ELECTRONIC AND STRUCTURAL-PROPERTIES OF ALUMINUM IN THE ZSM-5 FRAMEWORK

The relative importance of the geometry and size of clusters involved in the calculation of the electronic structure of ZSM-5 using MNDO (modified neglect of differential overlap) quantum chemical cluster calculations is reported. Calculations were carried out on Al-containing pentamer cluster models with a tetrahedral symmetry, and their geometrical parameters were systematically varied. Calculations were also performed for cluster models of varying size whose geometry was derived from the crystal structure reports of ZSM-5. The electronic properties such as density of states, energy of frontier molecular orbitals and contribution from different atomic orbitals could be derived from the results of even small cluster models, while pentamer clusters were needed to study the energetically favorable substitution sites of aluminum.