On the influence of tin and bismuth UPD on Pt(111) and Pt(332) on the oxidation of CO

Deposition of Sn on Pt(lll) electrode gives rise to a sharp redox peak whic h is not due to the adsorption/desorption of Sn. The catalytic effect of th is Sn-UPD on the oxidation of adsorbed CO is negligible. UPD of Sn on Pt(33 2) and Pt(755) on the other hand, has a remarkable catalytic effect; the on set of CO oxidation is shifted down to 0.25 V. Comparative experiments are presented for Bi deposition on these surfaces. Even when the bismuth covera ge is high enough to block H-adsorption completely, CO is coadsorbed. Imped ance measurements show that the rate of hydrogen adsorption is decreased by Sn UPD on Pt(lll). (C) 1998 Elsevier Science Ltd. All rights reserved.