TEMPERATURE-PROGRAMMED REDUCTION OF V2O5 AND COPRECIPITATED V2O5-TIO2BY HYDROGEN

Temperature-programmed reductions (TPR) with H-2 of both pure V2O5 and coprecipitated V2O5-TiO2 systems with different titanium concentratio ns was performed. The original and the reduced samples following each TPR step were characterized by X-ray diffraction, Fourier transform in frared analysis and scanning electron microscopy. Within the temperatu re;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 t he TiO2 phase (anatase or rutile) was observed. In the first reduction step only superficial reduction of the oxides was detected. In the fo llowing 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 vanadiu m 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 tem perature of the bulk V2O5 decreased markedly.