CHARACTERIZATION OF MIXED COPPER-MANGANESE OXIDES SUPPORTED ON TITANIA CATALYSTS FOR SELECTIVE OXIDATION OF AMMONIA

Titania-supported copper-manganese mixed oxides were investigated in view of the selective oxidation of ammonia to dinitrogen and characterized by X-ray diffraction, photoelectron spectroscopy and temperature programmed reduction. The mixed oxides proved to be more active than the corresponding individual oxides. The TPR-results show that the reduction occurs at lower temperatures than that of the unsupported oxides. It is concluded that titania facilitates the change of oxidation states. Most active and selective for N2-formation is a catalyst with a molar ratio of Cu:Mn = 20:80. It contains a crystalline Cu1+xMn2-xO4 spinel phase (determined by XRD) and an additional X-ray amorphous Mn2+-containing species (determined by XPS), possibly Mn3O4 or MnO. Copper is present in the mono- and divalent oxidation state (shown by XPS). All catalysts hardly loose activity with time on stream, above all the copper-rich catalysts are very stable.