<![CDATA[Carbon capture from humid flue gas is problematic. Many microporous adsorbents are poisoned by water vapor. This research aims to study the effect of the Si/Al ratio on the competitive adsorption of CO₂ and H₂O in FAU-type zeolites, as well as evaluate their performance in capturing humid flue gases. Grand Canonical Monte Carlo (GCMC) simulations were performed to study the competitive adsorption of equimolar CO₂/H₂O mixtures at 298 K in two FAU zeolites: Zeolite 13X (Na₇₇, Si/Al ≈ 1.5) and Zeolite Y (Na₄₉, Si/Al≈2.92). The results showed that Zeolite 13X shows higher adsorption of CO₂ under low pressures, with the phenomenon of the roll-over occurring in the case of high pressure because of competitive adsorption with H₂O. In turn, the adsorption of CO₂ for Zeolite Y remained stable over the entire pressure range and exhibited lower H₂O uptake. Isosteric heats of CO₂ adsorption on the zeolites are 15.71 kcal/mol for Zeolite 13X and 13.23 kcal/mol for Zeolite Y. The energy of CO₂ binding in the presence of H₂O decreased by 1.14 kcal/mol for Zeolite 13X and for 2.03 kcal/mol for Zeolite Y. These findings indicate that high-silica FAU zeolites, such as Zeolite Y, are efficient CO₂ adsorbents. Copyright © 2026 by Authors, Published by Universitas Diponegoro and BCREC Publishing Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).]]>
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