Preparation, characterization, and catalytic properties of NdSrCu_1-xCo_xO_4-δ and Sm_1.8Ce_0.2Cu_1-xCo_xO _4+δ (x = 0, 0.2 and 0.4) for methane combustion

Single-phase perovskite-like oxides NdSrCu_1-xCo_xO_4-δ and Sm_1.8Ce_0.2Cu_1-xCo_xO_{4+ δ} (x = 0, 0.2, and 0.4) were prepared using the citric acid complexing method coupled with ultrasonic treatment. We characterized the materials by a number of analytical techniques. It was found that the NdSrCu_1-xCo_xO_4-δ and Sm_1.8Ce_0.2Cu_1-xCo_xO_{4+ δ} catalysts possess T and T′ crystal structures, respectively. There are Cu³⁺/Cu²⁺ ions and oxygen vacancies in the former and Cu²⁺/Cu⁺ ions and extra (over-stoichiometric) oxygen in the latter. We examined the catalytic activity of the materials for methane combustion. Methane conversion increased with a rise in the amount of nonstoichiometric oxygen over the two series of catalysts. It is concluded that oxygen nonstoichiometry and Cu³⁺/Cu²⁺ or Cu²⁺/Cu⁺ redox couples facilitate the oxidation of methane over the NdSrCu_1-xCo_xO_4-δ and Sm_1.8Ce_0.2Cu_1-xCo_xO_{4+ δ} catalysts.