PNNL

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 × 10-9 ? 1.0 × 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 Ba(OH)2 layers were prepared by exposing a thick BaO (> 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 and nitrates) following their exposure to elevated NO2 pressure (~1.0 × 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, both releasing NO and O2, in accord with the melting/decomposition scheme for bulk Ba(NO3)2.