Hydrogen adsorption equilibrium and kinetics in metal–organic framework (MOF-5) synthesized with DEF approach

Abstract

MOF-5, also known as isoreticular MOF-1 (IRMOF-1) was successfully synthesized with diethyl formamide (DEF) as a solvent using modified procedures aiming at improving its crystal structure, pore texture and ultimately the hydrogen adsorption performance. The MOF-5 adsorbent was characterized with nitrogen adsorption for pore textural properties, scanning electron microscopy for crystal structure, and XRD for phase structure. Hydrogen adsorption in MOF-5 was measured at low pressure in a volumetric unit at 77 K, 194.5 K and 298 K and at hydrogen pressure up to 120 bar and 77 K in a gravimetric adsorption unit. The MOF-5 synthesized in this work has ideal pore textural properties with a large Langmuir (3917 m 2/g) and BET specific surface area (2449 m 2/g), a median pore size of 8.6 Å and a pore volume of 1.39 cm 3/g. The MOF-5 adsorbent synthesized in this work has a hydrogen adsorption capacity of 1.46 wt.% at 77 K and 1 bar, an excess hydrogen adsorption capacity of 6.9 wt.% at 77 K and 100 bar, and an absolute hydrogen adsorption capacity of 11.8 wt.% at 77 K and 120 bar. Hydrogen diffusivity in MOF-5 estimated from the adsorption kinetic data measured at low pressure are 2.4 × 10 −5 cm 2/s, 5.2 × 10 −5 cm 2/s and 6.0 × 10 −5 cm 2/s at 77 K, 194.5 K and 298 K, respectively. The activation energy for hydrogen diffusion and the isosteric heat of adsorption for hydrogen adsorption in MOF-5 are 0.8 kJ/mol and 2.2–2.6 kJ/mol, respectively.