O₂ Activation on Au/CeO<i>_X</i>(111) Model Catalysts and Its Role in CO Oxidation

Abstract The O 2 activation mechanism of Au/CeO x (111) (1.5 &lt; x ≤ 2) model catalysts has been systematically studied through an integrated surface science approach that combines infrared reflection absorption spectroscopy (IRAS), low‐energy electron diffraction (LEED), resonant photoemission spectroscopy (RPES), work function measurements, and isotope‐labeled temperature‒programmed desorption (TPD). The key findings reveal that, in contrast to the fully oxidized CeO 2 (111) and Au/CeO 2 (111) surfaces, which are inert toward O 2 adsorption, superoxide species (O 2 − ) are detected on the oxygen‐deficient CeO 1.85 (111) and Au/CeO 1.85 (111) surfaces upon O 2 adsorption at 105 K, which subsequently undergo dissociation as the surfaces are annealed, leading to formation of atomic oxygen, which reoxidizes the reduced ceria surfaces. Isotopic labeling TPD experiments using 13 C 16 O and 18 O 2 uncover the critical role of 18 O 2 activation in 13 C 16 O oxidation on the Au/CeO 1.85 (111) surface, which proceeds in the dual pathways: i) reaction of adsorbed 13 C 16 O on the Au nanoparticles with lattice oxygen ( 16 O) of the ceria to form 13 C 16 O 2 , generating oxygen vacancies, and ii) activation of 18 O 2 at vacancies to form O 2 ‐ , which dissociates and oxidizes 13 C 16 O to 13 C 16 O 18 O while replenishing lattice oxygen. These findings establish superoxide as the key intermediate and highlight the Mars–van Krevelen redox mechanism in sustaining catalytic CO oxidation.