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

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 it...