Alkali Carbonate Molten Salt Coated Calcium Oxide with Highly Improved Carbon Dioxide Capture Capacity

Abstract CO 2 reduction is crucial if the effects of this gas on global warming are to be alleviated. We report for the first time an alkali carbonate molten salt promoted CaO‐based CO 2 sorbent with CO 2 capture performance superior to that of neat CaO. The influences of chemical composition, loading, and melting temperature of the (Li–Na–K) 2 CO 3 molten salts and of the calcination and adsorption temperatures on CO 2 capture were evaluated systematically. The microstructural and morphological evolution of the samples during CO 2 adsorption was studied by X‐ray diffraction, scanning electron microscopy, and Fourier‐transform infrared spectroscopy analyses. The (Li–K) 2 CO 3 molten salt coating was found not only to promote CO 2 uptake but also to facilitate CO 2 desorption from CaO. In particular, at low temperatures of 500 and 600 °C, the CO 2 capture capacity increased significantly from 1.19 and 3.26 mmol g −1 to 6.93 and 10.38 mmol g −1 , respectively. The melting point of the molten salts was also a crucial factor in the improvement of CO 2 uptake. Kinetic studies based on fractal‐like models indicated that the rate coefficients for (Li–K) 2 CO 3 /CaO were approximately 3.3 to 3.8 times larger than those for neat CaO. The coating of alkali carbonate molten salts is believed to prevent the formation of a rigid CaCO 3 layer on the surface of the CaO particles and to provide continuous delivery of CO 3 2− to promote CO 2 capture. During the CO 2 adsorption/desorption cycling tests, (Li–K) 2 CO 3 /CaO resulted in a stable and reversible CO 2 uptake of 6.0–6.3 mmol g −1 , which is much higher than that of neat CaO (2.0 mmol g −1 ).