Adsorption and diffusion of benzene in the nanoporous catalysts FAU, ZSM-5 and MCM-22: a molecular dynamics study.
Molecular dynamics (MD) simulations of benzene in siliceous zeolites (FAU, ZSM-5, and MCM-22) were performed at loadings of 1, 2, 4, 8, and 16 molecules per supercell. The potential energy functions for these simulations were constructed in a semi-empirical way from existing potentials and experimental energetic data. The MD simulations were employed to analyze the dynamic properties of the benzene-zeolite systems. The adsorption energies of benzene/siliceous zeolite complexes increase with increasing loading number, due to the intermolecular attraction between benzene molecules. The self-diffusion coefficient of benzene in siliceous zeolites decreases with increasing loading due to the steric hindrance between the sorbates passing each other. From the zeolite-benzene radial distribution functions it was found that the benzene molecules are relatively far from each other, about 5.2A for siliceous FAU, 5.2A for siliceous ZSM-5, and 4.8A for siliceous MCM-22. In the case of FAU, the benzene molecules prefer to be adsorbed parallel to the surface of the sodalite cage above the six-membered-ring. In ZSM-5, we found a T-structure of the benzene molecules at loadings 2, 4, and 8 molecules per supercell. At loadings of 16 molecules per supercell, the molecules are lined up along the straight channel and their movement is highly correlated. For MCM-22 we found adjacent benzene molecules at a loading of 4 molecules with an orientation similar to the stacked conformation of benzene dimer in the gas phase.
Rungsirisakun
Ratana
R
Laboratory for Computational and Applied Chemistry, Physical Chemistry Division, Department of Chemistry, Faculty of Science, Kasetsart University, Bangkok 10900, Thailand.
Nanok
Tanin
T
Probst
Michael
M
Limtrakul
Jumras
J
D000327:Adsorption; D001554:Benzene / Q000493:pharmacokinetics*; D002384:Catalysis; D003198:Computer Simulation; D004058:Diffusion; D008958:Models, Molecular; D008968:Molecular Conformation; D049329:Nanostructures; D016062:Porosity; D017641:Zeolites / Q000737:chemistry*
D017641:Zeolites; D001554:Benzene