MONTE-CARLO SIMULATION OF THE SI, AL DISTRIBUTION IN A-TYPE ZEOLITES

The Si, Al distribution in A-type zeolites has been studied by a Monte Carlo method. The simulations were performed in the canonical (NVT) ensemble at the synthesis temperature of these compounds, and the results were compared with earlier Si-29 nuclear magnetic resonance spectra. Simulations including long-range interatomic potentials are compared with others performed by assuming only Al-O-Al group exclusion. In both cases, the atom ordering in different structural groups (four-, six-, and eight-membered rings) of the framework is analyzed. We conclude that atom interactions further than nearest tetrahedra are necessary to explain the experimental NMR data. An effective charge difference of 0.26e between Si and Al is found for these zeolites.