Probing into the effects of cluster size and Pd ensemble as active center on the activity of H2 dissociation over the noble metal Pd-doped Cu bimetallic clusters

Abstract

Abstract Aiming at probing into the effects of cluster size and Pd ensemble as active center on H2 dissociation over Pd-doped Cu bimetallic cluster, density functional theory calculations are employed to investigate H2 adsorption and dissociation over the Cu and Pd-doped Cu clusters with different sizes. The results show that compared to Cu cluster, the doped Pd atom and its ensemble composed of outermost layer and its connected sub-layer Pd atoms as active center greatly enhance catalytic activity of H2 dissociation at the same size of Pd-doped Cu clusters, which is attributed to the interaction enhancement between H2 and the clusters since d-band centers gradually approach the Fermi level and the electron-rich regions are formed around Pd ensemble. Moreover, among the Pd-doped Cu clusters with different sizes, the Bader charge indicate that when the number of doped-Pd atoms is same, the amount of charge on Pd ensemble increases with the size increasing of Pd-doped Cu catalysts, the cluster with larger size is beneficial for promoting the activity of H2 dissociation; thus, the size effect of Pd-doped Cu cluster on H2 dissociation is dominantly attributed to the electronic effect. This work not only provides a valuable clue for evaluating catalytic activity of other promoter metal-doped Cu catalysts for H2 dissociation, but also gives out the ways that adjusting the cluster size and the promoter ensemble can facilitate the dissociation of H2 atoms as an initially key step in the heterogeneous hydrogenation.