EFFECTS OF LA EXCHANGE ON NAY AND NAX ZEOLITES AS CHARACTERIZED BY SI-29 NMR

The effects of lanthanum exchange in zeolite Y and zeolite X were stud ied by Si-29 NMR. The spectra of calcined LaNaY were curve-fitted by t wo functions derived from the spectrum of pure NaY, by keeping the Si/ Al ratios of the two functions constant and similar to NaY. The fracti on of the spectra shifted upfield as a result of lanthanum migration w as consistent with the percent La exchange and not with the fractional occupancy of the SI' sites. Curve fitting of Si-29 NMR spectra of LaN aX was more complicated due to a selective ion exchange of cations clo se to the Si(4Al) sites in zeolite X. However, when a redistribution o f intensity between the two functions was allowed, while keeping the o verall Si/Al ratio constant, high consistency between the observed and simulated spectra of LaNaX was found. It is evident from this work th at the influence of lanthanum is different for the two zeolites. The r esults from the combination of the selective ion exchange and Si-29 NM R spectra of LaNaX were found to correlate with those from Monte Carlo simulations and may be used as a complement in the study of the local ordering of framework elements.