AVS 51st International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM3
The CO-oxidation Reaction on Pt(111) and Pt(553): The Role of Steps

Tuesday, November 16, 2004, 9:00 am, Room 210B

Session: Catalytic Reactions: The Role of Surface Steps and Structure
Presenter: J.N. Andersen, Lund University, Sweden
Authors: J.N. Andersen, Lund University, Sweden
J. Gustafson, Lund University, Sweden
M. Borg, Lund University, Sweden
A. Mikkelsen, Lund University, Sweden
J. Weissenrieder, Lund University, Sweden
E. Lundgren, Lund University, Sweden
W.X. Li, Aarhus University, Denmark
B. Hammer, Aarhus University, Denmark
Correspondent: Click to Email
Catalytic materials often consist of small metallic particles dispersed on a support. The large proportion of undercoordinated (edge) atoms on such small particles may substantially influence the catalytic activity. Experimentally, the influence of undercoordinated atoms may be scrutinized by studying vicinal surfaces using methods that allow separate monitoring of what happens at the steps. Theoretically, the effects may be simulated using density functional theory (DFT) based total energy calculations. We present experimental and theoretical results for the adsorption of O and CO as well as for the CO-oxidation on Pt(111) and Pt(553) surfaces using high resolution core level spectroscopy and DFT based slab calculations. The results directly demonstrate that Pt(553) is more efficient in oxidizing CO than Pt(111), and allow us to obtain a very detailed picture of the microscopic processes responsible for this increased reactivity. A crucial result is the experimental and theoretical demonstration that CO molecules adsorbed at steps and on terraces, respectively, can be distinguished via their C 1s binding energies. These C1s fingerprints allow us to follow in a very detailed manner where CO molecules adsorb and react with preadsorbed oxygen. We study the CO oxidation by preadsorbing oxygen at 310K followed either by exposure to CO at the chosen reaction temperature or by annealing at the chosen reaction temperature of a CO overlayer adsorbed at low temperature. The results show that the CO2 production is more efficient on Pt(553) than on Pt(111). By utilizing the mentioned core level fingerprints, we show directly that the increased oxidation rate on Pt(553) is due to that the oxygen adsorbed in the proximity of steps is more reactive than oxygen adsorbed on the terraces. Comparison to theoretical results from DFT proves vital in fully understanding these experimental results and constructing the detailed microscopic model.