INVESTIGATION OF THE ROLE OF CATIONS IN THE EFFECTIVE AROMATIZATION OF N-HEXANE OVER ZEOLITE L USING MOLECULAR DYNAMICS SIMULATION

摘要

In this work, molecular dynamics simulation with realistic Si/AI is used to shed light on the role of potassium in the unique aromatization behavior of n-hexane over zeolite L. A random configuration was chosen for the Al framework atoms followed by a Monte Carlo sampling of cation positions. This has allowed the exploration of the importance of the Al ordering that has been proposed in the literature. MD simulation was then done for purely zeolite-L without simple adsorbates. The first set of calculations concentrated on the extra framework cation diffusion. Molecular dynamics studies have shown that only Na~+ cations in the main channel D-sites are mobile, with the environment of other cations being too restrictive to allow diffusion even at elevated temperatures. The motion of the main channel cations consists of a series of rapid jumps between preferred cation locations, and it has been demonstrated that cation motion around the circumference of the channel is more facile than along its length. Finally, MD simulation was done for simple adsorbate (ethane). MD results show that the diffusion of small probe molecules such as ethane is controlled by the extra-framework cation mobility.