Finding ideal material models for studying the role of catalytic active sites remains a great challenge. Here we propose pits confined in an atomically thin sheet as a platform to evaluate carbon monoxide catalytic oxidation at various sites. The artificial three-atomic-layer thin cerium(IV) oxide sheet with approximately 20% pits occupancy possesses abundant pit-surrounding cerium sites having average coordination numbers of 4.6 as revealed by X-ray absorption spectroscopy. Density-functional calculations disclose that the four- and five-fold coordinated pit-surrounding cerium sites assume their respective role in carbon monoxide adsorption and oxygen activation, which lowers the activation barrier and avoids catalytic poisoning. Moreover, the presence of coordination-unsaturated cerium sites increases the carrier density and facilitates carbon monoxide diffusion along the two-dimensional conducting channels of surface pits. The atomically thin sheet with surface-confined pits exhibits lower apparent activation energy than the bulk material (61.7 versus 122.9 kJ mol−1), leading to reduced conversion temperature and enhanced carbon monoxide catalytic ability. Catalytic carbon monoxide oxidation is an industrially important process. Here, the authors show that ultrathin cerium(IV) oxide with surface confined pits provides an ideal platform for investigating and optimizing the role of local atomic structure on carbon monoxide adsorption and oxygen activation.

Pits confined in ultrathin cerium(IV) oxide for studying catalytic centers in carbon monoxide oxidation