Abstract
The location of cobalt in two porous metal-substituted zeolites, mordenite and ZSM5, and in a reference amorphous silicoalumina material, was investigated by solid-state NMR spectroscopy. The hyperfine shift and pseudoshift effects due to the paramagnetic metal on the NMR spectra of silicon and aluminum were used to estimate the number of aluminum and silicon framework sites in proximity of the cobalt. It was possible to confirm previous IR findings that only a fraction of the SiOHAl sites were involved directly in the bonding of the metal. A semiquantitative solid-state NMR analysis proved that siloxane bridges, and preferentially those close to aluminum locations, played a concurrent marked binding role in zeolites. It was found that for both zeolites the metal penetrates deeply into the structure. Furthermore, analysis of the NMR spectra implies that the cobalt position must be crystallographically well determined.
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