Local Order in Depolymerized Silicate Lattices Graciela Pacheco-Malago ´ n, † Patricia Pe ´ rez-Romo,* ,‡ Norma A. Sanchez-Flores, † Marı ´a L. Guzma ´ n-Castillo, ‡ Carlos Lo ´ pez, ‡ Jose ´ M. Saniger, † Francisco Herna ´ ndez-Beltra ´n, ‡ and Jose ´ J. Fripiat †,‡ Centro de Ciencias Aplicadas y Desarrollo Tecnolo ´ gico, Cd. UniVersitaria AP 70-186, C.P. 04510 Me ´ xico, D.F., and Instituto Mexicano del Petro ´ leo, Eje Central La ´ zaro Ca ´ rdenas, 152, Col. San Bartolo Atepehuacan, C.P. 07730 Me ´ xico, D.F. Received April 11, 2005 In glycerol, near 200 °C, the silicate networks of mesoporous silicates and zeolites undergo a deep depolymerization process. In a few hours, depending on the initial concentration of the solid in glycerol and on the temperature, amorphous gels are obtained. In these gels, a fraction of the Si-O-Si bonds are transformed into Si-O-C. The constitutional aluminum remains bound to the silica network in the gel. The short range ordering is maintained to some extent: the size of the smallest structural unit in gels obtained from zeolites is in the range of the cubic nanometer, nm 3 . Introduction The silicates, which are the main constituents of earth crust, are quite resistant to chemical agents operating in a moderate pH range. For instance, in water, 140 ppm silica is dissolved at room temperature, and the solubility is even lower in alcohols. The origin of this work is the observation that crystalline mesoporous silicas, such as MCM-41 1-3 or FSM-16, 4-6 dissolve rapidly below 200 °C in glycerol forming soft gels or viscous liquids, depending on the reaction conditions. The solubility of the organo-complex in glycerol is in the percent range, that is to say, more than 10000 times the solubility in water. The silica network is depolymerized. The gel is X-ray amorphous. Thus, the probability of a silicon tetrahedron sharing its four corners with identical tetrahedra is statistically and significantly lowered. High surface area xerogel, 7 synthetic acid faujasite HY, 8,9 a member of the MF1 group, H-ZSM5, 8-9 acid Clinoptilo- lite, 10 a member of the Heulandite family, can be jellified as well. The depolymerized material is similar to a hyper- branched silicon alkoxide, the depolymerization reaction proceeding by a condensation process between a silanol group and an alcohol function of glycerol, liberating water (etherification). In zeolites, the fate of the constitutional aluminum, and, in particular, its coordination, deserves special consideration. The structures of silicates may be quite complicated, but the essential building block is the Si tetrahedron of symmetry T d . Long-range order is revealed by the interference based techniques, such as X-ray or neutron diffraction. Local ordering is approached by IR spectroscopy, or by MAS NMR. The efficiency of the depolymerization process can be appreciated by the ratio C/Si characteristic of the final product. * To whom correspondence should be addressed. E-mail: pperezr@ imp.mx. † Centro de Ciencias Aplicadas y Desarrollo Tecnolo ´gico. ‡ Instituto Mexicano del Petro ´leo. (1) Kresge, C. T.; Leonowicz, M. E.; Roth, W. J.; Vartuli, J. C.; Beck, J. S. Nature 1992, 359, 710. (2) Beck, J. S.; Vartulli, J. C.; Roth, W. J.; Leonowicz, M. E.; Kresge, C. T.; Schmitt, K. D.; Chu, C. T. W.; Olson, D. H.; Sheppard, E. W.; McCullen, S. B.; Higgins, J. B.; Schlenker, J. L. J. Am. Chem. Soc. 1992, 114, 10834. (3) Beck, J. S.; Vartulli, J. C.; Kennedy, G. C.; Kresge, C. T.; Roth, W. J.; Schramm, S. E. Chem. Mater. 1994, 6, 1816-1821. (4) Yanagisawa, T.; Shimizu, T.; Kurado, K.; Kato, C. Bull. Chem. Soc. Jpn. 1990, 63, 988. (5) Chen. C.-Y.; Xia, S.-Q.; Davis, M. E. Microporous Mater. 1995, 4, 1. (6) Pe ´rez-Romo, P.; Guzma ´n-Castillo, M. L.; Armenda ´riz-Herrera, H.; Navarrete, J.; Acosta, D. R.; Montoya, J. A. Langmuir 2003, 19, 3446- 3452. (7) Poncelet, G. Personal communication. (8) Baerlocher, Ch.; Meier, W. M.; Olson, D. H. The Atlas of Zeolite Framework Types, 5th revised ed.; Elsevier: New York, 2001. (9) Treacy, M. M. I.; Higgins, J. B. Collection of Simulated XRD Powder Patterns for Zeolites, 4th ed.; Elsevier: New York, 2001. (10) Iler, R. K. The Chemistry of Silica; J. Wiley and Sons: New York, 1979. Inorg. Chem. 2005, 44, 8486-8494 8486 Inorganic Chemistry, Vol. 44, No. 23, 2005 10.1021/ic050562p CCC: $30.25 © 2005 American Chemical Society Published on Web 10/21/2005