Issue 2, 1994

Pillared hydroxycarbonates and mixed oxides. Part 1.—Copper–zinc–cobalt–aluminium system

Abstract

Cu–Zn–Co–Al mixed oxides with different Cu : Zn : Co : Al atomic ratios have been obtained by thermal treatment of hydroxycarbonate precursors at different temperatures (623, 723, 823 and 973 K in air). The characterization has been performed by X-ray powder diffraction (XRPD), diffuse reflectance spectroscopy (DRS), thermal analysis (TG/DTA), BET surface-area determination and measurements of magnetic susceptibility. The XRPD patterns showed that the precursors were almost pure pillared-layered (PLS) hydrotalcite-like materials with general stoichiometric formula M6II M2III(OH)16CO3.4H2O (MII= Cu, Zn, Co, MIII= Al). The thermal decomposition of the precursors occurred in four steps, the first three (up to T= 673 K) consisting of complete dehydration of the sample, the fourth (843 ⩽T/K ⩽ 923) due to the release of CO2. The precursor structure collapsed at T⩽ 623 K, giving rise to poorly crystalline materials, in which the Cu2+ ions retained a distorted octahedral symmetry. Crystalline oxide mixtures were formed only after complete release of CO2. XRPD showed that the oxides obtained by calcination at 973 K consisted of a mixture of CuO, ZnO and spinels such as CuAl2O4, ZnAl2O4, ZnCo2O4, and/or spinel solid solutions. According to DRS and magnetic susceptibility, the formation of ZnCo2O4 seems to be privileged with respect to that of Co3O4 and ZnO.

Article information

Article type
Paper

J. Mater. Chem., 1994,4, 197-204

Pillared hydroxycarbonates and mixed oxides. Part 1.—Copper–zinc–cobalt–aluminium system

S. Morpurgo, M. Lo Jacono and P. Porta, J. Mater. Chem., 1994, 4, 197 DOI: 10.1039/JM9940400197

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