A density functional theoretical study on the stability of Pt clusters in MOF-808

Abstract

Metal organic framework (MOF)-encapsulated metal clusters have shown superior catalytic activity due to geometric and electronic properties of metal clusters, which are largely determined by adsorption sites and sizes and morphologies of encapsulated metal clusters. In the present work, anchoring sites, the stability, and the agglomeration probability of Pt_n (n = 1–23) clusters over an MOF-808 framework structure were studied using density functional theory calculations and ab initio molecular dynamics simulation. It has been found that Pt_n (n = 1–7) clusters bind more strongly at the Zr₆ metal node sites than at the interface and linker sites. Upon adsorption, significant amounts of electrons (+0.92 to +1.96 |e|) are transferred from Pt_n clusters to the MOF framework. The agglomeration of single Pt₁ atoms at the Zr₆ metal node to form a Pt_n cluster is unlikely, while the agglomeration at the interface or the linker is energetically feasible. Compared with the single Zr₆ node, the bonding of Pt_n clusters with two Zr₆ metal nodes is weaker, with less electron (+0.12 to +0.89 |e|) transfer. Finally, our calculations show that CO adsorption at the single Pt atom is stabilized at the interface site, preventing its further agglomeration with Pt_n clusters between the two Zr₆ metal nodes.