MAS-NMR STUDY OF PILLARED ALPHA-TIN AND ALPHA-ZIRCONIUM PHOSPHATES WITH ALUMINUM OLIGOMERS

The nature of the interaction of Keggin-like aluminum oligomers with l ayered alpha-tin and alpha-zirconium phosphates (alpha-SnP and alpha-Z rP) has been studied by P-31 and Al-27 MAS-NMR, complemented with infr ared and X-ray photoelectron spectroscopies. According to the type of aluminum solution used, monolayers and bilayers of the tridecamer ion [AlO4Al12(OH)(24)(H2O)(12)](7+) or dimeric polyoxocations, derived fro m this ion, are intercalated into the layered phosphates. The interact ion of the phosphate layer with aluminum species causes a shift of the P-31 Signal toward high field. The Al-27 spectra show the typical res onance Lines corresponding to octahedral and tetrahedral aluminum, tog ether with a third resonance at ca. 30 ppm assigned to pentacoordinate d aluminum, that increases in pillared phosphates formed by calcinatio n at 400 degrees C. From these results interlayer Al oxide pillars wou ld be cross-linked to the phosphate layer through pentacoordinated Al. The interaction of aluminum with the phosphate layer is stronger in a lpha-ZrP than in alpha-SnP.