The liquid phase oxidation of styrene with tungsten modified silica as a catalyst

Tungsten was incorporated into silica matrix using sodium silicate from rice husk at pH 10,7 and 3. These catalysts were labeled as RHW-10, RHW-7 and RHW-3. The pH was found to have a strong influence on the structure of the resulting silica-tungsten species and its catalytic activity. Analysis suggests that the catalysts were composed of isolated [WO4](2-) species, isolated tungsten species or low oligomeric tungsten oxide species and crystalline WO3 species. The catalytic activity was tested in the liquid phase oxidation of styrene using H2O2 as oxidant. RHW-3 showed better catalytic activity than RHW-10 and RHW-7 due to its higher tungsten loading. The reaction is proposed to be catalyzed by pertungstic acid like intermediate which was formed upon the interaction of tungsten oxo species (W=O) with H2O2. Benzaldehyde was obtained via styrene oxide as the major product with 100% selectivity. RHW-3 could be re-used several times without losing its catalytic activity even though a small amount of tungsten species leached out from the support. (C) 2011 Elsevier B.V. All rights reserved.