▎ 摘　　要

Engineering of high-performance catalysts is of great importance for reducing the greenhouse gas emission by the electrocatalytic oxidation of CO. Single-atom-catalysts (SACs) have gained substantial attention thanks to their superior catalytic activity for CO oxidation, and graphene has been considered as one most promising supporting material owing to its peculiar physicochemical properties. In this work, the mechanism of CO oxidation over iridium (Ir) embedded on both single vacancy graphene (Ir-GN(SV)) and di-vacancy graphene (Ir-GN(DV)) has been investigated with the aid of density functional theory (DFT). The structural properties of Ir-GN(SV) and Ir-GN(DV) were analyzed by Bader charge analysis and electron density difference map. The calculated adsorption energy values of CO and O-2 molecules on both the Ir-GNSV and Ir-GN(DV) have validated that both molecules can be molecularly adsorbed on the surface of each catalyst at room temperature. The results put forth that the reaction mechanism of CO + O-2 -> OOCO -> CO2 + O* prefers to Langmuir Hinshelwood (LH) mechanism. The activation energy for the transition-state for Ir-GNSV has been calculated to be 0.31 eV, whereas the first transition state (TS1) and the second transition state (TS2) of Ir-GN(DV) have been determined as 0.30 eV and 0.26 eV, respectively. Moreover, the results have confirmed that Ir-GN(SV) and Ir-GN(DV) surfaces have high catalytic activity and selectivity towards CO oxidation. On the basis of these findings, the proposed Ir-GN(SV) and Ir-GN(DV) catalysts are considered to be promising SAC for CO oxidation at low-temperature. It can be speculated that this work paves the way for the engineering of boosted-performance Ir-based heterogeneous catalysts by providing deeper mechanistic insights.