AVS 47th International Symposium
    Surface Science Monday Sessions
       Session SS1-MoM

Paper SS1-MoM5
Reactivity of Carbonate and Chemisorption of Carbon Dioxide on Ag(110):A Combined STM, LEED, and TPRS Study

Monday, October 2, 2000, 9:40 am, Room 208

Session: Atomic-Scale Studies of Model Catalysts
Presenter: R.J. Madix, Stanford University
Authors: X.-C. Guo, Stanford University
R.J. Madix, Stanford University
Correspondent: Click to Email
Twenty years have passed since we first indentified the surface carbonate species formed by the reaction of carbon dioxide with preadsorbed oxygen on Ag(110) by isotope-labeled TPRS (temperature programmed reaction spectroscopy) studies. In the intervening years the same system has been extensively investigated by many groups with various surface techniques including LEED, HREELS, XPS, UPS, NEXAFS, and STM. The carbonate species was confirmed and a bonding configuration proposed. However the stoichiometry of this basic reaction has recently come into question as a result of STM studies by three independent research groups - each believing to image the carbonate structure on Ag(110). Here we present new results of a combined STM, LEED, and TPRS study in this laboratory. Carbonate is shown to form at modest exposures of preadsorbed oxygen to carbon dioxide, and its structure is readily imaged. However, a high reactivity of the carbonate toward CO is observed, which leads to a stable chemisorbed state of CO2 chemisorption on a Ag(110)-(1x2) reconstructed surface, in dramatic contrast to the weakly adsorbed physisorbed state of CO2 on Ag(110)-(1x1). Thus high exposures of preadsorbed oxygen to carbon dioxide in ultrahigh vacuum are expected to lead to the formation of this species, since one expects there to be a background CO partial pressure accompanying the carbon dioxide dose. Indeed we have duplicated this result with high CO2 exposures. The STM images of the chemisorbed CO2 we obtain agree precisely with those previously attributed to carbonate by other groups, and they are distinctly different from those of carbonate. The carbonate species was correctly imaged with STM and its formation was followed in situ at 300 K. We also report here on the structure and surface mobility of the chemisorbed CO2 species.