Double perovskite-type oxide (La0.5Sr0.5)(2)FeNiO6-delta (LSFN) was invented as the precursor of a catalyst for the partial oxidation of methane (POM). The catalyst derived from LSFN is the K2NiF4-supported Ni(0) system, where K2NiF4 denotes the oxide (La0.5Sr0.5)(2)Ni1-xFeO4+delta, a chemically stable structure with mixed ionic and electronic conducting properties. Among the four catalysts derived from LSFN, the best catalyst showed a high CH4 conversion (X-CH4 > 99%), high syngas selectivity (>98%) and, most importantly, nil coke formation at 900 degrees C. Detailed structural characterizations revealed that the presence of a small amount of SrCO3, left initially by incomplete formation of LSFN, and of nano-Ni(0) domains (or clusters <5 nm on average) on the K2NiF4 support is vital to this extraordinary catalytic performance. Furthermore, the decrease of H-2/CO molar ratio with the increase in methane conversion happening in the course of activation was simulated using a group of the proposed key reaction steps of POM. (C) 2009 Elsevier B.V. All rights reserved.