Single Pd atomic catalyst on Mo₂CO₂ monolayer (MXene): unusual activity for CO oxidation by trimolecular Eley-Rideal...

The geometric stability, electronic structure and catalytic properties of a single Pd atom deposited on a pristine Mo₂CO₂ monolayer and a defective Mo₂CO₂ monolayer with an oxygen vacancy (denoted as Pd/O_V-Mo₂CO₂) are systematically investigated through density functional theory. We find that the oxygen vacancy (O_V) can stabilize the single Pd atom and make the Pd/O_V-Mo₂CO₂ system an excellent mono-dispersed atomic catalyst. The Pd dopant serves as an active center which makes the intermediates react productively around it. Three reaction mechanisms are considered for CO oxidation to test the catalytic activity of Pd/O_V-Mo₂CO₂, which exhibits high activity for CO oxidation via a tri-molecular Eley-Rideal (TER) mechanism with a rate-limiting energy barrier of 0.49 eV. The pre-adsorbed CO molecules on the Pd dopant could transfer electrons to the O₂-2π* orbitals, which would promote O₂ molecule activation and induce O-O bond scission. This work demonstrates that the defective monolayer MXene may serve as a promising sort of support to fabricate single atomic catalysts (SACs) for CO oxidation or other reactions, agreeing well with the experimental reports, which opens up a new avenue for the design and fabrication of SACs of MXene-based materials.