Ultrafast and Stable CO₂ Capture Using Alkali Metal Salt-Promoted MgO-CaCO₃ Sorbents

As a potential candidate for precombustion CO₂ capture at intermediate temperatures (200-400 °C), MgO-based sorbents usually suffer from low kinetics and poor cyclic stability. Herein, a general and facile approach is proposed for the fabrication of high-performance MgO-based sorbents via incorporation of CaCO₃ into MgO followed by deposition of a mixed alkali metal salt (AMS). The AMS-promoted MgO-CaCO₃ sorbents are capable of adsorbing CO₂ at an ultrafast rate, high capacity, and good stability. The CO₂ uptake of sorbent can reach as high as above 0.5 g_CO g_sorbent^-1 after only 5 min of sorption at 350 °C, accounting for vast majority of the total uptake. In addition, the sorbents are very stable even under severe but more realistic conditions (desorption in CO₂ at 500 °C), where the CO₂ uptake of the best sorbent is stabilized at 0.58 g_CO g_sorbent^-1 in 20 consecutive cycles. The excellent CO₂ capture performance of the sorbent is mainly due to the promoting effect of molten AMS, the rapid formation of CaMg(CO₃)₂, and the plate-like structure of sorbent. The exceptional ultrafast rate and the good stability of the AMS-promoted MgO-CaCO₃ sorbents promise high potential for practical applications, such as precombustion CO₂ capture from integrated gasification combined cycle plants and sorption-enhanced water gas shift process.