High-temperature CO₂ sorption on Na₂CO₃-impregnated layered double hydroxides

Layered double hydroxide (LDH), one of representative high-temperature CO₂ sorbents, has many advantages, including stable CO₂ sorption, fast sorption kinetics, and low regeneration temperature. However, CO₂ sorption uptake on LDH is not high enough for practical use; thus it is usually enhanced by impregnation with alkali metals such as K₂CO₃. In this study, LDH was impregnated with Na₂CO₃, and analyses based on scanning electron microscopy, N₂ gas physisorption, in situ X-ray diffraction, and Fourier transform infrared spectroscopy were carried out to elucidate the characteristics of sorbents and the mechanism of CO₂ sorption. Although the surface area of LDH decreased after Na₂CO₃ impregnation, CO₂ sorption uptake was greatly enhanced by the additional basicity of Na₂CO₃. The crystal structure of Na₂CO₃ in the Na₂CO₃-impregnated LDH changed from monoclinic to hexagonal with increasing temperature, and the sorbed-CO₂ was stored in the form of carbonate. Thermogravimetric analysis was used to measure CO₂ sorption uptake at 200–600 °C. The sample of Na₂CO₃: LDH=0.35: 1 weight ratio had the largest CO₂ sorption uptake among the tested sorbents, and the CO₂ sorption uptake tended to increase even after 400 °C.