Abstract
The interaction of NO2 with amorphous and crystalline Ba(OH)(2) supported on Pt(111) was studied in the wide pressure range of 1.0 x 10(-9) to 1.0 x 10(-4) Torr and compared to that with a thick (>20 monolayer equivalent (MLE)) BaO film using infrared reflection absorption spectroscopy (IRAS), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). The amorphous and crystalline Bi(OH)(2) layers were prepared by exposing a thick BsO (>20 MLE) layer on Pt(111) to H2O at 300 and 425 K, respectively. The amorphous and crystalline Ba(OH)(2) layers partially convert to Ba(NOx)(2) (nitrites anti nitrates) following their exposure, to elevated NO2 pressure (similar to 1.0 x 10(-4) Torr) at 300 K. The exposure of the crystalline Ba(OH)(2)/Pt(111) system to NO2 at 425 K, however, leads to the desorption of H2O and the complete conversion of the crystalline Ba(OH)(2) layer to Ba(NOx)(2), which consists of mainly crystalline nitrates and a small amount of nitrites. The amounts of NOx stored by BaO (>20 MLE)/Pt(111) and crystalline Ba(OH)(2)/Pt(111) systems upon their exposure to NO2 at 425 K are comparable. The thus-formed bulk crystalline Ba(NO3)(2) phase decomposes in two steps, twill releasing, NO and O-2, in accord with the melting/decomposition scheme for bulk Ba(NO3)(2).