Evidence of Multiple Cation Site Occupation in Zeolite NaY with High Si/Al Ratio

Abstract

23Na MAS NMR and 23Na 2D MQMAS NMR spectra of dehydrated NaY zeolite with different Si/Al ratios were analyzed. Particularly, the cation distribution was examined in both as synthesized NaY with a Si/Al ratio of 2.7 and a dealuminated NaY with a framework Si/Al ratio of 8.6, prepared by ion-exchange of a dealuminated NH4Y zeolite CBV712. This is, to the best of our knowledge, the first experimental investigation of the cation distribution in dealuminated NaY. Careful analysis of 23Na MAS NMR and 23Na 2D MQMAS NMR spectra of dealuminated NaY revealed the occupation of at least three different sites, contrary to what was expected from previous computational studies where site II was the only occupied site. Moreover, two new features could be observed. First, a split of the contribution of site I into two relatively close and similar narrow peaks in the MQMAS NMR spectra, and second a new narrow signal, interpreted in terms of fast cation movement inside the sodalite cage. This work also allows a clear identification of the contribution of site II to the 23Na MAS and MQMAS NMR spectra of as synthesized NaY (Na52Y). This was hardly possible in previous 23Na MAS NMR studies of NaX or NaY due to strong overlap of the broad quadrupolar pattern of site II with the one of the cations located in site I′.