Selective Sorption of Olefins by Halogen-Substituted Macrocation-Polyoxometalate Porous Ionic Crystals

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• 作者：Sayaka Uchida ; Ryo Eguchi ; Shinnosuke Nakamura ; Yoshiyuki Ogasawara ; Noriyuki Kurosawa ; Noritaka Mizuno
• 刊名：Chemistry of Materials
• 出版年：2012
• 出版时间：January 24, 2012
• 年：2012
• 卷：24
• 期：2
• 页码：325-330
• 全文大小：360K
• 年卷期：v.24,no.2(January 24, 2012)
• ISSN：1520-5002

文摘

Ionic crystals [Cr₃O(OOCCH₂X)₆(H₂O)₃]₄[伪-SiW₁₂O₄₀]路14H₂O (X = Cl [Ia], Br [IIa]) are synthesized by complexation of halogen-substituted macrocations with a silicododecatungstate. Compounds Ia and IIa possess analogous one-dimensional winding channels, and the channel walls are composed of oxygen atoms of silicododecatungstates and 鈭扖H₂X groups of macrocations. Water of crystallization in Ia (IIa) is desorbed by the treatment in vacuo or under a dry N₂ or He flow at 298鈥?03 K, and the corresponding guest free phases Ib (IIb) are obtained. Propylene/propane and ethylene/ethane sorption ratios of Ib at 298 K and 100 kPa are 6.1 and 3.6, respectively. The ethylene/ethane sorption ratio of IIb at 298 K and 100 kPa is 2.8. These values are much larger than those of conventional sorbents. In situ¹³C MAS NMR spectra of ethylene or ethane sorbed in Ib suggest that host鈥揼uest interaction for ethylene is larger than that for ethane. DFT calculation and Monte Carlo simulation are carried out to elucidate the nature of the high ethylene/ethane sorption ratios: The bridging carboxylates (鈭扥OCCH₂X) are polarized by incorporation of highly electronegative halogens. Ethylene resides along the channel wall with the 蟽_h plane facing the channel wall, while ethane resides randomly in the channels of Ib and IIb. These results suggest that the olefin sorption is enhanced by electrostatic interaction between the 蟺-electron of olefins and highly polarized halogen-substituted macrocations and/or silicododecatungstates.

Keywords:

microporous materials; ionic crystal; ethylene/ethane separation; polyoxometalate