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

Abstract

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 . 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.

Optimization and Synthesis of a La-TMA MOF with Some Improvements in Its Properties

“…In Figure c–f shown is the equally uniform distribution of all elements. A little bit of physically adsorbed molecules and solvents that were trapped in the pores of open channels in the main backbone of the La-TMA MOF, during the heating procedure and by increasing the temperature, − were removed the framework, simultaneously (this step is an endothermic procedure as exhibited in the DSC curve that is shown in Figure b). The onset decomposition temperature of the La-TMA MOF is ∼350 °C, and the peak is at 405.86 °C as shown in the TGA/DTG curves of the La-TMA MOF (Figure a).…”