Alternative routes for catalyst preparation: use of ultrasound and microwave irradiation for the preparation of vanadium phosphorus oxide catalyst and their activity for hydrocarbon oxidation Original Research Article

Vanadium phosphorus oxide (VPO) has been prepared using ultrasound and microwave irradiation methods and compared with the catalyst prepared by conventional method for both the phase composition and activity for hydrocarbon oxidation. It is found that ultrasound irradiation method generates a catalyst in a relatively shorter time of 6 h that has similar surface composition and comparable hydrocarbon oxidation activity with that prepared by conventional heating method. On the other hand, the VPO catalyst prepared via microwave activation method appears to have a different surface morphology when compared to the conventional and sonochemical preparations. All the catalysts, irrespective of their preparative origin or surface morphology display good activity for hydrocarbon oxidation using aqueous hydrogen peroxide. The selectivity of the products is dependent on the nature of the catalyst with a combination of (VO)2P2O7 (V4+) and VOPO4 (V5+) being ideal for high oxidative conversion. All the VPO catalysts, irrespective of the preparation method are found to be soluble in the reaction mixture forming a homogeneous solution. The catalysts can however be re-used after isolation from the reaction mixture by evaporation and drying.