Yutaka Tai

C-3 alkylation of oxindole with alcohols by Pt/CeO2 catalyst in additive-free conditions

In a series of transition metal-loaded CeO2 catalysts and Pt-loaded catalysts on various supports, Pt-loaded CeO2 shows the highest activity for the selective C-3 alkylation of oxindole with octanol. The catalyst is effective for alkylation of oxindole and N-substituted oxindole with a series of substituted benzyl, linear, hetero-aryl alcohols under additive-free conditions and is recyclable. Our results demonstrate the first additive-free catalytic system for this reaction. Mechanistic studies show that this system is driven by the borrowing-hydrogen pathway. Structure–activity relationship studies show that co-presence of surface Pt0 species on Pt metal clusters and basic support is indispensable for this catalytic system.

Size- and support-dependent selective amine cross-coupling with platinum nanocluster catalysts

γ-Alumina-supported Pt nanoclusters with an average particle size of 0.8 nm, Pt/Al2O3-0.8, act as an effective heterogeneous catalyst for mono-N-alkylation of amines with different amines. To establish a catalyst design concept, systematic studies on the structure–activity relationship are carried out, combined with characterization by Pt L3-edge XAFS (X-ray absorption fine structure), X-ray photoelectron spectroscopy (XPS), and infrared (IR) study of CO adsorption. By changing the particle size of Pt over the size range of 0.8–24 nm, it is demonstrated that the present reaction is a structure-sensitive reaction, demanding coordinatively unsaturated Pt atoms on metallic nanoclusters. The support also affects the activity and electronic state of Pt. The electron density of Pt increases with basicity of the support oxide, and the support with moderate basicity (Al2O3) gives the highest activity probably due to a moderate electron density of Pt. Kinetic studies suggest that the present reaction proceeds through a “hydrogen-borrowing” mechanism.

Hydrogenation of C60 on alumina-supported nickel and thermal properties of C60H36

Hydrogenation of C60 was carried out in toluene using Ni/Al2O3 catalyst. C60H36 was obtained in the temperature range 150–250°C and the hydrogen pressure range 25–75 kgf cm-2 (1 kgf=9.80665 N). Degradation of the fullerene giving lighter hydrocarbons was not observed under the experimental conditions. C60 conversion was estimated from the decrease of absorbance of solution at 600 nm and compared with toluene conversion to methylcyclohexane. C60 hydrogenation was faster than toluene hydrogenation. Thermogravimetry and differential thermal analysis of C60H36 were performed in air and compared with those of C60, active carbon and diamond. C60H36 was partially oxidized at 277°C giving C60H36Ox (x=ca. 4.8) followed by combustion at 472°C. The temperature was much lower than that of C60, of which the partial oxidation and the combustion were observed at 432 and 615°C, respectively. The number of oxygen atoms added was larger for C60H36 than for C60. These results strongly suggest that C60H36 is more reactive for oxygen than C60.

Fe K-Edge X-ray Absorption Fine Structure Determination of γ-Al2O3-Supported Iron-Oxide Species

The structure of FeOx species supported on γ-Al2 O3 was investigated by using Fe K-edge X-ray absorption fine structure (XAFS) and X-ray diffraction (XRD) measurements. The samples were prepared through the impregnation of iron nitrate on Al2 O3 and co-gelation of aluminum and iron sulfates. The dependence of the XRD patterns on Fe loading revealed the formation of α-Fe2 O3 particles at an Fe loading of above 10 wt %, whereas the formation of iron-oxide crystals was not observed at Fe loadings of less than 9.0 wt %. The Fe K-edge XAFS was characterized by a clear pre-edge peak, which indicated that the FeO coordination structure deviates from central symmetry and that the degree of FeOFe bond formation is significantly lower than that in bulk samples at low Fe loading (<9.0 wt %). Fe K-edge extended XAFS oscillations of the samples with low Fe loadings were explained by assuming an isolated iron-oxide monomer on the γ-Al2 O3 surface.

Palladium-alumina Cryogel with High Thermal Stability and CO Oxidation Activity

Palladium-alumina cryogel was prepared from palladium nitrate and aluminum sec-butoxide through a sol–gel processing and subsequent freeze drying. The cryogel showed higher thermal stability of palladium and catalytic CO oxidation activity than the corresponding xerogel and impregnation catalysts. The superior stability and activity were ascribed to the uniform distribution of palladium ions in the boehmite gel by the one-pot preparation of palladium-boehmite co-gel, and also to the suppression of transfer and aggregation of the metal during the subsequent freeze drying. As a result palladium ions were finely distributed and stabilized throughout the alumina cryogel support, which consequently suppressed the sintering of palladium at elevated temperatures.Graphical Abstract

Catalytic Oxidation of Toluene over Fe2O3/Al2O3 Catalyst

Fe2O3/Al2O3 catalyst was prepared and the catalytic oxidation of toluene over the catalyst was investigated. The catalyst was prepared by wet impregnation of commercial alumina support. The support was impregnated with an aqueous solution of iron nitrate. The wet support was dried and calcined at 600-800 °C. The catalytic property of the catalyst was measured by the light-off curve of CO2 yield. All these catalysts were active for total oxidation of toluene above 250 °C. The catalytic activity of catalyst calcined at 600 °C was better than those of catalysts calcined at 700 and 800 °C.

Generation of Novel Aluminum Nano Balls

Aluminum nano balls have been generated by the magnetron sputtering-gas aggregation method. The analyses of transmission electron microscope (TEM) images and electron diffraction patterns revealed that the balls are made of aluminum crystals covered with a thin layer of θ-type alumina. The balls deposited on a copper substrate were observed by scanning tunneling microscopy (STM). They were found to land softly on the substrate without decomposition.

Structure and formation process of the water-pretreatedPt/FeOx-Al2O3 catalyst capable of CO oxidation below room temperature

Structure and formation process of water-pretreatedPt/FeOx-Al2O3 catalyst capable of CO oxidation below room temperaturehas been investigated usingPt LIIIX-ray absorption fine structure (XAFS) measurementand high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM).Before the water-pretreatment,Pt monomers and small clusters were detected while formation of Ptnanoparticles (PtNPs) having an average diameter of ≈1.3 nm and Pt-O-Fe interaction were confirmed after the pretreatment, implying that Pt monomers and small clusters aggregated at FeOx on alumina upon the pretreatment.The present results seem to indicate that the formation of Pt monomersand small clusters prior to the water-pretreatment is important for the high mobility of the Pt species and the contact formation between the Pt particles and FeOxon the resultant catalyst which is a key to the high CO oxidation activity at low temperatures.

Preparation of Porous Alumina Powder Using Sol Containing Trehalose Dihydrate

To obtain alumina powder with large surface area, the precursor sol was prepared by hydrolysis of aluminum isopropoxide and then mixing with trehalose dihydrate. The porous alumina powders were prepared by drying and calcination at 500-900 °C. The specific surface area went up to over 340 m2/g in the alumina powder calcined at 500 °C. The mean pore diameter of the alumina powder was increased by the addition of treahalose dihydrate. The porous alumina powder was successfully prepared by the addition of trehalose dihydrate to the precursor sol.

The Relation between Catalytic Activity of CO Oxidation and Support Structure in Oxidation Catalysts using Gold Nanoparticles

Thiol-passivated gold nanoparticles were adsorbed on several kinds of support materials such as titania-coated silica aerogels and xerogels etc., and then the thiol was removed by heat treatment. The catalytic activity of the prepared composites for CO oxidation reaction was measured, and the effects of the support on the catalytic activity were investigated. Density of the supports, namely, whether aerogel supports or xerogel ones, hardly affected the catalytic activity. It was found that the catalysts having high catalytic activity could be obtained by this preparation method, even using the xerogels as the support. Calcination of the supports before adsorption of the gold nanoparticles affected the activity. The difference of the catalytic activity was observed between the composites with same gold nanoparticle size, so it was considered that the surface condition of the support materials affects the state of gold nanoparticles in composite.