The reduction of MoO3 in hydrogen or hydrogen sulfide was studied by means of high temperature X-ray diffraction. It was revealed that MoO3 was reduced to MoO2 through the formation of MoO3-x (Mo4O11, Mo8O23 and Mo17O47). It was also observed that the rate of the reduction of MoO3 was much enhanced when H2S was employed as a reducing gas. This could be explained by the fact that the dissociation constant of H2S is much higher than that of H2 at any temperature studied.
The effect of the addition of Al2O3 on the reduction of MoO3 was also investigated. It was found that the rate of the reduction of MoO3 becomes faster by the presence of Al2O3, though the mechanism of the reduction of MoO3 by Al2O3 could not be explained in the present work.
