The self-diffusion of hydrogen in NaX zeolite was studied using molecular-dynamics simulations for various temperatures and pressures. The results indicated that, at 77 to 293K, over a pressure range of 10 to 2700kPa, the self-diffusion coefficients ranged from 1.61 x 10-9 to 3.66 x 10-8m2/s; in good agreement with the experimental values from the quasi-elastic neutron scattering and pulse field gradient nuclear magnetic resonance measurements. The self-diffusion coefficients decreased with increasing pressure due to packing of sorbate-sorbate molecules which caused frequent collisions among hydrogen molecules in pores and increased with increasing temperature because increasing the kinetic energy of the gas molecules enlarged the mean free path of gas molecules. The activated energy for hydrogen diffusion, determined using the simulation, was pressure-dependent.

Molecular-Dynamics Simulation of Self-Diffusion of Molecular Hydrogen in X-Type Zeolite. X.Du: Journal of Chemistry, 2013, 545367