Behavior of Adsorbed Hydrogen Molecules on Zeolites

A general model for hydrogen adsorption was derived using Ono-Kondo lattice theory. The maximum monolayer adsorption capacities of hydrogen molecules on zeolites of NaX, CaA, NaA, and ZSM-5 were determined by fitting experimental adsorption data at different temperatures to the general model. The interaction potential between hydrogen molecules and pore surface atoms in the zeolite was calculated using gas-surface Virial coefficients and the Lennard-Jones (12-6) potential model for cylindrical pores. Results show that the general model can correctly describe supercritical experimental adsorption data of hydrogen on zeolites. Maximum monolayer adsorption capacities of hydrogen molecules on zeolites are dependent on the type of zeolite but independent of temperature. The adsorption interaction potential of the hydrogen-zeolite obtained from the above cylindrical pore model and gas-surface Virial coefficients agrees with a previously reported isosteric heat of hydrogen on zeolites. Our results indicate that the adsorption of hydrogen into zeolite pores is predominately caused by physisorption and a hydrogen-hydrogen attractive interaction.