Study of the stability of AlPON catalysts in an aqueous environment

Aluminophosphate oxynitride (AlPON) stability is studied by dispersing the solid in pure water and analysing the product by X-ray photoelectron spectroscopy (XPS), diffuse reflectance infra-red spectra (DRIFTS), thermogravimetry (TG) and X-ray absorption near edge structure (XANES). The presence of phosphate ions and the absence of Al3+ cations in the aqueous phase indicates that no dissolution but real hydrolysis of AlPON occurs. Upon hydrolysis, AlPON loses a quite significant amount of P and N from surface. The result is a nitrogen-impoverished surface phase in which aluminum keeps its original first co-ordination sphere. This new surface phase may be ascribed to either AlPO or AlPON with a lower nitrogen content. A third possibility, phosphorous oxynitride (PON), may not be discarded due to the similarity between its P/N ratio and that of hydrolysed AlPON. (C) 1997 Elsevier Science Limited.