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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

The effect of thiamine and its antagonists on plasma and tissue lactic dehydrogenase in rats

Park, Dong Hwa 01 August 1968 (has links)
The lactic dehydrogenase activity in plasma and tissues was measured in the thiamine-deprived, the oxythiamine-treated and the pyrithiamine-treated rats as well as the control rats. The lactic dehydrogenase levels of brain and kidney were significantly increased by oxythiamine treatment. The enzyme activity in heart was markedly decreased only in the thiamine-deprived rats. Unlike the above tissues, the enzyme levels in liver were decreased by 29-44 per cent in all three types of thiamine deficiency, However, the enzyme activity in plasma was significantly increased only by pyrithiamine administration. The distribution patterns of lactic dehydrogenase isozymes were electrophoretically examined in these deficiencies. No significant difference among the three thiamine-deficient groups was observed in brain, kidney, and heart. All five isozymes were observed in proportions that are highly specific for the tissues involved. Two extra bands, in addition to five major bands, were found in liver. In thiamine deprivation liver LDH_3 was noticeably more abundant than LDH_2 in some cases, which is opposite to that found in the control. One extra band between LDH_2 and LDH_3 was absent in liver after pyrithiamine treatment. No noticeable difference in the isozyme distribution of plasma was found among the three thiamine-deficient groups. Blood pyruvate along with lactate was significantly increased by oxythiamine treatment. Pyrithiamine administration also caused a marked increase of blood pyruvate along with lactate only in the phase of the polyneuritic convulsion. Remarkable increases in weight of the adrenal glands were observed in all three cases.
22

Effect of Gallium and Platinum distribution encapsulated in Silicalite-1 (MFI) zeolite on controlled propane dehydrogenation reaction

Almukhtar, Fadhil 04 August 2022 (has links)
The preparation method of the catalyst highly impacts its properties and activity. Optimizing the synthesis conditions mainly targets improving the catalyst performance and overcoming the bottlenecks such as sintering of metal active sites, deactivation, short catalyst lifetime and poor selectivity. In this study, we investigated the influence of the design and preparation method of Silicalite-1 bearing Pt and Ga active species on the properties and the performance of the catalysts for propane dehydrogenation reaction aiming to increase propylene yield. Various synthesis routes, leading to different Pt and Ga location and distances were tested: (1) supporting metals on the zeolite where both Pt and Ga are randomly distributed on the surface, (2) confining of Pt and Ga within the zeolite pores following in-situ approach with no control of their relative positions, and (3) core-shell design where one metal is confined within Silicalite-1 is covered by a Silicalite-1 layer including the second metal. The influence of structure, textural properties, location of Pt and Ga nanoparticles and their synergetic interaction to form Pt-Ga alloys were studied using several characterization techniques such as XRD, BET, TEM-EDX and NMR. Catalytic performance revealed that confining metals improved the selectivity and lifetime of the catalyst. Moreover, spatial separation of Pt and Ga through the core-shell design further boosted the reaction yield with conversions hitting the equilibrium limit. Ga/Pt ratio played a crucial role in tuning the catalyst performance. 0.26%Pt(core)-2.65%Ga(shell)@S-1 catalyst with Ga/Pt of 10 exhibited superior results of 70.5% conversion and 98% selectivity.
23

Molybdenum, Tungsten and Nickel Compounds as Catalysts for the Dehydrogenation of Formic Acid

Neary, Michelle Catherine January 2016 (has links)
Though petroleum fuels are currently a crucial part of our daily life, there is interest in developing energy sources that are more sustainable and better for the environment. One possible energy source is hydrogen, which burns cleanly to produce only water as a byproduct. However, hydrogen itself cannot be easily transported and, therefore, other storage mediums are necessary. One such storage medium that has been investigated in recent years is formic acid, which is a liquid at room temperature and easier to handle. A crucial aspect of using formic acid is the ability to release hydrogen on demand. Testing possible catalysts for this transformation has driven my research over the last five years. Chapter 1 investigates the ability of a series of cyclopentadienyl molybdenum hydrides, Cp^RMo(PMe₃)_{3-x}(CO)_xH (Cp^R = C₅H₅, C₅Me₅; x = 0, 1, 2, 3), to catalyze formic acid dehydrogenation. Though several compounds in the series CpRMo(PMe₃)_{3-x}(CO)_xH have been structurally characterized before, we were able to characterize several more by X-ray diffraction. Since the compounds are structurally similar, differences in catalytic activity are governed by the electronics, which are determined primarily by the number of PMe₃ ligands relative to CO. The best catalysts are the hybrid compounds, Cp^RMo(PMe₃)₂(CO)H, due to the fact that they can be easily protonated by formic acid and readily release hydrogen to continue the catalytic cycle. Additionally, I observed that methanol and methyl formate were being produced as side products. Since methanol is also a potential hydrogen storage medium, its production is of interest. In this case, the tricarbonyl compounds, Cp^RMo(CO)₃H, were most selective for formic acid disproportionation relative to dehydrogenation. This is likely due to their relative propensity to transfer a hydride ligand to formic acid rather than to become protonated by it. We also investigated the ability of formic acid to reduce ketones and aldehydes via transfer hydrogenation. Because the phosphine-rich compounds were such effective catalysts, we sought to investigate the reactivity of other compounds with phosphine ligands towards formic acid. To this end, Chapter 2 focuses on studies involving Ni(PMe₃)₄, and Chapter 3 looks at Mo(PMe₃)₆ and W(PMe₃)₄(η²-CH₂PMe₂)H. Ni(PMe₃)₄ is indeed able to catalyze formic acid dehydrogenation. Density Functional Theory studies suggest that the mechanism involves formation of a formate-hydride followed by decarboxylation to produce a dihydride species. The ability of the PMe₃ ligand to induce decarboxylation also provides a route to synthesize Ni(PMe₃)₄ from Ni(O₂CH)₂•2H₂O and Ni(py)₄(O₂CH)₂•2py, which has been structurally characterized. To expand on the nickel phosphine reactivity, a heteroleptic nickel phosphine complex employing the bisphosphine ligand 1,2-bis(diphenylphosphino)benzene (bppb), namely (bppb)Ni(PMe₃)₂, was synthesized, characterized and tested with formic acid. It also catalyzes dehydrogenation, but rearranges to Ni(PMe₃)₄ and the inactive compound, (bppb)₂Ni. The structural characterization of these and other (bppb)Ni compounds shows that the bppb ligand allowed for extreme flexibility in crystallization. Chapter 3 reveals that Mo(PMe₃)₆ and W(PMe₃)₄(η²-CH₂PMe₂)H are likewise catalysts for formic acid dehydrogenation. However, the compounds produced along the way are also of interest. The known carbonate species, Mo(PMe₃)₄H₂(O₂CO), is formed from Mo(PMe₃)₆ and formic acid, and we have structurally characterized it. The tungsten carbonate species is also produced in the analogous reaction with W(PMe₃)₄(η²-CH₂PMe₂)H. Other compounds observed include W(PMe₃)₄H₂(O₂CH)₂ and W(PMe₃)₄H₃(O₂CH), the latter of which has also been characterized by X-ray diffraction. Finally, both Mo(PMe₃)₆ and W(PMe₃)₄(η²-CH₂PMe₂)H react with formic acid to make trimeric species, [M(PMe₃)₃(CO)(O₂CH)(μ-O₂CH)]₃ (M = Mo, W), which display an unusual anti/anti configuration of the bridging formate ligands. Chapter 4 revisits some of the side products from Chapter 1 in more detail, particularly [CpMo(CO)₃]₂ and [CpMo(μ-O)(μ-O₂CH)]₂. The presence of semi-bridging and bridging ligands, respectively, makes it difficult to determine whether there is actually a metal-metal bond. Natural Bond Orbital (NBO) analysis reveals that there is indeed a Mo-Mo bond in [CpMo(CO)₃]₂, but not in [CpMo(μ-O)(μ-O₂CH)]₂. The Covalent Bond Classification method can be used to depict these and other compounds in a way that more accurately reflects the true bonding in the molecule.
24

Characterisation of the NADH dehydrogenases associated with isolated plant mitochondria

Soole, Kathleen Lydia. January 1988 (has links) (PDF)
Typescript (Photocopy) Bibliography: leaves i-xii. (3rd paging sequence)
25

The oxidative dehydrogenation of n-Hexane and n-Octane over vanadium magnesium oxide catalysts.

Chetty, Jonathan. January 2006 (has links)
Vanadium magnesium oxide (VMgO) catalysts with different vanadium loadings were synthesized and tested for catalytic activity using pure «-hexane and «-octane as feeds. High surface area catalysts were obtained by the wet impregnation of magnesium oxide with an aqueous ammonium metavanadate solution. The optimum loading of vanadium was shown to be 19 % (calculated as weight % of V205). Catalysts were characterized by x-ray diffraction (XRD), inductively coupled plasma - atomic emission spectroscopy (ICP-AES), Brunauer-Emmet-Teller (BET) surface area, differential scanning calorimetry - thermogravimetric analysis (DSC-TGA), Fourier transform infrared spectroscopy (FTIR), laser Raman spectroscopy (LRS), x-ray induced photoelectron spectroscopy (XPS), energy dispersive x-ray spectroscopy (EDS) and scanning electron microscopy (SEM). Magnesium oxide (MgO) and magnesium orthovanadate (Mg3(V04)2 were the only phases observed in each catalyst. VMgO catalysts were tested under both oxygen-rich and oxygen-lean conditions. «-Hexane as feed yielded benzene, 1-hexene, 2-hexene, propane, propene, carbon oxides and water as products, n- Octane as feed yielded styrene, ethylbenzene, xylene, benzene, octenes, carbon oxides and water. 19VMgO was promoted with different loadings of molybdenum oxide (M0O3), cesium oxide (Cs20), antimony oxide (Sb20s), niobium oxide (Nb205), bismuth oxide (Bi203) and tellurium oxide (Te02). The promoted catalysts were tested in specially designed and constructed parallel fixed bed continuous flow reactors. / Thesis (Ph.D.)-University of KwaZulu-Natal, 2006.
26

Development of PCP pincer complexes as catalysts for organic transformations involving the activation of "unreactive" bonds

Wang, Zhaohui, 1972 January 2005 (has links)
Thesis (Ph. D.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references (leaves 101-111). / Also available by subscription via World Wide Web / xii, 111 leaves, bound ill. 29 cm
27

Characterisation of the NADH dehydrogenases associated with isolated plant mitochondria /

Soole, Kathleen Lydia. January 1989 (has links) (PDF)
Thesis (Ph. D.)--University of Adelaide, 1990. / Typescript (Photocopy). Includes bibliographical references (leaves i-xii. (3rd paging sequence)).
28

Development of PCP pincer complexes as catalysts for organic transformations involving the activation of "unreactive" bonds

Wang, Zhaohui, January 2005 (has links)
Thesis (Ph. D.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references (leaves 101-111).
29

The catalytic dehydrogenation of heterocyclic nitrogen compounds

Lundsted, Lester Gordon, January 1942 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 1942. / Typescript. Includes abstract and vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 61-62).
30

Dehydrogenation of Formic Acid by a N,N-Bidentate Ru(II) Complex: Synthesis, Characterization, and Catalytic Performance

Alshehri, Rawan 04 1900 (has links)
Alternative energy sources have been investigated for utilization in various applications to mitigate carbon dioxide emissions. The transportation sector is one of the major sectors that require the adaptation of renewable energy storage technologies for onboard applications. Formic acid is a liquid energy carrier that has the potential of replacing current fuels and mitigating carbon dioxide emissions through a circular carbon economy. The production of energy from formic acid can be achieved by homogenous catalysis to extract hydrogen from formic acid. The most promising metals for formic acid dehydrogenation in aqueous solution have been mainly ruthenium and iridium. While iridium has mostly surpassed ruthenium, further exploration of ruthenium is necessary because it is more economical. This work presents the synthesis and catalytic performance of a N,N-bidentate Ru(II) complex. X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and Mass spectrometry (MS) were used to confirm the structure of the catalyst. The title complex was found to be an efficient system for formic acid dehydrogenation to hydrogen gas and carbon dioxide in the aqueous phase. The highest TOF achieved is 656 h-1 in the presence of two equivalents of sodium formate to formic acid in water at 90 °C. There was no detection of carbon monoxide throughout the reaction process, suggesting the high selectivity of this catalytic system.

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