Unravelling the Role of Structural Geometry and Chemical State of Well-Defined Oxygen Vacancies on Pristine CeO₂ for H₂O₂ Activation

Although H₂O₂ has been often employed as a green oxidant for many CeO₂-catalyzed reactions, the underlying principle of its activation by surface oxygen vacancy (V_o) is still elusive due to the irreversible removal of postgenerated V_o by water (or H₂O₂). The metastable V_o (ms-V_o) naturally preserved on pristine CeO₂ surfaces was adopted herein for an in-depth study of their interplay with H₂O₂. Their well-defined local structures and chemical states were found facet-dependent affecting both the adsorption and subsequent activation of H₂O₂. It is concluded that a strong adsorption of H₂O₂ on ms-V_o may not guarantee its subsequent activation. The ms-V_o can be only free for the next catalytic cycle when the electron density of surface Ce is high enough to reduce/break the O-O bond of adsorbed H₂O₂. This explains the 211.8 and 35.8 times enhancement in H₂O₂ reactivity when the CeO₂ surface is changed from (111) and (110) to (100).