Role of Na 2 CO 3 as Nucleation Seeds to Accelerate the CO 2 Uptake Kinetics of MgO-Based Sorbents

There is an urgent need for inexpensive, functional materials that can capture and release CO under industrial conditions. In this context, MgO is a highly promising, earth-abundant CO sorbent. However, despite its favorable carbonation thermodynamics and potential for high gravimetric CO uptakes, MgO-based CO sorbents feature slow carbonation kinetics, limiting their CO uptake during typical industrial contact times. The addition of molten alkali metal nitrate promoters, such as NaNO , can partially mitigate the slow kinetics. Here, we investigate how the CO uptake kinetics of NaNO -promoted MgO can be increased further through the addition of finely dispersed Na CO . The incorporation of Na CO significantly increases the CO uptake rate from 1.4 to 14.6 mmol MgCO (mol MgO) s . Using synchrotron X-ray powder diffraction (XRD), we track the formation of MgCO and elucidate the mechanism through which Na CO promotes the CO uptake of MgO. Our findings demonstrate that Na CO rapidly converts within seconds into Na Mg(CO ) during carbonation, acting subsequently as nucleation seeds for MgCO formation, in turn significantly enhancing CO uptake kinetics. Further, the presence of Na Mg(CO ) considerably enhances the mobility of ions in the sorbent, leading to sintering of MgCO . Importantly, Na Mg(CO ) promotes MgCO formation even in the presence of molten RbNO , a salt with a limited ability to dissolve [Mg ···CO ] ion pairs, indicating that Na Mg(CO ) lowers the critical ion pair concentration required for MgCO nucleation. Additionally, the partial dissolution of Na CO in NaNO may increase the concentration of carbonate ions in the melt, further accelerating carbonation kinetics in MgO-(Na CO /NaNO ).