Encapsulation of molecular hydrogen in ion-exchanged a zeolites at 1 atm

Abstract

About 1.5 and 2.0 μmol/g of molecular HZ is encapsulated in the sodalite and supercages, respectively, of NaA zeolite at 1 atm H2 pressure and temperatures higher than 200°C. At 37°C and 1 atm Hz pressure, encapsulation of molecular H2 occurs only in the supercages. For these conditions, equilibrium (2.3 μmol/g) is obtained only after 24 h of sorption in HZ flow. The site of encapsulation of H2 is probed by exchanging Cs+, Ni2+, and Eu3+ for Na+ cations into the supercage, near the six-membered oxygen window, and sodalite cage, respectively, of zeolite A. The removal of H2 encapsulated in NaA can be studied by programming the temperature in 1 atm Ar gas flow. This method provides an apparent activation energy for diffusion of 26.0 and 11.5 kcal/mol for the H2 encapsulated in the sodalite and supercages, respectively, of NaA zeolite. Diffusivities of H2 for NaA and Eu/NaA zeolites have been determined from isothermal uptake data. © 1992.