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Abstract

The target of this work was to investigate phase development in the catalyst system consisting of TiO2 (Anatase) and V2O5 (Shcherbinaite). Thus a set of V2O5/TiO2 specimens was prepared by ball milling and exposed to subsequent annealing in air in the temperature range from 400 to 700 °C. The XRD-results showed the presence of Anatase and Shcherbinaite as the only phases up to 525 °C. For temperatures above 525 °C Rutile as a new TiO2-phase occured. Peak intensities and positions were shifted. No loss of oxygen or vanadium was detected. The reaction involves the formation of a Rutile solid solution containing VOx species. XPS studies showed an oxidation state of 4.75 for V in the Rutile solid solution as compared to 4.65 in the Shcherbinaite. The Rutile solid solution was first found at 525 °C < T < 550 °C for compositions of 3 mole % < V2O5 < 5 mole %. The phase field for Rutile solid solutions extends to 10 mole%< V2O5 <12.5 mole % at 675 °C. For very high V2O5 concentrations an eutectic reaction was found at 631 °C (95 mole% V2O5 A Shcherbinaite structure remained with shifted peak intensities and positions due to the alloying of Ti-ions. SEM inspections showed that the Rutile formation and the eutectic reaction both cause a substantial grain growth and a loss of surface area. The catalytic activity is entirely lost. The knowledge of phase relations helps to find the appropriate processing conditions and to understand the aging phenomena of catalysts.