Adsorption of hydrogen in zeolite NaX and its nickel and rhodium exchanged forms were investigated at 77.4 K using a static volumetric adsorption system up to 1 bar, and at 303 and 333 K in a gravimetric adsorption system up to S bar. Hydrogen adsorption at 77.4 K for NaX and the nickel and rhodium exchanged zeolite X was found to be reversible with pressure. However, chemisorption of hydrogen was observed at 303 and 333 K. The highest adsorption capacities for hydrogen in NaX, NiNaX and RhNaX were observed to be 24.28, 34.51 and 51.85 molecule/u.c at 333K and 5 bar. Hydrogen uptake capacities of the nickel and rhodium exchanged zeolite X at 303 and 333 K were found increasing initially up to 70% of nickel and 55% of rhodium exchange, beyond which it showed a decreasing trend. The observed decrease in adsorption capacity at higher Ni and Rh cation exchange is explained in terms of partial degradation of the zeolite structure during cation exchange and the high temperature vacuum dehydration process. Grand Canonical Monte Carlo simulations were also performed to study the adsorption of hydrogen in NaX as well as nickel and rhodium exchanged zeolites X at 77.4, 303 and 333 K and the simulated data were compared with experimentally measured values. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.