Permanganic acid: a novel precursor for the preparation of manganese oxide catalysts

Unsupported and ψ-alumina supported MnOx catalysts (1-10 wt-% Mn) were preparedfrom aqueous solutions of HMnO4 and compared with nitrate based samples. They were characterized by XRD, XPS, BET area, oxygen storage capacity and by their catalytic behaviour versus ammonia DeNOx reaction. The unsupported oxide is amorphous at 300°C with a high surface area (45 m2.g−1) and transforms to α-Mn2O3 below 600°C. The supported samples show high dispersion which correlates well with high catalytic activity and the absence of detectable crystalline phase. The difference between HMnO4 and manganese nitrate precursors vanishes after calcination at 1000°C, with the formation of Mn3O4 and the transformation of the carrier into α-alumina; the DeNOx activity remains high but the selectivity towards N2 decreases as the temperature increases.