Spin glass formation in La0.9Sr0.1CoO3 catalyst for flameless combustion of methane

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.