Density functional theory (DFT) are used to carry out the trends in the adsorption chemistry of NO_x (x＝1, 2), CO₂, H₂O on the BaO(001) surface. NO adsorbs on the surface O atom in the formation of species|CO₂ is adsorbed on the surface O via its C atom and a carbonate-type structure is identified|while for the H₂O adsorption, it is observed that H₂O adsorbs dissociatively, forming hydroxyl on the surface|as for the adsorption structures of NO₂, two important geometries are identified: one is N-bonded adsorbate, and the other is O-bonded adsorbate. The adsorption strength increases in the order NO≈H₂O＜CO₂＜NO₂. For all adsorption species, the adsorption energies are markedly descending as the surface coverage increasing. It is worth noting that the simultaneous formation of surface / pairs by adsorptions of two NO₂ is most energetically favorable, and the cooperation effect probably could be the driving force for the BaCO₃ and Ba(OH)₂ eventual conversion into Ba(NO₃)₂.

Key words: lean-burn, NSR catalyst, density functional theory (DFT), NO_x adsorption, BaO(001)