Structures of Bimetallic Copper Ruthenium Nanoparticles: Incoherent Interface and Surface Active Sites for Catalytic Nitric Oxide Dissociation

Bimetallic alloy nanoparticles are promising candidates for replacing platinum group metals utilized in the catalytic removal of nitrogen oxides in exhaust gas. In this study, we investigated the electronic, interfacial, and surface structures of copper/ruthenium alloy nanoparticles by quantum chemical computations using 135-atomic cluster models. We employed Ru-core/Cu-shell models in which the Ru-core takes both fcc (face-centered cubic) and hcp (hexagonal closed-packed) structures. The fcc-core model has a coherent Cu/Ru interface, while the hcp-core model involves an incoherent interface. This incoherence results in discontinuity in the lattice structure and the valence electronic structure, and generates step-like structures on the surface of the particle. Such a step-likesite enhances the catalytic activities for nitric oxide dissociation. The orbital energies suggest that the alloying can control the oxidation tendency of clusters. Charge-transfer occurs between the Cu shell and Ru core; the surface layer of the clusters has a positive charge, although the surface atoms are not directly binding to the core Ru atoms. The interfacial structure of core-shell inteiphase is a crucial factor to be considered in designing the properties of alloy nanoparticles.