Copper-manganese mixed oxides: formation, characterization and reactivity under different conditions

Cu-Mn hydroxycarbonate-carbonate precursors, prepared by coprecipitation of nitrates, consist of Mn-containing malachite and Cu-containing rhodochrosite. Cu-Mn mixed oxides were obtained by heating the precursors at 723 K for 24 h in N2 and in air. The decomposition of the precursors depends on the atmosphere conditions (air, N2 or CO2) used during the thermal treatment and leads to several Cu-Mn oxides. For the Cu(I)xCu(II)1-xMn(III)2-xMn(IV)xO4 cubic spinel the redox equilibrium Cu(II)+Mn(III)⇆Cu(I)+Mn(IV) is shifted towards right or left for samples decomposed in air or in N2, respectively. In situ XRD and XPS reduction studies have shown that the final products of reduction are metallic copper and MnO, and that the N2-treated samples are more or less reducible than the air-treated ones depending on the initial CuO/CuMn2O4 compositional ratios.