SYNTHESIS AND CHARACTERIZATION OF GE-ZSM-5 ZEOLITES

Ge-ZSM-5 zeolites have been synthesized and characterized by SEM, n-hexane adsorption, XRD, MAS NMR, IR, and Raman spectroscopy. Despite the large size of the germanium atoms, up to 12.8 Ge/unit cell could be incorporated into the MFI framework. In order to rationalize this, a site preference of the germanium atoms in the lattice is proposed. Although a large amount of germanium is incorporated, only small changes in the unit cell parameters and lattice vibration frequencies are observed, suggesting that the T-T and T-O distances in the framework are nearly unchanged. However, the T-O-T deformation band is significantly broadened and shifted to higher wavenumber. From these findings it is deduced that the incorporation of germanium leads mainly to a decrease in the T-O-T angle.