Magic angle spinning NMR investigations on amorphous aluminophosphate oxynitrides

Multinuclear magic angle spinning NMR spectroscopy has been applied to char acterise the nitrogen species present in aluminophosphate oxynitrides, i.e. AlPONs, prepared by ammonolysis of high surface area aluminophosphates. At room temperature, the NH3 enters the coordination sphere of some tetrahedr al Al in the amorphous AlPO4 to increase its coordination to 5 and 6. The I R spectra show bands characteristic of NH3 and NH4+, while the P-31 spectru m gives a new low field component that reflects the influence of adsorbed N H3 and/or NH4+. When the aluminophosphate precursor is treated with ammonia at temperatures within the interval 1073-1123 K, a deeper modification of the AlPO4 occurs giving rise to new nitrogen species, which remain after ou tgassing above room temperature, and are tentatively assigned to -P-NH2 ter minal groups. When the ammonolysis is carried out at 1273 K an aluminophosp hate trydimite phase appears, and nitrogen must be engaged in the formation of moieties of the type PO4-xNx, with x > 1.