CO adsorption on the model catalyst Pd/CeO2-x(111)

COLL 450

Geoff Thornton,, London Centre for Nanotechnology and Chemistry Department, UCL, 20 Gordon Street, London WCiH 0AJ, United Kingdom
Single crystal CeOx is an important model for a potential automobile catalyst support. Here we create ultrathin CeO2-x(111) films on Pt(111) and Rh(111) with controlled stoichiometry. X-ray photoelectron spectroscopy (XPS) is used to follow the average oxidation state of Ce and to examine the effect of Pd growth on the ultrathin films and subsequent CO adsorption. For stoichiometries more O rich than CeO1.8, Pd reduces the film, although below this stoichiometry charge is transferred between the thin film and Pd. This is probably a result of Pd growth on areas of the surface that are Ce2O3(0001). CO adsorbs only in the presence of Pd, independent of the stoichiometry of the original film, and without changing the stoichiometry. Reflection absorption infrared spectroscopy (RAIRS) has also been used to investigate the adsorption of CO on CeO2-x-supported Pd nanoparticles at room temperature. The results show that when CeO2-x is initially grown on Pt(111), a small proportion of the surface remains as bare Pt sites. However, when Pd is deposited onto CeO2-x/Pt(111), most of the Pd grows directly on top of the CeO2-x(111). RAIRS spectra of CO adsorption on 1ML Pd/CeO2-x/Pt(111) show a broad CO–Pd band, which is inconsistent with a single crystal Pd surface. However, the 5 ML and 10 ML Pd/CeO2-x/Pt(111) spectra show vibrational bands consistent with the presence of Pd(111) and (100) faces, suggesting the growth of Pd nanostructures with well defined facets.