https://www.nature.com/articles/s41467-018-04794-5
“the main drawback associated with limestone-derived CaO is its low cyclic stability owing to the sintering-induced deterioration of the microstructure of as-derived CaO. Indeed, the Tammann temperature (TT) of CaCO3 (~530 °C), a measure for the onset of sintering, is well below the operating temperatures of calcium looping11, i.e., 600–700 °C for carbonation (CO2 capture step) and 900 °C for calcination (regeneration step).”
“One of the approaches that have been attempted to reduce the sintering-induced capacity decay of CaO-based CO2 sorbents is the incorporation of high-TT stabilizers such as Al2O3, MgO, TiO2, or ZrO2 which are typically inactive for CO2 capture. Several works have demonstrated that the utilization of such stabilizers can improve appreciably the cyclic CO2 uptake of CaO10,11,12,16,17,18,19,20,21. In general, stabilizers can be grouped into two categories: (i) the ones that form a solid solution with CaO (e.g., Al2O3 that can yield Ca12Al14O33 or Ca9Al6O18, or ZrO2 forming CaZrO3), and (ii) the ones that do not form a solid solution under relevant operating conditions (e.g., MgO or Y2O3). Although Al2O3 has received arguably the highest attention so far, the latter group of stabilizers is potentially more attractive in terms of preserving the intrinsically high CO2 uptake of CaO, as active CaO is not “consumed” through the formation of a solid solution that is inactive for CO2 capture22. Furthermore, a recent study focusing on the deactivation mechanism of Ca3Al2O6-stabilized, CaO-based CO2 sorbents demonstrated the segregation of Al2O3 from Cal-Al mixed oxides, leading to a sintering-induced structural collapse of the material after a certain number of cycles23. Hence, considering also its high TT (i.e., ~1290 °C), MgO is an attractive structural stabilizer. In addition, similar to CaO, MgO is inexpensive and environmentally benign24.”
DOI: 10.1038/s41467-018-04794-5