M. Ferrandon et al., Total oxidation catalysts based on manganese or copper oxides and platinumof palladium I: Characterisation, APP CATAL A, 180(1-2), 1999, pp. 141-151
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.