Electronic and structural effects of MgO(100) support on CO adsorption in coinage metal hexamers

We present a comprehensive DFT investigation of CO adsorption on six-atom coinage metal clusters (Cu6, Ag6, Au6) and their bimetallic analogues (Ag3Cu3, Au3Cu3, Au3Ag3), both in the gas phase and supported on a MgO(100) surface. Global optimization techniques were employed to identify the most stable geometries. Upon adsorption, pronounced structural rearrangements emerge, particularly in Cu-containing systems, leading to planar-to-3D transitions that enhance orbital hybridization with the CO molecule and modulate charge transfer pathways. Adsorption energies, projected density of states (PDOS), and Bader charge analysis confirm significant support-induced electronic reorganization. Among the studied systems, Ag3Cu3 supported on MgO exhibits the most favorable sensing performance, with a recovery time of 2.39 × 10−5 s and moderate adsorption strength. Overall, the MgO(100) support enhances charge donation to the clusters and stabilizes the adsorbed species, thereby improving sensor response in the supported configurations. These results highlight the critical role of cluster geometry, composition, and support in tuning adsorption behavior and gas sensing performance in coinage metal clusters.