Nanocrystalline zeolites synthesis

S.C. Larsen (2007) J. Phys. Chem. C, vol. Ill, p. 18464 Nanocrystalline zeolites and zeolite stmcmres Synthesis, characterization, and applications . 

The weak Raman scattering from water allows the direct observation of the oxide species in the aqueous phase, the nanocrystalline nucleation seeds, and the solid phases present during zeolite synthesis, which are not as readily detectable with x-ray diffraction (XRD). The transformation of aluminosilicate gel to zeolite A was investigated with Raman spectroscopy by several researchers [150,179,180], but one outstanding investigation also... 

The synthesis of Sn-beta (68,151) with isolated single tin sites was accomphshed in a fluoride medium TEOS was hydrolyzed in a stirred aqueous solution of TEAOH. Then a solution of SnC 5H2O in water was added and the mixture stirred until the ethanol formed by hydrolysis of the TEOS had evaporated. HF was added to the resulting clear solution, and a thick paste formed. Then a suspension of nanocrystalline seeds (20 nm in diameter) of dealuminated zeolite beta in water was added. The crystallization was carried out in aTeflon-hned stainless-steel autoclave, which was heated to a temperature of 140 °C and continuously rotated for 20 days. After drying and calcining of the resultant sohd, XRD showed that a highly crystalline material with BEA structure was obtained, which contained 1.6 wt% Sn according to chemical analysis. Further characterization by XRD and UV, IR, and Sn MAS NMR spectroscopies verified the structure and the isomorphous substitution of siHcon by tin. 

---