Unravelling the role of alkaline earth metal carbonates in intermediate temperature CO2 capture using alkali metal salt-promoted MgO-based sorbents

Alkali metal salt (AMS)-promoted MgO sorbents are promising for intermediate temperature CO(2)capture due to their high capacity, but suffer from slow sorption kinetics and poor stability which hinder their applications. Herein, we report that incorporation of alkaline earth metal carbonates (CaCO3, SrCO(3)or BaCO3) into AMS-promoted MgO can improve the CO(2)capture performance of the sorbent in multiple sorption/desorption cycles. Experimental studies reveal that CaCO(3)and BaCO(3)participate in MgO carbonation with fast and reversible formation of dolomite and norsethite, respectively, thus resulting in a rate enhancement, while SrCO(3)is inert for CO(2)sorption but acts as a stabilizer to prevent sintering of MgO particles and in turn improve the sorbent stability. Kinetic studies show that the activation enthalpy of sorption at the surface reaction-controlled stage is 36.9, 28.1, 35.3, and 30.6 kJ mol(-1)for AMS-MgO and AMS-MgO doped with CaCO3, SrCO(3)and BaCO3, respectively, which agrees well with the rate enhancement of the CaCO3- or BaCO3-doped sorbent. This discovery offers new opportunities to develop high-performance MgO-based CO(2)sorbents by doping with alkaline earth metal carbonates.