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ALTERNATIVE ROUTES FOR CATALYST PREPARATION: USE OF ULTRASOUND AND MICROWAVE IRRADIATION FOR THE PREPARATION OF VANADIUM PHOSPHORUS OXIDE CATALYST AND ITS ACTIVITY FOR HYDROCARBON OXIDATION
Citation:
Pillai**, U R., E SahleDemessie*, AND R S. Varma*. ALTERNATIVE ROUTES FOR CATALYST PREPARATION: USE OF ULTRASOUND AND MICROWAVE IRRADIATION FOR THE PREPARATION OF VANADIUM PHOSPHORUS OXIDE CATALYST AND ITS ACTIVITY FOR HYDROCARBON OXIDATION. Presented at AICHE, New York, NY, September 07 - 12, 2003.
Impact/Purpose:
To inform the public
Description:
Vanadium phosphorus oxide (VPO) is a well-known catalyst used for the vapor phase n-butane oxidation to maleic anhydride. It is prepared by a variety of methods, all of which, however, eventually result in the same active phase. The two main methods for the preparation of its precursor involve the reduction of V5+ (V2O5) to V4+ either in water by HCl or hydrazine and the reduction in an organic phase (2-butanol) in the presence of another reducing agent such as benzyl alcohol. After the reduction, required amount of phosphoric acid is added followed by separation of the solid by evaporation, filtration or centrifugation. Thus, the overall preparation of the VPO catalyst usually is time consuming requiring 16 to 20 h. Consequently, the quest for the development of alternative methods, which are capable of generating this catalyst in a faster and cost effective manner is a highly desirable pursuit. Some of the important alternative routes may be the use of microwave (MW) and ultrasound (US) as alternative energy sources for the preparation. They have diverse effects on chemical processes including wide ranging applications in organic synthesis, catalytic reactions, and environmental and engineering sciences. We herein report the utility of ultrasound and microwave irradiation in the preparation of VPO catalyst 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 expedites the VPO preparation with a significant (70 %) reduction in the preparation time from 20 h to 6 h to generate a catalyst that has similar surface composition and comparable hydrocarbon oxidation activity with the conventionally prepared catalyst. 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 conversion.