Katsuhiko Wakabayashi

Catalytic oxidative decomposition of chlorofluorocarbons (CFCs) in the presence of hydrocarbons

Abstract The catalytic oxidative decomposition of CFCs containing two carbon atoms was investigated in the presence of hydrocarbons (C 1 –C 4 alkanes) over silica and various acidic metal oxides. It was found that CFC-115 was the most difficult to be decomposed among CFC-113, CFC-114, and CFC-115, and that γ-alumina was the most active catalyst. The CFC-115 conversion over γ-alumina was lower in the presence of methane than in the presence of the other hydrocarbons. In addition, the activities of γ-alumina-supported metal and metal oxide catalysts were investigated for the oxidative decomposition of CFC-115 in the presence of n-butane. Tungsten (VI) oxide and vanadium (V) oxide catalysts exhibited the highest activity.

Hydrogenation of carbon dioxide over metal catalysts prepared using microemulsion

Abstract This paper relates to a novel preparation method of metal supported catalysts using microemulsions. The size distribution of metal particles in the catalysts, thus, prepared was appreciably narrow and the average particle size was much smaller than that of the conventional catalyst prepared from impregnation. It was found that the particle size could be controlled by the conditions of microemulsions regardless of metal content. The Rh, Pd and Pt catalysts prepared from microemulsions were found to exhibit a much higher activity for the hydrogenation of carbon dioxide than those from impregnation.

Methanol synthesis from syngas over supported palladium catalysts prepared using water-in-oil microemulsion

The hydrogenation of carbon monoxide was carried out over palladium catalysts prepared by a novel preparation method using water-in-oil microemulsion. The catalytic performance of those catalysts was compared with that of the catalysis prepared by the conventional impregnation method. The catalysts prepared by the microemulsion method were found to exhibit a much higher activity for the hydrogenation of CO than those prepared by the impregnation method. The size distribution of the palladium particles of the catalysts prepared by the microemulsion method was remarkably narrow, and the average particle size was much smaller than that of the catalysts prepared by the impregnation method. It was found that palladium particle size of the catalyst was controlled by the preparation conditions of microemulsions, regardless of palladium content. The catalyst prepared at the palladium concentration of 1.0 mol/l had the smallest palladium particles, and exhibited the highest activity. In the case of the microemulsion method, some of the palladium particles were wholly or partially embedded in the support. Nevertheless, the catalysts have exhibited an extremely high activity, because the specific activity of palladium was much higher than that in the case of the impregnated method. Furthermore, the activity of the catalyst prepared by the microemulsion method increased with increasing the amount of palladium exposed to the surface of the support.

Synthesis of silica-coated rhodium nanoparticles in reversed micellar solution

Silica (SiO2)-coated rhodium (Rh) nanoparticles were prepared using a water-in-oil microemulsion of polyoxyethylene (15) cetyl ether, cyclohexane and water. SiO2-coated Rh nanoparticles were obtained by hydrolyzing metal alkoxide (tetraethylorthosilicate, TEOS) in the solution containing Rh complex nanoparticles followed by thermal and reduction treatments. In the SiO2-coated Rh nanoparticle, a Rh particle with an average diameter of 4.1 nm was located nearly at the center of each spherical SiO2 particle. The SiO2 layer was approximately 15 nm thick. Since the Rh particle was wholly surrounded by SiO2, the Rh particle of the SiO2-coated Rh nanoparticle exhibited an extremely high thermal stability. Furthermore, the porous structure of the SiO2 layer could be controlled by the hydrolysis conditions of TEOS.

Preparation method for supported metal catalysts using w/o microemulsion: Study on immobilization conditions of metal particles by hydrolysis of alkoxide

Abstract It was previously found that the silica-supported rhodium catalyst prepared using water-in-oil microemulsion had rhodium particles partly, or wholly, embedded in silica. In this work, consequently, we investigated the effect of hydrolysis conditions of tetraethylorthosilicate, employed as the source of silica, on the atomic ratio of surface rhodium in contact with the gas phase, to total surface rhodium of nanoparticles. This ratio is denoted as R in this paper. R became higher when the catalyst was prepared under the following hydrolysis conditions: a shorter hydrolysis time and a smaller amount of tetraethylorthosilicate. On the other hand, R showed the minimum value when the water content in the preparation solution was 33 vol%. From these results, it is demonstrated that it was important to form silica as early as possible in hydrolysis of TEOS in order to increase R values. In addition, the effect of R on the catalytic behavior in CO hydrogenation was investigated. At R values below 30%, the turnover frequencies increased with a decrease in R.

Effects of Rh content on catalytic behavior in CO hydrogenation with Rh–silica catalysts prepared using microemulsion

Rh–silica catalysts having the same physical parameters despite their different Rh contents were prepared using water‐in‐oil (w/o) microemulsions, and the effects of Rh content on the catalytic behavior were investigated in the hydrogenation of carbon monoxide. It was found that both the product selectivity and the turnover frequency changed dramatically with the Rh content. The selectivity to C2+ oxygenated compounds increased with increasing Rh content, while the selectivity to hydrocarbons and the turnover frequency decreased.

Hydrogenation of carbon monoxide over zirconia-supported palladium catalysts prepared using water-in-oil microemulsion

Abstract The hydrogenation of carbon monoxide was carried out over palladium catalysts prepared by a novel preparation method using water-in-oil microemulsion. Their catalytic performance was compared with that of the catalysts prepared by the conventional impregnation method. The size distribution of the palladium particles prepared by the microemulsion method was remarkably narrow, and the average particle size was much smaller than that prepared by the impregnation method. The catalysts prepared by the microemulsion method were found to exhibit a much higher activity for the hydrogenation of carbon monoxide than the catalysts prepared by impregnation.

Size control of rhodium particles of silica-supported catalysts using water-in-oil microemulsion

Abstract Effects of components of water-in-oil microemulsions on rhodium particle sizes of silica-supported rhodium catalysts were investigated in the catalyst preparation method using microemulsion. In the case of the microemulsion of polyoxyethylene(23)dodecyl ether/ n -alcohols/RhCl 3 aq., the rhodium particle size increased from 3.4 to 5.0 nm as the specific permittivity of the organic solvent increased. The chain length of hydrophilic group of polyoxyethylene- p -nonylphenyl ether ( n = 5 to 15) employed as surfactants had an effect on the rhodium particle size where the rhodium size ranged between 2.0 and 3.6 nm. The rhodium particle size was 1.5 nm in the case of sodium bis(2-ethylhexyl) sulfocuccinate and this value was found to be the smallest. These results could be interpreted in terms of the adsorption of the surfactant on rhodium-hydrazine particle surface.

Preparation of size-controlled Pt catalysts supported on alumina

It was found that Pt particles on Al2O3-supported Pt catalysts prepared using Pt complex nanoparticles formed in a water-in-oil microemulsion became very small and uniform compared to those prepared using reduced Pt metal nanoparticles or by an impregnation method. Moreover, the catalytic activity of the catalyst composed of very small Pt particles, which was prepared using the complex nanoparticles, was higher in the NO–CO reaction than those of the other catalysts.

Metal-Support Interaction and Catalysis of the Catalysts Prepared Using Microemulsion

We have developed a new preparation method (ME method) of supported metal catalysts by using microemulsion. The metal particles in the catalyst prepared by this method were interacted strongly with support and were considered to be positively charged, and the SiO2-supported Rh and Fe catalysts prepared by this method exhibited a unique activity and a good selectivity to oxygenates in the hydrogenation of CO. The Al2O3-supported Ni catalyst also exhibited an excellent activity and a strong resistance to carbon deposition in the methane-steam reforming. In this review, these interesting catalytic behaviors of the catalysts prepared by ME method were elucidated from the view-point of the electronic state of metals.