Study of the reaction of zeolites A (LTA), and X and Y (FAU) with NH4H2PO4 melts at 230 degrees C for varying time periods (30 min to 36 h) found the final product formed in each case to have a powder X-ray diffraction pattern consistent with ammonium aluminum pyrophosphate, NH4AlP2O7, the single crystal structure of which has not been reported. No intermediate crystalline phases were detected. Si-29 MAS NMR confirmed, however, that some Si was still present, and X-ray photoelectron spectroscopy revealed it to be located primarily at the crystallite surfaces. The crystallites were found to have an extremely low surface area (ca. 10 m(2) g(-1)), and hence not to be porous. MAS NMR studies found it to consist of six-coordinate aluminum and four-coordinate phosphorus in the aluminum pyrophosphate, and four-coordinate silicon in a highly siliceous environment. These results contradict the previous report of this reaction producing 'phosphated aluminosilicates in which phosphorus substitutes into the zeolite framework sites thereby forming promising anion exchangers' (A. Dyer, S.A. Malik, A. Araya, T.J. McConville, in: P.A. Williams, M.J. Hudson (Eds.), Recent Developments in Ion Exchange (Pap. Int. Conf. Ion Exch. Processes), 1987, pp. 257-263.). (C) 1997 Elsevier Science B.V.
- phosphated aluminosilicates
- ammonium aluminum pyrophosphate