Density functional calculations were carried out on a series of metal-exchanged and H-form ZSM-5 zeolite clusters with or without H2O molecules adsorbed. By comparing the H2O adsorption on H-fom and metal exchanged zeolite clusters, the model for H2O adsorption on M/ZSM-5 zeolites was put forward, confirmed by the consistence of our frequency calculations, With previous IR experiments. The binding energies of the metal cations, which decreased as La/ZSM-5 > Ca/ZSM-5 > Mg/ZSM-5 > K/7SM-5 > Rb/ZSM-5 > Na/ZSM-5 > Zn/ZSM-5 (> H/ZSM-5). determined the relative hydrothermal stabilities of different metal exchanged ZSM-5 zeolites Detailed atialysis on the three parts to the binding energies was performed, concluding that the part between the metal cations, and the zeolite framework has played the most important role. which can be reflected by the consistency of the sequences of the elongated of M---O-i distances, and the binding energies. Here the mean square deviation H was adopted to characterize the [AlOi] tetrahedron, which showed that the process, of H or M falling off was facilitated at higher water pressure. When the Bronsted acidic proton was exchanged with the metal cation or adsorbed with some water, the [AlOi](-) tetrahedron can restore somewhat towards ideal regularity, and this is probable the reason why Al MAS NMR signals are illegible in H/ZSM-5 zeolite and will be much improved by the introduction of some water or the exchange with metal cautions, (c) 2005 Elsevier B.V. All rights reserved.