In Situ Observation of Carbon Dioxide Capture on Pseudo-Liquid Eutectic Mixture-Promoted Magnesium Oxide

Eutectic mixtures of alkali nitrates are known to increase the sorption capacity and kinetics of MgO-based sorbents. Underlying principles and mechanisms for CO₂ capture on such sorbents have already been established; however, real-time observation of the system was not yet accomplished. In this work, we present the direct-observation of the CO₂ capture phenomenon on a KNO₃-LiNO₃ eutectic mixture (EM)-promoted MgO sample, denoted as KLM, via in situ transmission electron microscopy (in situ TEM). Results revealed that the pseudoliquid EM undergoes structural rearrangement as MgCO₃ evolves from the surface of MgO, resulting in surface roughening and evolution of cloudy structures that stay finely distributed after regeneration. From this, we propose a nucleation and structural rearrangement scheme for MgCO₃ and EM, which involves the rearrangement of bulk EM to evenly distributed EM clusters due to MgCO₃ saturation as adsorption proceeds. We also conducted studies on the interface between EM over solid MgO and MgCO₃ formed during sorption, which further clarifies the interaction between MgO and EM. This study provides better insight into the sorption and regeneration mechanism, as well as the structural rearrangements involved in EM-promoted sorbents by basing not only on intrinsic evolutions but also on real-time observation of the system as a whole.