Co-thermal in-situ reduction of inorganic carbonates to reduce carbon-dioxide emission

Thermal decomposition of inorganic metal carbonates is the main path to prepare metal oxides; nonetheless, it is always accompanied by the emission of large amounts of CO2 as one of the gas products. This study reports a concept of co-thermal in-situ reduction of inorganic carbonates by using the energy released by carbonate decomposition under pure hydrogen atmosphere, which reduces the decarboxylation temperature and significantly inhibits the CO2 emissions. A combination of hydrogen-deuterium exchange, isotope experiment, and density functional theory calculations demonstrates that the CO results from the selective cleavage of Ca-O bonds at the surface of CaCO(3)via the direct hydrogenation mechanism at relatively low temperature. However, it undergoes the reverse water-gas shift reaction path at high temperature, i.e., CO being produced by the reduction of CO2 released by the decomposition of carbonates. This study sheds light on the potential of green hydrogen technology for inorganic carbonate valorization toward high value-added products, which can facilitate the large-scale industrial applications.