Book excerpt: This thesis reports the discovery of metal nanoparticles having new structures that do not exist in bulk state and that exhibit hydrogen storage ability or CO oxidation activity. Research into the reaction of hydrogen with metals has attracted much attention because of potential applications as effective hydrogen storage materials, as permeable films, or as catalysts for hydrogenation. Also, CO oxidation catalysts have been extensively developed because of their importance to CO removal from car exhaust or fuel-cell systems. At the same time, atomic-level (solid solution) alloying has the advantage of being able to continuously control chemical and physical properties of elements by changing compositions and/or combinations of constituent elements. This thesis provides a novel strategy for the basis of inter-elemental fusion to create highly efficient functional materials for energy and material conversions.