THE EFFECTS OF GEL AGING ON THE SYNTHESIS OF NAY ZEOLITE FROM COLLOIDAL SILICA

We have investigated the effects of gel aging on the synthesis of NaY zeolite. Gels were prepared by adding a sodium aluminate solution to a colloidal silica sol. After aging at room temperature for fixed periods of time, the gels were heated to 100-degrees-C. The kinetics of crystallization were followed by powder X-ray diffraction. Compositional and structural information was provided by elemental chemical analysis; n.m.r., i.r., and Raman spectroscopies; and scanning electron microscopy. The rate of crystallization and the composition of the crystalline products depend strongly on the quantity and composition of an amorphous aluminosilicate solid produced during aging. Initial aging produces an Al-rich aluminosilicate solid that readily reacts to form NaY nuclei upon heating. The number of nuclei is directly related to the amount of aluminosilicate precipitated. Prolonged aging leads to incorporation of additional Si into the aluminosilicate solid. This gives rise to a larger number of smaller nuclei and results in a higher final yield of NaY.