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

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 CuOx 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 (O2-) species. The activated O2- 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─NHx···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.