The Origin of Selective Adsorption of CO₂ on Merlinoite Zeolites

Abstract

Abstract The CO 2 adsorption behavior at 25–75 °C and 0–1.0 bar of various alkali cation‐exchanged forms of merlinoite (framework type MER) zeolites with Si/Al=2.3 and 3.8 is described. The adsorption isotherms at 25 °C on the Na + , K + , Rb + , and Cs + forms of MER zeolite with Si/Al=2.3 are characterized by a clear step, the CO 2 pressure of which differs notably according to the type of their extraframework cations. Structural analysis shows that CO 2 adsorption on the former three zeolites includes the relocation of gating cations with high site occupancy and the remarkable concomitant structural breathing. We define this unusual adsorption phenomenon as a cooperative cation gating‐breathing mechanism. The overall results suggest that the actual mechanism of selective CO 2 adsorption on intermediate‐silica small‐pore zeolites can change from cation gating to cooperative cation gating‐breathing to breathing, depending on a combination of their topological and compositional flexibilities.