AVS 51st International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM10
Novel NO Adsorption States on Pd (111) at Elevated Pressures: Irreversibility of the Effects of Temperature and Pressure on Heterogeneous Catalytic Systems

Tuesday, November 16, 2004, 11:20 am, Room 210B

Session: Catalytic Reactions: The Role of Surface Steps and Structure
Presenter: E. Ozensoy, Texas A&M University
Authors: E. Ozensoy, Texas A&M University
Ch. Hess, Fritz-Haber-Institut der Max-Planck-Gesellschaft,Germany
C. Yi, Texas A&M University
D. Loffreda, Institut de Recherches sur la Catalyse, Centre National de la Recherche Scientifique, France
D.W. Goodman, Texas A&M Univeristy
Correspondent: Click to Email
NO adsorption states on Pd (111) single crystal model catalyst surface were investigated using in-situ polarization modulation infrared reflection absorption spectroscopy (PM-IRAS) and density functional theory (DFT) calculations within 10@super -9@ - 400 mbar and 25-600 K. Vibrational spectroscopic data and DFT calculations indicate that besides the well-known monomeric NO adsorption states, a novel high-coverage monomeric adsorption state was observed at elevated pressures which was identified to have a (3x3)-7NO structure. NO-dimer states were also determined to exist under both ultra high vacuum (UHV) and elevated pressure conditions, however the nature of the NO-dimers that are formed at low and high pressures were found to be different in terms of their surface coverage, the strength of their interaction with the Pd (111) surface and the intrinsic N-N bond strength. In addition, the formation of dinitrosyls at @theta@@sub NO@ > 0.778 ML was also observed and found to take place only at elevated pressure and temperature conditions suggesting that not all of the thermodynamic equilibrium states at elevated temperatures and pressures are kinetically available at low temperatures and pressures for NO/Pd (111), emphasizing the danger of extrapolating the results of traditional surface scientific experiments performed under to UHV conditions to elevated pressure and temperature cases where the behavior of the system can show remarkable deviations from the expectations.