MCM-22 and its related structures MCM-36 and ITQ-2, as well as Fe-substituted MCM-22 (Fe-MCM-22), were synthesized and evaluated collectively as a CO2 capturing agent with or without post-synthesis amine (NH2)-functionalization. The amount of the grafted amine was measured by elemental analysis (EA), and the corresponding properties of the zeolite samples were examined by XRD, SEM, and BET surface area measurement. CO2 adsorption isotherms of the zeolites were obtained at 273, 298, and 303 K, and the corresponding heats of adsorption were estimated by the Clausius-Clapeyron equation. CO2 adsorption capacity varied in the sequence of MCM-22 (2.09) > NH2-ITQ-2 (1.73) > ITQ-2 (1.64) > NH2-MCM-22 (1.52) > MCM-36 (1.32) > NH2-MCM-36 (1.20) > Fe-MCM-22 (1.20 mmol/g) at 298 K. For the zeolites without amine-grafting, aluminum content was the governing factor determining the adsorption capacity. Fe-MCM-22 resulted in low CO2 adsorption due to its low surface area. Amine-grafting on zeolites in general resulted in an enhancement in CO2/N-2 selectivity and increased heats of CO2 adsorption at the expense of reduction in CO2 capture capacity. NH2-ITQ-2 showed exceptionally high CO2/N-2 selectivity (10.8) accompanied by the best separation capacity (0.88 mmol/g) among the samples in the fixed bed breakthrough curve analyses. Cyclic CO2 adsorption-desorption performance of the samples were examined by TGA in a flow system, and were found to exhibit stable cyclic runs. (C) 2012 Elsevier Ltd. All rights reserved.