K₂CO₃-containing composite sorbents based on a ZrO₂ aerogel for reversible CO₂ capture from ambient air

In this work, K₂CO₃-containing composite materials were synthesized based on a mesoporous zirconia aerogel prepared by an epoxide-assisted sol-gel method using supercritical drying in ethanol. The porous ZrO₂ was impregnated with an aqueous solution of potassium carbonate to obtain composite materials with K₂CO₃ weight content ranging from 9 to 29 wt%. All the composites were tested in the process of CO₂ absorption from the air with a relative humidity of 25% followed by thermal desorption at 200 °C. The samples after the CO₂ absorption step were characterized by Fourier transform infrared spectroscopy and X-ray diffraction methods. Among the materials studied, the composite sorbent containing 23 wt% K₂CO₃ demonstrated the highest dynamic CO₂ absorption capacity (4.6 wt%) in the temperature-swing absorption (TSA) cycles. The results indicate that a certain part of K₂CO₃ loaded into zirconia mesopores forms surface species which do not actively participate in the CO₂ absorption and desorption processes. For the composite K₂CO₃/ZrO₂ material with the optimal K₂CO₃ loading, CO₂ absorption capacity is higher compared to the values obtained for K₂CO₃/γ-Al₂O₃ composite sorbents studied under the same conditions. Taking into account that this material demonstrates stable CO₂ absorption capacity values in the consecutive TSA cycles and needs a relatively low temperature for regeneration, it should be considered for application in Direct Air Capture units.