MOLECULAR-DYNAMICS SIMULATION OF DIFFUSION IN PILLARED CLAYS

The thermodynamics and transport properties of Lennard-Jones particles in pillared catalytic clays are studied by molecular dynamics simulat ion. The clays are represented by parallel sheers separated by a given distance and connected by pillars of a given size. Two different spat ial distributions of the pillars are studied to determine their Effect on the properties of the system. Calculations did not indicate a stro ng dependence of the diffusivity on the spatial distribution of the pi llars, except at low porosities. The solvation force increases monoton ically with decreasing porosity of the clays and increasing density of the molecules. The percolation threshold cp, of the system is estimat ed from the diffusivity measurements in the limit of infinitely low so l bate densities. Near cp, the diffusivity D vanishes according to the power law, D similar to (phi - phi(c))(n), where phi is the porosity of the system, and n is a universal constant. The simulations yield n similar or equal to 1. 7. Since 2-D percolation systems require n simi lar or equal to 1.3 and 3-D systems n similar or equal to 2.0, pillare d clays behave as a system with an effective dimensionality between 2 and 3.