Surface structure of catalytically-active ceria nanoparticles

Catalytic mechanisms, and therefore activity, depend on the structure of catalyst surfaces. In turn, surfaces may reconstruct and/or exhibit local configurations that vary from bulk composition and structure. CeO₂ (ceria) is a redox catalyst of interest in numerous automotive, energy and, increasingly, biomedical applications. Previous studies aimed at understanding catalytic mechanisms on ceria have limited consideration to systems with bulk-like stoichiometric or sub-stoichiometric surfaces. Here we summarize previous computational studies on ceria surfaces, nanoclusters, and nanoparticles, and highlight challenges in constructing physically- representative ceria nanoparticle (CNP) structures. Setting aside assumptions of bulk-like stoichiometric or sub-stoichiometric ceria surface terminations, we report results of DFT + U calculations and show that sufficiently small CNPs are not bulk-terminated, but rather are stabilized by the formation of O _x^q groups (-2 ≤ q ≤ 0, x ≤ 3) at corners, edges, and {1 0 0} facets. These surface structures, not the annihilation and regeneration of O-vacancies, may directly control reduction/oxidation catalysis at CNPs below a critical size. As anion groups other than O_x ^q groups could be incorporated in stable CNP surfaces, this suggests the possibility of tailoring small CNP structures and mechanisms for particular catalytic reactions.