Abstract
CO adsorption and coadsorption with O 2 on a Pd{001}c(2×2)−Mn ordered alloy surface were studied with low energy electron diffraction (LEED) and high-resolution electron energy loss spectroscopy (HREELS). At room temperature, the energy loss at 253 meV in the EEL spectra of CO on Pd{001}c(2×2)−Mn, is attributed to the C-O stretching vibration of CO molecules at on-top sites of first layer Pd atoms. This peak diminished as the surface was exposed to oxygen. At 140 K, a new feature located at 285 meV has been observed in the EEL spectra of the coadsorption of CO and O 2. The peak position is near the asymmetric stretch mode of the CO 2 gas phase (293 meV). As the oxygen precoverage was increased under constant CO exposure, the intensity of this peak was increased. This peak disappeared upon annealing to 300 K for 1 min. Analyses indicate that the 285 meV peak is caused by CO 2 chemisorbed on Pd{001}c(2×2)−Mn with the molecular axis perpendicular to the surface. The reaction that produced CO 2 could be explained by the microscopic process of the interaction between the oxygen atoms, which are dissociatively adsorbed at the hollow sites between two Mn and two Pd atoms, and CO molecules, at on-top sites of neighboring Pd atoms.
Published Version
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