AVS 53rd International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP25
First Principles Studies of the Reactivity of Pt Islets on Ru(0001)*

Tuesday, November 14, 2006, 6:00 pm, Room 3rd Floor Lobby

Session: Surface Science Poster Session
Presenter: M. Alcantara Ortigoza, Kansas State University
Authors: M. Alcantara Ortigoza, Kansas State University
S. Stolbov, Kansas State University
T. Rahman, Kansas State University
Correspondent: Click to Email
A key element of direct methanol fuel cells is a catalyst for electro-catalytic oxidation of methanol. However, during this reaction, intermediate CO adsorbed on the surface blocks the active sites and poisons the reactivity of commercial catalysts. It was recently reported that nanoclusters of Ru with sub-monolayer of Pt are much more tolerable to CO than commercial alloy catalysts.@footnote 1@ The mechanism of the reaction on this nano-catalyst is not clear. It apparently depends on the size of Pt islands whose optimum size is small (about 10 atoms). As a step towards understanding of the nature of this phenomenon, we have performed first principles studies, based on density functional theory, of the stability and reactivity of small Pt islands on Ru(0001), whose geometry represents that of the dominant facets of the Ru nanoparticles in the experiments of Brankovic et al. We have calculated energetics and geometric structures for 1-to 9-atom islands and one monolayer of Pt adsorbed on Ru(0001) using the pseudopotential method with the plane wave expansion for the wave function. We find the formation energy per atom of the islands to decrease monotonically from -5.1 eV to -6.1 eV, as the number of Pt atoms in the 2D island increases from one atom to one monolayer. The propensity of the systems to form as many interatomic bonds as possible thus overpowers the effect of stress caused by some misfit of Ru and Pd interatomic bonds. CO molecules are found to adsorb preferentially at the Pt island edges with a bond tilted towards the Ru atoms. The energetics of diffusion of CO and OH and their reaction pathways, as an intermediate step in methanol decomposition, are examined. @FootnoteText@ @footnote 1@S. R. Brankovic, J. X. Wang, and R. R. Adzic, Electrochem. Sol.-St. Lett. 4 (12) A217 (2001). *Work supported in part by DOE under grant DE-FG02-03ER15465 and DE-FG02-03ER46058.