SIMULATION STUDIES OF THE STRUCTURE AND ENERGETICS OF SORBED MOLECULES IN HIGH-SILICA ZEOLITES .1. HYDROCARBONS

Theoretical methods are used to study the adsorption of linear hydrocarbons, Cl-C8, in silicalite, H-ZSM-5, and siliceous faujasite. The aim is to model the behavior of sorbed species in zeolites and evaluate the influence of the zeolite structure and composition on the sorption process. The method of calculation is energy minimization using the Born model of solids with specified interatomic potentials. Atom-atom potentials are used to model the zeolite and zeolite-hydrocarbon interactions. The effect of relaxation both of the zeolite framework and of the molecule is investigated. The location of adsorption sites and heats of adsorption for the molecules are presented. The sorption process is controlled by the shape and volume of the available cavity and the packing ability of the molecule concerned. In silicalite and H-ZSM-5, adsorption at the straight channel is preferred to that of sinusoidal channel. The simulations show the extent to which hydrocarbons sorb more strongly in ZSM-5 zeolites than in siliceous faujasites.