Reverse Hydrogen Spillover onto Zeolite-Supported Metal Clusters: An Embedded Cluster Density Functional Study of Models M6(M = Rh, Ir, or Au)

Abstract

A density functional study using isolated cluster models of the zeolite framework (Vayssilov, G. N.; Rosch, N. Phys. Chem. Chem. Phys. 2005, 7, 4019) on supported metal clusters M6/zeo in a hydroxylated faujasite cage showed that for 12 metals M of the groups 8−11 the hydrogenated state, M6(3H)/zeo, is energetically preferred over the bare form M6/zeo(3H). The former state was obtained as result of reverse hydrogen spillover from zeolite OH groups onto the metal particle. In the present work, we reinvestigated this problem of identifying the favorable chemical state of zeolite-supported metal species for selected M6 model clusters (M = Rh, Ir, or Au) using an accurate quantum mechanics/molecular mechanics (QM/MM) approach where a QM partition is embedded in an extended zeolite lattice (MM). The embedding method covEPE, an improved variant of the elastic polarizable environment model EPE, adapted for polar-covalent materials, properly accounts for both the mechanical rigidity of the zeolite framework and t...