Sorption-desorption properties of nitric oxide over La2–xSr1+xCu2O6–δ (0≤x≤2)

Abstract

The NO sorption/desorption properties of substituted layered cuprates, La _{2– x} Sr _{1+ x} Cu ₂ O ₆ , have been studied to use them as an NO _x storage material. The cumulative amount as well as the initial rate of NO uptake at 250 °C increased with Sr-substitution, x, giving rise to the maximum at x=1.4, where a mixture of a orthorhombic layered cuprate and two binary oxides (Sr ₂ CuO ₃ and SrCuO ₂ ) was produced. The latter binary oxides play a key role in promoting the oxidation of NO and thus solid-gas reactions with the layered cuprate phase, which is accompanied by the formation of nitrate and nitrite species. The absorbed NO was liberated reversibly when heated at 200-600 °C in a stream of He. Sorption/desorption of NO could be cycled by employing a temperature-swing operation. The NO reactivity of the La _{2– x} Sr _{1+ x} Cu ₂ O ₆ system is compared with that of the La _{2– x} Ba _x SrCu ₂ O ₆ system in our previous study, which shows NO uptake based on intercalation into the layered structure and dissociative desorption to produce N ₂ and O ₂ .