HYDROGEN STORAGE IN ZEOLITIC MATERIALS: A FT-IR STUDY

In the last years zeolites have been often proposed as microporous materials for molecular hydrogen storage, exploiting either their ability to physisorb the gas or to trap it in their smaller cavities.
In order to understand the basic mechanisms of the H₂ / zeolite interactions which are at the basis of such phisisorption and trapping effects, the FT-IR spectroscopy at variable temperature (300 − 20 K) has been used to study the hydrogen adsorption in a large variety of zeolitic materials. Due to their high surface area, their great structural variety, the variable dimension and shape of the channels and cavities, and the presence of a variety of monovalent and divalent cations inside of them, zeolitic materials represent in fact an ideal play ground to test the role played by dispersion forces, local electric fields and overlap forces in hydrogen adsorption.
It was found that the spectra in the ν(HH) region depend on the nature of the framework as well as on the chemical properties of counterions. Experiments performed at variable temperature also allowed to calculate the H₂ adsorption enthalpy upon formation of 1:1 adducts with the strong acid sites of zeolites.