CO preoxidation on Ru-modified Pt(111)

Electrochemical scanning tunneling microscopy was used to study the structural evolution of adsorbed CO during preoxidation on Pt(111) modified with spontaneously deposited Ru. During the preoxidation process. a phase transition was observed from (2 x 2)-3CO-alpha to (root 19 x root 19)R23.4 degrees-13CO via the transient structures (2 x 2)-3CO-beta and (1 x 1)-CO. A comparison of these structural changes with those that occur on unmodified Pt(111) revealed that the presence of Ru resulted in higher populations of transient structures at lower potentials and a cathodic shift in the potential at which preoxidation is complete. These observations are discussed in terms of increased mobility of adsorbed CO in the presence of Ru. (C) 2010 Elsevier B.V. All rights reserved.