Grand Canonical Monte Carlo (GCMC) method was employed to simulate the adsorption properties of molecular hydrogen on ion-exchanged X zeolites at 100–293？K and pressures up to 10？MPa in this paper. The effect of cation type, temperature, and pressure on hydrogen adsorption capacity, heat of adsorption, adsorption sites, and adsorption potential energy of ion-exchanged X zeolites was analyzed. The results indicate that the hydrogen adsorption capacity increases with the decrease in temperatures and the increase in pressures and decreases in the order of . The isosteric heat of adsorption for all the three zeolites decreases appreciably with the increase in hydrogen adsorption capacity. The hydrogen adsorption sites in the three zeolites were determined by the simulated distribution of hydrogen adsorption energy and the factors that influence their variations were discussed. Adsorption temperature has an important effect on the distribution of hydrogen molecules in zeolite pores. 1. Introduction The utilization of hydrogen as a possible substitute for fossil fuels requires the solution of a number of problems related to hydrogen production, transportation, storage, and fuel cell technology [1]. Among them, safe and efficient storage of hydrogen is very important for hydrogen energy applications. Various methods for storing hydrogen were developed which include high-pressure tanks for gaseous hydrogen, cryogenic vessel for liquid hydrogen, and metal hydride for solid-state storage systems [2–4]. The first two methods bear the danger of explosion if handled improperly, and the latter one suffers high cost and weight. Recently, attention has been focused on light microporous materials such as carbon [5], aluminosilicate zeolites [6, 7], and metal organic frameworks (MOFs) [8] for storing hydrogen by adsorption because the adsorption is reversible and thus the sorbent can be recycled. Zeolites are a large class of crystalline aluminosilicate materials that have high thermal stability and regular and single size pores and the diameter of the pores can be controlled by changing the size and charge of the exchangeable cations. Thus, they offer enormous potential for storage of gases. The hydrogen storage capacity of various types of zeolites had been reported experimentally and theoretically [9–12]. However, little attention was previously paid to the distribution of adsorption sites and adsorption potential energy for the molecular hydrogen on zeolites. Li and Yang [13] reported experimentally that the alkali-metal cations (Li+, Na+, K+) and the framework atoms
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