Controlling the Adsorption Enthalpy of CO2 in Zeolites by Framework Topology and Composition

Zeolites are often investigated as potential adsorbents for CO2 adsorption and separation. Depending on the zeolite topology and composition (Si/Al ratio and extra-framework cations), the CO2 adsorption heats at low coverages vary from -20 to -60 kJ?mol-1, and with increasing surface coverage adsorption heats either stay approximately constant or they quickly drop down. Experimental adsorption heats obtained for purely siliceous porous solids and for ion-exchanged zeolites of the structural type MFI, FER, FAU, LTA, TUN, IMF, and -SVR are discussed in light of results of periodic density functional theory calculations corrected for the description of dispersion interactions. Key factors influencing the stability of CO2 adsorption complexes are identified and discussed at the molecular level. A general model for CO2 adsorption in zeolites and related materials is proposed and data reported in literature are evaluated with regard to the proposed model.