Fig. 2: CO interaction and reaction with the CeO2(111) surface and ceria clusters supported on CeO2(111).
From: Dynamic control and quantification of active sites on ceria for CO activation and hydrogenation
a, b STM images of the CeO2(111) surface after the exposure to 250 L CO at 300 K. c C 1 s spectra of planar CeO2(111) and reduced CeO2-x(111) surfaces before and after the exposure to 0.1 mbar CO at 300 K. The stoichiometry of the reduced CeO2-x(111) surface was determined as CeO1.93 by XPS Ce 3 d spectra. d C 1 s spectra of the CeO2(111) film taken after sequential treatments: 1. the as-gown film; 2. the exposure of 250 L CO at 300 K; 3. the annealing to 500 K in 5 × 10−7 mbar CO and then cooling to 300 K in CO. e–h STM images of (e) Ce3O7, (g) Ce15O31 and (h) Ce21O43 clusters after the exposure to 5 × 10−7 mbar CO at 300 K. The corresponding structural model of Ce3O7 after CO adsorption was shown in (f). Adsorbate could be observed at the corner site of Ce3O7 and along the step/corner sites of Ce15O31 and Ce21O43. i STM image of Ce3O3 after the exposure to 5 × 10−7 mbar CO at 300 K. Adsorbate could be observed at the hollow site, and the corresponding structural model was shown in (j). k C 1 s spectra of supported ceria clusters taken after exposing to 250 L CO at 300 K (1. the ns-CeOx surface; 2. supported ceria clusters prepared by evaporating Ce in 1 × 10−7 mbar O2 at 300 K onto CeO2(111); 3. the r-CeOx surface). The intensities of carbonate and carbon peaks from (k) are plotted in (l), as a function of surface Ce3+ concentration, which was obtained from RPES taken simultaneously.
