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

Temperature-programmed reduction (TPR), oxidation (TPO), Raman spectroscopy , X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) were u sed to characterise catalysts based on manganese oxides, copper oxides or o ne of them mixed with platinum or palladium-supported on gamma-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, mixe d MnOx-Pt and MnOx-Pd revealed the presence of a mixture of manganese oxide s, particularly Mn2O3. In the fresh mixed MnOx-Pd and CuOx-Pd samples, Pd c atalysed the reduction of both MnOx and CuOx, whereas Pt only catalysed the reduction of MnOx. After hydrothermal treatment at 900 degrees C of the Mn Ox, mixed MnOx-Pt and MnOx-Pd samples, there was a formation of new mangane se oxide phase, Mn3O4 detected by Raman spectroscopy. TPR revealed increasi ng interaction between the metal oxides and the noble metals in the hydroth ermally 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 t han the oxides. Also, the reduction temperature of sulphates was lowered wh en noble metals are present. (C) 1999 Elsevier Science B.V. All rights rese rved.