CO chemisorption on both clean Ni(111) and AlOx(x is between 0.5 and 1.1)-modified Ni(111) surfaces at 200 K has been studied by Auger electron spectroscopy (AES), thermal desorption spectroscopy (TDS), and high-resolution electron energy loss spectroscopy (HREELS). The AIOx/Ni(111) specimen was prepared by evaporating AI onto the Ni surface and then oxidizing and reducing the specimen at 700 K. TDS results showed that the presence of surface AIOx species suppresses CO chemisorption and that the suppression is almost a linear function of the AlOx coverage. The most prominent CO desorption peak on Ni occurs at 415 K. This peak intensity decreases with increasing Al0x coverage, indicating a site-blocking effect. An additional CO desorption peak at 300 K was found on the AIOx-modified Ni surface. This 300 K peak intensity attains a maximum at some intermediate AIOx coverage. HREELS results showed a new CO stretching frequency of 1613 cm-1 for CO adsorbed on the A1Ox/Ni surface. The disappearance of this 1613-cm-1 energy loss peak upon heating the surface to 325 K suggests that both the 300 K TDS peak and the 1613-cm- 1 energy loss peak represent the same adsorbed CO state, which is attributed to CO absorbed on A1Ox/Ni perimeter sites. Surface morphology of the oxide islands and significance of the perimeter sites are discussed.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry