CO₂ retention ability on alkali cation exchanged titanium silicate, ETS-10

ETS-10 was ion exchanged by various alkali cations (Li+, Na+, K+, Rb+ and Cs+) and the BET surface area and pore volume was exactly consistent with cationic size; that is, in the order of Li+ > Na+ > K+ > Rb+ > Cs+. It was observed that a single point adsorption capacity was inversely proportional to cationic size. The largest CO2 capacity was observed for Li+-ETS-10 and it is attributed to greater cation-quadrupole interactions with CO2 than larger cation. The results also suggests that as the CO2 loading is increased, the accessibility of adsorbing CO2 to framework basic O- sites should have become difficult with the increase in cationic size due to the blocking effect by extra-framework CO2-M+. The slight decrease in the slope of adsorption capacity with temperature, especially beyond 373 K for Li+-ETS-10 and K+-ETS-10 suggests that the adsorption of CO2 on small alkali cation exchanged-ETS-10 at high temperature is somewhat associated with basic oxygen anion sites in framework due to the existence of large pore. The CO2-TPD results show that the amount of desorbed CO2 at higher temperature was proportionally increased due to the increased basicity of oxygen anions in framework. It also shows that the desorption temperature associated with alkali cations in extra-framework (corresponding to low temperature desorption peak) has been lowered with the increase in cationic size, indicating weak cation-quadrupole interactions with CO2 for larger cations.