Immobilized polyoxometalates onto mesoporous organically-modified silica aerogels as selective heterogeneous catalysts of anthracene oxidation |
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Authors: | Rami Al-Oweini Shant Aghyarian Houssam El-Rassy |
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Institution: | (1) Department of Chemistry, American University of Beirut, P.O. Box 11-0236, Riad El-Solh, 1107 2020 Beirut, Lebanon; |
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Abstract: | Immobilized molybdovanadophosphoric acids onto organically surface-modified silica aerogels were successfully prepared and
investigated in heterogeneous catalysis of anthracene oxidation. The catalysts were obtained by supporting mono- and di-vanadium
substituted molybdophosphoric acids on hybrid silica materials synthesized via the sol–gel process followed by surface amino-functionalization.
The FTIR, DR UV–vis, and AA spectroscopy confirmed the loading and distribution of the polyoxometalate molecules on the surface
of the aerogels. The nitrogen adsorption–desorption technique revealed a systematic decrease in the specific surface area
and pore volume after the immobilization of the polyoxometalates. The application of the supported molecules as catalysts
for anthracene oxidation showed 100% selectivity for 9,10-anthraquinone as opposed to the reactions conducted under homogeneous
conditions. Moreover, at certain conditions, the catalytic activity of the supported polyoxometalates was greater than their
corresponding free polyoxometalates with a clear effect of the surface chemical groups of the supporting silica aerogels.
Additionally, the oxidant and solvent nature showed a crucial effect on the catalytic activity and selectivity of the immobilized
polyoxometales. The heterogeneous catalysts were regenerated and reused over consecutive catalytic cycles reflecting a potential
economic interest in these materials besides their high efficiency in heterogeneous catalysis. |
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