Mobility of Aromatic Molecules in Zeolite NaY by Molecular Dynamics Simulation

Molecular dynamics (MD) simulations of benzene, p - and m -xylene, and m -nitroaniline in zeolite NaY were performed between 20 and 700 K at guest molecule coverages of 1, 16, and 32 molecules per unit cell (uc) to interpret and compare the results of quasi-elastic neutron scattering (QENS) and nuclear magnetic resonance (NMR) studies at the atomic scale. The predominant rotational motion of benzene and xylenes is the rotation about the 6-fold (pseudo-6-fold) axis in good agreement with QENS studies. The rotational motions of m -nitroaniline are predicted to be essentially slower than those of benzene and xylenes. The diffusional mechanism for benzene and xylenes can be described as a jump model with high residential probability at the cation adsorption site. The jumps are tetrahedral rearrangements of the arene molecules, in good agreement with recent NMR studies.