An investigation was undertaken to determine the feasibility of increasing the hydrogen production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process (HyS). This investigation also involved the technical and economical analysis of the water gas shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical analysis of the water gas shift reaction was determined under the operating conditions selected on the basis of some information available in the literature. The high temperature system (HTS) and low temperature system (LTS) reactors were assumed to be operated at temperatures of 350ºC and 200ºC, respectively. The operating pressure for both reactors was assumed to be 30 atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was 242T/D, which is approximately two times the amount produced by the HyS process alone. The PSA was used for the purification process leading to a hydrogen product with a purity of 99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2 is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with CO2 and traces of CH4, CO, and saturated H2O. The estimated capital cost of the WGS plant with PSA is about US$50 million. The production cost is highly dependent on the cost of all of the required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2 based on the input cost of synthesis gas as produced by the POX process. In this case the production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg. / Thesis (M.Sc. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2006.

An investigation was undertaken to determine the feasibility of increasing the hydrogen production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process (HyS). This investigation also involved the technical and economical analysis of the water gas shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical analysis of the water gas shift reaction was determined under the operating conditions selected on the basis of some information available in the literature. The high temperature system (HTS) and low temperature system (LTS) reactors were assumed to be operated at temperatures of 350°C and 200°C, respectively. The operating pressure for both reactors was assumed to be 30 atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was 242T/D, which is approximately two times the amount produced by the HyS process alone. The PSA was used for the purification process leading to a hydrogen product with a purity of 99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2 is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with C02 and traces of CH4, CO, and saturated H20. The estimated capital cost of the WGS plant with PSA is about US$50 million. The production cost is highly dependent on the cost of all of the required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2 based on the input cost of synthesis gas as produced by the POX process. In this case the production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg. / Thesis (M.Sc. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2009.

An investigation was undertaken to determine the feasibility of increasing the hydrogen production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process (HyS). This investigation also involved the technical and economical analysis of the water gas shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical analysis of the water gas shift reaction was determined under the operating conditions selected on the basis of some information available in the literature. The high temperature system (HTS) and low temperature system (LTS) reactors were assumed to be operated at temperatures of 350°C and 200°C, respectively. The operating pressure for both reactors was assumed to be 30 atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was 242T/D, which is approximately two times the amount produced by the HyS process alone. The PSA was used for the purification process leading to a hydrogen product with a purity of 99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2 is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with C02 and traces of CH4, CO, and saturated H20. The estimated capital cost of the WGS plant with PSA is about US$50 million. The production cost is highly dependent on the cost of all of the required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2 based on the input cost of synthesis gas as produced by the POX process. In this case the production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg. / Thesis (M.Sc. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2009.

Esta dissertação mostra um estudo preliminar da preparação de precursores catalíticos a base de níquel (II) e de sua conversão em catalisadores de xerogéis contendo níquel (NS), bem como o estudo da sua atividade catalítica na reação de deslocamento gás-água. Esta reação foi escolhida como reação modelo para avaliar a atividade catalítica, em especial frente a adição do ácido fosfotungstico (HPW) como promotor catalítico e de organosilanos como agentes promotores da dispersão do Ni. Foram preparados catalisadores NS e NS-x (x = 0,5; 1; 2; 3; 5 e 10% em massa de HPW) via processo sol-gel. A caracterização estrutural foi realizada utilizando-se as técnicas de Energia Dispersiva de Raios X, Difratometria de Raios X, Redução a Temperatura Programada, Fisissorção de Nitrogênio, Espectroscopia de Absorção de Raios X e Espectroscopia de Absorção na Região do Infravermelho. Os testes catalíticos foram realizados no Laboratório de Catálise Heterogênea do IQSC/USP numa temperatura de 250-425 °C, em uma lin ha de reação acoplada a um cromatógrafo a gás para análises in situ dos produtos reacionais gasosos. Os resultados obtidos da primeira parte mostraram que a adição do HPW até 2% em massa de precursor catalítico leva a uma melhora gradual na atividade catalítica de 10 a 31 % medido pela taxa de conversão do CO. Contudo acima de 2% ocorre uma queda de atividade catalítica resultando num comportamento global da conversão de CO do tipo gaussiano com o máximo em 2%. Para explicar este comportamento um modelo qualitativo é proposto baseado na formação de fosfotungstato de níquel amorfo acima de 2%. Na segunda parte do trabalho, a concentração de HPW foi fixada em 2% e a temperatura de reação em 425 °C e foram adicionados organosilanos nitrogenados (amino e nitrila) para avaliar a sua capacidade de funcionar como agentes de dispersão do cátion metálico no precursor híbrido (Ormosil) e do metal no catalisador. O catalisador proveniente do precursor contendo grupo amina possui maior atividade catalítica que aquele contendo nitrila, porém ambos possuem menor atividade que o xerogel catalítico obtido de precursores sem grupos nitrogenados. Contudo, os catalisadores preparados a partir de Ormosils mostravam-se estáveis ao longo do tempo da reação estudada quando comparados com os xerogeis NS-x. / This dissertation describes the preparation of Ni (II)-based catalyst precursor material and its subsequent conversion to Ni-based xerogels catalyst as well as the catalytic activity of the resultant catalyst in water-gas shift reaction. The water-gas shift reaction was selected as a model reaction for the evaluation of catalytic activity of the prepared catalysts. The effect of addition of phosphotungstic acid (HPW) as an activity promoting agent and organosilane as dispersing agents of Ni was also studied. For this purpose, Ni-based catalyst (NS-x) containing various amounts (x) of HPW (x= 0, 0.5, 1, 2, 3, 5, 10 wt. %) were prepared using the sol-gel process. These catalysts were characterized by x-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDX), temperature-programmed reduction (TPR), nitrogen adsorption measurements (BET method) and Fourier transform infrared spectroscopy (FTIR). The catalytic tests were performed at a temperature of 250-425 °C in a reactor coupled with gas chromatograph (GC) for direct in situ analysis of the reaction products. The results obtained showed that addition of HPW up to 2 wt % leads to an increase in the efficiency of the catalyst from 10% to 31%, as measured by the rate of conversion of CO. However, further increase in the amount of HPW above 2 wt. % leads to a decrease in activity of the catalyst. A qualitative model based on the formation of amorphous Ni-phosphotungstate salt is proposed to explain this behaviour of the catalyst. In a second part of this study, the amount of HPW (2 wt. %) and temperature (425 °C) were fixed and nitrogenate d silanes with amine and nitrile functional groups were added to the catalyst to evaluate the role of these ormosils as dispersing agents for metallic cations in the hybrid precursor material as well as metallic nickel in the final catalyst. The catalyst derived from precursor containing ormosils with ammine functional groups (3-Aminopropyltriethoxysilane) showed better catalytic activity than those containing nitrile functional groups (4-(Triethoxysilyl)butyronitrile). However, the catalytic activity of the catalysts obtained using ormosils bearing nitrogenated silanes was lower than xerogels catalyst prepared without addition of these silanes. Although, the catalysts prepared using the ormosils bearing nitrogenated silanes showed higher stability than NS-x catalyst.

Orientador: Daniela Zanchet / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-26T07:36:24Z (GMT). No. of bitstreams: 1 Kokumai_TathianaMidori_M.pdf: 2185484 bytes, checksum: f809cfde78398806bc98554749cf01c8 (MD5) Previous issue date: 2014 / Resumo: Nanobastões de céria (CeO2) funcionalizados com grupos amino foram utilizados como suporte em catalisadores de cobre para a reação de deslocamento gás-água (WGS). A funcionalização da superfície do óxido foi realizada visando uma melhor dispersão da fase metálica no suporte, através da interação entre o grupo amino e o precursor Cu2+, com a posterior correlação entre esta modificação e a atividade do catalisador. Utilizou-se o método hidrotérmico para a síntese dos nanobastões, que foram posteriormente funcionalizados com 3-(aminopropil)trimetoxisilano. A adição do precursor Cu2+ ao suporte foi feita via impregnação, seguida de calcinação e redução (ativação do catalisador), etapa na qual se formaram as nanopartículas metálicas (Cu0) suportadas. Comparando os catalisadores com suporte de céria pura e de céria funcionalizada, observou-se que de fato a funcionalização resultou na maior dispersão do Cu2+ na superfície. No entanto, ela causou a menor dispersão do metal (Cu0) após a redução, a diminuição da redutibilidade da céria superficial, a fragmentação dos bastões e o menor desempenho catalítico frente à reação de WGS. Visando a compreensão destes sistemas, verificou-se que a calcinação após a adição de Cu2+ na amostra funcionalizada formou uma camada de SiO2 na superfície da céria, o que diminui a atividade por reduzir as interações Cu-CeO2 (formação de Cu-O-Si), corroborando a grande influência desta interface no desempenho destes catalisadores. Além disso, a menor dispersão de Cu0 na superfície funcionalizada após a redução demonstrou a importância da céria também na estabilização da fase metálica. Desta maneira, a funcionalização da superfície se mostrou uma abordagem interessante no que se refere à dispersão do precursor metálico no suporte / Abstract: Amino functionalized ceria nanorods were explored as support on copper catalysts for the water-gas shift (WGS) reaction. The purpose of the design of a functionalized oxide surface was to obtain a better metal phase dispersion on the support provided by amino-Cu2+ interaction, in addition to further correlation between this modification and the catalyst activity. The hydrothermal method was used to synthetize the nanorods, which were subsequently functionalized with 3-(aminopropyl)trimethoxysilane. The Cu2+ precursor was added to the support by impregnation, followed by calcination and reduction (catalyst activation), when the supported metallic (Cu0) nanoparticles were formed. By comparison of the catalysts obtained with pure ceria and functionalized ceria supports it was observed that the functionalization indeed caused a greater Cu2+ dispersion on the oxide surface. However, it gave rise to a lower metal dispersion (Cu0) after reduction step, along with the decrease of surface ceria reducibility, nanorods fragmentation and inferior catalytic performance towards WGS reaction. In order to understand these systems, it was confirmed that the calcination step (after Cu2+ addition) on functionalized sample created a SiO2 layer above ceria surface, therefore lowering the activity due to the decrease of Cu-CeO2 interactions (formation of Cu-O-Si), which corroborated the great influence of Cu-CeO2 interface on the activity. Also, the lower Cu0 dispersion on the functionalized surface after reduction showed the importance of ceria on the metallic phase stabilization. Hence, the surface functionalization demonstrated to be an interesting approach to the dispersion of metal precursor on the catalyst support / Mestrado / Quimica Inorganica / Mestra em Química

Le projet Européen UNIfHY a vu le jour dans une optique de production d’hydrogène à partir de biomasse pour le remplacement des énergies fossiles. La purification des gaz produits par la gazéification de la biomasse permet l’obtention d’hydrogène pur pour une utilisation dans les piles à combustible. Cette thèse s’inscrit dans ce projet avec pour but le développement de catalyseurs Fe/CeO2 et Cu/CeO2 déposés sur des supports de mousse céramique pour la réaction de conversion du gaz à l’eau à haute et basse températures, de manière à augmenter la production d’hydrogène et diminuer la perte de charge dans le système. Les principaux objectifs de la thèse sont la synthèse et les caractérisations des catalyseurs à base de fer et de cuivre, l’optimisation des conditions réactionnelles dans la limite du cadre fixé par le projet, la modélisation cinétique en présence des catalyseurs Fe/CeO2 et Cu/CeO2 et la transposition à grande échelle des catalyseurs pour une utilisation en réacteur pilote. / The UNIfHY European project was launched in an optic of producing hydrogen from biomass to replace fossil fuels. Purification of gases produced by biomass gasification allows obtaining pure hydrogen which can be used in fuel cells. This thesis takes part in this project with the development of Fe/CeO2 and Cu/CeO2 catalysts deposited on ceramic foam supports for high temperature and low temperature water gas shift reaction to increase the production of hydrogen and decrease the pressure drop in the system. The main objectives of this thesis are the synthesis and characterizations of iron and copper based catalysts, the optimization of reaction conditions within the limits of the framework set by the project, the kinetic modeling of the reaction in the presence of Fe/CeO2 and Cu/CeO2 catalysts and the scale-up of catalysts to use them in a pilot reactor.

Ceria based materials have attracted a great deal of interest particularly in area of UV shielding, oxide ion conductivity, solid state electrolyte for fuel cells, automotive exhaust catalysis, water gas shift (WGS) reaction catalysis and also in thermo-chemical water splitting cycles to generate hydrogen. Therefore great deal of efforts was devoted to synthesize nanocrystalline ceria and related materials with different shape and sizes. For example, hierarchically mesostructured doped CeO2 showed potential photvoltic response for solar cell applications. Substitution of lower valent metal ions (Ca2+, Gd3+, Tb3+, Sm3+) in CeO2 enhances oxide ion conductivity for solid oxide fuel cell applications. Eventhough ZrO2 is a nonreducible oxide, CeO2-ZrO2 solid solution has attracted a lot of attention in exhaust catalysis because it exhibited high oxygen storage capacity (OSC). Noble metal ion (M = Pt4+/2+, Au3+, Rh3+, Pd2+ and Ag+) substituted CeO2 (Ce1-xMxO2-δ and Ti1-xMxO2-δ, x = 0.01-0.03) prepared by solution combustion method have shown much higher three-way catalytic property compared same amount of noble metal impregnated to CeO2. Ionically substituted Pt and Au in CeO2 also showed high WGS activity. CeO2-MOx (M= Mn, Fe, Cu, Ni) mixed oxides have shown high activity for hydrogen generation by thermal splitting of water. In chapter 1, we have discussed recent developments on various synthesis strategies of ceria based materials for specific catalytic application. In this thesis, we have explored new route to synthesize Ce1-xMxO2-δ and Ti1-xMxO2-δ (M = transition metal, noble metal) nanocrystallites. Specifically we have addressed the effect of reducible metal ion substitution on the OSC of CeO2 for auto exhaust treatment, hydrogen generation and electro-chemical applications. Controlled synthesis of CeO2 and Ce1-xMxO2-δ (M = Zr, Ti, Y, Pr and Fe) nanocrystallites by hydrothermal method is presented in Chapter 2. The method is based on complexation of metal ion by diethylenetriamine (DETA) or melamine and the simultaneous hydrolysis of metal ion complexes in hydrothermal condition. Size of the crystallites can be controlled by varying the time and temperature of the reaction. 15% Fe3+ ion substituted CeO2 (Ce0.85Fe0.15O2-δ) nanocrystallites have shown higher oxygen storage capacity than Ce0.5Zr0.5O2 at lower temperature. A brief description of material characterization techniques such as powder X-ray diffraction (XRD) and Rietveld refinement of structure, high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) is presented. The home-built hydrogen uptake measurement system for OSC study and temperature programmed catalytic reaction system with a quadrupole mass spectrometer and an on-line gas-chromatograph for gas analysis is also described in this chapter. In chapter 3, hydrothermal synthesis of Ce1-xCrxO2+δ (0≤x≤1/3) nanocrystallites is presented. Up to 33% Cr ion substitution in CeO2 could be achieved only by the complexation of Ce(NH4)2(NO3)6 and CrO3 with DETA and simultaneous hydrolysis of the complexes in hydrothermal condition at 200 oC. Powder XRD, XPS and TEM studies confirm that the compound crystallizes in cubic fluorite structure where Ce exist in +4 oxidation state and Cr exist in 4+ and +6 (mixed valance) oxidation states in the ratio of 2: 1. Composition x = 0.33 (Ce2/3Cr1/3O2+δ) showed higher OSC (0.33 mol of [O]) than the maximum OSC observed for CeO2-ZrO2 solid solutions. Formation and higher OSC of Ce2/3Cr1/3O2+δ is attributed to interaction of Ce4+/3+ and Cr3+/4+/6+ redox couples in fluorite structure. The material shows oxygen evolution at ~400 oC in air and hence it is a true oxygen storage material. Oxygen evolution property of Ce0.67Cr0.33O2.11 and subsequent generation of hydrogen by thermal splitting of water is presented in chapter 4. Among the ceria based oxides, Ce0.67Cr0.33O2.11 being the only compound like UO2+δ to have excess oxygen possessing fluorite structure, it releases a large proportion of its lattice oxygen (0.167 M [O]/mole of compound) by heating the material under N2 flow at relatively low temperature (465 oC) directly and almost stoichiometric amount of H2 (0.152 M/Mol of compound) is generated at much lower temperature (65 oC) by thermosplitting of water. The reversible nature of oxygen release and intake of this material is attributed to its fluorite structure and internal coupling between the Ce4+/Ce3+ and Cr4+/6+/Cr3+ redox couples. In chapter 5, we present the hydrothermal synthesis and three-way catalytic activity of Ce1-xRuxO2-δ (0≤x≤0.1) nanocrystallites. Powder XRD, Rietveld refinement, TEM and XPS reveals that the compounds crystallized in fluorite structure where Ru exist in +4 state and Ce in mixed valent (+3, +4) state. Substitution of Ru4+ ion in CeO2 activated the lattice oxygen and Ce0.9Ru0.1O2-δ can reversibly releases 0.42[O]/mol of compound, which is higher than maximum OSC of 0.22 [O]/mol of compound observed for Ce0.50Zr0.50O2. Utilization of higher OSC of Ce1-xRuxO2-δ (x = 0.05 and 0.10) is also shown by low temperature CO oxidation with these catalysts, both in presence/absence of feed oxygen. Ru4+ ion act as active centre for reducing molecules (CO, hydrocarbon ‘HC’) and oxide ion vacancy acts as an active centre for O2 and NOx in this compound. Ce1-xRuxO2-δ not only act as a high oxygen storage material but it also shows high activity towards CO, hydrocarbon ‘HC’ oxidation and NO reduction by CO at low temperature with high N2 selectivity for 3-way catalysis. Study of water gas shift reaction over Ce0.95Ru0.05O2-δ catalyst is presented in chapter 6. The catalyst showed very high WGS activity in terms of high conversion rate (20.5 μmol.g-1.s-1 at 275 oC) and low activation energy (~50.6 kcal/mol). The reason for this seems to be high adsorption propensity of CO on Ru4+ ion and easy extraction of oxygen from lattice to form CO2. This step creates oxide ion vacancy in the catalyst lattice and H2O can adsorb on lattice sites oxygen vacancy and regenerate the lattice by releasing H2. Even in presence of externally fed CO2 and H2, complete conversion of CO to CO2 was observed with 100 % H2 selectivity with Ce0.95Ru0.05O2-δcatalyst in the temperature range of 305-385 oC and no trace of methane formation was observed in this temperature range. Catalyst does not deactivate in long duration on/off WGS reaction cycle because sintering of noble metal or active sites is avoided in this catalyst as Ru4+ ion is substituted in CeO2 lattice. Due to highly acidic nature of Ru4+ ion, surface carbonated formation is prohibited. In chapter 7, synthesis of Ce1-xFexO2-δ (0≤x≤0.45) and Ce0.65Fe0.33Pd0.02O2-δnanocrystallites is presented by sonochemical method. Powder XRD, XPS and TEM studies confirm that the compounds of ~4 nm sizes is crystallized in fluorite structure where Fe is in +3, Ce is in +4 and Pd is in +2 oxidation state. Due to substitution of smaller Fe3+ ion in CeO2, lattice oxygen is activated and Ce0.67Fe0.33O1.835 reversibly releases 0.31[O] up to 600 oC which is higher or comparable to the maximum OSC observed for CeO2-ZrO2 based solid solutions. Due to internal interaction of Pd2+/0(0.89 V), Fe3+/2+ (0.77 V) with Ce4+/3+ (1.61 V) redox couples, Pd ion accelerates the electron transfer from Fe2+ to Ce4+ in Ce0.65Fe0.33Pd0.02O1.815, making it a high oxygen storage material as well as highly active catalyst for CO oxidation and WGS reaction. Activation energy for CO oxidation with O2 over Ce0.65Fe0.33Pd0.02O1.815 is found as low as 38 kJ/mol. CO conversion to CO2 is 100% H2 specific in WGS reaction with these catalysts. Conversion rate was found as high 27.2 μmol.g-1.s-1 and activation energy was found 46.4 kJ/mol for Ce0.65Fe0.33Pd0.02O1.815. Only 1-3% Pt, Pd ion can be substituted in CeO2 is by the solution combustion method. We show that even up to 10% of Pt and Pd ion can be substituted in CeO2 by sonication method. In chapter 8, we present the sonochemical synthesis redox property and methanol electro-oxidation activity of hierarchical Ce1-xMxO2-δ (M = Pt and Pd, 0≤x≤0.1) nanocrystallites. Powder XRD, TEM, SEM and XPS study confirms that hierarchical structure compound crystallize in fluorite structure. Pt exists in +4 state and Ce in mixed valent (+3, +4) state in Ce1-xPtxO2-δ and Pd exist in +2 state and Ce in mixed valent (+3, +4) state in Ce1-xPdxO2-δ. Substitution of Pt and Pd ion in CeO2 activated the lattice oxygen. Hydrogen absorption study show higher H/Pt ratio ~8.1 and H/Pd ratio ~4.2 in respective oxides. Reversible nature of higher oxygen storage capacity or higher H/P, H/Pd ratio is due to interaction of redox couples of Pt4+/2+(0.91V), Pt2+/0(1.18V), Pd2+/0(0.92V) and Ce4+/3+(1.61V). Due to participation of lattice oxygen, Ce0.95Pt0.05O1.95 and Ce0.95Pd0.05O1.90 have shown higher electro-oxidation of methanol compared to same moles of Pt in 5%Pt/C. In chapter 9, we present sonochemical synthesis of Ti1-xPtxO2 (0≤x≤0.1) nanocrystallites: a new high capacity anode material for rechargeable Li ion battery. Continuing our interest in synthesis of nanomaterials, we thought if we can extend the same sonochemical method to synthesize metal ion doped TiO2. Doping of TiO2 with a suitable metal ion where dopant redox potential couples with that of titanium (Ti4+) and act as catalyst for additional reduction of Ti4+ to Ti2+ (Ti4+ →Ti3+→Ti2+) is envisaged here to enhance lithium storage even higher than one Li/TiO2. 10 atom % Pt ion substituted TiO2, Ti0.9Pt0.1O2 nanocrystallites of ~4 nm size was synthesized by sonochemical method using diethylenetriamine (DETA) as complexing agent. Powder XRD, Rietveld refinement, TEM and XPS studies reveal that Ti0.9Pt0.1O2 nanocrystallites crystallize in anatase structure and both Ti and Pt are in 4+ oxidation state. Due to Pt4+ ion substitution in TiO2, reducibility of TiO2 was enhanced and Ti4+ was reduced up to Ti2+ state via coupling of Pt states (Pt4+/Pt2+/Pt0) with Ti states (Ti4+/Ti3+/Ti2+). Galvanostatic cycling of Ti0.9Pt0.1O2 against lithium showed very high capacity of 430 mAhg-1 or exchange of ~1.5Li/Ti0.9Pt0.1O2 which is much higher than the highest capacity of 305 mAhg-1 or insertion of ~0.9Li/TiO2 achieved for TiO2(B) nanowires. In chapter 10, we present the conclusions and critical review on the study of transition metal and noble metal ion substituted CeO2 and TiO2.

No description available.

京都大学 / 新制・論文博士 / 博士(理学) / 乙第13460号 / 論理博第1577号 / 新制||理||1683(附属図書館) / (主査)教授 北川 宏, 教授 吉村 一良, 教授 竹腰 清乃理 / 学位規則第4条第2項該当 / Doctor of Science / Kyoto University / DGAM

This study concerned the preparation, characterisation and evaluation of different proton conductors for the Reverse Water Gas Shift Reaction (RWGS) and their evaluation as electrolytes for Solid Oxide Fuel Cells (SOFC) under H₂ and O₂. Materials with both catalytic and conductive properties are of a great interest, as their use in electrocatalytical systems may be very important. Sr₃CaZr₀.₅Ta₁.₅O₈.₇₅ (SCZT), BaCe₀.₉Y₀.₁O₂.₉₅ (BCY10) and Ba₃Ca₁.₁₈Nb₁.₈₂O₈.₇₃ (BCN18), were the initial materials in this study. Thermogravimetric analysis under different atmospheres (5%H₂/Ar, Ar, 5%CO₂, etc), were performed on SCZT and BCN18; with both materials being shown to be stable under reducing and oxidising conditions. Conductivity measurements by two terminal a.c. impedance were also conducted on SCZT and BCN18 under oxidising and reducing atmospheres. As found in literature, BCN18 showed mixed conductivity; with electronic conductivity at high temperatures and pure ionic conductivity below 550ºC, This behaviour was shown in chapter 3, where the change on conduction process was observed upon different gas feeds. Its maximum conductivity values for the different atmospheres were: 8.50x10⁻⁵ S/cm (Dry 5%H₂/Ar at 200ºC), 4.24x10⁻⁴ S/cm (Wet 5%H₂/Ar at 500ºC) and 4.48x10⁻³ S/cm (Air at 900ºC). SCZT proton conducting behaviour was also measured (wet and dry 5%H₂/Ar). Exhibiting an order of magnitude higher in total conductivity upon hydration of the gas feed (σdry=1.01x10⁻⁶ and σwet=1.07x10⁻⁵ at 450ºC). The doping of barium cerate with Zr and Zn by Tao and Irvine, lead to a more stable and easily sinterable BaCe₀.₅Zr₀.₃Y₀.₁₆Zn₀.₀₄O₃ (BCZYZ). Following this work, the introduction of ZnO as a sintering aid to SCZT and BCN18 resulted in Sr₃CaZr₀.₄Ta₁.₅Zn₀.₁O₈.₇₅ (SCZTZ), and Ba₃(Ca₁.₁₈Nb₁.₇₀Zn₀.₁₂)O₈.₅₅ (BCNZ); with higher final densities (above 90% dense). As with BCN18, BCNZ also exhibited mixed conductivity; with higher total conductivity values than BCN18. A maximum of total conductivity of 1.85x10⁻³ S/cm at 900ºC for BCNZ was measured against 6.99x10⁻⁴ S/cm at 900ºC for BCN18. A change in conductivity process was observed when using air or wet 5%H₂/Ar, achieving a maximum of 3.85x10⁻⁴ S/cm at 400ºC when under wet hydrogen. All materials (as powders) have shown catalytic activity for the reverse water gas shift (RWGS) reaction, with the lowest conversion temperature onset at 400ºC for SCZT and a maximum conversion of CO₂ to CO of 42%, with circa 0.52 and 0.59 mmol/s.m² of CO produced at 900ºC by BCN18 and BCZYZ, respectively. No relation between mechanisms for the RWGS and σ for these materials were expected below 10% conversion, as no correlation was found between their activation energies. BCY10 as shown a partial decomposition when exposed to the RWGS reaction, for what BCZYZ After fuel cell testing under H₂ and O₂ both SCZTZ and BCNZ showed mixed conductivity. SCZTZ under different hydrogen partial pressures, exhibited a behaviour close to a pure proton conductor, however, when exposed to both reducing and oxidising conditions, its behaviour did not follow the theoretical values. On the other hand, BCNZ behaves as a pure ionic conductor below 500ºC; with increasing influence of the electronic conductivity on temperature increase. However, as seen for BCNZ conductivity data from 2 terminal a.c. impedance, below 650ºC wet 5%H₂ exhibited the highest conductivity values. This, in additions to the pure ionic conductive behaviour below 400ºC (from the effective ionic transport number), suggests that BCNZ becomes closer to a pure proton conductor with temperature decrease.