REACTION OF LTA AND FAU ZEOLITES WITH NH4H2PO4 MELTS YIELDS CRYSTALLINE NH4ALP2O7

Study of the reaction of zeolites A (LTA), and X and Y (FAU) with NH4H 2PO4 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 dif fraction pattern consistent with ammonium aluminum pyrophosphate, NH4A lP2O7, the single crystal structure of which has not been reported. No intermediate crystalline phases were detected. Si-29 MAS NMR confirme d, however, that some Si was still present, and X-ray photoelectron sp ectroscopy revealed it to be located primarily at the crystallite surf aces. The crystallites were found to have an extremely low surface are a (ca. 10 m(2) g(-1)), and hence not to be porous. MAS NMR studies fou nd it to consist of six-coordinate aluminum and four-coordinate phosph orus in the aluminum pyrophosphate, and four-coordinate silicon in a h ighly siliceous environment. These results contradict the previous rep ort of this reaction producing 'phosphated aluminosilicates in which p hosphorus substitutes into the zeolite framework sites thereby forming promising anion exchangers' (A. Dyer, S.A. Malik, A. Araya, T.J. McCo nville, 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.