensitivity of electron capture negative ionization GC-MS. Secondly, to avoid possible artefactual problems associated with the derivatisation step in GC-MS, an assay for 3-nitrotyrosine based on combined LC-MS-MS was developed. When a selection of peptides was exposed to peroxynitrite under physiological conditions in vitro, the hydrolysis products showed that 3-nitrotyrosine was the major product. Detectable minor products were 3,5-dinitrotyrosine and DOPA. The GC-MS assay was found to be fraught with difficulty due to artefactual formation of 3-nitrotyrosine. In order to quantify and correct for artefact formation, this complication was approached by incorporating a second isotopomer. This method, however, was confounded by large errors that reduced the overall sensitivity. Either negative or zero levels of endogenous 3-nitrotyrosine were found in tested samples after correction for artefact formation. The LC-MS-MS assay was then used to analyse 3-nitrotyrosine levels in a range of biological samples, including human plasma from healthy volunteers, synovial fluid samples from arthritis patients and tissue extracts from a mouse model of amyotropic lateral sclerosis. In contrast to published data, 3-nitrotyrosine levels were found to be below the limit of detection (1 pg/????L, 10 pg o/c) for all samples - a result somewhat consistent with the negative GC-MS data. It is suggested that the high 3-nitrotyrosine levels previously reported in the literature might reflect artefactual generation of 3-nitrotyrosine and that other approaches to assessing pathophysiological nitration should be sought in future.

Bibliography: leaves 192-193. / ix, 214, ix leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / The focus of the thesis is to investigate the fundamental kinetics of the pyrite-nitric acid system. Particular attention is paid to the formation and oxidation of elemental sulfur. The study aims to elucidate the chemistry of the sulfide oxidation and of elemental sulfur formation and oxidation. / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemical Engineering, 1997?

Includes bibliographical references (34 leaves). / xxi, 204 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Investigates the in vitro antioxidant properties of red wine containing polphends and the isoflavone genistein. Subsequently the effect of red wine on low density lipoprotein oxidation and fatty streak lesion development in cholesterol-fed rabbits was examined. / Thesis (Ph.D.)--University of Adelaide, Dept. of Clinical and Experimental Pharmacology, 1998

Techn. Universiẗat, Diss., 2001--Berlin.

Humans have dramatically increased the amount of reactive nitrogen cycling through the biosphere. In coastal systems, excess nitrogen can lead to negative impacts. Thus, it is crucial to understand how nitrogen is cycled within, and eventually removed from, marine systems and the variables that regulate these processes. Sediment denitrification (the microbial conversion of nitrate (NO3^-) to dinitrogen (N2) gas) and water column nitrification (the two step oxidation of ammonium (NH4^+) to nitrite (NO2^-) and then nitrate (NO3^-)) rates were quantified along an in situ gradient of environmental conditions from an estuary to the continental shelf off Rhode Island, USA. Sediment net denitrification rates were directly measured over multiple seasonal cycles using the N2/Ar technique. Denitrification rates ranged from 20-75 μmol m^-2 hr^-1 (mean 44±4), indicating that this process removes ~5% of total reactive nitrogen entering the North Atlantic shelf region per year. Based on model results, these rates also represented a three-fold decrease in sediment nitrogen removal in New England continental shelf sediments over the past century. A literature review of marine water column nitrification observations were compiled to evaluate how ammonium, nitrite, and total oxidation rates vary worldwide. Rates of ammonium, nitrite, and total oxidation differed among estuary, continental shelf, and open ocean environments (p<0.05). This review highlights that as we continue to study marine "nitrification," it is necessary to consider both individual oxidation processes and environment type. Water column ammonium and nitrite oxidation rates were measured using stable isotope tracers off Rhode Island. At all study sites, nitrite oxidation rates (0-99 nM d^-1) outpaced ammonium oxidation rates (0-20 nM d^-1). These oxidation processes responded in dissimilar ways to in situ water column conditions (depth, salinity, dissolved oxygen, and pH), and these relationships varied with location. Nitrous oxide (N2O) production rates up to 10 times higher than ammonium oxidation indicated that ammonium oxidation may be underestimated if this byproduct is not measured. For the first time, the link between sediment metabolism and water column nitrification was also examined, and the results highlight the importance of benthic-pelagic coupling as controlling factor of water column ammonium and nitrite oxidation. / 2019-04-30T00:00:00Z

Carbon-carbon composite brakes are one third the weight of typical steel brakes, and they attain strength and frictional properties at temperatures up to 1600°C. C/C composite brakes can endure high temperatures, but in the presence of oxygen they will begin to oxidize at 400°C. Anti-oxidant systems must be applied to the non-rubbing surfaces of the C/C composite stators and rotors to prevent oxidation. Currently, commercial phosphorus based coating materials are made of crystalline metal phosphates that are derived from heat treated phosphoric acid-based liquid precursors painted on the non-rubbing surface of C/C composites. These crystalline metal phosphate coatings are very porous and tend to move to the friction surface when exposed to increased levels of relative humidity. This anti-oxidant migration towards the rubbing surface causes a drop in frictional properties. Migration reduction and oxidation inhibition was improved upon with advanced anti-oxidant systems. The advanced antioxidants analyzed protected the C/C composite from thermal and catalytic oxidation six to ten times better at 650°C than commercial materials. At 871°C, the antioxidants protected the C/C composite from thermal oxidation ten times better than commercial materials. Migration of the antioxidant to the rubbing surfaces was eliminated through the use of advanced antioxidant compositions. The predicted life of the antioxidants was modeled using Avrami's equation. Characterization of the antioxidants was further analyzed through the use of SEM, EDS, and XRD systems.

Plasma electrolytic oxidation, or PEO, is a surface modification process for the production of ceramic oxide coatings upon substrates of metals such as aluminium, magnesium and titanium. Two methodologies for the quantitative study of electrical breakdown (discharge) events observed during plasma electrolytic oxidation processes were developed and are described in this work. One method presented involves direct measurement of electrical breakdowns during production of an oxide coating within an industrial scale PEO processing arrangement. The second methodology involves the generation and measurement of electrical breakdown events through coatings pre-deposited using full scale PEO processing equipment. The power supply used in the second technique is generally of much lower power output than the system used to initially generate the sample coatings. The application of these techniques was demonstrated with regard to PEO coating generation on aluminium substrates. Measurements of the probability distributions of discharge event characteristics are presented for the discharge initiation voltage; discharge peak current; event total duration; peak instantaneous power; charge transferred by the event and the energy dissipated by the discharge. Discharge events are shown to increase in scale with the voltage applied during the breakdown, and correlations between discharge characteristics such as peak discharge current and event duration are also detailed. Evidence was obtained which indicated a probabilistic dependence of the voltage required to initiate discharge events. Through the scaling behaviour observed for the discharge events, correspondence between the two measurement techniques is demonstrated. The complementary nature of the datasets obtainable from different techniques for measurement of PEO discharge event electrical characteristics is discussed with regards to the effects of interactions between concurrently active discharge events during large scale PEO processing.

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