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Synthetic Studies of ABB'O 3 (A: La, Pr, Nd; B: Fe, Mn; B': Pd, Pt) Perovskites. -The perovskites O3 (Ln: La, Pr, Nd; M 1 : Fe, Mn; M 2 : Pd, Pt) are synthesized by a sol-gel method using malic acid as complex former. The samples are characterized by powder XRD, surface areas, oxygen desorption, and reduction properties. The surface areas are between 10 and 29 m 2 g -1 . Cubic structures of the perovskites are stable at elevated temperatures. -(KOPONEN, M. J.; SUVANTO, M.; PAKKANEN*, T. A.; KALLINEN, K.; KINNUNEN, T.-J. J.; HAERKOENEN, M.; Solid State Sci. 7 (2005) 1, 7-12; Dep. Chem., Univ. Joensuu, SF-80101 Joensuu, Finland; Eng.) -W. Pewestorf

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Barium, lanthanum, and praseodymium perovskites were prepared by malic acid complexation. Surface areas of the La and Pr perovskites were between 17.1 and 21.6 m 2 g )1 . The moderate low surface areas (5.7 m 2 g )1 ) observed for corresponding barium perovskites were due to the high calcination temperatures. The calcination temperature also affected the shapes and sizes of the perovskite particles. According to SEM images the nanoparticles of the La and Pr perovskites were spherical, whereas those of barium perovskites were flakes. The conversion of methane increased in the order of A-site metal Ba < Pr < La. The CH 4 conversion after SO 2 treatment correlated with size of the perovskite particles: the smaller the particles the better the activity. The highest methane conversion after SO 2 treatment was achieved with lanthanum perovskite with B-site metal combination Mn 0.4 Fe 0.6 .