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 Adsorption of CO2 in FAU Zeolites: Effect of Zeolite Composition
Tác giả hoặc Nhóm tác giả: Ho Viet Thang, Lukáˇs Grajciar, Petr Nachtigall, Ota Bludsk´y, Carlos Otero Areán,Eva Fr´ydová, Roman Bulánek
Nơi đăng: Catalysis Today; Số: 227;Từ->đến trang: 50-56;Năm: 2013
Lĩnh vực: Khoa học; Loại: Bài báo khoa học; Thể loại: Quốc tế
TÓM TẮT
Many technological processes, mainly in the energy sector, require separation of carbon dioxide fromgas mixtures. For that purpose medium and large pore zeolites can be used, provided that the differen-tial CO2adsorption energy allows thermodynamic separation under equilibrium conditions. Hence theconvenience to have a precise knowledge (at the molecular level) about the factors that control CO2inter-action with zeolites, and faujasite-type zeolites in particular, are most relevant in this context on accountof their relatively high adsorption capacity. We report on a detailed spectroscopic, calorimetric and the-oretical study on the effect of composition on equilibrium CO2adsorption in alkali-metal exchangedfaujasite-type zeolites, which, by combining experimental results with calculations performed at theDFT/CC level on a periodic model of the zeolite yields fine details on the CO2adsorption complexes andcorresponding gas–solid interaction energy. The results obtained are discussed in the broader context ofother literature reports; showing, in particular, how the DFT/CC computational approach gives interac-tion energy values that are in better agreement with experimental data than those obtained using someother computational methods, which show larger limitations to account properly for dispersion inter-actions. We found out that: (i) dispersion interactions account for about 50% of the overall adsorptionenthalpy of CO2molecules in FAU zeolites, (ii) a very low (experimentally non-detectable) populationof sites III and IIIwas found for FAU zeolite with Si/Al ratio 2.55:1 and all CO2molecules are adsorbedon sites II and are tilted toward the zeolite wall due to the stabilizing effect of dispersion interactionsbetween CO2and zeolite, and (iii) minor heterogeneity of adsorption sites present in the FAU samplesoriginating from differences in the number and geometry of Al atoms in the 6R of sites II.
ABSTRACT
Many technological processes, mainly in the energy sector, require separation of carbon dioxide fromgas mixtures. For that purpose medium and large pore zeolites can be used, provided that the differen-tial CO2adsorption energy allows thermodynamic separation under equilibrium conditions. Hence theconvenience to have a precise knowledge (at the molecular level) about the factors that control CO2inter-action with zeolites, and faujasite-type zeolites in particular, are most relevant in this context on accountof their relatively high adsorption capacity. We report on a detailed spectroscopic, calorimetric and the-oretical study on the effect of composition on equilibrium CO2adsorption in alkali-metal exchangedfaujasite-type zeolites, which, by combining experimental results with calculations performed at theDFT/CC level on a periodic model of the zeolite yields fine details on the CO2adsorption complexes andcorresponding gas–solid interaction energy. The results obtained are discussed in the broader context ofother literature reports; showing, in particular, how the DFT/CC computational approach gives interac-tion energy values that are in better agreement with experimental data than those obtained using someother computational methods, which show larger limitations to account properly for dispersion inter-actions. We found out that: (i) dispersion interactions account for about 50% of the overall adsorptionenthalpy of CO2molecules in FAU zeolites, (ii) a very low (experimentally non-detectable) populationof sites III and IIIwas found for FAU zeolite with Si/Al ratio 2.55:1 and all CO2molecules are adsorbedon sites II and are tilted toward the zeolite wall due to the stabilizing effect of dispersion interactionsbetween CO2and zeolite, and (iii) minor heterogeneity of adsorption sites present in the FAU samplesoriginating from differences in the number and geometry of Al atoms in the 6R of sites II.
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