Hydrogen storage in ion-exchanged zeolites

The hydrogen storage properties of zeolites X, Y, A and Rho containing various exchangeable cations have been investigated. All hydrogen storage capacities were measured at a temperature of - 196 degrees C and a pressure range of 0-15 bar, using a constant pressure thermogravimetric analyser. The results show that, zeolites exhibit diverse behaviour with respect to hydrogen uptake, dependent on both the framework structure and the nature of the cations present. A major factor influencing uptake is the available void space: in zeolites A and Rho pore blocking by large extraframework cations is a major factor restricting hydrogen uptake, but in zeolites X and Y, blocking does not occur. This study also suggests that cations may act as binding sites for hydrogen molecules. For zeolites X and Y, hydrogen uptake relates closely to the measured BET surface area. The highest gravimetric storage capacity of 2.19 wt.% was obtained for CaX. Volumetric storage densities of up to 31.0 kg H-2/m(3) (143 H-2 molecules/unit cell) and 30.2 kg H-2/m(3) (144 H-2 molecules/unit cell) were achieved for CaX and KX, respectively. (c) 2005 Elsevier B.V. All rights reserved.