Investigation on the effect of zeolite precursor on the formation process of MCM-41 containing zeolite Y building units

The formation process of MCM-41 containing zeolite Y building units has been investigated by UV Raman spectroscopy, 29Si and 27Al MAS NMR spectroscopy, X-ray diffraction (XRD), N2 adsorption and electron microscopy (SEM and TEM). It is found that the precursor containing zeolite Y secondary building units promotes the formation of a metastable mesopore structure just after mixing the zeolite precursors with CTAB. In contrast, the low-polymerized aluminosilicates and well-crystallized zeolite crystals cannot be assembled with CTAB at this stage. The result supports that the zeolite secondary building units should promote to the formation of the mesopore wall. This has been ascribed to its high anionic charge density as well as the appropriate multidentate coordination. Lowering down the pH value to 9.3 facilitates the further polymerization of the aluminosilicate species to build up a stable mesoporous phase.

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► Zeolite Y secondary building units promotes a metastable mesopore formation.
► Low-polymerized silicates cannot induce mesopore formation at high pH.
► Well-crystallized zeolite crystals cannot induce mesopore formation at high pH.
► During the synthesis process the structure and locations of CTAB changes.