The adsorption energies of NH3 at different positions in acidic mordenite, viz., main channel, side pocket, and double four-membered rings, are investigated using periodic density functional theory method. Furthermore, for the first time, the dynamic behavior of NH3 interacting with Bronsted acid site in the main channel has been monitored. The results reveal that the adsorption energies of ammonia on Bronsted acid sites in the main channel (T-4, T-2, and T-1) are higher than that in the side pocket (TA Consequently, the strength of Bronsted acid sites follows the same order. Ammonia dynamics results show that the protons are in continuous transfer, where NH3 acts as a bridge for transferring protons in between ammonium ion and framework oxygen ions. (c) 2005 Elsevier B.V. All rights reserved.