Alignment-Controlled O2 Chemisorption and Catalytic CO Oxidation on Curved Pt(111)

Steric effects in O₂ chemisorption and catalytic CO oxidation on stepped Pt(111) surfaces have been investigated by scanning a narrow alignment-controlled O₂ beam across a curved Pt(111) surface, on which the densities of {100} (A-type) and {111} (B-type) steps vary smoothly with the distance from the center of the crystal. The contributions of trapping-mediated and activated chemisorption to these processes on the terraces and steps were discussed based on the dependence of these processes on the kinetic energy (80–500 meV) and alignment of O₂. The results indicate that (i) the probability of activated O₂ chemisorption on surfaces with type-B steps is slightly lower than that on surfaces with type-A steps and (ii) CO oxidation proceeds both at terraces and steps at the sample temperature of 593 K, while it happens only at terraces at 423 K. The results of CO oxidation experiments at 423 K indicate that the rate of CO₂ production at terraces of the stepped Pt(111) surface is lower than that at a flat (111) surface and depends on the step structure.