Phase Relations in the System TiO2-V2Ox under Oxidizing and Reducing Conditions

The target of this work was to investigate the phase development in the catalyst system consisting of TiO2 (Anatase) and V2O5 (Shcherbinaite) under several gas atmospheres. Thus a set of V2O5/TiO2 specimens was prepared by ball milling and exposed to subsequent annealing in air and feed gas in the temperature range from 400 to 700 degrees C. The XRD-results showed that the initial phases Anatase and Shcherbinaite remain stable for all atmospheres containing oxygen. In the temperature range above 525 degrees C the formation of a Rutile solid solution (Rutile-ss) containing VOx species takes place. However, under reducing conditions (lower oxygen partial pressure) the reduction of V2O5 to V2O3 was found by X-ray diffraction measurements. There is no miscibility up to 1300 degrees C followed by the formation of V2TiO5 (Berdesinskiite). SEM images underline the reduction by monitoring the change in morphology with respect to the V-containing phases. TiO2 remains without much alteration. The two phases V2Ti7O17 and V2Ti3O9 (Schreyerite) as described in mineralogy have not been observed in these experiments. The knowledge of phase relations helps to find the appropriate processing conditions and to understand the aging phenomena of catalysts.