THERMOGRAVIMETRIC ANALYSIS OF VANADIUM PHOSPHORUS OXIDE CATALYSTS DOPED WITH COBALT AND IRON

The transformation of VOHPO4. 0.5H(2)O (VPO) precursor doped with coba lt or iron for n-butane oxidation to maleic anhydride was investigated by thermogravimetric analysis under air and nitrogen, with and withou t n-butane in the flow. While almost no effect was observed in nitroge n or air, a strong influence of the doping was observed when n-butane was added to the nitrogen or air. This resulted in a delay of the deco mposition of the precursor and a further reoxidation of the VPO cataly st, particularly for doping with cobalt at low percentage (1%). This s hows that doping can change the oxidation state of vanadium phosphorus oxide catalysts, which can explain differences in their catalytic per formances and the favourable effect of doping by cobalt.