Total oxidation catalysts based on manganese or copper oxides and platinum or palladium I: Characterisation Original Research Article

Temperature-programmed reduction (TPR), oxidation (TPO), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were used to characterise catalysts based on manganese oxides, copper oxides or one of them mixed with platinum or palladium-supported on γ-alumina. The catalysts were characterised before and after they had been exposed either to high temperature in the presence of steam or to sulphur dioxide. Raman spectroscopy, XRD, XPS and TPR performed on the fresh samples of MnOx, mixed MnOx–Pt and MnOx–Pd revealed the presence of a mixture of manganese oxides, particularly Mn2O3. In the fresh mixed MnOx–Pd and CuOx–Pd samples, Pd catalysed the reduction of both MnOx and CuOx, whereas Pt only catalysed the reduction of MnOx. After hydrothermal treatment at 900°C of the MnOx, mixed MnOx–Pt and MnOx–Pd samples, there was a formation of new manganese oxide phase, Mn3O4 detected by Raman spectroscopy. TPR revealed increasing interaction between the metal oxides and the noble metals in the hydrothermally treated mixed MnOx–Pd and CuOx–Pd samples, and also the appearance of interaction in the treated mixed CuOx–Pt sample. The sulphur adsorbed in all the MnOx samples formed sulphate, which was more difficult to reduce than the oxides. Also, the reduction temperature of sulphates was lowered when noble metals are present.