Silica supported amorphous molybdenum catalysts prepared via sol–gel method and its catalytic activity

Silica supported amorphous molybdenum catalysts had been synthesized in alkali, neutral and acidic medium via sol–gel technique. The catalysts were found to be amorphous and free from bulk MoO3. UV–Vis diffuse reflectance analysis and XPS analysis indicated the co-existence of Mo5+ and Mo6+ species when the incorporation was done in acidic medium. The catalytic activity was tested in the liquid phase oxidation of styrene by using hydrogen peroxide as oxidant. The catalyst prepared in acidic medium showed better catalytic activity compared to the catalysts prepared in alkali and neutral medium. The co-existence of Mo5+ and Mo6+ species is believed to enhance the catalytic activity. Benzaldehyde was the major product detected. The structure of the catalyst was proposed based on the results obtained from XPS, 29Si MAS NMR, UV–Vis diffuse reflectance and FT-IR spectroscopy.

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► Inorganic silica from rice husk was used as a support for amorphous molybdenum catalysts prepared at alkali, neutral and acidic pH.
► The catalytic activity of the catalysts was studied in the liquid phase oxidation of styrene using H2O2 as oxidant.
► Catalyst prepared at acidic pH was the most active. The styrene conversion was 82.2% with 87.9% selectivity towards Bza.
► Surface structure of the most active catalyst was analyzed to correlate to its catalytic activity.