The reaction of CaO with CO2 is a promising approach for separating CO2 from hot flue gases. The main issue associated with the use of naturally occurring CaCO3, that is, limestone, is the rapid decay of its CO2 capture capacity over repeated cycles of carbonation and calcination. Interestingly, dolomite, a naturally occurring equimolar mixture of CaCO3 and MgCO3, possesses a CO2 uptake that remains almost constant with cycle number. However, owing to the large quantity of MgCO3 in dolomite, the total CO2 uptake is comparatively small. Here, we report the development of a synthetic Ca-rich dolomite using a coprecipitation technique, which shows both a very high and a stable CO2 uptake over repeated cycles of calcination and carbonation. To obtain such an excellent CO2 uptake characteristic it was found to be crucial to mix the Ca~(2+) and Mg~(2+) on a molecular level, that is, within the crystalline lattice. For sorbents which were composed of mixtures of microscopic crystals of CaCO3 and MgCO3, a decay behavior similar to natural limestone was observed. After 15cycles, the CO2 uptake of the best sorbent was 0.51 g CO2/g sorbent exceeding the CO2 uptake of limestone by almost 100.
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