- Decatungstate catalyst supported on silica and γ-alumina: Efficient photocatalytic oxidation of benzyl alcohols
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Four supported catalysts with the same tungsten loading were prepared by depositing decatungstate species W10O4-32, through wet impregnation, on the surface of γ-alumina and silica at different pH values. The prepared samples were characterized using BET measurements as well as XRD, UV-vis DR, and XP spectroscopies. Higher dispersion of W(VI) oxo-species was obtained in the silica-supported catalysts compared with the corresponding alumina-supported ones. Within the same support, the dispersion was higher when the impregnation pH is lower than the point of zero charge (pzc) of the support. The decatungstate anions were present mainly on the silica surface without any modification, whereas these underwent a partial depolymerization on their deposition on the γ-alumina surface. The extent of depolymerization was less in the sample prepared at pH above pzc. These findings were explained in terms of the mode of deposition of the W(VI) species from the solution onto the support surface. The photocatalytic activity of the aforementioned catalysts, concerning the photooxidation of 1-phenylethanol, depends on the fraction of the W10O4-32 supported species rather than on the W(VI) dispersion. Thus, extremely high conversions have been obtained over the silica-based catalysts and also over the γ-alumina-based catalyst prepared at relatively high pH. These catalysts also are very effective in the photooxidation of a series of secondary and primary benzyl alcohols, in which benzyl ketones and benzoic acids were formed as the only or major products, respectively. The easy separation of the solid catalyst from the reaction mixture, the high activity, selectivity, and stability as well as the retained activity in subsequent catalytic cycles, make these supported catalysts suitable for a small-scale synthesis. Based on product analysis and kinetic data on the heterogeneous oxidation of benzyl alcohols, we suggest that a hydrogen abstraction transfer (HAT) mechanism predominates with respect to an electron transfer (ET) one in these reactions.
- Tzirakis, Manolis D.,Lykakis, Ioannis N.,Panagiotou, George D.,Bourikas, Kyriakos,Lycourghiotis, Alexis,Kordulis, Christos,Orfanopoulos, Michael
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p. 178 - 189
(2008/09/18)
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- Predominant role of basicity of leaving group in α-effect for nucleophilic ester cleavage
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It has been found that α-effects in nucleophilic reactions, unexpectedly large nucleophilicity due to adjacent unpaired electrons, are strongly dependent on the structure of substrate. The nucleophilic cleavages of 4-nitrobenzoate esters and 4-methylbenzo
- Nomura, Yasuo,Kubozono, Takayasu,Hidaka, Makoto,Horibe, Mineko,Mizushima, Naoki,Yamamoto, Nobuyuki,Takahashi, Toshio,Komiyama, Makoto
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- Process for producing per-p-toluic acid and utilizing the same
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P-Tolualdehyde freed from reaction-inhibiting substances is autooxidized by a gas containing molecular oxygen in an aliphatic ketone or fatty acid ester solvent under pressure in the absence of catalyst to produce per-p-toluic acid. The resulting per-p-toluic acid is brought into contact with a lower olefin in the absence of catalyst to produce p-toluic acid and an alkylene oxide at the same time, or said per-p-toluic acid is reacted with allyl alcohol to produce glycidol and p-toluic acid at the same time, and further the resulting glycidol is hydrolyzed to produce glycerin, or said per-p-toluic acid is reacted with methanol in the presence of an esterification catalyst to produce hydrogen peroxide and methyl p-toluate at the same time. The foregoing reactions can be carried out easily and safely in simple processes in high yields.
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