X-Ray Powder Rietveld Analysis of Ni Ion-Exchanged Y Zeolite

Coordination structure of nickel species in Y zeolite was investigated by means of X-ray Rietveld analysis in association with a Fourier transform method. All Ni2+ introduced into Y zeolite by ion exchange were situated at the three kinds of crystallographic positions, sites I, I ', and II. No Ni2+ was found at site II' in contrast to the result reported by Olson. In NiY, Ni2+ is probably coordinated by six basal oxygens of hexagonal prism to form an unstable planar hexagonal structure. On treating NiY with aq ueous NaOH solution at pH 10.8 - 11.0, a part of the Ni2+ was migrated from site I into the supercage to form nickel hydroxide species, whereas the remains were coordinated octahedrally by six oxygen atoms in the hexagonal prism. Several models based on the Fourier electron density map were presented for the structure of nickel hydroxide clusters formed in supercages. The formation of nickel hydroxo cluster complex with a unique structure, composed of seven nickel atoms, was suggested for NaOH-treated NiY zeolite.