Synthesis and characterization of zincosilicates with MFI-type structure

Zincosilicates were hydrothermally crystallized in the presence of tetrapro pylammonium cations (TPA). Crystals having the MFI-type structure were obta ined. The isomorphous substitution and other physico-chemical properties of the samples were explored and to some extent compared with silicalite-I im pregnated with zinc to similar levels. X-ray diffraction and scanning elect ron microscopy ensured the crystallinity and purity of the samples. Element al composition showed that the level of zinc influenced the water, sodium, and TPA contents of the unit cell. Scanning electron microscopy showed the morphology of the crystals changed on introducing zinc in the synthesis. Th ermal analysis showed that the temperature of the TPA decomposition increas ed with the zinc level in the samples. Mid-infrared spectroscopy of the as- synthesized zincosilicates has shown a band at 1084 cm(-1) in addition to t he band at 1100 cm(-1). This extra band disappeared upon calcination. NH3-T PD showed that there is probably a low concentration of only Lewis acid sit es. Although no direct evidence has been obtained indicating zinc isomorpho us substitution in the framework, XPS showed that zinc is homogeneously dis tributed throughout the crystals of zincosilicate relative to zinc impregna ted silicalite-I. The presence of zinc in the pores of zincosilicates reduc es the pore volume of the materials relative to that of silicalite-I.