Temperature effects on the size of anatase crystallites in Mo-TiO2and W-TiO2powders

The substitution effects of Ti by Mo and W ions on the stability of anatase in commercially available TiO2powders have been studied by X-ray diffraction, transmission electron microscopy, and surface area measurements in the 300-1000 K temperature range. The powder containing W shows smaller microstrains compared to those of pure anatase phase and those containing Mo. The stabilization effect of vacancies in the anatase phase is discussed and the anatase to rutile transformation caused by annealing is proposed to be related to the disappearance of Ti3+ions in the anatase structure. Finally, a possible redox mechanism Ti3+⇔ Ti4++ e-is proposed to play a fundamental role in the catalytic and sensor properties of this material.