Interaction of NO₂ with BaO:  From Cooperative Adsorption to Ba(NO₃)₂ Formation

Abstract

The adsorption and reaction of NO 2 on a thick (>30 ML), pure BaO film deposited onto an Al 2 O 3 /NiAl(110) substrate were investigated using temperature-programmed desorption, infrared reflection absorption spectroscopy, and X-ray photoelectron spectroscopy techniques. For the first time, it was clearly demonstrated that BaO reacts with NO 2 to initially form nitrite−nitrate ion pairs by the cooperative adsorption mechanism predicted by theoretical calculation. These NO 2 - /NO 3 - ion pairs readily form even at 90 K. In the decomposition process of these ion pairs, first the nitrite species release an NO molecule and then form BaO 2 . At higher temperatures, nitrate species decompose in two steps: at lower temperature as NO 2 only, then, at higher temperature, as NO + O 2 . The results of NO 2 adsorption/reaction on this model system are identical to those we have found on a high surface area 20 wt % BaO/γ-Al 2 O 3 sample with the exception of surface nitrates that were only observed on the high surface area material.