Masanao Orihara

Reduction processes of rare-earth nickelate perovskites LnNiO3 (Ln=La, Pr, Nd)

Neutron diffraction technique was applied to PrNiO 2.34 and the unit cell of PrNiO 2.34 was reinvestigated. The diffraction peaks could be assigned by the monoclinic cell of a=8.656(6) A, b=3.655(2) A, c=5.442(4) A and β=71.50(7)°. The cell can be expressed as √5 × 1 × √2 of the fundamental perovskite. This suggests PrNiO 2.34 should be the compound Pr 3 Ni 3 O 8 . The existence of Ln m+n [Ni 3+ O 6/2 ] m [Ni + O 4/2 ] n homologous series can be proposed, where m sheets of octahedral layers alternate with n sheets of square planar layers along the [110] direction of the fundamental perovskite-type lattice. All the compounds appeared in the reduction processes of the perovskite-type LnNiO 3 (Ln=La, Pr, Nd), La 3 Ni 3 O 8 , La 2 Ni 2 O 5 and Ln 3 Ni 3 O 7 (Ln=Pr, Nd) belong to the homologous series.

Structural Property and Activity for Methane Oxidation of Iron Oxides Prepared by NaOH and FeSO4 Solution

Iron oxides were prepared by air oxidation of suspension obtained by mixing solutions of NaOH and FeSO4•7H2O. The ratio R was defined by mixing molar ratio of cations in the respective solutions (Na/Fe). Goethite (α-FeOOH) was mainly obtained in the range of R ≤ 1.9 (acidic region) and R ≥ 2.6 (basic region). Methane oxidation over the iron oxides started at as low temperature as

In Situ XRD and In Situ IR Spectroscopic Analyses of Structural Change of Goethite in Methane Oxidation

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, at which the goethite changed to a hematite (α-Fe2O3). The conversion ratio was low by the acidic goethite, in spite of its low crystallinity and high specific surface area. The basic goethite showed high activity for methane oxidation and the activity decreased grddually with increasing R. The low activity by the acidic goethite is attributable to the existence of some more percents of residual sulfate ion. And the sulfate ions disturbed the arrangement of oxide ions in the crystal structure of hematite.