Characterization of the carbonation reaction of potassium-based composite adsorbents for direct air capture of CO2

Direct air capture (DAC) represents a promising carbon capture technology for the reduction of CO2 concentrations from ambient air. However, the partial pressure of CO2 in the air of only 40 Pa and the high energy consumption involved in the process raise certain challenges to air capture. In response to the problem, many researchers have directed their attention towards the promising adsorbents of composite solid adsorbents, which are fabricated by impregnating metal oxides with K2CO3 for capturing CO2 from ambient air. But still, this method is fraught with a complex and energy-intensive adsorbent preparation process, together with a high desorption temperature. This study impregnated the micron-sized ZrO2 with a solution of tetrabutyl titanate, which was prepared as a support, and then impregnated it with K2CO3. The samples were first characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction methods. Then the composite adsorbents were subjected to testing in the process of CO2 adsorption from the air with a relative humidity of 75-85 %, followed by thermal desorption at 150 degrees C. It demonstrated that the composite adsorbent modified with tetrabutyl titanate containing 11 wt% K2CO3 exhibited the highest CO2 adsorption capacity of 0.64 mmol/g in the temperature-swing adsorption (TSA) cycles, indicating an advantageous adsorption capacity in DAC. The adsorption capacity stabilized at 0.45 mmol/g after 7 cycles, exhibiting a marked improvement over K2CO3/ZrO2 adsorbent. Analysis proved that the addition of tetrabutyl titanate enhanced the surface densification and heat resistance of ZrO2 and further increased the number of hydroxyl groups to facilitate the carbonation reaction. As a result, the adsorbents showed enhanced hydrophilicity, reactivity, and thermal stability. In light of the aforementioned characteristics of the composite adsorbents, namely the stable CO2 adsorption capacity values in the consecutive TSA cycles and a relatively low temperature required for both the adsorption and desorption, K2CO3 impregnated by ZrO2, which was modified with tetrabutyl titanate, could be considered for application in Direct Air Capture devices.