(626f) Simulating Gas and Liquid Water in Faujasite

Zeolites are porous materials with a wide array of applications, in both the gas and liquid phase, such as ion exchangers, absorbents, and catalysts. In the catalytic cracking of petroleum, the addition of lanthanum improves the hydrothermal stability of faujasite. Despite its extensive use for decades, unknowns remain on how lanthanum increases faujasite hydrothermal stability. The hydrothermal stability of zeolites decreases by dealumination, which occurs via reactions that involve water molecules. Brønsted acid sites give desired catalytic properties to zeolites, however, they reduce hydrothermal stability by attracting water molecules to aluminum tetrahedra and promoting dealumination. In the gas phase, favorable binding sites for water and lanthanum were determined with density functional theory (DFT) calculations and ab initio molecule dynamics (AIMD) simulations. Rare event simulation techniques were used to generate potentials of mean force of proton transfer, that quantified how lanthanum exchange changes the Brønsted acidity of faujasite. In the liquid phase, the structure of water in faujasite was modeled with AIMD simulations with explicit water molecules because Brønsted acid sites and charged water clusters may impact catalysis or separations applications. Simulations resolve how the structure of water changes with zeolitic confinement, changes in zeolite hydrophilicity and Brønsted acidity, and exchanged cations.