The separation of carbon dioxide (CO₂) and methane (CH₄) in zeolite is significantly influenced by extra-framework cations. Through grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations, the adsorption and diffusion properties of CO₂ and CH₄ in diverse M-ZSM-5 zeolites (M = Li, Na, and K) were analyzed. Metal cations, especially at low pressures, enhance the adsorption of CO₂. Also, Li-ZSM-5 exhibits the highest CO₂ loading, followed by Na-ZSM-5 and K-ZSM-5. However, the interaction between CH₄ and the cations is relatively insignificant. For binary mixtures, CO₂ dominates the competitive adsorption process. Also, M-ZSM-5 zeolites offer superior adsorption selectivity compared to silicalite-1, with a trend of Li-ZSM-5 > Na-ZSM-5 > K-ZSM-5. Additionally, MD simulations revealed that the metal cations will limit the diffusion of molecules. The combined effect of interaction and spatial constraint induced by cations has a joint influence on the diffusion of CO₂, and the self-diffusion coefficients in three models are close.

中文翻译：

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阳离子交换 ZSM-5 沸石中 CO2/CH4 吸附和扩散特性的分子洞察

沸石中二氧化碳(CO ₂ )和甲烷(CH ₄ )的分离受骨架外阳离子的显着影响。通过大正则蒙特卡罗（GCMC）和分子动力学（MD）模拟，分析了CO ₂和CH ₄在不同M-ZSM-5沸石（M = Li、Na和K）中的吸附和扩散特性。金属阳离子，特别是在低压下，增强CO ₂的吸附。此外，Li-ZSM-5表现出最高的CO ₂负载量，其次是Na-ZSM-5和K-ZSM-5。然而，CH ₄和阳离子之间的相互作用相对不显着。对于二元混合物，CO ₂主导竞争吸附过程。此外，与silicalite-1相比，M-ZSM-5沸石具有优异的吸附选择性，其趋势为Li-ZSM-5 > Na-ZSM-5 > K-ZSM-5。此外，MD模拟表明金属阳离子会限制分子的扩散。阳离子引起的相互作用和空间约束的综合作用对CO ₂的扩散产生共同影响，并且三个模型的自扩散系数接近。