Thermodynamic studies on hydrogen adsorption on the zeolites Na-ZSM-5 and K-ZSM-5

Adsorption of dihydrogen onto the zeolites Na-ZSM-5 and K-ZSM-5 renders the fundamental H-H stretching mode infrared active. The corresponding infrared absorption bands were found at 4101 and 4112 cm(-1) for H-2/Na-ZSM-5 and H-2/K-ZSM-5, respectively. Thermodynamic characterization of the adsorbed state was carried out by means of variable-temperature infrared spectroscopy; simultaneously measuring integrated band intensity, temperature and equilibrium pressure of the gas phase. For the H-2/ Na-ZSM-5 system, the standard adsorption enthalpy and entropy resulted to be Delta H degrees = - 10.3 (+/- 0.5) kJ mol(-1) and AS degrees= -121 (+/- 10) J mol(-1) K-1. For H-2/K-ZSM-5 corresponding values were -9.1 (+/- 0.5) kj mol(-1) and -124 (+/- 10) J mol(-1) K-1, respectively. (c) 2004 Elsevier Inc. All rights reserved.