CHARACTERIZATION OF COPPER-MANGANESE MIXED OXIDES

Copper-manganese mixed oxides were obtained by decomposition at 723 K for 24 h, in nitrogen and in air, of hydroxycarbonate and/or carbonate precursors containing both Cu(II) and Mn(II) ions in the same structure. It is shown that even at this relatively low temperature a spinel phase, Cu(I)xCu(II)1-xMn(III)2-xMn(IV)xO4, is formed. The redox equilibrium Cu(II) + Mn(III) = Cu(I) + Mn(IV) is shifted toward right or left when the samples are decomposed in air or in nitrogen, respectively . In Situ XRD and XPS reduction studies have demonstrated that: (i) the final products of reduction are metallic copper and MnO; (ii) if in the initial mixed oxide composition CuO is present in larger amount than CuMn2O4 the N2-treated product is more reducible than the air-treated one; (iii) when the CuMn2O4 spinel phase predominates the sample as a whole becomes less reducible; (iv) the N2-treated sample which contains the spinel Cu(II)Mn(III)2O4 is less reducible than the corresponding air-treated one containing the spinel with all Cu(I), Cu(II), Mn(III) and Mn(IV) species.