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 simulation, and computer graphics to the investigation of the sites and distribution of framework aluminum atoms in faujasites, which cannot be derived from experimental techniques is shown. By using MD calculations, we successfully predicted the adequate aluminum distribution in NaY zeolite (Si/Al = 2.43), as it reproduces the sites and occupancies of Na⁺ cations which have been reported by neutron diffraction techniques. The validity of our aluminum distribution model in the NaY was strongly confirmed by the simulated ²⁹Si MAS NMR spectra in agreement with the experimental chemical shifts and intensities. Although the sites and occupancies of the exchanged cations in faujasites can be determined by analytical experimental techniques, their atomistic detailed distribution cannot be derived experimentally. A methodology is proposed to predict the detailed distribution of the Na⁺ cations in NaY by using neutron diffraction spectrum simulation.