Reaction of NO2 with a Pure, Thick BaO Film: The Effect of Temperature on the Nature of NOx Species Formed

Abstract

The adsorption and reaction of NO2 on a thick (>30 ML), pure BaO film deposited onto an Al2O3/NiAl(110) substrate were investigated in the temperature range of 300 − 660 K using temperature programmed desorption (TPD), infrared reflection absorption spectroscopy (IRAS), and X-ray photoelectron spectroscopy (XPS) techniques. The adsorption of NO2 on BaO at room temperature and the subsequent decomposition of the thus formed Ba(NOx)2 species follow the same mechanisms we have reported previously for NO2 adsorption at cryogenic temperatures. In cyclic experiments when the BaO film was exposed to NO2 at 300 K, followed by annealing to 575 K, a large amount of NOx was stored as nitrates, and no saturation was achieved even after the 10th adsorption/anneal cycle. This suggests the gradual conversion of the BaO film into barium nitrate clusters at elevated temperatures. The rate of nitrate formation increases as the sample temperature during NO2 exposure increases up to 610 K, while at even higher temperatures t...