AVS 53rd International Symposium
    Surface Science Thursday Sessions
       Session SS1-ThA

Paper SS1-ThA8
Molecular Understanding of NOx-Storage-Reduction Catalysts: NO2 and H2O Adsorption on BaO/theta-Al2O3/NiAl(100)

Thursday, November 16, 2006, 4:20 pm, Room 2002

Session: Reactivity of Oxide Surfaces II
Presenter: E. Ozensoy, Pacific Northwest National Laboratory
Authors: E. Ozensoy, Pacific Northwest National Laboratory
J. Szanyi, Pacific Northwest National Laboratory
C.H.F. Peden, Pacific Northwest National Laboratory
Correspondent: Click to Email
NOx storage-reduction (NSR) catalysts were introduced very recently as an alternative way to treat NOx emissions originating from diesel mobile sources that are operating with high air to fuel ratios where traditional three way catalysts fail to perform. Unfortunately current understanding of NSR technology is mostly based on the industrial combinatorial studies which are focused on the product development rather than the fundamental molecular aspects of these interesting systems. Therefore here in this work, we present the very first detailed surface science study on the NSR systems where BaO nanoparticles deposited on an atomically ordered θ-Al2O3 ultrathin film grown on a clean NiAl(100) surface, is used as a model catalyst to mimic the industrial counterpart. BaO growth behavior on Al2O3/NiAl(100) was studied using X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), temperature programmed desorption (TPD) and low energy electron diffraction (LEED). Chemical and catalytic behavior of the BaO/Al2O3/NiAl(100) system is also investigated using H2O and NO2 as probe molecules in comparison with the clean θ-Al2O3/NiAl(100) surface. Preliminary results indicate that BaO deposition on θ-Al2O3/NiAl(100) at 300 K results in three dimensional BaO clusters which tend to wet the alumina surface upon heating up to 800 K. At higher temperatures (i.e. within 800-1200K), BaO desorption from the surface as well as interdiffusion of Ba into the Al2O3 lattice is observed. TPD studies indicate that NOx storage capacity of the BaO phase is significantly higher than that of the Al2O3 support. Our XPS and TPD data reveals that in the BaO phase, NOx is stored in the form of nitrates (NO3-) and nitrites (NO2-) that are stable up to 850 K. Co-adsorption of H2O and NO2 on BaO/Al2O3/NiAl(100) and θ-Al2O3/NiAl(100) surfaces was also studied using TPD to address competition for the different adsorption sites in NSR catalysts.