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Calculated Magnetic Properties for the Characterization of Zeolite Active Sites by Annick Goursot; Dorothée Berthomieu is a Chemistry article available to read on EtoBox.

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Detailed structures of zeolite catalysts, including Al and cation distribution, framework and catalytic site geometries, are not fully accessible from experiment. Since the magnetic properties of framework elements and extra-framework cations are strongly dependent on their environment, the combined use of magic angle spinning NMR or ESR techniques with quantum chemical calculations is very useful to establish the local structure around specific sites. General effects of Al and B substitution in the zeolite framework, coupled with H(+) or Na(+) counter-ions, on the (29)Si, (27)Al and (11)B NMR spectra were studied, using a density functional theory (DFT)-based methodology, for a model of the zeolite mazzite. In agreement with experiment, the exchange of Na(+) by H(+) in the boron compound is accompanied by a change of B coordination from tetrahedral to trigonal, with a characteristic downfield shift of around 10 ppm, whereas the presence of water restores the tetrahedral boron and its NMR chemical shift. Further, ESR spectra of zeolites exchanged with open-shell cations provide useful data on the metal coordination and its reactivity compared with calculated model ESR properties. T

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Author

Annick Goursot; Dorothée Berthomieu

Publisher

John Wiley and Sons; Wiley (John Wiley & Sons); John Wiley & Sons Inc.; John Wiley and Sons Ltd; Wiley (ISSN 0749-1581)

Published

2004

Language

EN

Field

Chemistry (Physical Sciences)