Effect of preparation parameters on the properties of La0.9Ce0.1CoO3 catalysts: an EMR investigation

A few La1−xCexCoO3 (x = 0; 0.1) catalysts, prepared by the traditional sol–gel (SG) or by flame pyrolysis (FP) procedures have been analysed by EPR spectroscopy at 120≤T≤300 K. No EPR line was noticed with all of the x = 0 samples. The x = 0.1 SG catalysts gave a single EPR feature at g∼= 2, both when fresh and after catalytic reaction. This line was Lorentzian shaped at 120 K, broadening with increasing temperature, and also becoming a bit asymmetric after catalytic use. The x = 0.1 FP samples gave an EPR spectrum only after catalytic reaction. This pattern was rather similar to that obtained with the fresh SG sample with the same composition, but shifted towards lower magnetic field values. Furthermore, all the FP samples showed an intense ferromagnetic signal (FMR) after degassing treatment, while they remained EPR silent after oxygenation. An interpretation of most of these observations is here proposed on the base of polaron propagation and of formation of ferromagnetic spin bags. A correlation between catalytic performance, XRD patterns and electron magnetic resonance (EMR) (i.e. EPR or FMR) spectra, has been also highlighted.