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 100percent 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. © Springer Science+Business Media, LLC 2011.