29Si NMR Studies of Zeolite Precursor Solutions

Chil-Hung Cheng and Daniel F. Shantz*
Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843-3122
J. Phys. Chem. B, 2006, 110 (1), pp 313–318
DOI: 10.1021/jp055124i
Publication Date (Web): December 15, 2005
Copyright © 2006 American Chemical Society
*

 Author to whom correspondence should be addressed. Phone:  (979) 845-3492; fax:  (979) 845-6446; e-mail:  Shantz@che.tamu.edu.

Abstract

Solution 29Si NMR spectroscopy results of zeolite precursor solutions of composition 1 SiO2:4 C2H5OH:0.36/n R+n[OH-]n:20 H2O are reported. This work employs isotopically enriched 29Si materials to aid in spectral interpretation. Using both 1D and 2D methods, spectra of solutions containing tetrapropylammonium hydroxide are wholly consistent with the existing silicate chemistry literature and indicate that the majority of the species are high-symmetry silicate clusters previously observed in aqueous solutions. The results are inconsistent with the nanoblock or nanoslab model proposed by Kirschhock and co-workers. Mixtures containing the 4,4‘-trimethylene-bis(1,1‘-dimethylpiperidinium) dihydroxide cation were also studied. These mixtures have similar speciation to the TPA solutions, although the relative populations of the species are different. Preliminary variable temperature 29Si NMR of these mixtures shows that the exchange properties of the high-symmetry silicate species, most notably the tetrahedral tetramer, depend on the organocation identity.

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History

  • Published In Issue January 12, 2006
  • Received September 10, 2005
    Revised November 9, 2005

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