Dynamics of adsorbed hydrocarbon in nanoporous zeolite framework.

We report quasielastic neutron scattering (QENS) and molecular dynamics (MD) simulation study of the dynamics of propylene molecules adsorbed in Na-ZSM5 zeolite. MD simulation studies suggest that rotational motion is almost an order of magnitude faster than translational motion. Therefore, spectrometers having different energy resolutions were used to determine the translational and rotational contributions. Translational motion, being slower, was distinctly observed in a narrower window spectrometer while both contribute to the wider one. Diffusion of propylene in the channels of Na-ZSM5 zeolite was found to follow jump diffusion model. Dynamical parameters corresponding to translational diffusion obtained from experiment are found to be consistent with MD simulation. Variation of elastic incoherent structure factor (EISF) suggests that rotational motion of propylene is isotropic. Although at short times the rotational motion was found to be anisotropic, as indicated in the MD simulation depicting restricted channel framework, but at long time it results in isotropic rotational motion.