Laser raman study on the crystallization of zeolites A, X and Y

UV Raman spectroscopic study on the synthesis mechanism of zeolite X

“…At the same time the bands at 307 and 1020 cm À1 split into the double bands at 298, 380 cm À1 and 995, 1068 cm À1 , respectively. These are the characteristic Raman bands of zeolite X [15,43]. All Raman bands remain unchanged during the crystallization of 2.0±4.0 h, indicating that the nucleation process was completed after heating the mixture for 2.0 h. This result is consistent with that of the X-ray di raction patterns in Fig.…”

“…The bands at 519, 620 and 498 cm À1 , which are associated with the amorphous polymeric silicate species, Al OH À 4 species and the seed solution, are absent in the spectra of the liquid phase during crystallization from 2.0 to 4.0 h. The bands at 774 and 924 cm À1 are observed in the spectra, and the intensities of these bands increase with prolonged crystallization time. These bands are associated with monomeric silicate species in the liquid phase [15,32]. It is clearly shown that the Al OH À 4 species in the solution have been incorporated into the solid phase, then polymerized with silicate ions.…”

“…2 gives the UV Raman spectra of the liquid phase in the zeolite X synthesis after 0, 1.0, 2.0, 2.5, 3.0, 3.5 and 4.0 h. Bands at 519, 620 and 1070 cm À1 are observed in the Raman spectra of the initial gel. The band at 620 cm À1 is assigned to the Al±O symmetric stretching mode of Al OH À 4 species in the solution [15,16,19,30,31]. The band at 519 cm À1 is attributed to amorphous silicate [16].…”

“…For zeolite X, it has been proposed that four-membered aluminosilicate rings formed in the gel of zeolite X evolve to form nuclei and crystals [19]. However, past Raman studies on the synthesis of zeolite X failed to provide the information on how the building blocks interconnect with each other to form the zeolite framework [15,19]. In this study, we report the ®rst UV Raman spectroscopic study on the crystallization of zeolite X, and propose a model for the formation mechanism of zeolite X.…”

“…There have been extensive Raman spectroscopic studies on the mechanisms of structural formation Roozeboom and coworkers proposed a solution transport mechanism for A, X and Y zeolites using Raman spectroscopy and chemical analysis [15]. Raman spectroscopic studies of the synthesis of zeolites Y and A have been reported by Dutta [16,17].…”