Preparation, characterisation and catalytic activity of Cu-Zn-based manganites obtained from carbonate precursors

Copper-zinc manganites with general formula CuxZn1-xMn2O4 (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, CuxZnyMn1-x-yCO3, with Cu2+, Zn2+ and Mn2+ 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 Cu2+ and Mn3+ 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 CuxZn1-xMn2O4 spinels with respect to ZnMn2O4. Preliminary results of the catalytic activity of copper-zinc-based manganites for the reduction of NO by hydrocarbons are presented. (C) 1998 Elsevier Science B.V.