UV Raman spectroscopic study on the synthesis mechanism of zeolite X

The synthesis of zeolite X is characterized by UV Raman spectroscopy, NMR s pectroscopy, and X-ray diffraction. UV Raman spectra of the liquid phase of the synthesis system indicate that AI(OH); species are incorporated into s ilicate species, and the polymeric silicate species are depolymerized into monomeric silicate species during the early stage of zeolite formation. An. intermediate species possessing Raman bands at 307, 503, 858 and 1020 cm(- 1) is detected during the crystallization ill the solid phase transformatio n. The intermediate species is attributed to the beta cage, the secondary b uilding unit of zeolite X. A model for the formation of zeolite X is propos ed, which involves four-membered rings connecting to each other via six-mem bered ring to form beta cages, then the beta cages interconnect via double six-membered rings to form the framework of zeolite X. (C) 2001 Elsevier Sc ience B.V. All rights reserved.