Cooperative H2 Activation at Ag Cluster/θ-Al2O3(110) Dual Perimeter Sites: A Density Functional Theory Study

Abstract

H2 dissociation by Ag clusters supported on the θ-Al2O3(110) surface has been investigated using density functional theory calculations. The crucial role of the dual perimeter site of Ag cluster and the surface oxygen (O) site of the alumina support is demonstrated with three theoretical models: anchored cluster, isolated cluster, and anchored cluster on hydroxylated alumina. The heterolytic cleavage of H2 at the silver–alumina interface, yielding Ag–Hδ− and O–Hδ+, is thermodynamically and kinetically preferred compared with H2 cleavage at two Ag atomic sites on top of the Al2O3-supported Ag cluster and the homolytic cleavage of H2 on the isolated Ag cluster. The hydroxylation at the O site of the alumina reduces the H2 dissociation activity, which indicates that the interfacial bare O site is indispensible. It is concluded that the interfacial cooperative mechanism between the Ag cluster and Lewis acid–base pair site (bare Al–O site) is essentially relevant for the H2 activation over Ag-loaded Al2O3 catalysts.