Structural Transitions in the MIL-53(Al) Metal–Organic Framework upon Cryogenic Hydrogen Adsorption

Abstract

The energetics and phase behavior of the MIL-53­(Al) metal–organic framework upon low-temperature (15–260 K), subatmospheric H2 adsorption are studied experimentally using a volumetric technique and theoretically by grand canonical Monte Carlo simulation. The adsorption equilibrium data are recorded for a fixed amount of H2 in the system at stable increasing temperature steps starting from 15 K while recording the equilibrium pressure attained at each step. The adsorption isotherms are generated by repeating the experiments for different fixed amounts of adsorbate in the system and connecting the equilibrium points obtained at the same temperature. The solid–fluid interactions are modeled using the TraPPE-UA force field and the fluid–fluid interactions using a parametrization consistent with the same force field; quantum effects on H2 adsorption are taken into account via a quartic approximation of the Feynman–Hibbs variational approach. The use of a consistent force field with proven transferability of its parameters provides an accurate description of the experimental adsorption equilibria and isosteric heats of adsorption. Because of the weak solid–fluid interaction, the Henry constant for H2 adsorption in the large-pore (LP) form of MIL-53­(Al) surpasses that for H2 adsorption in the narrow-pore (NP) form at a temperature lower than that at which the dehydrated structure of the material collapses. However, the saturation capacity of the LP form is always higher than that of the NP phase. The phase behavior of MIL-53­(Al) upon temperature-induced H2 desorption is interpreted in terms of the osmotic thermodynamic theory. For the conditions spanned in the experiments MIL-53­(Al) exhibits at most a single structural transition and its phase behavior depends not only on pressure and temperature but also on the thermal history of the bare material.

Surface Area and Porosity of Co3(ndc)3(dabco) Metal–Organic Framework and Its Methane Storage Capacity: A Combined Experimental and Simulation Study

“…In fact, as shown below, no reparameterization of the solid–fluid interaction parameters for the CH 4 @Co 3 (ndc) 3 (dabco) system is needed when this force field is used. This is in accordance with our previous work on the adsorption of CH 4 , C 2 H 4 , C 2 H 6 , and H 2 in MIL-53­(Al) MOF. ,, In TraPPE-UA, all CH x groups are treated as pseudo-atoms and the nonbonded interactions are governed by a (12,6) LJ potential plus a fixed-point charge Coulombic form . Unlike LJ interactions are computed using the Lorentz–Berthelot combining rules .…”

“…This is in accordance with our previous work on the adsorption of CH 4 , C 2 H 4 , C 2 H 6 , and H 2 in MIL-53(Al) MOF. 40,41,47 In TraPPE-UA, all CH x groups are treated as pseudo-atoms and the nonbonded interactions are governed by a (12,6) LJ potential plus a fixed-point charge Coulombic form. 48 the Lorentz−Berthelot combining rules.…”

“…The good predictions obtained with the TraPPE-UA force field appear to confirm its transferability to different MOFs, as we have previously observed for CH 4 , C 2 H 4 , C 2 H 6 , and H 2 adsorption in MIL-53(Al). 40,41,47 It thus seems that the good balance between enthalpic and entropic contributions to the free energy in the TraPPE-UA force field makes it transferable to different physical conditions, including those where the "solvent" is a rigid lattice dominated by an organic ligand in which the metal atoms are more or less shielded from the influence of the adsorbate molecules by organic or inorganic groups (in this case, the oxygens and hydroxyl groups of the inorganic octahedra).…”

Adsorption of Carbon Dioxide, Methane, and Nitrogen on Zn(dcpa) Metal-Organic Framework

“…Zn(dcpa) is an example of such materials. In these cases, an "osmotic subensemble" [15,[39][40][41][42] can be employed to describe the equilibrium between host structures when exposed to gaseous adsorbates. Alternatively, Ghysels et al [42] proposed another free energy model able to describe the thermodynamics of breathing phenomena in flexible materials.…”

Theoretical Model and Numerical Simulation of Adsorption and Deformation in Flexible Metal–Organic Frameworks

“…The aforementioned deformation and structural transition in flexible MOFs that are induced by adsorption have been studied both experimentally and theoretically. − Coudert et al studied gas adsorption and the structural transition that it induces in such materials by formulating the problem based on the thermodynamics of the system and calculated the variation of the free energy of the system during the phase transition in the structure of the material. Neimark et al .…”