Structure and Guest Dynamics in Binary Clathrate Hydrates of Tetrahydropyran with Carbon Dioxide/Methane

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• 作者：Thaneer Malai Narayanan ; Kazuki Imasato ; Satoshi Takeya ; Saman Alavi ; Ryo Ohmura
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：November 19, 2015
• 年：2015
• 卷：119
• 期：46
• 页码：25738-25746
• 全文大小：433K
• ISSN：1932-7455

文摘

Binary structure II (sII) clathrate hydrates of tetrahydropyran (THP) with methane and carbon dioxide are synthesized and characterized with powder X-ray diffraction (PXRD) and molecular dynamics (MD) simulations. Analysis of PXRD results shows that 83% of the small 12-sided (dodecahedral, D) sII cages are occupied by CO₂ in CO₂ + THP hydrate, whereas 93% of the D cages are occupied by CH₄ in CH₄ + THP hydrate. The effects of the tighter fit of CO₂ molecules in the D cages of the binary hydrate were observed in longer lattice constants and lower cage occupancies compared to binary THP hydrates with CH₄ molecule in the D cage. MD simulations of 1,4-twist-boat and chair conformers of the THP in the sII clathrate hydrate phase with the CO₂ and CH₄ help gases are performed at temperatures between 153 to 250 K. Simulations suggest shape and size of D cage guest molecules does not affect the conformation of H cage guest molecule, but the steric repulsions between CO₂ molecule and cage鈥檚 water molecules limits its motion and promotes interaction between H cage guest molecule and the cage at higher extent compared to CH₄ molecule.