AVS 51st International Symposium
    Surface Science Monday Sessions
       Session SS-MoP

Paper SS-MoP6
Study of the Low-Temperature CO+O@sub 2@ Reaction Over Pd and Pt Surfaces

Monday, November 15, 2004, 5:00 pm, Room Exhibit Hall B

Session: Poster Session
Presenter: E. Podgornov, University of California, Riverside
Authors: E. Podgornov, University of California, Riverside
A. Matveev, Boreskov Institute of Catalysis, Russia
V. Gorodetskii, Boreskov Institute of Catalysis, Russia
F. Zaera, University of California, Riverside
Correspondent: Click to Email
The kinetics of CO oxidation at low temperature has been studied with effusively-collimated molecular beams (MB) and reactive thermal desorption, combined with an isotope-labeling technique. High-resolution electron energy loss spectroscopy (HREELS), field electron microscopy (FEM), and photoelectron microscopy (PEM) have also been applied to determine the roles of subsurface atomic oxygen and surface reconstruction in self-oscillatory phenomena on Pd(111), Pd(110) and Pt(100) single crystals and on Pd and Pt tip surfaces. It was found that high local concentrations of adsorbed CO during the transition from a Pt(100)-hex reconstructed surface to the unreconstructed 1x1 phase apparently prevents oxygen atoms from occupying hollow sites on the surface, and leads to the formation of a weakly-bound adsorbed atomic oxygen. It was inferred from MB experiments with oxygen isotope that the weakly-bound atomic oxygen is the active form that reacts with CO to form CO@sub 2@ at T = 140-160 K. In the experiments involving FEM, sharp tips of Pd and Pt were used to perform in situ investigations of dynamic surface processes. It was concluded that non-linear reaction kinetics is not restricted to macroscopic planes, since planes as small as 200 Å in diameter show the same non-linear kinetics as larger flat surfaces; regular waves appear under oscillatory reaction conditions and propagate through adjacent crystal nanoplanes because of an effective coupling between them. Additional results from isotope-labeling MB experiments led to the conclusion that adsorbed weakly-bound atomic oxygen, and not "hot" oxygen adatoms (excited transient states of adsorbed oxygen which may appear due to excess energy after the dissociation of O@sub 2@), is the active form of oxygen that reacts with carbon monoxide at low temperatures.