| AVS 54th International Symposium | |
| Surface Science | Wednesday Sessions |
| Session SS1-WeA |
| Session: | Reactions on Metal Surfaces |
| Presenter: | E.Z. Ciftlikli, Rutgers, The State University of New Jersey |
| Authors: | E.Z. Ciftlikli, Rutgers, The State University of New Jersey A.V. Ermakov, Rutgers, The State University of New Jersey J. Lallo, Rutgers, The State University of New Jersey S. Rangan, Rutgers, The State University of New Jersey I.G. Shuttleworth, Rutgers, The State University of New Jersey E.Y.-M. Lee, Rutgers, The State University of New Jersey B.J. Hinch, Rutgers, The State University of New Jersey S.D. Senanayake, Oak Ridge National Laboratory |
| Correspondent: | Click to Email |
We report on high-resolution quantitative XPS studies, and complementary NEXAFS and TPD studies of adsorbed isocyanate (NCO) species on Cu(001). Adsorbed NCO can be prepared by room temperature dissociative adsorption of isocyanic acid (HNCO).1 XPS and NEXAFS confirm that, following hydrogen desorption, solely NCO remains. This is stable to at least 473K. However this species is prone to oxidation from any coadsorbed atomic oxygen. At temperatures as low as 373K, quantitative XPS results indicate CO2 desorption, while the surface N concentration is conserved. NCO oxidation to adsorbed nitrogen and CO2, continues until the atomic oxygen is depleted. This chemistry, while observed over a wide range of initial O surface coverages, is however modified in the presence of CN coadsorbates. We have also prepared NCO containing surfaces, through room temperature O2 and C2N2 exposures. Under these conditions, conversion of O and adsorbed CN, to NCO, is substantial though not complete, i.e. the resulting surface hosts NCO, CN and O species. These surfaces, on annealing to 373K again demonstrate N atom production but now also, in large part, CO desorption. This apparently direct NCO decomposition, to N(a) and CO, is observed only in the presence of coadsorbed O(a) and CN(a). At temperatures in excess of 573K, another thermally activated process is observed that is in common to both isocyanate containing surface types; i.e. those prepared with HNCO exposure or O2 + C2N2 exposures. In this latter process any coadsorbed CN appears to be only a passive bystander. We discuss possible mechanisms for these thermally activated reactions, and implications of these chemistries on other more catalytic surfaces commonly used for NOx reduction.
1H. Celio, K. Mudalige, P. Mills, M. Trenary, Surface Science 394 (1997) L168-L173.