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, CuCrO, ZnCr(2)O(4)(,) CoCr(2)O(4), and Co(x)Cu(1-x)Cr(2)O(4), Mg(x)Cu(1-x)Cr(2)O(4), Co(2+)Co(x)(3+)Cr(2-x)O(4) 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, CuCrO(4), tetragonal Co(x)Cu(1-x)Cr(2)O(4) and Mg(x)Cu(1-x)Cr(2)O(4) spinels, with metallic copper and cubic spinels as final products of reduction. (C) 2000 Academic Press.