Temperature-programmed and X-ray diffractometry studies of hydrogen-reduction course and products of WO3 powder: Influence of reduction parameters

The hydrogen-reduction course and products of synthetic tungsten(VI) oxide (WO3) were examined by means of temperature-programmed reduction (TPR) and X-ray powder diffractometry (XRD) studies. A set of model tungsten compounds was procured and examined similarly for reference purposes. Results obtained could help resolving two subsequent reduction stages: (i) a low-temperature stage (<1050 K) through which WO3 is reduced to the tetravalent state (WO2) via formation and subsequent reduction of intermediate WO2.96, WO2.9, WO2.72 oxides; and (ii) a high-temperature stage (>1050 K) through which WO2 thus produced is reduced to the metallic state (Wo) via two intermediate oxide species (tentatively, WO and W2O–W3O). Reduction events involved in the high-temperature stage were found to be relatively more sensitive to the reduction parameters; namely, the starting oxide mass, heating temperature and rate, and gas flow rate and composition. They were also found to require lower activation energies than those required by events occurring throughout the low-temperature stage, a fact that may suspect compliance of the high-temperature reduction events to autocatalytic effects.