NMR CHARACTERIZATION OF SYNTHETIC AND MODIFIED ALUMINUM ORTHOPHOSPHATES

31P, 27Al, and 1H MAS-NMR spectra of aluminum phosphates (Al/P = 1), obtained from different salts (nitrate, chloride, and sulfate) have been analyzed. Thermal treatment of samples results in the transformation of amorphous into crystalline AlPO4 samples (tridymite or α-cristobalite polymorphs). Structural changes induced by thermal treatments or incorporation of foreign ions (Li+, F-, or SO42-) are also analyzed and related to the catalytic activity of these samples. In particular, the amount and nature of hydroxyls are important factors that determine the surface physicochemical properties of these catalysts. © 1991.