New mechanistic pathways for CO oxidation catalyzed by single-atom catalysts: Supported and doped Au1/ThO2

Single-atom catalysts are of great interest and importance for designing new high-performance low-cost catalysts. We investigated CO oxidation catalyzed by single gold atoms supported on thoria (Au/ThO2) and doped ThO2 using density functional theory with Hubbard-type on-site Coulomb interaction (DFT + U). The calculation results show that the Au-doped ThO2(111) catalyst exhibits remarkable catalytic activity for CO oxidation via the Eley-Rideal mechanism in three steps, where the rate-determining step is decomposition of the OCOO* intermediate with an energy barrier of 0.58 eV. Moreover, our results also reveal a new mechanism of CO oxidation on a gold adatom supported by ThO2(111), where O-2 is adsorbed only at the Th site on the surface, and the gas-phase CO then reacts directly with the activated O-2* to form CO2, which is the rate-limiting step, with a barrier of 0.46 eV. It is found that CO oxidation can occur without CO and O-2 coadsorption on Au, which was previously considered a key intermediate. Therefore, these results provide new insights into CO oxidation on isolated gold atoms supported by the 5f-element compound ThO2(111). This mechanism can help clarify the catalytic cycle of CO oxidation, support the design of high-performance low-cost catalysts, and elucidate the redox properties of actinide oxides.