Issue 26, 2006

Do zeolite precursor species really exist in aqueous synthesis media?

Abstract

The authors of a recent report in this journal (Houssin, et al., Phys. Chem. Chem. Phys., 2003, 5, 3518, ) claim that a tetrapropylammonium (TPA) silicate mixture with molar composition 4.41 TPAOH : 10 SiO2 : 117 H2O contains high concentrations of two silicate oligomers, the prismatic double five-ring and a novel pentacyclic dodecamer. The latter species is derivative of the framework structure of silicalite-1, a MFI-type zeolite that spontaneously crystallizes from this system, and, indeed, the authors declare it to be a “nanoprecursor” in the TPA-mediated growth of silicalite-1. Using two-dimensional 29Si COSY NMR spectroscopy to examine an equivalent mixture enriched in the 29Si isotope, we show that the published peak assignments are erroneous. The signal assigned to the double five-ring corresponds, in reality, to the well-characterized pentacyclic octamer, while the three signals assigned to the pentacyclic dodecamer arise from three completely separate species. We find no evidence, therefore, to support the suggestion that silicalite-1 is formed by sequential condensation of precursor species any more complex than the simple orthosilicate anion.

Graphical abstract: Do zeolite precursor species really exist in aqueous synthesis media?

Article information

Article type
Paper
Submitted
08 May 2006
Accepted
22 May 2006
First published
02 Jun 2006

Phys. Chem. Chem. Phys., 2006,8, 3099-3103

Do zeolite precursor species really exist in aqueous synthesis media?

C. T. G. Knight, J. Wang and S. D. Kinrade, Phys. Chem. Chem. Phys., 2006, 8, 3099 DOI: 10.1039/B606419A

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