Synthesis and Properties of Spinel-Type Co-Cu-Mg-Zn-Cr Mixed Oxides

Different mixed oxides containing Cu, Zn, Co, Mg, and Cr were obtained by calcining hydroxycarbonate precursors at different temperatures (653 or 873 K). Characterization was performed by X-ray diffraction, thermal analysis, infrared and reflectance spectroscopy, and BET surface area determination. Depending on metal composition the mixed oxides were constituted by CuO, ZnO, CuCrO4 ZnCr2O4, CoCr2O4, and CoxCu1-xCr2O4, MgxCu1-xCr2O4, Co2+Co3+xCr2-xO4 solid solutions. The phase evolution during reduction of the mixed oxides, followed by in situ X-ray diffraction up to 973 K, showed that the reducible species, when present, were CuO, CuCrO4, tetragonal CoxCu1-xCr2O4 and MgxCu1-xCr2O4 spinels, with metallic copper and cubic spinels as final products of reduction.