Effect of preparation parameters on La(0.9)Ce(0.1)CoO(3) catalyst: an EPR investigation

Effect of preparation parameters on La0.9 Ce0.1 CoO3 catalyst: an EPR investigation. C.Oliva (a), S.Cappelli (a), A.Kryukov (b), G.L.Chiarello (a), A.V.Vishniakov (b) and L.Forni (a). (a) Dipartimento di Chimica Fisica ed Elettrochimica, Università degli Studi di Milano, and CNR Institute, via C.Golgi, 19 20133 Milano, Italy. Fax:+39-02-70638129 (b) D.I.Mendeleev Chemical-Technological University of Russia, Moscow, Russia. A few La1-xCexCoO3 (x = 0; 0.1) catalysts, prepared by traditional sol-gel or by flame pyrolysis1 (SG or FP samples, respectively) have been analysed by EPR at 120  T  300 K. Only 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, but broadened and became a bit asymmetric with increasing temperature. Its integrated area decreased only with the fresh sample. The x = 0.1 FP samples behaved in a different way. In fact, no EPR signal was recorded with them when fresh, but only after catalytic reaction. This pattern was rather similar to that obtained with the fresh SG sample with the same composition. 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 EPR/FMR spectra, XRD patterns and catalytic performance has been also highlighted. ____________ 1 G.L.Chiarello, I.Rossetti, L.Forni, J. of Catalysis, 236 (2005) 251.