Understanding Carbon Dioxide Adsorption on Univalent Cation Forms of the Flexible Zeolite Rho at Conditions Relevant to Carbon Capture from Flue Gases

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• 作者：Magdalena M. Lozinska ; Enzo Mangano ; John P. S. Mowat ; Ashley M. Shepherd ; Russell F. Howe ; Stephen P. Thompson ; Julia E. Parker ; Stefano Brandani ; Paul A. Wright
• 刊名：The Journal of the American Chemical Society
• 出版年：2012
• 出版时间：October 24, 2012
• 年：2012
• 卷：134
• 期：42
• 页码：17628-17642
• 全文大小：737K
• 年卷期：v.134,no.42(October 24, 2012)
• ISSN：1520-5126

文摘

A series of univalent cation forms of zeolite Rho (M_9.8Al_9.8Si_38.2O₉₆, M = H, Li, Na, K, NH₄, Cs) and ultrastabilized zeolite Rho (US-Rho) have been prepared. Their CO₂ adsorption behavior has been measured at 298 K and up to 1 bar and related to the structures of the dehydrated forms determined by Rietveld refinement and, for H-Rho and US-Rho, by solid state NMR. Additionally, CO₂ adsorption properties of the H-form of the silicoalumino-phosphate with the RHO topology and univalent cation forms of the zeolite ZK-5 were measured for comparison. The highest uptakes at 0.1 bar, 298 K for both Rho and ZK-5 were obtained on the Li-forms (Li-Rho, 3.4 mmol g^鈥?; Li-ZK-5, 4.7 mmol g^鈥?). H- and US-Rho had relatively low uptakes under these conditions: extra-framework Al species do not interact strongly with CO₂. Forms of zeolite Rho in which cations occupy window sites between 伪-cages show hysteresis in their CO₂ isotherms, the magnitude of which (Na⁺,NH₄⁺ < K⁺ < Cs⁺) correlates with the tendency for cations to occupy double eight-membered ring sites rather than single eight-membered ring sites. Hysteresis is not observed for zeolites where cations do not occupy the intercage windows. In situ synchrotron X-ray diffraction of the CO₂ adsorption on Na-Rho at 298 K identifies the adsorption sites. The framework structure of Na-Rho 鈥渂reathes鈥?as CO₂ is adsorbed and desorbed and its desorption kinetics from Na-Rho at 308 K have been quantified by the Zero Length Column chromatographic technique. Na-Rho shows much higher CO₂/C₂H₆ selectivity than Na-ZK-5, as determined by single component adsorption, indicating that whereas CO₂ can diffuse readily through windows containing Na⁺ cations, ethane cannot.