Two samples of composition La0.9M0.1CoO3 (M = Sr, Ce) have been compared as
catalysts for the flameless combustion of methane. The former showed a low
er activity than the latter and this difference was enhanced at lower tempe
rature. Aiming at understanding the origin of this behaviour, EPR analysis
was carried out at temperatures down to 100 K. At T < 245 K a zero-field in
tense feature appeared with the M = Sr sample only, characterized by opposi
te phase with respect to the g similar to 2 line. This zero-field line was
attributed to microwave absorption by spin glass formed by cobalt- and oxyg
en-based paramagnetic ions. The tendency to strong interaction among these
species could also be a reason of the low oxygen availability for the catal
ytic methane oxidation at higher temperature. (C) 2000 Elsevier Science B.V
. All rights reserved.