Abstract
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.
Highlights
Carbon dioxide (CO2) is an abundant chemical species. It is present in all three aggregate states: in gaseous form in the atmosphere, in the dissolved state in the hydrosphere, and in the solid state fixed in carbonate rocks.[1]
An admixture of transition metals to main-group metal carbonates opens up a new pathway in metal carbonate hydrogenation: because many transition metals catalyze hydrogenation reactions, CO2 evolved from the carbonate is converted into carbon monoxide (CO), CH4, or higher hydrocarbons CxHy and CxHyOz
The combination of decarboxylation and CO2 reduction with the renewable energy carrier hydrogen transforms the conventional endothermic process into an overall exothermic process, which allows for significant energy savings
Summary
Whereas the decarboxylation products of main-group elements (e.g., alkaline-earth-metal carbonates) are the corresponding metal oxides and CO2 [Eq (1)], the decomposition of transition-metal carbonates follows a more complex reaction pathway [Eq (2)] because redox processes may take place. Matthäus Siebenhofer studied chemical engineering and received his doctoral degree in 1983 from the Graz University of Technology in Austria.
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