https://doi.org/10.1016/j.ccst.2021.100011
“Qin et al. studied the detail mechanism of CO2 capture by the (110) surface of K2CO3/TiO2. The co-adsorption of H2O and CO2 mainly occurred at the interfaces of K2CO3/TiO2, which followed a “two-step mechanism”, involving the dissociation of the chemisorbed H2O into OH and H, and the interaction between OH and the physisorbed CO2 to form HCO3. Besides, the dissociated H transferred through the interface and combined with CO32− to form bicarbonate. TiO2 support had a double functionality with respect to accelerating the carbonation process, namely, to offer more active sites between the K2CO3 and TiO2 interfaces and to promote H2O dissociation for increased OH coverage. Considering that H2O dissociation was the rate-determining step and the pivotal role of OH coverage, suggestions were made to select TiO(OH)2 support, dope suitable promoters and pretreat the K2CO3/TiO2 adsorbent to enhance the OH coverage for accelerated carbonation Qin et al., 2018). TiO2 also played an important role in facile regeneration of potassium-based adsorbents. Zhao et al. studied the role of TiO2 in CO2 desorption of KHCO3/TiO2/Al2O3 using DFT method. H2O molecules could be easily adsorbed on the (101) surface of TiO2 to form unstable intermediary TiO(OH)+ and OH−. Thereafter, TiO(OH)+ combined with HCO3− to form water and CO2, and OH− reacted with HCO3− to form water and CO32− (Eqs. 7–(9). Hence, the addition of TiO2 had changed the regeneration pathways, since the formed transition state TiO(OH)+ and OH− had accelerated HCO3− consumption. This would promote the CO2 desorption kinetics and reduce the energy demand for regeneration. It was suggested that humid atmosphere could be more suitable for facile regeneration of KHCO3/TiO2/Al2O3 (Zhao, W. et al., 2017).”
