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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.
1

The hydrogen production capability of free-living Nostoc filagelliforme

Lichtl, Rixa Regina January 1996 (has links)
No description available.
2

Exploring Simple Catalyst for Transfer Hydrogenation of Ketones and Photocatalytic Hydrogen Production Using Homogeneous Metal Complexes

Ahmadi, Sara 13 September 2019 (has links)
Transfer hydrogenation has been recognized to be an important synthetic method in both academic and industrial research to obtain valuable products including alcohols. Transition metal catalysts based on precious metals, such as Ru, Rh and Ir, are typically employed for this process. This thesis starts with a study on the potential of an Fe based complex carrying a PNP ligand (2,6-{Ph2PNH}2(NC5H3)) to function as an active transfer hydrogenation catalyst for the conversion of ketones to alcohols. During the analysis of the performance parameters of this potential catalyst, it was discovered that the added base, KOtBu, was the actual catalyst. Other bases were explored as catalysts for this transformation as well as the general performance features of this simple alkali metal base. In a separate project described in Chapter 3, the search for catalysts shifted focus to a study of the potential of a series of first row transition metal-based complexes supported by a bis(thioether)pyridine “SNS” ligand for photocatalytic hydrogen production. This initial study led to the observation that the Fe complex [Fe(k3-2,6-(CH3SCH2)2C5H3N)Br2]2 was a capable photocatalyst for H2 production in combination with a photosensitizer (Ru(bpy)3)2+) and an electron donor (triethanolamine). Although water was initially believed to be the source of protons that were reduced to H2, analysis of control experiments pointed to the hydrogen source being the electron donor.
3

Multiphase flow and chemical reactor thermodynamics for hydrolysis and thermochemical production

Pope, Kevin 01 August 2012 (has links)
Current techniques of hydrogen production (primarily reformation of fossil fuels) are unsustainable, releasing CO2 into the atmosphere, as well as consuming limited reserves of fossil fuels. The copper-chlorine cycle is a promising thermochemical process which can cost-effectively produce hydrogen with less environmental impact. In this thesis, new predictive formulations and experimental data are presented to improve the conversion extent and reaction rates of the hydrolysis reactor in the Cu-Cl cycle. This reactor has critical implications for the design, operation, and efficiency of the Cu-Cl cycle and hydrogen production. The relatively high temperature needed to drive the reaction requires a significant input of thermal energy. This thesis focuses on methods and analysis to reduce the unreacted steam in the hydrolysis reactor, in order to reduce the thermal energy input and improve the cycle’s thermal efficiency. A key outcome from this thesis is the experimental verification of reducing the steam to copper chloride ratio from 16:1 (past studies) to about 3:1. The results of this thesis provide key new data to design a more efficient hydrolysis reactor that can be effectively integrated within the Cu-Cl cycle. / UOIT
4

Reduction-oxidation cycling of metal oxides for hydrogen production

Sim, Andrew Gregory, Chemical Sciences & Engineering, Faculty of Engineering, UNSW January 2010 (has links)
A process for the production of clean hydrogen from methane based upon the sequential reduction and oxidation of metal oxides has been studied. The original process, based on iron oxide, suffers from significant disadvantages including deactivation by sintering and coke deposition. Improvement of the iron based system and identification and development of alternative metal oxides for hydrogen production has formed the basis of this study. The literature review outlines current methods for hydrogen production, followed by a review of the Steam-Iron Process as an improved and simpler method for clean hydrogen production. Thermodynamic assessment shows Fe3O4/FeO/Fe, WO3/WO2/W and SnO2/SnO/Sn to be the most prospective systems for the Steam-Metal Process. Experimental testing showed that Fe and W based systems were suitable for hydrogen production, but Sn based systems were unsuitable due to poor reducibility using methane. Attention was then focused on the addition of CeO2/ZrO2 promoters to Fe and W based systems in order to improve reactivity and prevent catalyst deactivation. CeO2/ZrO2 promoted Fe2O3 showed improved redox reactivity and increased stability, with formation of FeO. This aided in mitigation of sintering and introduced the possibility of prevention of coking, as catalysed by methane decomposition over fully reduced Fe metal. Although WO3 was found to be a suitable oxide, complete reduction to tungsten metal resulted in the formation of tungsten carbide and contamination of hydrogen produced. The formation of 31mol% [CeO2/ZrO2] / 69 mol% WO3 showed stabilised reduction using methane, allowing for redox cycling of the WO3-WO2 couple and preventing complete reduction to W metal. The use of the doped metal oxide showed the best performance of all the metal oxides tested, with clean hydrogen production over multiple redox cycles and high metal oxide stability. Further kinetic studies of both the reduction and oxidation reactions show reduction is chemical reaction controlled process (WO3/WO2.9 → WO2) with an apparent activation energy of 142 ?? 3 kJ/mol. Oxidation is also fitted to a chemically controlled process, with a reaction rate expression derived as: rH2 = [0.064 + (F x 0.00038)].e^(-108750/8.314xT).[PH2O]^(0.75) The apparent activation energy for oxidation was calculated as 109 ?? 1 kJ/mol.
5

Reduction-oxidation cycling of metal oxides for hydrogen production

Sim, Andrew Gregory, Chemical Sciences & Engineering, Faculty of Engineering, UNSW January 2010 (has links)
A process for the production of clean hydrogen from methane based upon the sequential reduction and oxidation of metal oxides has been studied. The original process, based on iron oxide, suffers from significant disadvantages including deactivation by sintering and coke deposition. Improvement of the iron based system and identification and development of alternative metal oxides for hydrogen production has formed the basis of this study. The literature review outlines current methods for hydrogen production, followed by a review of the Steam-Iron Process as an improved and simpler method for clean hydrogen production. Thermodynamic assessment shows Fe3O4/FeO/Fe, WO3/WO2/W and SnO2/SnO/Sn to be the most prospective systems for the Steam-Metal Process. Experimental testing showed that Fe and W based systems were suitable for hydrogen production, but Sn based systems were unsuitable due to poor reducibility using methane. Attention was then focused on the addition of CeO2/ZrO2 promoters to Fe and W based systems in order to improve reactivity and prevent catalyst deactivation. CeO2/ZrO2 promoted Fe2O3 showed improved redox reactivity and increased stability, with formation of FeO. This aided in mitigation of sintering and introduced the possibility of prevention of coking, as catalysed by methane decomposition over fully reduced Fe metal. Although WO3 was found to be a suitable oxide, complete reduction to tungsten metal resulted in the formation of tungsten carbide and contamination of hydrogen produced. The formation of 31mol% [CeO2/ZrO2] / 69 mol% WO3 showed stabilised reduction using methane, allowing for redox cycling of the WO3-WO2 couple and preventing complete reduction to W metal. The use of the doped metal oxide showed the best performance of all the metal oxides tested, with clean hydrogen production over multiple redox cycles and high metal oxide stability. Further kinetic studies of both the reduction and oxidation reactions show reduction is chemical reaction controlled process (WO3/WO2.9 → WO2) with an apparent activation energy of 142 ?? 3 kJ/mol. Oxidation is also fitted to a chemically controlled process, with a reaction rate expression derived as: rH2 = [0.064 + (F x 0.00038)].e^(-108750/8.314xT).[PH2O]^(0.75) The apparent activation energy for oxidation was calculated as 109 ?? 1 kJ/mol.
6

Relation between hydrogen production and photosynthesis in the green algae Chlamydomonas reinhardtii

Basu, Alex January 2015 (has links)
The modernized world is over-consuming low-cost energy sources that strongly contributes to pollution and environmental stress. As a consequence, the interest for environmentally friendly alternatives has increased immensely. One such alternative is the use of solar energy and water as a raw material to produce biohydrogen through the process of photosynthetic water splitting. In this work, the relation between H2-production and photosynthesis in the green algae Chlamydomonas reinhardtii was studied with respect to three main aspects: the establishment of prolonged H2-production, the involvement of PSII in H2-production and the electron pathways associated with PSII during H2-production. For the first time, this work reveals that PSII plays a crucial role throughout the H2-producing phase in sulfur deprived C. reinhardtii. It further reveals that a wave-like fluorescence decay kinetic, before only seen in cyanobacteria, is observable during the H2-producing phase in sulfur deprived C. reinhardtii, reflecting the presence of cyclic electron flows also in green algae.
7

Analysis of the Large Scale Centralized Hydrogen Production and the Hydrogen Demand from Fuel Cell Vehicles in Ontario

Liu, Hui January 2009 (has links)
The ‘Hydrogen Economy’ is a proposed system where hydrogen is produced from carbon dioxide free energy sources and is used as an alternative transportation fuel. The application of hydrogen on board fuel cell vehicles can significantly decrease air pollutants and greenhouse gases emission from the transportation sector. There must be significant transition of infrastructure in order to achieve the hydrogen economy with the investment required in both production and distribution infrastructure. This research focused on the projected demands for infrastructure transition of ‘Hydrogen Economy’ in Ontario, Canada. Three potential hydrogen demand and distribution system development scenarios were examined to estimate hydrogen fuel cell vehicle market penetration, as well as the associated hydrogen production and distribution. Demand of transportation hydrogen was estimated based on the type of hydrogen fuel cell vehicle. Upon the estimate of hydrogen demand from fuel cell vehicles in Ontario, the resulting costs of delivered hydrogen were investigated. In the longer term hydrogen is expected to be produced by utilizing nuclear heat and a thermochemical production cycle. A brief survey of thermochemical hydrogen production cycles was presented with a focus on S-I cycle. Sequential optimization models were developed to explore the minimum utility energy consumption and the minimum number of heat exchangers. Finally an optimal heat exchanger network for S-I thermochemical cycle was defined by a mixed integer optimization model using GAMS.
8

Analysis of the Large Scale Centralized Hydrogen Production and the Hydrogen Demand from Fuel Cell Vehicles in Ontario

Liu, Hui January 2009 (has links)
The ‘Hydrogen Economy’ is a proposed system where hydrogen is produced from carbon dioxide free energy sources and is used as an alternative transportation fuel. The application of hydrogen on board fuel cell vehicles can significantly decrease air pollutants and greenhouse gases emission from the transportation sector. There must be significant transition of infrastructure in order to achieve the hydrogen economy with the investment required in both production and distribution infrastructure. This research focused on the projected demands for infrastructure transition of ‘Hydrogen Economy’ in Ontario, Canada. Three potential hydrogen demand and distribution system development scenarios were examined to estimate hydrogen fuel cell vehicle market penetration, as well as the associated hydrogen production and distribution. Demand of transportation hydrogen was estimated based on the type of hydrogen fuel cell vehicle. Upon the estimate of hydrogen demand from fuel cell vehicles in Ontario, the resulting costs of delivered hydrogen were investigated. In the longer term hydrogen is expected to be produced by utilizing nuclear heat and a thermochemical production cycle. A brief survey of thermochemical hydrogen production cycles was presented with a focus on S-I cycle. Sequential optimization models were developed to explore the minimum utility energy consumption and the minimum number of heat exchangers. Finally an optimal heat exchanger network for S-I thermochemical cycle was defined by a mixed integer optimization model using GAMS.
9

Synthesis and characterization of semiconductor thin films for photoelectrochemical energy conversion

Hahn, Nathan Taylor 13 November 2012 (has links)
The field of solar energy conversion has experienced resurgence in recent years due to mounting concerns related to fossil fuel consumption. The sheer quantity of available solar energy and corresponding opportunity for technological improvement has motivated extensive study of novel light-absorbing semiconductors for solar energy conversion. Often, these studies have focused on new ways of synthesizing and altering thin film semiconductor materials with unique compositions and morphologies in order to optimize them for higher conversion efficiencies. In this dissertation, we discuss the synthesis and electrochemical characterization of a variety of candidate semiconductor materials exhibiting promising characteristics for photoelectrochemical solar energy conversion. Three specific methods of thin film deposition are detailed. The first is a physical vapor deposition technique used to independently tune the morphology and composition of hematite (α-Fe2O3) based materials. Because of hematite’s poor electronic properties, these modifications were able to significantly improve its performance as a photoanode for water oxidation. The second technique is electrodeposition, which was employed to deposit the novel ternary metal oxide, CuBi2O4. The study of these films, along with those prepared by physical vapor deposition, provided insight into the factors limiting the ability of this photo-active material to function as a photocathode for hydrogen evolution from water. The third technique is chemical spray pyrolysis, which was employed to deposit and optimize films of the bismuth chalco-halides BiOI and BiSI. These studies were used to obtain previously unknown properties of these materials relevant to their utilization in photoelectrochemical cells. The manipulation of deposition temperature had significant effects on these properties and dictated the films’ overall photoconversion performance. / text
10

Análise técnica e econômica de um reformador de etanol para produção de hidrogênio /

Souza, Antonio Carlos Caetano de. January 2005 (has links)
Resumo: Neste trabalho efetua-se análises técnica e econômica de um reformador a vapor de etanol para a produção de 0,7 Nm3/h de hidrogênio, capacidade esta suficiente para acionar uma célula de combustível do tipo PEMFC de 1 kW. A análise técnica abrange análises físico-química e termodinâmica (que envolve inclusive análise exergética), que consiste em fornecer as faixas de temperatura e pressão necessárias à reforma a vapor, e na determinação dos volumes de reagentes consumidos (neste caso, etanol e água). Foi possível obter informações sobre os principais produtos da reforma a vapor (hidrogênio e dióxido de carbono) e o grau de avanço da reação de reforma do etanol. As informações necessárias para o início da modelagem foram obtidas da literatura. A análise exergética permitiu avaliar as melhores condições (temperatura e pressão) para a reforma, baseando-se nos níveis de irreversibilidades. Finalmente, através da análise econômica, avaliou-se os custos de produção de hidrogênio em função do custo de investimento, operação e manutenção no reformador e acessórios. Foram selecionadas quatro fontes de calor para o processo (gás natural, gás liquefeito de petróleo, álcool e eletricidade). Conclui-se que a reforma a vapor de etanol é tecnicamente viável, podendo colocar o hidrogênio combustível no rol dos insumos energéticos alternativos e renováveis. Do ponto de vista econômico, o kWh de hidrogênio produzido por reforma de etanol apresenta o menor valor (numa faixa de 0,06471 a 0,10863 US$/kWh), devido ao alto custo de investimento e ao pequeno volume de produção de reformadores de etanol. Estes custos energéticos do hidrogênio poderão ser mais baixos, desde que haja uma maior produção em escala de reformadores de etanol. / Abstract: In this work the technical and economic analysis of a steam reformer of ethanol is made. The objective is the production of 0.7 Nm3/h of hydrogen to be used in a 1 kW powered PEMFC. The technical analysis consists in physical and chemical, and thermodynamic studies (including the exergetic analysis). These analysis provide informations as temperature and pressure ranges for steam reforming and the volume of the used reactants (in this case, ethanol and water). Through a mathematic modeling, it’s possible to get informations as the products of reforming (the hydrogen and carbon dioxide are the principal products) and the advance degree of the reaction. The useful informations for the modeling were got in the literature. Also about the technical analysis, an exergetic analysis was carried out, permitting obtain the best conditions (temperature and pressure) for the reforming based in the lowest irreversibilities level for the process. Finally, through the economic analysis, the costs of hydrogen production as a function of investment, operation and maintenance costs was made. Four heat sources for the process (natural gas, liquefied petroleum gas, ethanol and electricity) were considered for this analysis. This study has indicated that the steam reforming of ethanol is technically feasible, for the production of hydrogen as one of the alternative and renewable fuel. Economically, the hydrogen produced by steam reforming of ethanol presents the lowest cost, but expensive (at a range from 0,06471 to 0,10863 US$/kWh) because the high cost of investment and the small production of ethanol reformer. / Orientador: José Luz Silveira / Coorientador: Maria Isabel Sosa / Banca: Diovana Aparecida dos Santos Napoleão / Banca: Celso Eduardo Tuna / Mestre

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