| Research Abstract |
Solid-state materials with nano-scale structures are expected to be potential catalysts for chemical reactions because the materials would have attractive catalytic properties due to their unique reaction field around catalytic active sites. In addition, three-dimensional organization of catalytic components is highly important for solid-state catalysts, particularly for a multi-functional one which is often necessary for various multi-steps catalytic reactions. Therefore, it appeared that nano-scale materials structuring using inorganic soft syntheses like sol-gel method, hydrothermal method, solvothermal method, organic template method, and so on, thought to be significantly important. In this research, the following three types of nano-structuring methods for complex metal oxide catalysts; (a) organic sphere template method for three-dimensionally ordered macroporous materials preparation, (b) carbon nano-fiber template method for nano-tube shaped materials, and (c) preparation of i
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mmobilized nano-fibrous complex metal oxides on ceramic fibers were developed.
First, three-dimensionally ordered macroporous materials of polycrystalline spinel-and perovskite-type materials were prepared. The materials were fabricated using colloidal crystal template method in extremely high yield and in high uniformity. The crystallites were found to construct struts connecting tetrahedral and square prism vertexes. In the synthesis of oxide nanotubes, uniform coating of templates with oxide was most important process. The present study demonstrated that various oxide nanotubes could be synthesized by the adsorption and hydrolysis of precursors on the surface of carbon nanofiber (CNFs) templates and by the oxidative removal of templates. A variety of oxide nanotubes such as thick, thin, and helical nanotubes reflecting the shapes of carbon nanofibers could be synthesized. In addition, we demonstrated the immobilization of nano-fibrous metal oxides on macro-structured materials, combining CVD process and CNFs template method. One of the notable features of CNFs is the formation on the various substrates through CVD process. Using this feature of CNFs, we attempted the immobilization of nano-fibrous metal oxide on the macrostructure materials like silica fibers. A small amount of Ni particles which catalyze CNF growth are attached on the silica fibers, followed by the contact of methane over silica fiber-supported Ni (i. e., CVD process) resulting in the growth of CNFs immobilized on silica fibers. The immobilized CNFs are used as templates for metal oxide nano-tubes/nano-fibers synthesis. All the nano-structured materials showed their own characteristic catalytic performance in organic oxidation. Less
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