Nanoscale Grain Boundary-Weakened Ce–O Covalency and Surface Confinement Intrinsically Boosting Ceria Surface Oxygen Reactivity

Abstract

Promoting the reactivity of surface lattice oxygen atoms of oxide nanomaterials is critical for enhancing their catalytic performances in oxidation, hydrogenation, and electrocatalytic reactions; however, the fundamental electronic mechanisms governing this surface reactivity have long remained insufficiently understood. Here, we reveal the electronic mechanism of how the nanoscale grain boundary (GB) boosts the intrinsic surface reactivity of CeO₂ nanomaterials, in which GBs are introduced by pyrolyzing the precursors of cerium carbonate and formate. The results of X-ray absorption near-edge structures (XANES) at the O K- and Ce L₃-edges reveal that GBs can reduce the degree of covalency of Ce-O bonds, while H₂-TPR and Raman spectra show that this decreased orbital overlap can further weaken the confinement strength of surface oxygen atoms by the lattice potential. This electronic effect can fundamentally boost the leaving activity of surface lattice oxygen atoms, which further promotes the formation of oxygen vacancies and the activation of the O₂ molecules to oxidize benzyl alcohol into benzaldehyde with 100% selectivity. This structure-function relationship based on reduction in lattice covalency provides a new electronic perspective to understand how GBs and size reduction enhance nanomaterial surface reactivity.