Absorption–desorption properties of nitric oxide over layered cuprates, La2 –xBaxSrCu2O6

Abstract

The layered cuprate La_{2 –x}Ba_xSrCu₂O₆(0⩽x⩽1.0) exhibited rapid absorption of gaseous nitrogen monoxide at 250 °C. The cumulative amount of NO absorption increased monotonically with Ba content, exceeding 0.9 mol mol^–1 at x= 1.0. X-Ray diffraction showed that NO absorption brought about significant expansion of the interlayer spacing of the cuprate without precipitation of other crystal phases. Since the original interlayer spacing could be reversibly restored after desorption of NO, the NO absorption is considered to proceed via intercalation of NO molecules into the layer structure. The desorption of NO-absorbed samples was studied by temperature-programmed desorption. Part of the absorbed NO was desorbed as NO–NO₂ mixtures below 600 °C, but the remainder was desorbed dissociatively as O₂at 620 deg;C and N₂ at 920 deg;C. The apparent conversion of absorbed NO to N₂, which was strongly dependent on the Ba content, reached a maximum (ca. 50%) at x= 0.5. This type of dissociative desorption of NO is in striking contrast to conventional NO absorption–desorption systems in the following respects: (a) NO absorption is not associated with the formation of nitrates or nitrites of barium; (b) the desorption temperature of N₂ is much higher than that of O₂.