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

Paper SS1-MoA5
Low Temperature CO Oxidation on the Pt(111) Surface Studied Over an Extended Pressure Range

Monday, October 2, 2000, 3:20 pm, Room 208

Session: Model Catalysts at High Pressures
Presenter: D.J. Burnett, University of Michigan
Authors: D.J. Burnett, University of Michigan
A.M. Gabelnick, University of Michigan
A.T. Capitano, University of Michigan
A.L. Marsh, University of Michigan
D.A. Fischer, National Institute of Standards and Technology
J.L. Gland, University of Michigan
Correspondent: Click to Email
In-situ Fluorescence Yield Soft X-ray methods and Temperature Programmed Reaction Spectroscopy (TPRS) experiments were used to characterize the oxidation of CO in the temperature range where molecular oxygen dissociates. Taken together, these experiments enable characterization of this reaction over an extended pressure range (UHV to 0.01 Torr). Coadsorbed molecular oxygen and carbon monoxide TPRS experiments show that molecular oxygen must be adsorbed prior to carbon monoxide in order for low temperature (145 K) carbon dioxide to be produced. When molecular oxygen is preadsorbed with CO, the leading edge of molecular oxygen desorption is lowered nearly 20 degrees with a shoulder emerging at 127 K. When CO is preadsorbed, the molecular oxygen desorption peak remains unchanged (single peak with maximum at 142 K). Temperature Programmed Fluorescence Yield Near Edge Spectroscopy (TP-FYNES) experiments, capable of monitoring reactions under reactive atmospheres, were performed in pressures up to 0.01 Torr. For preadsorbed molecular oxygen with a CO overlayer, the same amount of low temperature carbon dioxide is formed when heated in vacuum and in oxygen pressures up to 0.002 Torr. For preadsorbed partial CO monolayers, the low temperature CO oxidation channel can be reached using pressures of oxygen (0.0005 to 0.01 Torr), as opposed to UHV experiments. Based on these results, oxygen dissociation appears to be limited in the vicinity of CO. Since coadsorbed CO enhances molecular oxygen desorption, these results suggest that competition between desorption of molecular oxygen and dissociation limits the reaction with coadsorbed CO. Detailed isothermal kinetic studies were performed with preadsorbed CO to establish a more detailed understanding of the oxidation mechanism.