Adsorption of CO, NO, and H2 on the PdnAu55-n Nanoclusters: A Density Functional Theory Investigation within the van der Waals D3 Corrections

The PdAu nanoclusters have innumerable potential applications in catalysis, especially because of the changes of the physical and chemical properties as a function of the composition and geometric shape; however, the understanding of the adsorption process is far from satisfactory mainly because of the strong dependence of the adsorption properties on the size, shape, and composition of the nanoclusters. Here, we report a study, based on density functional theory calculations, of the CO, NO, and H-2 molecules adsorbed on PdAu nanoclusters, where we performed a systematic study for bimetallic PdnAu55-n nanoclusters, considering the main energetic, structural, and electronic properties in relation to the composition, and after that, for specific compositions, we performed the adsorption of one molecule (CO, NO, and H-2) on the nanoclusters. We have obtained the lowest energy structures for monometallic and bimetallic nanoclusters, based on the excess energy, where we identified the maximum stability, n = 20, with the Au atoms in the surface region (atoms directly exposed to the vacuum) and Pd atoms in the core region. For the molecular adsorption, we consider Pd-55, Au-55, and Pd20Au35, for which we find that the adsorbed NO systems have higher adsorption energies (in modulus) because of the highest position of the center of gravity of the d-states in relation to the Fermi level. In general, the molecules prefer the top site, with the Pd-molecule bonds being more intense than the Au-molecule bonds. The intermediate adsorption energy values obtained for Pd20Au35 nanoclusters, for CO and NO adsorptions, show the promising Pd-Au combination to build catalysts that are adequate to avoid catalyst poisoning.