A Computational Method for the Generation of Low-Energy Aluminum and Cation Configurations of Zeolite NaY

Abstract

This work presents a computational method for the generation of low-energy aluminum and cation configurations for zeolites with large unit cells. Periodic models of large unit cell zeolites, such as zeolite NaY, exceed the practical limitations of current quantum chemistry methods. This method utilizes a cluster model to simulate the aluminum and cation neighborhood of an aluminum atom substitution site, and the substitution energy associated with these environments is computed using a semi-empirical quantum chemistry method. A mathematical optimization model for the generation of low-energy configurations using these substitution energies is proposed,as well as a two-step optimization model for the optimal placement of cations in a zeolite structure. Potential areas of improvement for further research have been identified, and preliminary substitution energy results suggest that low-energy configurations are distinguishable from high energy configurations, and that these results may also be used to identify a new aluminum ordering rule. The methods developed can be easily adapted to zeolites other than NaY, and can also be incorporated into further computational research on zeolite models of selectivity, adsorption, diffusion and chemical conversion, or used for the prediction of stable zeolites with practical uses.