High-temperature molecular dynamics was used to investigate self-transport and cooperative transport of benzene in NaX (Si:Al = 1.2). The benzene-NaX force field was refined for use with a previously developed framework force field, for aluminosilicates, which explicitly distinguished between Si and Al atoms in the framework, and also between oxygen atoms in Si-O-Si and Si-O-Al environments. Energy minimization and molecular dynamics simulations were used to test the force field, and gave excellent agreement with experimental data on benzene heats of adsorption, benzene-Na distances and Na distributions for benzene in NaY (Si:Al = 2.4) and NaX (Si:Al = 1.2). Molecular dynamics simulations were performed at 600 to 1500K and various loadings (infinite dilution to 4 benzene molecules per super-cage) in order to evaluate simultaneously the self-diffusivities and cooperative (or Maxwell-Stefan) diffusivities. The simulated diffusivities agreed well with pulsed field-gradient nuclear magnetic resonance and quasi-elastic neutron scattering data.

Beyond Lattice Models of Activated Transport in Zeolites: High-Temperature Molecular Dynamics of Self-Diffusion and Cooperative Diffusion of Benzene in NaX. H.Ramanan, S.M.Auerbach, M.Tsapatsis: Journal of Physical Chemistry B, 2004, 108[44], 17171-8