TEMPERATURE-PROGRAMMED REDUCTION OF V2O5 AND COPRECIPITATED V2O5-TIO2 BY HYDROGEN

Temperature-programmed reductions (TPR) with H-2 of both pure V2O5 and coprecipitated V2O5-TiO2 systems with different titanium concentrations was performed. The original and the reduced samples following each TPR step were characterized by X-ray diffraction, Fourier transform infrared analysis and scanning electron microscopy. Within the temperature;range in which TPR analysis was carried out (100-600 degrees C) the V2O5 phase was reduced in two or three steps, while no variation in the TiO2 phase (anatase or rutile) was observed. In the first reduction step only superficial reduction of the oxides was detected. In the following steps, the H-2 reacted with oxygen atoms of the V = O and V-O-V bonds. This led to important changes in the structure and morphology of the system. The experimental evidence allowed the conclusion that titanium stabilizes certain phases of vanadium oxides in which vanadium appears as V(+4) or as a mixture of V(+4) and V(+5). Moreover, when moderate and high titanium concentrations were used, the reduction temperature of the bulk V2O5 decreased markedly.