Thermal Stability of Unary to Quinary Noble-Metal/3d-Transition-Metal Alloy Nanoparticles from Molecular Dynamics Simulations: Implications for Multimetallic Catalysis

Traditionally, noble-metal nanoparticles have been widely used as catalysts for various chemical reactions. Recently, 3d-transition metals have emerged as promising candidates for incorporation into next-generation high-performance noble-metal-based catalysts to maximize the utilization efficiency of these noble metals and simultaneously improve their catalytic performances under diverse reaction conditions. In this work, a series of noble metals (Pt, Pd, Au) and 3d-transition metals (Fe, Co), as well as their equimolar alloy nanoparticles, from binary to quinary, are modeled to investigate the thermal properties using molecular dynamics simulations. The heat of formation, melting point, bond order, and diffusive behaviors are studied. The results reveal that the melting points of most alloy nanoparticles are lower than the values predicted by Vegard’s law, and some binary and ternary nanoparticles even exhibit lower melting points compared with their unary counterparts. It is found that Co is unfavorable both energetically and thermally for forming chemically disordered alloys with noble metals. In contrast, the FePt system shows the strongest tendency to form a mixed phase among all of the binaries. Under the heating process, an alloy with a low heat of formation can retain a stable composition distribution, while composition redistribution and even segregation occur in an alloy with a high heat of formation. Furthermore, the regularity of atomic diffusivity in alloy nanoparticles is found to be markedly different from that in their unary counterparts, and the underlying reason is ascribed to the composition redistribution. These results significantly extend our understanding of the thermal evolution and stability of noble-metal/3d-transition-metal nanoparticles and provide important insights into design and preparation of multimetallic nanocatalysts with high performance and low cost.