Chemical activity of oxygen vacancies on ceria: a combined experimental and theoretical study on CeO₂(111)

Abstract

The chemical activity of oxygen vacancies on well-defined, single-crystal CeO2(111)-surfaces is investigated using CO as a probe molecule. Since no previous measurements are available, the assignment of the CO ν1 stretch frequency as determined by IR-spectroscopy for the stoichiometric and defective surfaces are aided by ab initio electronic structure calculations using density functional theory (DFT).

IR spectroscopy applied to metal oxide surfaces: adsorbate vibrations and beyond

“…Only a very weak, also negative, feature was observed for s-polarized light. Almost identical results were obtained for the IR-light incident along the [2 1 1] azimuthal direction [42]. In a next step, oxygen vacancies were deliberately introduced on the CeO 2 (1 1 1) surface by Ar + sputtering and annealing under UHV conditions ('reduced surface').…”

“…This behavior is different from the case of rutile-TiO 2 (1 1 0) [40] or CeO 2 (1 1 1) [42], where surface reduction resulted in the appearance of a secondary CO stretching peak either red-shifted or blue-shifted by about 10 cm −1 relative to the vibrational band observed on their stoichiometric counterparts. On anatase-TiO 2 (1 0 1), distinct additional CO vibrational peaks or strongly bound CO species were not detected (see Figure 4(b)).…”

“…This reduction-induced feature exhibits a blue-shift of roughly 10 cm −1 with respect to CO adsorbed on the stoichiometric CeO 2 (1 1 1) surface. At the same time, the analysis of temperature-dependent IRRAS data revealed a slightly larger binding energy of CO on the reduced surface relative to the fully oxidized surface, 0.31 eV vs. 0.27 eV [42].…”

“…The corresponding IRRAS data shown in Figure 16(b) revealed a substantial broadening of the CO stretching peak, which is centered at around 2163 cm −1 . By applying a fitting procedure, which assumes the presence of only a single additional species (in addition to that observed at 2154 cm −1 for the clean surface), the deconvoluted data [42] clearly reveal the presence of a new species at 2163 cm −1 . This reduction-induced feature exhibits a blue-shift of roughly 10 cm −1 with respect to CO adsorbed on the stoichiometric CeO 2 (1 1 1) surface.…”

“…Here, we present IRRAS results of CO adsorption on macroscopic monocrystalline ceria (1 1 1) and (1 1 0) surfaces. 2 (1 1 1) [42] In the work by Yang et al, first the stretching frequency of CO adsorbed on a fully-oxidized, single crystalline CeO 2 (1 1 1) surface ('stoichiometric surface') was determined using polarization-dependent IRRAS with the light incident along the [1 1 0] azimuth. The corresponding p-polarized data shown in Figure 16(a) reveal a single, sharp band at 2154 cm −1 , which can be assigned in a straightforward fashion to CO molecules bound to Ce 4+ cations embedded in a perfect monocrystalline surface environment (site 3 in Figure 17).…”