Abstract
Copper-zinc manganites with general formula Cu x Zn 1− x Mn 2O 4 ( x=0, 0.01, 0.05, 0.10) were prepared by thermal decomposition of carbonate precursors obtained by coprecipitation at constant pH. Precursors were characterised by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), thermogravimetric analysis (TGA-DTA) and FT-IR spectroscopy. For all samples a single rhodochrosite-like phase, Cu x Zn y Mn 1− x−y CO 3, with Cu 2+, Zn 2+ and Mn 2+ in solid solution was detected by XRD. Precursors were decomposed in air at 723 and 973 K giving spinel-like solid solutions, as evidenced by XRD and measurements of magnetic susceptibility. X-ray photoelectron spectroscopy (XPS) showed that Cu 2+ and Mn 3+ are present at the surface of the spinel structure and that the spinel surface is enriched in copper at higher calcination temperature. As evidenced by temperature programmed reduction (TPR), the presence of copper markedly enhances the reducibility of Cu x Zn 1− x Mn 2O 4 spinels with respect to ZnMn 2O 4. Preliminary results of the catalytic activity of copper-zinc-based manganites for the reduction of NO by hydrocarbons are presented.
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