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

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 MnO_x, mixed MnO_x–Pt and MnO_x–Pd revealed the presence of a mixture of manganese oxides, particularly Mn₂O₃. In the fresh mixed MnO_x–Pd and CuO_x–Pd samples, Pd catalysed the reduction of both MnO_x and CuO_x, whereas Pt only catalysed the reduction of MnO_x. After hydrothermal treatment at 900°C of the MnO_x, mixed MnO_x–Pt and MnO_x–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 MnO_x–Pd and CuO_x–Pd samples, and also the appearance of interaction in the treated mixed CuO_x–Pt sample. The sulphur adsorbed in all the MnO_x 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.