Critical Factors Driving the High Volumetric Uptake of Methane in Cu3(btc)2

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• 作者：Zeric Hulvey ; Bess Vlaisavljevich ; Jarad A. Mason ; Ehud Tsivion ; Timothy P. Dougherty ; Eric D. Bloch ; Martin Head-Gordon ; Berend Smit ; Jeffrey R. Long ; Craig M. Brown
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：August 26, 2015
• 年：2015
• 卷：137
• 期：33
• 页码：10816-10825
• 全文大小：575K
• ISSN：1520-5126

文摘

A thorough experimental and computational study has been carried out to elucidate the mechanistic reasons for the high volumetric uptake of methane in the metal鈥搊rganic framework Cu₃(btc)₂ (btc^{3鈥?/sup> = 1,3,5-benzenetricarboxylate; HKUST-1). Methane adsorption data measured at several temperatures for Cu₃(btc)₂, and its isostructural analogue Cr₃(btc)₂, show that there is little difference in volumetric adsorption capacity when the metal center is changed. In situ neutron powder diffraction data obtained for both materials were used to locate four CD₄ adsorption sites that fill sequentially. This data unequivocally shows that primary adsorption sites around, and within, the small octahedral cage in the structure are favored over the exposed Cu2+ or Cr2+ cations. These results are supported by an exhaustive parallel computational study, and contradict results recently reported using a time-resolved diffraction structure envelope (TRDSE) method. Moreover, the computational study reveals that strong methane binding at the open metal sites is largely due to methane鈥搈ethane interactions with adjacent molecules adsorbed at the primary sites instead of an electronic interaction with the metal center. Simulated methane adsorption isotherms for Cu₃(btc)₂ are shown to exhibit excellent agreement with experimental isotherms, allowing for additional simulations that show that modifications to the metal center, ligand, or even tuning the overall binding enthalpy would not improve the working capacity for methane storage over that measured for Cu₃(btc)₂ itself.}