Yoshiko Nakahara

Preparation of Highly Dispersed Gold on Titanium and Magnesium Oxide

Abstract Gold could be highly dispersed on titanium oxide and magnesium oxide in their aqueous dispersion containing Mg citrate. The mean diameter of gold particles are smaller than 5nm. These gold catalysts are active for the oxidation of CO even at a temperature below 0°C. On magnesia support, Mg citrate acts not as a reducing agent but as a sticking agent which blocks the coagulation of gold particles. On titania support dispersed in neutral solution Mg2+ ions instead of citrate ions are mainly adsorbed. It is likely that Mg2+ ion suppresses the transformation of amorphous titania to anatase during calcination and prevent gold particles from coagulation caused by earthquake effect.

Preparation of Hierarchical Architectures of Silica Particles with Hollow Structure and Nanoparticle Shells: A Material for the High Reflectivity of UV and Visible Light

Silica microcapsules (silica hollow particles) are readily prepared by a single step of the interfacial reaction method, where a W/O/W emulsion is employed effectively. This is a simple (one-step process), inexpensive approach (silica source is sodium silicate) to producing hollow silicas. The addition of NaCl to the sodium silicate solution as the inner water phase of the W/O/W emulsion plainly influenced the shell structure of the silica hollow particles. The increase of the addition of NaCl expanded the size of the mesopores in their silica shell, which reached to macropores (>50 nm). The nanoparticles in the shells of some silica hollow particles attained approximately 200-400 nm in size, which is comparable to the wavelengths of UV and visible light. According to the diffuse reflection spectra of the silica hollow particles in powder form, these particles showed the high reflection of UV and visible light, which increased with added NaCl in the preparation process of the interfacial reaction method. The reflectance of a silica hollow particle from 300 to 800 nm in wavelength was over 90%, which was significantly higher than a common solid (not hollow) silica gel. In addition, even the reflectance of UV light shorter than 300 nm in wavelength was greater than 60%. These characteristic reflections in a wide range of wavelengths were caused by both nanoparticle shells whose sizes are comparable with the wavelength of light and the hollow structures of the main micrometer-sized particles.

Effects of surfactants on CaCO3 spheres prepared by interfacial reaction method

Abstract Spherical particles of CaCO 3 powder were prepared by an interfacial reaction method in which CaCO 3 powder was formed by the reaction of K 2 CO 3 aqueous solution emulsified in benzene with CaCl 2 aqueous solution. The spherical particles were prepared under the following conditions; concentration of K 2 CO 3 was 3 mol/liter and concentration of CaCl 2 was 0.2 mol/liter. Five nonionic surface active agents in the form of sorbitan esters of fatty acids were used in the concentration range of 0.01–1.0 wt%, for examining the effects of the surfactants on the spherical particle content and vaterite fraction. The spherical particle content and the vaterite fraction were determined by X-ray diffraction and microphotographic methods, respectively. It was found that the spherical particle content depended on the vaterite fraction, and that the vaterite fraction was related to the concentration and HLB-number of the surfactant. These results suggest that the vaterite sphere is initially formed by the interfacial reaction in 100% yield. After that, the vaterite partially transforms into calcite while in contact with the water phase. It is concluded that differences in the vaterite fraction are caused by the conditions of contacting with water, which depend on the adsorption of surfactants on the surface of the spheres.

A study for the durability of catalysts in ethanol synthesis by hydrogenation of carbon dioxide

Absract The durability of catalysts in ethanol synthesis by the hydrogenation of CO 2 was investigated by means of XRD, TEM, and EDS. The K/Cu-Zn-Fe oxides catalyst was deactivated by the segregation of catalyst components to FeCO 2 , ZnO, and Cu during the reaction. The segregation was prevented by the addition of Cr component to the catalyst. Consequently, the K/Cu-Zn-Fe-Cr oxides catalyst indicates long catalytic life.