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 simulation. The clays are represented by parallel sheers separated by a given distance and connected by pillars of a given size. Two different spatial distributions of the pillars are studied to determine their Effect on the properties of the system. Calculations did not indicate a strong dependence of the diffusivity on the spatial distribution of the pillars, except at low porosities. The solvation force increases monotonically with decreasing porosity of the clays and increasing density of the molecules. The percolation threshold cp, of the system is estimated from the diffusivity measurements in the limit of infinitely low sol 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 similar or equal to 1.3 and 3-D systems n similar or equal to 2.0, pillared clays behave as a system with an effective dimensionality between 2 and 3.