Density Functional Theory Study of Surface and Bulk Nitrates of .-Al2O3 Supported Alkaline Earth Oxides

Introduction Alkaline earth oxides (AEOs) such as BaO have received considerable attention for their application in the lean-burn engine NOx storage/reduction (NSR) technology [1]. Previous experimental investigations have indicated that barium nitrate is the most stable form of the stored NOx in Ba-containing NSR catalysts. Two distinctive types of barium nitrates, Ba(NO3)2, i.e. “surface” and “bulk” nitrate species, have been postulated on the basis of infrared and NMR spectroscopic and TPD measurements [2]. However, the specific identities and the structures of these two types of nitrate species on BaO/γ-Al2O3 materials, and the nature of the interactions between NOx, BaO and the γ-Al2O3 substrate are still not well understood. Furthermore, other γ-Al2O3-supported AEO (MgO, CaO and SrO) materials are also potentially useful for the storage and release of NOx yet are much less well studied [2]. A systematic study of NOx interacting with a series of AEO/γ-Al2O3 surfaces at the atomic level will provide important details of this particular catalytic process for the further development of more effective NSR catalysts.