Molecular Basis for the High CO 2 Adsorption Capacity of Chabazite Zeolites

CO 2 adsorption in Li‐, Na‐, K‐CHA (Si/Al=6,=12), and silica chabazite zeolites was investigated by powder diffraction. Two CO 2 adsorption sites were found in all chabazites with CO 2 locating in the 8‐membered ring (8MR) pore opening being the dominant site. Electric quadrupole‐electric field gradient and dispersion interactions drive CO 2 adsorption at the middle of the 8 MRs, while CO 2 polarization due to interaction with cation sites controls the secondary CO 2 site. In Si‐CHA, adsorption is dominated by dispersion interactions with CO 2 observed on the pore walls and in 8 MRs. CO 2 adsorption complexes on dual cation sites were observed on K‐CHA, important for K‐CHA‐6 samples due to a higher probability of two K + cations bridging CO 2 . Trends in isosteric heats of CO 2 adsorption based on cation type and concentration can be correlated with adsorption sites and CO 2 quantity. A decrease in the hardness of metal cations results in a decrease in the direct interaction of these cations with CO 2 .