Department of Energy Science and Technology, Myongji University , Yongin 17058, Republic of Korea.
Department of Organic Material Science and Engineering, Pusan National University , Pusan 46241, Republic of Korea.
ACS Appl Mater Interfaces. 2018 Jan 24;10(3):2414-2422. doi: 10.1021/acsami.7b14256. Epub 2018 Jan 8.
Eutectic mixtures of alkali nitrates are known to increase the sorption capacity and kinetics of MgO-based sorbents. Underlying principles and mechanisms for CO 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 CO capture phenomenon on a KNO-LiNO 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 MgCO 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 MgCO and EM, which involves the rearrangement of bulk EM to evenly distributed EM clusters due to MgCO saturation as adsorption proceeds. We also conducted studies on the interface between EM over solid MgO and MgCO 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.
已知碱硝酸盐共晶混合物能提高基于氧化镁的吸附剂的吸附容量和动力学性能。此类吸附剂上 CO 捕获的基本原理和机制已经建立，但尚未实现对该系统的实时观察。在这项工作中，我们通过原位透射电子显微镜（in situ TEM）直接观察了在促进氧化镁的硝酸钾-硝酸锂共晶混合物（KLM）上的 CO 捕获现象。结果表明，随着氧化镁表面 MgCO 的形成，伪液态 EM 经历了结构重排，导致表面粗糙化和云状结构的演变，在再生后仍保持精细分布。由此，我们提出了 MgCO 和 EM 的成核和结构重排方案，该方案涉及到由于 MgCO 饱和，在吸附过程中，将大块 EM 重排为均匀分布的 EM 簇。我们还研究了 EM 覆盖在固体氧化镁和吸附过程中形成的 MgCO 之间的界面，这进一步澄清了氧化镁和 EM 之间的相互作用。这项研究不仅基于内在演变，而且还基于对整个系统的实时观察，从而更好地了解了 EM 促进的吸附剂的吸附和再生机制以及涉及的结构重排。
