Influence of the support and the size of gold clusters on catalytic activity for glucose oxidation.

Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, 1-1 Minami-osawa, Hachioji, Tokyo 192-0397, Japan.
Angewandte Chemie International Edition (Impact Factor: 11.34). 11/2008; 47(48):9265-8. DOI: 10.1002/anie.200802845
Source: PubMed
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    ABSTRACT: Monodisperse γ-Al2O3 beads with a diameter of 250 μm were prepared via a sol–gel method and the JetCutter. The bead-shaped support was used for the preparation of 0.23 % Au/γ-Al2O3 catalyst beads which were applied in the oxidation of glucose to gluconic acid. Simplified calculations of the effectiveness factor revealed that especially at high glucose concentrations the use of hydrogen peroxide would lead to much a higher catalyst activity than the use of oxygen as oxidant which was confirmed by the experimental results.
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    ABSTRACT: We have developed a quantitative particle size analytical method at the single atomic level employing electron microscopy and image processing for the investigation of supported metal catalysts. In the present study, a supported gold (Au) catalyst containing sub-nano clusters and individual atoms was globally observed by high-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) using spherical aberration (Cs)-corrected TEM. To fully extract structural information of the Au clusters and individual atoms from the HAADF-STEM images, a morphological image-processing operation was applied. The resulting mean particle size was in good agreement with particle sizes estimated from average information provided by X-ray absorption fine structure analysis. It is demonstrated that the present HAADF-STEM image analysis gives a quantitative particle size distribution measurement of supported Au clusters and individual atoms.
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    ABSTRACT: Aerobic oxidation of glucose in the presence of Au/Al2O3 catalysts with different dispersion of supported gold and Au/C catalysts containing highly dispersed gold nanoparticles was studied at varied glucose:Au molar ratios. The studies were focused on determining the contribution of the mass-transfer processes to the overall reaction kinetics in different regimes. The Au/Al2O3 catalysts were more active than the Au/C catalysts at high glucose:Au molar ratios. Among the alumina-supported catalysts with different metal dispersion, the highest TOF at high glucose:Au molar ratios was characteristic of the Au/Al2O3 catalysts bearing metal particles of 1–5 nm in size. Under these conditions, the high effectiveness factor of the Au/Al2O3 catalysts (>95%) was observed at a uniform gold distribution through the support granules. For the Au/C catalysts with the non-uniform distribution of gold nanoparticles through the catalyst grains, the apparent reaction rate was affected by internal diffusion (the effectiveness factor of a catalyst grain is ca. 70%), while the interface gas–liquid–solid oxygen transfer influenced the overall reaction kinetics as well. At a low glucose:Au molar ratio the reaction rate was limited by oxygen dissolution in the aqueous phase. In this mass transfer regime the rate of glucose oxidation over the carbon-supported catalysts exceeds the reaction rate over the alumina-supported catalyst, which is attributed to a higher adhesion of the hydrophobic carbon support to the gas–liquid interface facilitating the oxygen mass transfer towards catalytic sites.
    Chemical Engineering Journal. 223:921–931.