CO chemisorption on both clean Ni(111) and MnOx (x is between 0.2 and 0.5)-modified Ni(111) surfaces at 200 °K have been studied by Auger electron spectroscopy (AES), thermal desorption spectroscopy (TDS), and high-resolution electron energy loss spectroscopy (HREELS). The MnOx Ni specimen was prepared by evaporating MnO2 powder to the Ni surface and then reducing the specimen at 700 °K. TDS results showed that the presence of surface MnOx species suppresses CO chemisorption and that the suppression is almost a linear function of the MnOx coverage. The most prominent CO desorption peak on Ni occurs at 415 °K. This peak intensity decreased with increasing MnOx coverage, indicating a site-blocking effect. An additional CO desorption peak at 305 °K was found on the MnOx-modified Ni surface. This 305 °K peak intensity attains a maximum at some intermediate MnOx coverage. HREELS showed a new C-O stretching frequency of 1620 cm-1 for CO adsorbed on the MnOx Ni surface. The disappearance of this 1620-cm-1 energy loss peak upon heating the surface to 325 °K suggests that both the 305 °K TDS peak and the 1620-cm-1 energy loss peak represent the same adsorbed CO state, which is attributed to CO adsorbed on MnOx Ni perimeter sites. Surface morphology of the oxide islands and significance of the perimeter sites are discussed along with experimental results.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry