Computer Simulation of Zeolites : Adsorption, Diffusion and Dealumination

Abstract

Zeolites are microporous materials with pores that have about the same size as small molecules like water or benzene. They are important catalysts in the petrochemical industry, for example for catalytic cracking, and isomerization- and alkylation reactions. This thesis deals with molecular aspects of the application of zeolite catalysis for the production of cumene via benzene alkylation with propene using Mordenite (MOR-type zeolite). We will use classical force field based molecular simulations to study properties at the atomistic scale. In Chapter 1, an overview is given of the various properties of zeolites, as well as the simulation methods to study the adsorption and diffusion of guest molecules adsorbed in zeolites. In Chapter 2, it is shown that the adsorption and diffusion properties of alkanes in MOR strongly depend on the distribution of non-framework Al atoms. A model is presented to accurately describe this effect. A new method to efficiently compute the heat of adsorption for guest molecules adsorbed in zeolites with non-framework cations is presented in Chapter 3. It is found that this method is much more efficient than the existing methods. Furthermore, it is shown that for the simulation of polar molecules in zeolites, the Ewald summation is superior compared to the recently proposed Wolf-method. In Chapter 4, we study the adsorption selectivity of benzene/propene mixtures in various zeolites, and we evaluate their use as a potential catalysts for benzene alkylation. In Chapter 5, we propose an efficient method to accurately compute pore size distributions. This method is extensively used in Chapter 6, in which we study the dealumination mechanism of MOR-type zeolite using Kinetic Monte Carlo simulations. The results of these dealumination simulations are in very good agreement with various experiments. It is found that the pore size of the main channels is significantly increased. Finally, we propose several criteria for potential catalysts for the production of cumene from benzene and propene.