PREPARATION, CHARACTERIZATION 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 prec ursors obtained by coprecipitation at constant pH. Precursors were cha racterised by X-ray diffraction (XRD), diffuse reflectance spectroscop y (DRS), thermogravimetric analysis (TGA-DTA) and FT-IR spectroscopy. For all samples a single rhodochrosite-like phase, CuxZnyMn1-x-yCO3, w ith Cu2+, Zn2+ and Mn2+ in solid solution was detected by XRD. Precurs ors were decomposed in air at 723 and 973 K giving spinel-like solid s olutions, as evidenced by XRD and measurements of magnetic susceptibil ity. X-ray photoelectron spectroscopy (XPS) showed that Cu2+ and Mn3are present at the surface of the spinel structure and that the spinel surface is enriched in copper at higher calcination temperature. As e videnced by temperature programmed reduction (TPR), the presence of co pper markedly enhances the reducibility of CuxZn1-xMn2O4 spinels with respect to ZnMn2O4. Preliminary results of the catalytic activity of c opper-zinc-based manganites for the reduction of NO by hydrocarbons ar e presented. (C) 1998 Elsevier Science B.V.