Theoretical Insights into Stepwise NH3 Oxidation on Pocket-Reconstructed Cu/CeO2(100) under Oxygen-Rich Conditions

Abstract

Cu-modified CeO₂(100) (Cu/CeO₂(100)) has been widely studied for NH₃-selective catalytic oxidation (NH₃-SCO), although most previous theoretical studies considered predefined Cu single atoms, Cu clusters, or CuO_x species, leaving the oxygen-induced reconstruction of the active Cu/CeO₂ surface and its catalytic effect unclear. Here, we employ density functional theory calculations with on-site Coulomb interaction corrections (DFT + U) to identify the stable reconstructed Cu/CeO₂(100) under O₂-rich conditions and elucidate the complete NH₃ oxidation pathways. The calculations reveal that the unique “pocket-like” reconstructed CeO₂(100) surface can drive the aggregation of the isolated Cu atoms into a stable Cu₃O₂ cluster within the pocket area. This restructuring generates active motifs comprising geometrically flexible CuO₄ units and adjacent Ce³⁺ sites, and each CuO₄ unit can facilitate the heterolytic NH₃ dissociation to NH₂*, while the Ce³⁺ site can activate O₂ into superoxide (⁠$O_2^{–}$⁠) species. The activated $O_2^{–}$ species then reacts with NH₂* to form stable NH₂O* and O* intermediates. Moreover, a cooperative dynamic restructuring between NH₂O* and nearby O* species gives rise to a distinctive Ce─O─NH_x···O five-membered ring. This unique configuration enables a nearly barrierless (0.02 eV) proton transfer to produce NHO* and OH* species, ultimately driving the deep oxidation to form NO* and H₂O*. These findings reveal a previously unrecognized pocket-confinement effect on Cu aggregation and redox-site cooperation on Cu/CeO₂(100), providing mechanistic guidance for the rational design of Cu/CeO₂-based NH₃-SCO catalysts under oxygen-rich conditions.