THE DISTRIBUTION OF FRAMEWORK ALUMINUM ATOMS AND EXTRAFRAMEWORK EXCHANGED CATIONS IN FAUJASITE AS STUDIED BY MOLECULAR-DYNAMICS, NMR SIMULATION, NEUTRON-DIFFRACTION SIMULATION AND COMPUTER-GRAPHICS

The effectiveness and applicability of molecular dynamics (MD), NMR si mulation, and computer graphics to the investigation of the sites and distribution of framework aluminum atoms in faujasites, which cannot b e derived from experimental techniques is shown. By using MD calculati ons, we successfully predicted the adequate aluminum distribution in N aY zeolite (Si/A1=2.43), as it reproduces the sites and occupancies of Na+ cations which have been reported by neutron diffraction technique s. The validity of our aluminum distribution model in the NaY was stro ngly confirmed by the simulated Si-29 MAS NMR spectra in agreement wit h the experimental chemical shifts and intensities. Although the sites and occupancies of the exchanged cations in faujasites can be determi ned by analytical experimental techniques, their atomistic detailed di stribution cannot be derived experimentally. A methodology is proposed to predict the detailed distribution of the Na+ cations in NaY by usi ng neutron diffraction spectrum simulation.