Stability and Structures of Silver Subnanometer Clusters in EMT Zeolite with Maximum Aluminum Content

Abstract

The stability of small silver clusters, Agn with n = 3, 4, 6, and 8, supported in a sodalite of EMT zeolite with a maximum possible aluminum content (Si/Al = 1) was studied with the density-functional-theory-based cluster approach. The results showed that various silver clusters, partially or completely reduced, can be stabilized in this zeolite with the maximum negative defects. Computed formation energies for two reduction reactions reveal that completely reduced Ag clusters can be stabilized through hydrogenation, giving some preference to the formation of hydrogenated Ag6 species. The hydrogenated neutral AgnHm/EMT clusters remain stable at T = 300 K, as obtained from the analysis of the Born–Oppenheimer molecular dynamics trajectories. Ion exchange of Na+ by Ag+ cations is obtained to be exothermic with energy gain of 0.5 eV per Ag cation. The formation of Ag–O ionic bonds, known to stabilize metal clusters in zeolitic frameworks, is found to be preponderant in the structures with fewer than six silv...