The Reduction of Group 6–8 Transition Metal Oxides with Hydrogen—From Ore Smelting to Reaction Pathways#

Abstract

The reduction of transition metal oxides with hydrogen is currently used in the production of various transition metals, e.g., molybdenum, tungsten, rhenium, and may potentially be applied to others, especially iron, in the future. The gas–solid reduction process is well suited for investigations using in situ X-ray powder diffraction. This method allows for the study of influences such as temperature, heating rate, reaction time, impurities, or water partial pressure on crystal structures, reaction pathways, intermediates, crystallite sizes, or phase transitions with high time resolution. For some transition metals, extensive investigations have already been conducted while others have not been subject of in situ studies so far. Herein, the production processes for transition metals of groups 6–8 have been summarized, including how well the production method has been studied, whether in situ methods are employed and what results the use of such methods promises.