Phase development in the catalytic system V2O5/TiO2 under oxidising conditions |
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| Affiliation: | 1. Institute for Material Science and Technologies, TU Berlin, Englische Straße 20, D-10587 Berlin, Germany;2. Institute for Applied Geosciences, TU Berlin, Straße des 17. Juni 135, D-10669 Berlin, Germany;3. Institute for Physical Chemistry and Electrochemistry, University of Hanover, Callinstraße 3-3a, D-30167 Hanover, Germany;4. Fritz-Haber-Institute of the Max Planck Society, Department of Inorganic Chemistry, Faradayweg 4-6, D-14195 Berlin, Germany;1. Department of Earth Sciences, University of Western Ontario, London, Ontario N6A 5B7, Canada;2. Fachbereich Materialforschung & Physik, Abteilung Mineralogie, Universität Salzburg, Hellbrunnerstrasse 34, 5020 Salzburg, Austria;1. Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 10617, Taiwan;2. Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan;3. Institute of Environmental Engineering, National Chiao Tung University, Hsin Chu 300, Taiwan;1. Laboratory of Solid State Microstructures, Nanjing University, Nanjing 210093, China;2. College of Physical Science and Electronic Techniques, Yancheng Normal University, Yancheng 224002, China;1. College of Electrical and Photoelectronic Engineering, West Anhui University, Lu’an 237012, China;2. Department of Physics and Materials Science, University of Memphis, Memphis, TN 38152, USA;3. Research Center of Atoms Molecules and Optical Applications, West Anhui University, Lu’an 237012, China |
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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 the peak intensities were diminishing and rutile as a new TiO2-phase occurred. 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. A rutile solid solution once formed could not be re-transformed.The rutile solid solution was first found at 525 °C < T < 550 °C for compositions of 3 mol% < V2O5 < 5 mol%. The phase field for rutile solid solutions extends to 10 mol% < V2O5 < 12.5 mol% at 675 °C. For very high V2O5 concentrations (95 mol% V2O5) a eutectic reaction was found at 631 °C. The DTA runs showed a widened endothermic melting peak and a very sharp crystallization peak on cooling. 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 when the rutile formation occurs. The knowledge of phase relations helps to find the appropriate processing conditions and to understand the aging phenomena of catalysts. |
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