Properties of iron-containing ZSM-5 zeolite: A theoretical study based on quantum chemical calculations

Abstract

We report here the results of cluster calculations on ferrisilicate zeolite models. The different possible sites in the ZSM-5 zeolite are modelled by the H6T2O7 cluster (where T = Si). Further, one of the ‘T’ sites is substituted with Fe, and the electronic properties of the resulting clusters are studied by performing EHMO (Extended Huckel Molecular Orbital) calculations. The properties studied include the preference energy for substitution of Fe at various ‘T’ sites, the pore size modifications and variations in the Brönsted as well as Lewis acidity due to Fe substitution. The acidity determination carried out by TPD of NH3 on ZSM-5 type zeolites containing ‘Fe’ at framework positions and their shape selectivity for ethylbenzene conversion reactions are compared with the results of the calculations. The observed catalytic and acidic behaviour of iron-containing ZSM-5 zeolites is explained on the basis of their electronic structure.