The co-catalytic effect of Sn, Ru and Mo decorating steps of Pt(111) vicinal electrode surfaces on the oxidation of CO

Model bimetallic catalyst surfaces were generated by depositing small submo nolayer amounts of Ru, Sn and Mo on Pr(111) and Pt(332) single crystal elec trodes. In particular, in the case of Pt(332), a step decoration was achiev ed and thus a catalyst surface with a known atomic arrangement of the const ituents. Ternary catalysts were modelled by sequential deposition of Sn and Ru. To study the influence on the rate of oxidation of adsorbed CO in cycl ic voltammetry, CO2 formation rates were monitored by differential electroc hemical mass spectrometry (DEMS), which allows a separation from pseudocapa citive effects, e.g. oxygen adsorption. Contrary to PtRu alloy electrodes, adsorbed CO on the Ru modified single crystal electrodes is oxidized in two oxidation peaks. In accordance with Monte Carlo simulations [I], this is d ue to slow diffusion of adsorbed CO to Ru sites. The CO adsorption state co rresponding to the 2nd peak is also not oxidized during an extended potenti al stop at the onset of the Ist peak. Ternary model catalysts were used to test whether a synergetic effect of Ru and Sn. which influence the CO oxida tion guile differently, is possible. The ternary model catalyst behaved lik e a superposition of the corresponding binary catalysts, probably because s eparate 2D ton Pt(lll) or 1D ton Pt(332)) islands of Ru or Sn were formed i nstead of an atomically mixed overlayer. Mo shifts the onset potential for oxidation of adsorbed CO to even lower potentials (0.15 to 0.2 V) than sn. However, at such a low potential only about 10% of the adsorbate is oxidize d, the main oxidation peak is hardly influenced. (C) 2000 Elsevier Science Ltd. All rights reserved.