CO oxidation on Pt-group metals has gained an enormous amount of attention in surface science for a long time, the reason being heterogeneous catalysis. One of the more common metals used is Pd, which is a widely used catalyst for oxidation and reduction catalysis [1]. The use of Pd has increased significantly during the last decade; a major reason being the increasing use of Pd in automotive catalysis as a so-called Pd-only three-way catalyst (TWC) or Pd-Rh based TWC. Despite a significant amount of research under ultra high vacuum conditions, many questions remain concerning the actual active phase of the Pd surface with respect to CO-oxidation, as well as issues concerning the details of the reaction pathways, in particular under more realistic conditions.
Here we report on the evolution of the O induced structures on the Pd(110) surface, using a combination of Low Energy Electron Diffraction, High Resolution Core Level Spectroscopy, Scanning Tunneling Microscopy, Surface X-Ray Diffraction and Density Functional Theory. We show that the that the previously observed c(2x4) [2] transforms above an oxygen pressure of 10-5 mbar via the formation of antiphase c(2x4) domain boundaries to structures which we denote (7x1) and (9x1), previously known as the "complex" [3] oxygen induced structure on Pd(110). The model contains segments of the Pd(110)-(1x1) in which the Pd rows are decorated by O in a zig-zag pattern. The segments are periodically separated by domain boundaries, inducing large distortion of the Pd(110) surface.
[1] R. lmbihl and G. Ertl Chem. Rev. 1995, 95, 697-733
[2] Kazutoshi Yagi, Hirohito Fukutani Sur .Sci 412/413, 1998, 489-494
[3] G. Ertl, P. Rau, Surf. Sci. 15 (1969) 443.
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