Dynamics in Complex Systems: Computer Simulation of the Migration of Ions and Neutrals in Zeolites

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

Horia Metiu of UC Santa Barbara is supported by the Theoretical and Computational Chemistry Program to perform computer simulations of forces acting on ions and water molecules inside a zeolite, and to use these results to explore how the species move through the zeolite. Also, proton transfer rates will be calculated, and complete kinetic descriptions and mechanisms will be evaluated. Rigorous methodology will be applied to small unit cell zeolites, with specific studies of sodium ion and water migration through sodalite and the reaction of ammonia with acidic chabazite. These processes are widely used in industrial applications, yet very little is known about them at an atomic level. All energy calculations will be performed with density functional theory, which considers the full unit cell of the solid. Rate constants of the important processes will be calculated using correlation function theory or transition state theory. The results will be used in a kinetic Monte Carlo program to simulate migration and kinetics over very long time and space scales. It is anticipated that the ability to calculate the properties of molecules inside zeolites will be improved to the point that this methodology will assist in the rational design of industrial processes. Zeolites are crystalline, porous solids that have the ability to absorb inside them a variety of molecules. This absorption is selective (certain molecules are preferred to others) and the selectivity can be used to separate various gases, to remove noxious products from a gas stream, or to replace undesirable ions with benign ones. Zeolites and their absorbed guest molecules interact strongly enough to induce unusual chemical reactions within the zeolite frame. This property has practical importance and is exploited to modify the hydrocarbon content of various products in the oil industry. The outcomes from this computer simulation project will improve the understanding of how fast molecules move inside a zeolite, what determines absorption selectivity, and what causes changes in the chemical behavior of the absorbed species.