A series of samples having the compositon of La~2~-~xSr~xNiO~4~-~λ(0≤x≤1) were prepared and used as catalysts for NH~3 oxidation. It was found that the La and oxygen vacancies exist in the La~2~-~xSr~xNiO~4~-~λ(0≤x≤1). The unit cell volume decreases with the increase of x. For both c and α parameters there appeared a turning point at x=0.5. Doping with a lower valence cation Sr^2^+ in the case of La~2NiO~4 resulted in an increase of Ni^3^+, consequently the formation of oxygen vacancies, the increase of reducing ability and the increase of catalytic activity. In the oxygen TPD of La~2~-~xSr~xNiO~4~ (0≤x≤1) appeared three peaks, the α peak at about 400K was attributed to the surplus oxygen desorption, the α peak at 700K which approaches to a maxium at x=0.6 was attributed to the oxygen adsorbed at oxygen vacancies. The β peak at about 1000K which depends closely on the x and favors the catalytic activity was attributed to the reduction of Ni^3^+. The catalytic activity of La~2~-~xSr~xNiO~4~ mixed oxides in the NH~3 oxidation in general could be attributed to the extent of the redox reaction : 2Ni^2^+＋O~2＋V~0 2Ni^3^+＋2O^- where V~o representes the oxygen vacancies and O^- the oxygen species adsorbed at the vacancies.

Key words: OXIDATION, OXIDATION REDUCTION REACTION, METAL CATALYST, X-RAY DIFFRACTION ANALYSIS, NITRIC ACID, AMMONIA, NICKEL OXIDE, OXIDATION STATE, STRUCTURE AND PROPERTY CORRELATION, LANTHANUM OXIDE