Noble-Metal-Supported GeS Monolayer as Promising Single-Atom Catalyst for CO Oxidation

The selection of a suitable substrate material for single-atom catalysis (SAC) is a key step in designing a new catalyst to achieve enhanced performance and selectivity. In the present study, we have explored the feasibility of GeS monolayer to serve as substrate for noble-metal-atom (Pd, Pt, Au, Ag, Rh, and Ir) SAC. Our exploratory study indicates that metal atoms, namely, Pd, Pt, Rh, and Ir, show considerable binding energies to the GeS monolayer with moderate to high diffusion barriers, which thereby reduces their clustering tendency. Examination of their catalytic activity toward CO oxidation reveals that both the Ir–GeS and Rh–GeS systems possess appreciable binding energies toward CO and O₂, an essential requirement for the initiation of catalytic cycle. CO oxidation on Ir–GeS SAC is studied in detail for three distinct mechanisms, namely, Eley–Rideal (ER), bimolecular Langmuir–Hinshelwood, and trimolecular Eley–Rideal (TER) mechanisms. Computation of activation barriers shows that Ir–GeS SAC prefers the less common TER mechanism, where two CO molecules and one O₂ molecule react to form the OOC–Ir–COO intermediate, which then dissociates into two CO₂ molecules. Additionally, microkinetic analysis predicts a maximum CO oxidation rate of 5.34 × 10³ s^–1 following the TER mechanism for the Ir–GeS system. Thus, the present study suggests that Ir-supported GeS can act as a potent SAC for low-temperature CO oxidation.