Shuji Tanabe

Preparation of superparamagnetic magnetite nanoparticles by reverse precipitation method: contribution of sonochemically generated oxidants.

Magnetic iron oxide nanoparticles were successfully prepared by a novel reverse precipitation method with the irradiation of ultrasound. TEM, XRD and SQUID analyses showed that the formed particles were magnetite (Fe(3)O(4)) with about 10nm in their diameter. The magnetite nanoparticles exhibited superparamagnetism above 200K, and the saturation magnetization was 32.8 emu/g at 300 K. The sizes and size distributions could be controlled by the feeding conditions of FeSO(4).7H(2)O aqueous solution, and slower feeding rate and lower concentration lead to smaller and more uniform magnetite nanoparticles. The mechanisms of sonochemical oxidation were also discussed. The analyses of sonochemically produced oxidants in the presence of various gases suggested that besides sonochemically formed hydrogen peroxide, nitrite and nitrate ions contributed to Fe(II) ion oxidation.

Effect of preliminary treatment with ammonia on the reduction of CuY zeolite

Abstract The effect of ammonia pretreatment on the reduction of CuY zeolite was investigated by means of temperature-programmed experiments with the aid of transmission electron microscopy, electron spin resonance and IR techniques. With hydrogen the reduction of Cu 2+ ions occurred by a two-step mechanism, via Cu + ions to metallic copper. In the first step of the reduction, ammonia or carbon monoxide could be used as the reducing agent instead of hydrogen. With the ammonia pretreatment metallic copper was uniformly dispersed on the reduced CuY compared to that with CO pretreatment or without pretreatment. The average diameters of the copper particles on these samples were estimated to be 8.4, 19.5 and 18.5 nm, respectively. The reason why metallic copper was homogeneously dispersed by the ammonia pretreatment is discussed.

Synchrotron radiation microbeam X-ray fluorescence analysis of zinc concentration in remineralized enamel in situ

OBJECTIVE Remineralization is an indispensable phenomenon during the natural healing process of enamel decay. The incorporation of zinc (Zn) into enamel crystal could accelerate this remineralization. The present study was designed to investigate the concentration and distribution of Zn in remineralized enamel after gum chewing. METHODS The experiment was performed at the Photon Factory. Synchrotron radiation was monochromatized and X-rays were focused into a small beam spot. The X-ray fluorescence (XRF) from the sample was detected with a silicon (Si) (lithium (Li)) detector. X-ray beam energy was tuned to detect Zn. The examined samples were small enamel fragments remineralized after chewing calcium phosphate-containing gum in situ. The incorporation of Zn atom into hydroxyapatite (OHAP), the main component of enamel, was measured using Zn K-edge extended X-ray absorption fine structure (EXAFS) with fluorescence mode at the SPring-8. RESULTS A high concentration of Zn was detected in a superficial area 10-microm deep of the sectioned enamel after gum chewing. This concentration increased over that in the intact enamel. The atomic distance between Zn and O in the enamel was calculated using the EXAFS data. The analyzed atomic distances between Zn and O in two sections were 0.237 and 0.240 nm. CONCLUSION The present experiments suggest that Zn is effectively incorporated into remineralized enamel through the physiological processes of mineral deposition in the oral cavity through gum-chewing and that Zn substitution probably occurred at the calcium position in enamel hydroxyapatite.

Redispersion of cobalt particles supported on titanium dioxide

The particle size of cobalt in a Co/TiO2 catalyst increased with increasing reduction temperature up to 600 °C. At 700 °C, where the phase transformation of TiO2 from anatase to rutile occurred, the cobalt particles redispersed to individual crystallites. This redispersion has been confirmed by measuring the specific activity of the cobalt catalyst for the hydrogenation of propene. The relation between the phase transformation of TiO2 and the redispersion of cobalt has been studied kinetically using high-temperature X-ray diffraction spectroscopy.

Reaction mechanism of methane oxidation to synthesis gas over an activated PdY zeolite

The catalytic behaviour of PdY zeolite has been investigated in the partial oxidation of CH4 into CO and H2 under oxygen-deficient conditions. The PdY zeolite catalyst after reduction–reoxidation treatment showed excellent activity and selectivity in the temperature range 800–1000 K. Two possible pathways for the reaction were recognized from isothermal and temperature-programmed experiments, i.e. CO and H2 are produced (1) on the oxidized surface by direct reaction between the surface oxygen and CH4 in the gas phase, and (2) on the reduced surface by the reforming of residual CH4 with primary-formed CO2 and/or H2O. It was confirmed by EXAFS analyses, furthermore, that under the operating conditions two kinds of Pd species (small clusters of Pd and PdO) coexist in the zeolite crystals and that they can function as catalytic sites via a reversible redox mechanism.

Development of technologies to preserve the water environment and support its sustainable use in Asia

Through this project, successful applicants from Korea and China will be accepted into the Graduate School of Engineering Masters Course, that was established in April 2011, at Nagasaki University. They will be trained to become highly skilled professionals with practical knowledge who can contribute to solving water environment conservation issues, including sustainable water use, in East Asia.

Effect of Al loading on CaO catalysts for biodiesel production

Al loaded CaO catalysts for biodiesel synthesis were prepared with alkali co-precipitation method and investigated. The catalytic activities were examined with transesterification of triolein to oleic methyl ester (OME) as model reaction of biodiesel formation. The catalytic activity of these catalysts strongly depends on the amount of Al loading and formation of composite oxide phase on catalyst surface. The structure and nature of active sites on the catalyst surface were measured with XRD and temperature programmed desorption of CO2 and methanol. The TPD results revealed that the initial reaction activity strongly depended on the formation and stability of methoxide intermediate on the catalyst surface.

Mechanism of Soot Oxidation Over CeO2–ZrO2 Under O2 Flow

Soot oxidation over CeO2–ZrO2 (CZ) has been studied herein. The soot-CZ mixtures were observed under different contact conditions using transmission electron microscopy (TEM) and evaluated using thermogravimetric-differential thermal analysis (TG-DTA). These results indicate that the soot ignition temperature depends on the soot/CZ contact degree, and the soot oxidation rate depends on the soot/CZ contact area. The TEM observation of soot-CZ mixture quenched at T50 (50% soot conversion) indicates that soot oxidation occurs only at the soot/CZ interface. Furthermore, the soot oxidation under 18O2 flow and under He flow suggests that CZ lattice oxygen is a more active oxygen species than the adsorbed oxygen on the CZ. The CZ lattice oxygen mainly oxidizes soot; however, the adsorbed oxygen on the CZ surface does not oxidize soot at lower temperatures. Thus, the adsorbed oxygen oxidizes the reaction intermediates such as adsorbed CO on the CZ surface, which shows that CZ lattice is more active than the adsor...

Hydrogen production from steam reforming of woody biomass with cobalt catalyst

Catalytic steam reforming of woody biomass was carried out with metal oxide supported Co catalysts. These catalysts were prepared by impregnation of Co²⁺ into SiO₂, Y₂O₃ and CeO₂ powder and sol-gel method for Co/MgO. Their catalytic activities were examined as hydrogen formation from steam reforming of woody biomass with as functions of reaction temperature. As the results, the highest amount of H₂ formation shows Co/MgO at 973K while Co/SiO₂ has maximum activity at 873K. This is because of activation of MgO basic site due to CO₂ desorption from the active site. We suggest that the basicity of metal oxide supports affect the rate of steam reforming of tar rather than that of thermal decomposition of anhydrous cellulose.

Partial oxidation of methane to methanol in a newly developed selective discharge plasma reactor

Summary form only given. A selective discharge plasma reactor was developed and used to produce methanol from methane and nitrous oxide. The product distribution in the reaction depended on the activated reactant molecules. The selectivity to partial oxidation products such as methanol and formaldehyde increased when methane was excited and nitrous oxide was unexcited. Furthermore, the position where a reactant could contact the other one was a very important factor in effective methanol and formaldehyde production. Methanol is an important material from the point of view as a gasoline additive and as an automobile fuel. The partial oxidation of methane to methanol is desirable if high selectivity to methanol and reasonable conversion rate can be obtained. We were reported partial oxidation of methane with nitrous oxide in dielectric barrier discharge plasma, previously. In this report we show a newly developed dielectric barrier discharge (DBD) plasma reactor that can excite the reactant, selectively. The selective excitation DBD plasma reactor was basically similar to that of Chen et al. An Al tube was used as internal electrode (6mm od) that was supported in the center of quartz tube (10mm id, 200mm length) with the other Al tubes. Outer surface of the quartz tube was tightly covered by Cu foil as external electrode. Some reactants could flow along the inside of inner electrode and go out through small holes located on the electrode, and react with other gases on the surface of the electrode. Other reactants could flow between both electrodes, then be excited by electrons. High voltage electricity was applied to both electrodes by a high voltage power supply. The conversions of methane and nitrous oxide in the selective plasma reactor decreased in comparison with those of normal DBD plasma reactor. However, selectivity to methanol and formaldehyde reached ca. 30% while nitrous oxide was selectively excited by plasma. In this case, main product was carbon monoxide. On the other hand, no methanol formed while methane was selectively activated by plasma. Predominant reaction in this case was dimerization of methane molecules. From these results, it was clear that the selective excitation DBD plasma reactor could work well in this reaction.