DFT study of Li+ and Na+ positions in mordenites and hydration stability

Abstract

Mordenite is a type of zeolite used in catalysis processes and in the selective adsorption of gases. The properties of this material are related to the presence of aluminium atoms and exchangeable cations in the structure. In this work, we performed DFT periodic calculations of cationic mordenites X8Al8Si40O96 and X4Al4Si44O96 (X = Li+ or Na+) and the corresponding hydrated species. Calculations of Li+ and Na+ mordenites indicated preference for the aluminium atoms to occupy T3 and T4 sites. In this configuration,the alkaline cations have preference for the two channels 8MRz and 12MRz along [001] crystallographic axis. In the hydrated structures, the alkaline cations have preference for the side pockets (8MRy along [010] direction). Hydrated structures with high aluminium content have a stability caused by interaction of the alkaline cations with water molecules and oxygen atoms of the framework.