A study of coprecipitated Mn–Zr oxides and their behaviour as oxidation catalysts

Mn–Zr mixed oxide samples with the general formula MnxZr1−xOy, where x=0,0.1,0.2,0.5,0.8,0.9,1, have been prepared by a conventional coprecipitation procedure and characterised by X-ray diffraction (XRD), TG-DTA analyses, FT-IR and UV–VIS-diffuse reflectance (DR-UV–VIS) spectroscopies, BET specific surface measurements and surface acidity by pyridine adsorption techniques. It was found that Mn stabilises the metastable phase tetragonal zirconia and gives rise to low-concentration solid solutions (up to about 10% of Mn), remaining as Mn(IV) within the structure. Their catalytic behaviour was tested by the phenanthrene combustion and the isopropanol oxidation reactions. All samples were found to be active in the total oxidation of phenanthrene at quite a low temperature of 523–673 K. They are also very active in the oxidation of isopropanol, giving rise to acetone with high selectivity at partial conversion and producing CO2 with total selectivity at total conversion. These materials are relevantly more active than Mn–Ti catalysts and approach the activity of pure Mn oxides, but with higher thermal stability.