Crystallization of Zeolites from Organo-Silicic Colloids Graciela Pacheco-Malago ´ n, † Patricia Pe ´ rez-Romo,* ,‡ Norma A. Sa ´ nchez-Flores, † Marı ´a L. Guzma ´ n-Castillo, † Carlos Lo ´ pez-Franco, ‡ Jose ´ M. Saniger, † Francisco Herna ´ ndez-Beltra ´n, ‡ and Jose ´ J. Fripiat †,‡ Centro de Ciencias Aplicadas y Desarrollo Tecnolo ´ gico, Cd. UniVersitaria A. P. 70-186 C. P. 04510, Me ´ xico, D. F., and Instituto Mexicano del Petro ´ leo, Eje Central La ´ zaro Ca ´ rdenas No. 152, Col. San Bartolo Atepehuacan C. P. 07730, Me ´ xico, D. F. Received November 8, 2005 As shown recently, the networks of mesoporous high-surface-area silicates and zeolites undergo a deep depolymerization process in glycerol, near 200 °C. Within 1 h, X-ray diffraction analysis amorphous gels are obtained. However, some local ordering subsists as demonstrated by a striking similarity between the silicon and aluminum high-resolution solid-state NMR spectra before and after the reaction. The residual organization could be investigated indirectly in studying the recrystallization of these gels in the presence or absence of structure-directing agents. Were this attempt successful, the way should be opened for the synthesis of molecular sieves starting from gels obtained from naturally occurring zeolites. Here, it will be shown that an amorphous gel obtained from HZSM-5 recovers the initial long-range structure of the parent material in a few hours at 85 °C in the presence of an aqueous solution of tetrapropyl ammonium (TPA) or NH 3 . The recrystallization of HY requires the presence of tetramethylammonium, but about 25% of the crystallization is obtained rapidly (=1day) at 80 °C with ammonia. Hypotheses about the preorganized structural units are presented. The value of the Si-O-Si angle in the silica cluster seems to be of paramount importance. Introduction In most of the procedures used for the synthesis of zeolites, the starting material (SM) is an aqueous gel with a chemical composition comparable with the composition of the target. The alumino-silicate gel is obtained by controlling the hydrolysis of a mixture of alkali silicate and aluminate or by a sol-gel procedure, operating with a mixture of silicon and aluminum alkoxides 1 . Often, but not necessarily, the synthesis is mediated through templates and is sometimes assisted by seeding. Crystalline mesoporous silica, such as MCM-41, dissolves rapidly below 200 °C in glycerol, forming a stable gel. 2 The solubility of the organo complex in glycerol is in the percent range, that is to say, more than 10 000 times the solubility of silica in water. The long-range ordering of the silica network is lost, and the gel is X-ray amorphous. Synthetic acid faujasite HY, HZSM-5, acid Clinoptilolite, a member of the Heulandite family, can be jellified as well. The depolymerized material is a hyperbranched silicon alkoxide, the depolymerization reaction proceeding by a condensation process between a silanol group and an alcohol function of glycerol, liberating water. The water is continuously evapo- rated from the reacting mixture. The similarity between the 29 Si NMR and 27 Al NMR spec- tra of the gel and those of the corresponding starting material suggests that a limited, local ordering persists in the gel. In particular, the observation of tetrahedral aluminum permits an estimation of the size of the smallest structural unit in the gel. For instance, in HY, there are 12.7 tetrahedral units per cubic nanometer. Because the Si/Al ratio is 12.9, there is about 1 Al/nm 3 , and because both the 27 Al signal and the 29 Si signal are the same as that in bulk HY, the smallest structural unit in the gel must be about 1 nm 3 . If the same argument is used, this volume is 1.24 nm 3 in a HZSM-5 gel 2 . In these nanostructural units, it may be suggested that the interatomic distances and bond angles are unchanged with respect to the SM. If this hypothesis is correct, the recrystallization of a solid similar to the starting material from the gel should be much * Author to whom correspondence should be addressed. Phone: 52-55- 9175-8364. Fax: 52-55-9175-6239. E-mail: pperezr@imp.mx. † Centro de Ciencias Aplicadas y Desarrollo Tecnolo ´gico. ‡ Instituto Mexicano del Petro ´leo. (1) Davis, M. E.; Lobo, R. F. Chem. Mater. 1992, 4, 756. (2) Pacheco Malago ´ n, G.; Pe ´rez-Romo, P.; Guzma ´n-Castillo, M.; Sanchez Flores, N. A.; Lopez, C.; Saniger Blesa, J.; Hernandez Beltran, F.; Fripiat, J. J. Inorg. Chem. 2005, 44, 8486. Inorg. Chem. 2006, 45, 3408-3414 3408 Inorganic Chemistry, Vol. 45, No. 8, 2006 10.1021/ic051929t CCC: $33.50 © 2006 American Chemical Society Published on Web 03/15/2006