Hydrogen Adsorption in Metal-Organic Framework MIL-101(Cr)-Adsorbate Densities and Enthalpies from Sorption, Neutron Scattering, In Situ X-ray Diffraction, Calorimetry, and Molecular Simulations
Hydrogen Adsorption in Metal-Organic Framework MIL-101(Cr)-Adsorbate Densities and Enthalpies from Sorption, Neutron Scattering, In Situ X-ray Diffraction, Calorimetry, and Molecular Simulations
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DOI：
10.1021/acsaem.1c01196
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发表时间：
2021-08-10
影响因子：
6.4
通讯作者：
Ting, Valeska P.
中科院分区：
文献类型：
--
作者：
Bimbo, Nuno;Zhang, Kang;Ting, Valeska P.
本文通过吸附实验、实验等温线模拟、差示扫描量热法(DSC)、中子散射、原位同步辐射粉末X射线衍射和分子模拟等方法研究了氢在金属-有机骨架MIL-101(Cr)中的吸附。77K下H-2在材料中吸附的分子模拟与由实验等温线确定的过量吸收有很好的一致性。模拟还表明，低气压下H-2的吸附主要集中在0.7 nm的超四面体中，随着压力的增加，H-2开始在小的(2.9 nm)和大的(3.4 nm)笼中积累。非弹性中子散射结果表明，与相同条件下微孔碳的吸氢实验结果不同，MIL-101(Cr)的孔内没有H-2或更高密度的H-2相吸附。这表明，随着压力的增加，MIL-101(Cr)的吸附密度保持不变，但吸附体积增加；较高的吸氢密度要求孔径小于0.7 nm，这是MIL-101(Cr)中最小的孔尺寸。用Clapeyron方程模拟计算了该材料的吸附热，直接量热法在零覆盖度下与其他两种方法符合得很好。当覆盖率达到6wt%时，模拟结果与Clapeyron方程也符合得很好。
In this paper, hydrogen adsorption in metal-organic framework MIL-101(Cr) is investigated through a combination of sorption experiments, modeling of experimental isotherms, differential scanning calorimetry (DSC), neutron scattering, in situ synchrotron powder X-ray diffraction, and molecular simulations. The molecular simulations at 77 K for H-2 adsorption in the material show excellent correspondence with excess uptakes determined from experimental isotherms. The simulations also indicate that H-2 adsorption at a low pressure is mainly located in the 0.7 nm supertetrahedron and that, with increasing pressure, H-2 starts to accumulate in the small (2.9 nm) and large (3.4 nm) cages. The inelastic neutron scattering results show that, in contrast to reports for hydrogen adsorption under the same conditions for microporous carbons, there is no solid-like H-2 or any higher density H-2 phases adsorbed in the pores of MIL-101(Cr). This indicates that, with increasing pressures, the adsorbed density of the MIL-101(Cr) remains constant but the volume of adsorbate increases and that higher densities for adsorbed hydrogen require pore sizes smaller than 0.7 nm, which is the size of the smallest pore in MIL-101(Cr). The enthalpies of adsorption are also investigated for this material using simulations, the Clapeyron equation applied to the isosteres and DSC, with the direct calorimetric method showing good agreement at zero coverage with the other two methods. The simulations and the Clapeyron equation are also in good agreement up to 6 wt % coverage.