Simulations of benzene in the siliceous zeolites, FAU, ZSM-5 and MCM-22, were performed at loadings of 1, 2, 4, 8 or 16 molecules per super-cell. The potential energy functions for these simulations were constructed semi-empirically from existing potentials and experimental data. The molecular dynamics simulations were used to analyze the dynamic properties of the benzene-zeolite systems. The adsorption energies of benzene/siliceous zeolite complexes increased with increasing loading, due to intermolecular attraction between benzene molecules. The self-diffusion coefficient of benzene in siliceous zeolites decreased with increasing loading due to steric hindrance between the sorbates passing each other. From the zeolite-benzene radial distribution functions, it was found that the benzene molecules were relatively far from each other: about 5.2Å for siliceous FAU, 5.2Å for siliceous ZSM-5 and 4.8Å for siliceous MCM-22. In the case of FAU, the benzene molecules tended to be adsorbed parallel to the surface of the sodalite cage above the six-membered-ring. In ZSM-5, a T-structure of the benzene molecules was found at loadings of 2, 4 or 8 molecules per super-cell. At loadings of 16 molecules per super-cell, the molecules were lined up along the straight channel and their movement was highly correlated. In MCM-22 adjacent benzene molecules were found at a loading of 4 molecules, with an orientation similar to the stacked conformation of benzene dimers in the gas phase.

Adsorption and Diffusion of Benzene in the Nanoporous Catalysts FAU, ZSM-5 and MCM-22: a Molecular Dynamics Study. Rungsirisakun, R., Nanok, T., Probst, M., Limtrakul, J.: Journal of Molecular Graphics and Modelling, 2006, 24[5], 373-82