Investigation of trimethylacetic acid adsorption on stoichiometric and oxygen-deficient CeO2(111) surfaces

Abstract

We studied the interactions between the carboxylate anchoring group from trimethylacetic acid (TMAA) and CeO₂(111) surfaces as a function of oxygen stoichiometry using in situ X-ray photoelectron spectroscopy (XPS). The stoichiometric CeO₂(111) surface was obtained by annealing the thin film under 2.0 × 10⁻⁵ Torr of oxygen at ∼550 °C for 30 min. In order to reduce the CeO₂(111) surface, the thin film was annealed under ∼5.0 × 10⁻¹⁰ Torr vacuum conditions at 550 °C, 650 °C, 750 °C and 850 °C for 30 min to progressively increase the oxygen defect concentration on the surface. The saturated TMAA coverage on the CeO₂(111) surface determined from XPS elemental composition is found to increase with increasing oxygen defect concentration. This is attributed to the increase of under-coordinated cerium sites on the surface with the increase in the oxygen defect concentrations. XPS results were in agreement with periodic density functional theory (DFT) calculations and indicate a stronger binding between the carboxylate group from TMAA and the oxygen deficient CeO_2−δ(111) surface through dissociative adsorption.