The impact of metal centers in the M-MOF-74 series on carbon dioxide and hydrogen separation

The series of metal–organic frameworks M-MOF-74 gained popularity in the field of capture and separation of CO2 due to the presence of numerous, highly reactive open-metal sites. The description of effective interactions between guest molecules and open-metal sites without accounting for polarization effects is challenging but it can significantly reduce the computational cost of simulations. In this study, we propose a non-polarizable force field for CO2, and H2 adsorption in M-MOF-74 (M = Ni, Cu, Co, Fe, Mn, Zn) by scaling the Coulombic interactions of M-MOF-74 atoms, and Lennard-Jones interaction potentials between the center of mass of H2 and the open-metal centers. The presented force field is based on UFF and DREIDING parameters, characterized by high transferability and efficiency. The quantum behavior of H2 at cryogenic temperatures is considered by incorporating Feynman–Hibbs quantum corrections. To validate the force field, the experimental isotherms of CO2 at 298 K and 10−1 – 102kPa, the isotherms of H2 at 77 K and 10−5 – 102kPa, the corresponding enthalpy of adsorption, and the binding geometries in the M-MOF-74 series were reproduced using Monte Carlo simulations in the grand-canonical ensemble. The computed loadings, heats of CO2 and H2 adsorption, and binding geometries in M-MOF-74 are in very good agreement with the experimental values. The temperature transferability of the force field from 77 K to 87 K, and 298 K was shown for adsorption of H2. The validated force field was used to study the adsorption and separation of CO2/H2 mixtures at 298 K. The adsorption of H2 practically does not occur when CO2 is present in the mixture. As indicated from simulated breakthrough curves, the breakthrough time of CO2 in M-MOF-74 follows the same order a
Engineering Thermodynamics