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: In recent years supported gold nanoparticles have emerged as efficient catalysts with considerable synthetic potential for liquid-phase oxidation reactions based on molecular oxygen as oxidant. Here we critically review the most attractive applications related to the selective oxidation of functional groups containing O, N, or Si heteroatoms. The reactions include the oxidation of alcohols, aldehydes, and organosilanes; the diverse transformations of amines; benzylic oxidations; and some one-pot multistep reactions starting with alcohol or amine oxidation. In complex liquid-phase transformations relying on bifunctional catalysis, appropriate choice of the support is frequently more important than the size of the gold particles. In some oxidation reactions gold nanoparticles outperform the traditional platinum-group metal catalysts, but the latest results indicate the superiority of bimetallic particles containing gold and platinum, palladium, or rhodium. The environmentally benign nature of the transformations is discussed.
    Annual Review of Chemical and Biomolecular Engineering 01/2012; 3:11-28. · 7.51 Impact Factor
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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.
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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.
    Microscopy (Oxford, England). 01/2014;