Synthesis and characterization of zincosilicates with mfi-type structure

الملخص EN

-Zincosilicates were hydrothermally crystallized in the presence of tetrapropylammonium cations (TPA).

Crystals having the MFI-type structure were obtained.

The isomorphous substitution and other physico-chemical properties of the samples were explored and to some extent compared with silicalite-I impregnated with zinc to similar levels.

X-ray diffraction and scanning electron microscopy ensured the crystallinity and purity of the samples.

Elemental 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.

Thermal analysis showed that the temperature of the TPA decomposition increased 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 the band at 1100 cm-1.

This extra band disappeared upon calcination.

NH3-TPD showed that there is probably a low concentration of only Lewis acid sites.

Although no direct evidence has been obtained indicating zinc isomorphous substitution in the framework, XPS showed that zinc is homogeneously distributed throughout the crystals of zincosilicate relative to zinc impregnated silicalite-I.

The presence of zinc in the pores of zincosilicates reduces the pore volume of the materials relative to that of silicalite-I.

Keywords: silicalite, MFI, zinc, zeolite, isomorphous substitution, physico-chemical properties, synthesis