Abstract
Coadsorption of CO with Pb adlayers on Pt(111) was examined by in situ electrochemical and ex situ surface science methods. CO alters the Pb surface redox reaction, reducing the potential for the Pb2+ad■Pb0ad reaction from 0.65 V for Pb in 0.1 M HClO4 to 0.52 V with coadsorbed CO. Pb adlayers do not appreciably affect the potential for CO oxidation at moderate Pb coverages. At high Pb coverages, oxidation of CO occurs over a broad potential range, of 0.3–0.6 V. The CO/Pb/Pt(111) system exhibits dynamic emersion with a constant emersion potential of about 0.5 V that is set by the Pb surface redox reaction, Pb2+ad■Pb0ad. Pb adatoms act as site blockers to CO adsorption, a monolayer of Pb completely blocking CO adsorption in vacuum. The thermal desorption behavior of CO from Pb/Pt(111) surfaces was modeled using three parameters: Ea the CO activation energy for desorption in the limit of zero CO coverage, Eb the coverage dependent CO activation energy term, and ΔE the change in Ea and Eb with respect to Pb coverage.
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