Multinuclear MQMAS NMR study of NH4/Na-ferrierites

(MQ)MAS NMR is a powerful new method to study quadrupolar nuclei, enabling separation of the chemical shift interaction from the qundrupolar interaction. We showed that hydrated NH4-ferrierites have two distinct aluminum sites with an average ratio of 4:5. These sites were assigned to T(2) + T(3) and T(5) + T(1) + T(4) sites, respectively. Upon increase of the aluminum content, the ratio 4:5 remained the same. At higher Si/Al ratios, aluminum tends to form aluminum-rich zones, leaving some unit cells without aluminum atoms. Na+ exchange decreases the average T-O-T angles of the aluminum sites. It has been found that Na+ ions are preferentially located in the "ferrierite cages", formed at the intersection of six-membered ring channels and eight-membered ring channels.