H-MOR: Density functional investigation for the relative strength of Brønsted acid sites and dynamics simulation of NH₃ protonation-deprotonation

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 Brønsted acid site in the main channel has been monitored. The results reveal that the adsorption energies of ammonia on Brønsted acid sites in the main channel (T₄, T₂, and T₁) are higher than that in the side pocket (T₃). Consequently, the strength of Brønsted 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.