Studies on the redox behaviour of La_1.867Th_0.100CuO₄ and its catalytic performance for NO decomposition

La_1.867Th_0.100CuO₄ was prepared by means of the citric acid complexing method. The reduction-oxidation (redox) properties of this composite oxide have been investigated by using the XRD, TGA, EPR, TPD, and SEM methods. The fresh (non-reduced) La_1.867Th_0.100CuO₄ catalyst is single phase with tetragonal K₂NiF₄-type structure. There were three reduction steps observed over La_1.867Th_0.100CuO₄ in the temperature ranges of 25-100, 100-300, and 300-500°C, respectively. After reduction at 300°C, the material still retained its original single phase but there were oxygen vacancies generated in the lattice. After reduction at 500°C, it decomposed to a mixture of oxides In the course of reduction, trapped electrons were generated. During the oxidation of the reduced sample, O₂^- was detected Apparently, oxygen vacancies are able to stabilise O₂^- on the surface of the catalyst. NO adsorption on both the fresh and reduced La_1.867Th_0.100CuO₄ samples generated NO radicals and O₂^- species. On a La_1.867Th_0.100CuO₄ sample reduced at 300°C, [O₂NO₂]^2- was generated in NO adsorption and decomposed to N₂ and O^2- at ca. 730°C. After reduction, the O^2- inside the La_1.867Th_0.100CuO₄ lattice became more mobile and participated in the decomposition of [O₂NO₂]^2-. The fresh (non-reduced) La_1.867Th_0.100CuO₄ sample with cation defects in its lattice shows higher NO decomposition activity than the fresh La₂CuO₄ sample in which there are no cation defects. The 300°C-reduced La_1.867Th_0.100CuO₄ with cation defects and oxygen vacancies is more active than the fresh one for NO decomposition. The redox action between Cu⁺ and Cu²⁺ is an essential process for NO decomposition.