Effect of zeolite precursor on the formation of MCM-41 molecular sieve containing zeolite Y building units.

The effect of zeolite Y precursor on the formation of MCM-41 containing zeolite Y building units has been investigated by means of UV Raman spectroscopy, X-ray diffraction (XRD), infrared spectroscopy (IR) and electron microscopy (SEM and TEM). Study of the precursor formation shows that 4-membered ring species are formed at the early stages of crystallization. Zeolite Y begins to appear after crystallization for 4 h, and its crystallinity increases with increasing crystallization time. However, lowering the pH value to ∼9.3 in the second step not only facilitates the polymerization of silicate species, but also leads to the structural change of the precursors. Pure MCM-41 mesoporous phase containing zeolite Y building units and the mixture of zeolite Y and MCM-41 can be formed combining the effects of the precursor structure and the pH adjustment.