Interfacial Interactions Govern the Mechanisms of CO2 Absorption and Desorption on A2CO3-Promoted MgO (A = Na, K, Rb, and Cs) Absorbents

Abstract

In this study, we investigated the detailed mechanisms of CO2 absorption and desorption on A2CO3-promoted MgO absorbents (A = Na, K, Rb, and Cs). We analyzed the materials formed at various stages of the absorbents during CO2 absorption and desorption by thermal decomposition-gas chromatography/mass spectroscopy, in situ IR spectroscopy, solid-state magic-angle spinning NMR spectroscopy on 13C, 23Na, 25Mg, and 39K nuclei, diffuse reflectance UV–vis spectroscopy, and in situ X-ray diffraction as well as the conventional thermogravimetric analysis, ex situ X-ray diffraction, and elemental distribution mapping by energy-dispersive X-ray analysis using scanning electron microscopy. The absorption of CO2 of the absorbents occurs in two steps. The first step is a fast process involving basic sites on the MgO surface formed by the interaction between A2CO3 and MgO. Because the basicity of these sites depends on the size of A ion, the kinetics and capacity of CO2 absorption and the desorption properties of this p...