Promotion of co oxidation on bimetallic Au-Ag(110) surfaces: A combined microscopic and theoretical study
Journal
Journal of Physical Chemistry C
Journal Volume
113
Journal Issue
30
Start Page
13151
End Page
13159
ISSN
19327455
Date Issued
2009
Author(s)
Abstract
The clean-off reaction of AgO added rows by CO on Ag(110) and Au/Ag(110) bimetallic surfaces was studied by scanning tunneling microscopy (STM) and compared with density functional theory (DFT). This combined study of a model system illustrated the complexity of catalytic enhancement in bimetallic systems. By analyzing in situ time-lapsed STM image series, we found that CO oxidation on a Au-enriched Ag(110) surface leads to an exponential depletion of oxygen with time and a reaction rate that is synergistically enhanced by the presence of Au. First principles calculations indicate that the local atomic configuration around the active reaction sites at the chain ends and the preference of Au atom substitution into the subsurface second Ag layer are of critical importance. By calculating CO adsorption energies and reaction barriers for plausible reaction pathways, a detailed description of the CO oxidation reaction emerges. For the optimal reaction pathway, a large (∼0.09 eV) barrier reduction and a small barrier of ∼0.01 eV were found for the Eley-Rideal (ER) mechanism. In contrast, a small (∼0.03 eV) barrier reduction and a moderate barrier of ∼0.23 eV were obtained for the Langmuir-Hinshelwood (LH) mechanism. The ER transitional state was also found to be lower in energy. We conclude that, irrespective of whether the ER mechanism is actually rate dominating, it is definitively enhanced. © 2009 American Chemical Society.
Type
journal article