Low‐Temperature Adsorption/Storage of Hydrogen on FAU, MFI, and MOR Zeolites with Various Si/Al Ratios: Effect of Electrostatic Fields and Pore Structures

Abstract

Several zeolites, such as faujasite, mordenite, and ZSM‐5, with various aluminum contents have been used to analyze the effect of aluminum or cation concentration (strength of electrostatic field) on hydrogen adsorption at low temperature. Irrespective of the zeolite structure, the adsorption capacity, isosteric heat of adsorption (−ΔHads), surface coverage, and micropore occupancy increase with increasing aluminum content of a zeolite. Zeolites with a higher amount of aluminum favorably adsorb hydrogen at relatively low pressures. For zeolites with similar aluminum contents, the adsorption capacity, isosteric heat of adsorption, surface coverage, and micropore occupancy are in the order of mordenite>ZSM‐5>faujasite, probably due to differing pore sizes and the presence or absence of pore intersections. This work demonstrates that zeolites with strong electrostatic fields and narrow pores without intersections are beneficial for high hydrogen uptake.

Ab Initioinvestigation of the interaction of H2with lithium exchanged low-silica chabazites

“…In agreement with experimental findings [31], computed data show that the adsorption capacity increases with increasing the Al content of the zeolite. However, the overall effect is more related to the availability of exposed cation than to the role played by the increased ionicity of the zeolitic framework.…”

Chemical and Physical Solutions for Hydrogen Storage

“…For faujasite, a capacity of 172 cm 3 (STP) g À1 , corresponding the about 1.5 wt %, has been reported, [16] but even these capacities fall short of technically relevant values. A low Si/Al ratio and smaller pores is beneficial for high loading in such compounds, [16] but even if such considerations are taken into account, technically relevant capacities cannot be expected using zeolites. The zeolitic material with the highest micropore volume to date is ITQ-33, [17] for which a pore system of 0.37 cm 3 g À1 has been predicted for the pure silica polymorph.…”

“…Storage capacities substantially increase at À196 8C. For faujasite, a capacity of 172 cm 3 (STP) g À1 , corresponding the about 1.5 wt %, has been reported, [16] but even these capacities fall short of technically relevant values. A low Si/Al ratio and smaller pores is beneficial for high loading in such compounds, [16] but even if such considerations are taken into account, technically relevant capacities cannot be expected using zeolites.…”

Physisorption in Porous Materials

“…Beyond the specific surface area the interaction of hydrogen molecules with zeolites is strongly influenced by the type and the concentration of cations present in the framework channels. This is well reflected by, for example, the increase in the isosteric heat of adsorption in zeolites with increasing aluminum concentration, irrespective of the framework structure [75]. Since a higher Al concentration leads to a higher amount of cations in the framework the stronger interaction with H 2 can be directly correlated to the presence of polarizing cationic centers.…”