MOF-5 and activated carbons as adsorbents for gas storage

This paper reports comparatively the capacities of two activated carbons (ACs) and MOF-5 for storing gases. It analyzes, using similar equipments and experimental procedures, the density used to convert gravimetric data to volumetric ones, measuring the density (tap and packing at different pressures). It presents data on porosity, surface area and gas storage (H 2, CH 4 and CO 2) obtained under different temperatures (77 K and RT) and pressures (0.1, 4 and 20 MPa). MOF-5 presents lower volume of narrow micropores than both ACs, making its storage at RT lower, independently of the gas used (H 2, CH 4 and CO 2) and the basis of reporting data (gravimetric or volumetric). For H 2 at 77 K the reliability of the results depends too much on the density used. It is shown that the outstanding volumetric performance of MOF-5, in relation to ACs, is due to the use of an unrealistic high density (crystal density) that, not including the adsorbent inter-particle space, gives an apparently high volumetric gas storage capacity. When a density measured similarly in both types of adsorbents is used (e.g. tap or packing densities) MOF-5 presents, for all gases and conditions studied, lower adsorption capacities on volumetric basis and storage capacities than ACs. ► Adsorbents for gas storage applications. ► Effect of porosity and material density on the volumetric adsorption. ► Comparative study of gas storage in activated carbons and MOF-5. ► Carbon materials show better performance than MOF-5 for gas storage.