Geometrical features and chemical adsorptions of (Ag3Sn)n clusters

Abstract

The Ag-Sn alloys are famous ancient intermetallics, with the Ag₃Sn being a crucial component of the phase diagram. Recently, Ag₃Sn nanoparticles showcase efficient catalytic CO oxidation capabilities. Here, structural features and stability of (Ag₃Sn)_n (n = 1–6) clusters are first analyzed in detail. The results reveal that structures of them evolve from cages to close-packed icosahedra, where Ag are distributed on cores and gradually aggregated, whereas Sn occupy edge positions and become dispersed. Moreover, the icosahedral (Ag₃Sn)₃ has a higher stability than that of its neighbors and can maintain the structural integrity at 700 K. The molecular orbitals reveal that the (Ag₃Sn)₃ has an electronic open-shell configuration of 1S²1P⁶1D¹⁰2S²1F¹, which is confirmed by the density of states. Electrostatic potential surfaces show that (Ag₃Sn)_n have significant electron-deficient σ-hole regions at Ag sites, which can make CO stretching frequencies and bond lengths have red-shifts. Adsorption energies between (Ag₃Sn)_n and CO display odd–even oscillations, ranging from (0.43–0.68) eV, and the direction of charge flows is from CO → clusters. Our work provides inferences to structure evolutions and adsorptions of the Ag₃Sn alloy at the atomic level.