There is a great need to synthesize high-performance adsorbents for potential application in post-combustion CO 2 capture. In this study, molecular simulation was employed to mimic cation exchanges in 13X zeolite with different amounts of Li +, K +, and Ca 2+, providing guidance for the design of high-performance cation-exchanged zeolite. The separation performance of each cation-exchanged zeolite was evaluated in detail in terms of its pore volume, adsorption isotherm, energy, isosteric heat, and CO 2/N 2 selectivity. The simulated results showed that the fresh LiX-80 zeolite sample was the most promising adsorbent for CO 2/N 2 separation. On this basis, a novel polymetallic cation-exchanged zeolite was developed by introducing Pd 2+ and Ag + into LiX-80 (LiPdAgX). LiPdAgX exhibited a higher CO 2 loading and higher CO 2/N 2 selectivity than 13X and LiX-80 zeolites. Finally, adsorption experiments were performed on the 13X, LiX, and LiPdAgX zeolites, and the order of the experimental results (13X < LiX < LiPdAgX) agrees well with the simulated order. This study provides microscopic-level insights into gas adsorption and separation in polymetallic cation-exchanged zeolites, and suggests that LiPdAgX zeolite can effectively enhance CO 2 capture.