In Situ X-ray Diffraction Studies on the Reduction of V2 O5 and WO3 by Using Hydrogen.

ABSTRACT

The reduction of metal oxides with hydrogen is widely used for the production of fine chemicals and metals both on the laboratory and industry scale. In situ methods can help to elucidate reaction pathways and to gain control over such synthesis reactions. In this study, the reduction of WO3 and V2 O5 with hydrogen was investigated by in situ X-ray powder diffraction with regard to intermediates and the influence of heating rates and hydrogen flow rates. Mixtures of V4 O9 , V6 O13 and VO2 in two modifications were identified as intermediates on the way to phase-pure V2 O3 . None of the intermediates occurs in a single phase and therefore cannot be prepared this way. In contrast, the intermediates of the WO3 reduction, H0.23 WO3 and W10 O29 , appear consecutively and can be isolated. For both reactions, the heating and flow rates have little influence on the formation of intermediates.