Effect of a Distribution of Pore Dimension on Levitation Effect

Existence of levitation effect in noncrystalline porous solids is verified by means of molecular dynamics simulations. By introducing a normal distribution (characterized by the half-width at half-maximum, σG = 0.1 and 0.5 Å) of 12-ring window diameters disorder is introduced in crystalline faujasite. Investigation of motion of spherical sorbates within this disordered host suggests that levitation effect persists though the intensity of the anomalous peak is reduced compared to crystalline faujasite. In the disordered host there is a breakdown of the linear relationship between the self-diffusivity D and 1/σgg2, where σgg is the sorbate diameter. The activation energy is lowest and the energy barrier is negative for the particle whose sorbate diameter corresponds to the anomalous regime for most window diameters, σw, while for the sorbate whose diameter lies in the linear regime, the energy barrier is always positive.