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京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18778号 / 理博第4036号 / 新制||理||1581(附属図書館) / 31729 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 松田 和博, 教授 八尾 誠, 教授 田中 耕一郎 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

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<p> The alkali metal dichromates show extensive polymorphism. The crystal structures of the polymorphs α-Na2Cr2O7, β-Na2Cr2O7, β1-Rb2Cr2O7 and P21/c NaRbCr2O7 have been determined with x-ray methods. Crystal data were determined for β2-Rb2Cr2O7, P1 Cs2Cr2O7 and the P21/c NaCsCr2O7.</p> <p> The dichromate ions found in this work have been compared with the dichromate ions found in other crystal structure determinations. The anions are described in terms of the bridging oxygen angles b and the torsion angles α1 and α2. Many of the dichromate ions are close to having C2v symmetry with values for α1 and α2 close to zero and bridging angles of around 124°. But there is a number of dichromates with α1 = -α2 and 0°<|α|<60° for which the bridging angle varies between 131° to 141°.</p> <p> The structures determined in this work are discussed as part of a unified description of thortveitite like and dichromate like structures in terms of layers of Y2O7 anions. In terms of this description and Brown and Calvo's classification a structure is proposed for the β2Rb2Cr2O7, while for the structure of NaCsCr2O7 it is suggested that it is isostructural to that of P21/c NaRbCr2O7. The phase transition of α-Na2Cr2O7 to β-Na2Cr2O7 is considered and it is suggested that a twisting thermal mode plays an important role in this as well as in other transitions.</p> / Thesis / Doctor of Philosophy (PhD)

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This work presents an in-depth study of the crystal structures and hydrogen sorption potential of the Li - N - H and Li - Na - N - H systems. The structures of the materials have been studied using X-ray and neutron diffraction, Raman spectroscopy and inelastic neutron scattering. The behavior of the materials during heating was studied using variable temperature X-ray diffraction, intelligent gravimetric analysis in conjunction with neutron diffraction, intelligent gravimetric analysis combined with mass spectrometry and differential scanning calorimetry. The role of cation disorder in the Li - N - H (D) system has been explored, indicating that crystallographic ordering of the Li⁺ ions within lithium amide and lithium imide significantly affects the hydrogen sorption properties of the materials. Order-disorder transitions were observed both during hydrogen desorption from ordered LiNH₂ and during deuterium adsorption on ordered Li₂ND. Such transitions were not observed in disordered samples of the materials. The intrinsic disorder and the stoichiometry of Li - N - H(D) materials was shown to depend strongly on the techniques used during their synthesis. Studies regarding the synthesis, crystal chemistry and decomposition properties of the mixed Li / Na amides are presented. Two distinct mixed Li / Na amides of formulae Li₃Na(NH₂)₄ and LiNa₂(NH₂)₃ were observed in the LiNH₂ / NaNH₂ phase space. Na was also seen to be soluble in LiNH₂, forming sodium-doped LiNH₂ . Li₃Na(NH₂)₄ and Na-doped LiNH₂ were found to exhibit significant cation non-stoichiometry, whereas LiNa₂(NH₂)₄ was shown to exist as a line phase material. Thermogravimetric and calorimetric studies of the mixed Li / Na amides suggested that these materials decompose primarily with loss of H₂.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Bibligraphy: leaves 222-228. / by Paul Joseph Lemaire. / Ph.D.

Graduation date: 1995

The investigation of CO oxidation with supported noble metal catalysts to develop a fundamental understanding of the nature of the active sites, adsorbate-surface interactions, surface reaction pathways and the role of promoters is of prime importance for development of highly active and selective catalyst formulations for low temperature oxidation of carbon monoxide. Low temperature CO oxidation catalysts find applications in monitoring and elimination of CO in chemical process exhaust gases, in on-board control and diagnostics devices, automobile exhaust gas treatment systems for the development of zero-emission vehicles and, in closed-cycle CO2 lasers for remote sensing. Moreover, the investigation of the interaction of CO with noble metals and noble metals catalyzed oxidation of CO have important outcomes for upstream fuel processing systems and for the development of more CO tolerant anode materials for hydrogen fuel cell. Palladized tin dioxide is a well-known and highly active catalyst for CO oxidation which possesses the potential to satisfy the need for CO oxidation catalysts in the abovementioned areas however, research on this material is concentrated mostly around empirical studies which focus solely on CO sensing applications. This current research is undertaken to investigate both the mechanism of CO oxidation with Pd/SnO2 at the molecular scale and the possibility of promoting the CO activity of this catalyst by the application alkali-metal modifiers. Alkali-metal modified PdO/SnO2 catalysts were characterized by XPS, XRD and SEM and, tested with regard to their oxidation/reduction and CO oxidation behavior by in-situ dynamic methods such as, temperature-programmed reaction/reduction/desorption and impulse techniques. Modification of PdO/SnO2 by alkali-metals, namely Li, Na and K, resulted in catalyst formulations with different surface characteristics and reduction/oxidation behaviors that lead to superior activity in low temperature CO oxidation and selectivity towards CO in the presence of hydrogen. Studies have shown that these catalysts are potential candidates for CO oxidation catalysts in a wide range of areas.