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

Abstract

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 N 2 and in air. The decomposition of the precursors depends on the atmosphere conditions (air, N 2 or CO 2) used during the thermal treatment and leads to several Cu-Mn oxides. For the Cu(I) x Cu(II) 1− x Mn(III) 2− x Mn(IV) x O 4 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 N 2, respectively. In situ XRD and XPS reduction studies have shown that the final products of reduction are metallic copper and MnO, and that the N 2-treated samples are more or less reducible than the air-treated ones depending on the initial CuO/CuMn 2O 4 compositional ratios.