CaO-Based CO2 Sorbents Effectively Stabilized by Metal Oxides.

Abstract

Calcium looping (i.e., CO2 capture by CaO) is a promising second-generation CO2 capture technology. CaO, derived from naturally occurring limestone, offers an inexpensive solution, but due to the harsh operating conditions of the process, limestone-derived sorbents undergo a rapid capacity decay induced by the sintering of CaCO3 . Here, we report a Pechini method to synthesize cyclically stable, CaO-based CO2 sorbents with a high CO2 uptake capacity. The sorbents synthesized feature compositional homogeneity in combination with a nanostructured and highly porous morphology. The presence of a single (Al2 O3 or Y2 O3 ) or bimetal oxide (Al2 O3 -Y2 O3 ) provides cyclic stability, except for MgO which undergoes a significant increase in its particle size with the cycle number. We also demonstrate a direct relationship between the CO2 uptake and the morphology of the synthesized sorbents. After 30 cycles of calcination and carbonation, the best performing sorbent, containing an equimolar mixture of Al2 O3 and Y2 O3 , exhibits a CO2 uptake capacity of 8.7 mmol CO2 g-1 sorbent, which is approximately 360 % higher than that of the reference limestone.