First-Principles Study of O2 Activation over Pd Adclusters and Embedded Clusters in Pd–Au Bimetallic Surfaces

Abstract

Recent studies have revealed that metal adatom clusters exhibit distinct catalytic properties compared to conventionally modeled extended facets. Here, we used periodic density functional theory (DFT) to investigate differences in O₂ activation between two-dimensional clusters of Pd atoms supported on Au(111) (adclusters) and embedded within Au(111). We analyzed the barriers for O₂* dissociation and desorption on Pd clusters ranging in size from one to nine Pd atoms in a (4 × 4) surface unit cell. Our findings revealed that, while O₂* dissociation barriers between adclusters and embedded clusters are similar, adclusters exhibit significantly higher desorption barriers than embedded clusters by between 0.3 and 0.7 eV. This suggests that Au surfaces with Pd adclusters have enhanced selectivities for O₂* dissociation over desorption, which may yield faster rates for processes limited by O₂ activation. Additionally, we evaluated the stability of Pd–Au surfaces under vacuum and in the presence of O₂*, calculating the temperature required for Pd adatom formation from Pd atoms embedded in Au(111). Our predictions show that adatom formation is unlikely as the competing desorption or dissociation of O₂* occurs at lower temperatures for all considered cluster sizes. These findings highlight the role of surface roughness in catalytic processes on Pd–Au bimetallic surfaces.