In situ powder X-ray diffraction during hydrogen reduction of MoO3 to MoO2

Abstract

The hydrogen reduction of molybdenum trioxide to molybdenum dioxide is not yet fully understood as evident by continuous scientific interest. Especially the effect of the potassium content on the reduction process has not yet been considered. We prepared several samples of molybdenum trioxide containing varying amounts of potassium by addition of potassium molybdate (K2MoO4). In situ powder X-ray diffraction experiments were then conducted to study the hydrogen reduction of these samples. We especially focused on the influence of the alkali content and on gaining insight into the importance of the intermediary product γ-Mo4O11. During the reduction process, MoO2 is formed from the reduction of MoO3, which then reacts with the starting material to form γ-Mo4O11. With increasing potassium content, the reduction rate is decreased and the fractional content of γ-Mo4O11 built up during the reduction process is increased. As evident from bulk sample reduction, this results in a significant increase in the grain size visualized via scanning electron microscopy. Our investigations once again underline the importance of γ-Mo4O11 on the morphology of the resulting MoO2 powder.