Thermal evolution of a TiO2-V2O5 interface

The thermal evolution of the reference catalyst, EUROCAT EL10V8, containing 8% (w/w) of V2O5 deposited on anatase TiO2 has been followed by XRD, chemical analysis and XPS during annealing in oxygen for periods from 0 to 288 h and at temperatures from 420 degrees C to 640 degrees C, The anatase structure of the support is stable up to 520 degrees C. Above this temperature the rutile structure appears. The amount of NH3-insoluble vanadium, formed at 300 degrees C, increases with the time and temperature of annealing from 420 degrees C onwards. Below 560 degrees C the fraction of the TiO2 surface covered by vanadium oxide, as determined by XPS, falls with increasing time, This evolution is accelerated by water vapour. From 560 degrees C the specific surface decreases with the time, Half the insoluble vanadium is bound between the surface and a depth which increases from 2.5 Angstrom in the initial state of the catalyst up to about 28 Angstrom after 48 h annealing at 560 degrees C. At the same time, the extent of vanadium binding in the surface plane of TiO2 decreases from 0.30 atom per unit cell to 0.12. (C) 1999 Elsevier Science B.V. All rights reserved.