Can Subsurface Oxygen Species in Oxides Participate in Catalytic Reactions? An ¹⁷O Solid-State Nuclear Magnetic Resonance Study

The impacts of subsurface species of catalysts on reaction processes are still under debate, largely due to a lack of characterization methods for distinguishing these species from the surface species and the bulk. By using ¹⁷O solid-state nuclear magnetic resonance (NMR) spectroscopy, which can distinguish subsurface oxygen ions in CeO₂ (111) nanorods, we explore the effects of subsurface species of oxides in CO oxidation reactions. The intensities of the ¹⁷O NMR signals due to surface and subsurface oxygen ions decrease after the introduction of CO into CeO₂ nanorods, with a more significant decrease observed for the latter, confirming the participation of subsurface oxygen species. Density functional theory calculations show that the reaction involves subsurface oxygen ions filling the surface oxygen vacancies created by the direct contact of surface oxygen with CO. This new approach can be extended to the study of the role of oxygen species in other catalytic reactions.