Structural Characterization of the Redox Behavior in Copper-Exchanged Sodium Zeolite Y by High-Resolution Powder Neutron Diffraction

The results of structural refinements on high-resolution powder neutron diffraction data for copper(II)- and copper(I)-exchanged zeolite Y and for the parent sodium zeolite Y, with composition Na₆₂Si₁₂₈Al₆₄O₃₈₄, are presented. Rietveld refinement of ambient-temperature data shows that the Cu(I) and Cu(II) cations are located on different sites in the two materials and that the structures differ considerably from that adopted by NaY. In Cu^IIY, with composition Cu₃₃Na₁₂Si₁₃₀Al₆₂O₃₈₄, the copper cations are located on the I_A‘, I_B‘, and II‘ sites with occupancies of 0.552(4), 0.145(7), and 0.162(8), respectively, while some sodium, 0.36(2), remains on site II. For Cu^IY, there is a redistribution of the cations on sites I_A‘, I_B‘, II‘, and II to 0.39(2), 0.21(1), 0.24(1), and 0.18(2), respectively. In both zeolites, site I is vacant. The high-quality diffraction data provide direct evidence of structural changes associated with the redox behavior of the zeolite, including distortion of the framework and the location of charge-balancing species.