Abstract
The coadsorption of CO and K on Pt(111) has been investigated by HREELS and LEED, revealing a rather local influence of K on CO adsorption. The interaction strength depends on the [CO]/[K] stoichiometry and reduces the CO stretch frequency to values between 1390 and 1820 cm−1. Four separate CO stretch bands for K-affected CO can be distinguished. A quantitative evaluation of loss intensities and CO coverages leads to several discrete [CO]/[K] stoichiometries between 0.5 and at least 3. Each stoichiometry is related to a particular CO stretch band. Several LEED patterns characteristics of the coadsorbed CO/K layers are also observed at low temperature (∼ 120 K). At 300 K, CO adsorption on K-free Pt patches is possible up to a K coverage of θK = 0.11. The range of the K influence is estimated to be lower than 4.2 Å. A qualitative model of CO/K interaction suggests a weakened CO-substrate bond and a strong electrostatic KCO interaction, supported by the observed metal-CO stretch frequency at 350 cm−1 compared to 470 cm−1 for CO on K-free Pt(111). In the monolayer regime of K a complex HREEL spectrum is observed with a prominent loss at 1495 cm−1 and additional losses at 130, 235, 415, 730, 820, 1230 and 1690 cm−1, suggesting a carbon and oxygen containing K compound.
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