Carbonaceous minerals represent a valuable and abundant resource. Their exploitation is based on decarboxylation at elevated temperature and under oxidizing conditions, which inevitably release carbon dioxide into the atmosphere. Hydrogenation of inorganic metal carbonates opens up a new pathway for processing several metal carbonates. Preliminary experimental studies revealed significant advantages over conventional isolation technologies. Under a reducing hydrogen atmosphere, the temperature of decarboxylation is significantly lower. Carbon dioxide is not directly released into the atmosphere, but may be reduced to carbon monoxide, methane, and higher hydrocarbons, which adds value to the overall process. Apart from metal oxides in different oxidation states, metals in their elemental form may also be obtained if transition‐metal carbonates are processed under a hydrogen atmosphere. This review summarizes the most important findings and fields of the application of metal carbonate hydrogenation to elucidate the need for a detailed investigation into optimized process conditions for large‐scale applications.
The conversion of mineral magnesite to magnesium oxide, methane, carbon dioxide, and carbon monoxide in a hydrogen atmosphere at ambient pressure and overpressure without catalysts is discussed. Low temperature and elevated pressure facilitate CH4 formation whereas moderate to high temperature and low pressure facilitate CO formation. Methane is formed directly without any additional catalyst. CO2 emissions are decreased substantially in reductive calcination. Additional experiments revealed that reductively calcined magnesium oxide is a highly active reverse water‐gas shift catalyst. CO formation from gaseous CO2 and H2 at catalytically active magnesium oxide was reproducibly confirmed. Further reduction of carbon monoxide to methane is not catalyzed by reductively calcined magnesium oxide.
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