Structure optimization and support effect of metal-organic frameworks on Pd-Ir bimetallic nanoclusters

Abstract

Structure optimization of metal nanoclusters supported on metal-organic framework (MOFs) materials is very important for understanding and improving their both catalytic activity and selectivity. In this paper, a systematic study on the structure optimization of Pd-Ir bimetallic nanoclusters on MOFs (UiO-66) is presented based on basin hopping genetic algorithm (BHGA) and density functional theory (DFT) calculation. In addition, the structural characteristics, electronic properties and the support effect of UiO-66 on Pd-Ir nanoclusters are explored by analyzing the adsorption energy, binding energy, skeleton deformation energy and charge transfer. The results show that Pd-Ir clusters tend to bind with organic connectomes and remain thermodynamically stable near the support site. Meanwhile, among the three Pd-Ir alloy clusters supported on UiO-66, Pd32Ir6 cluster has the strongest interaction with UiO-66 framework, while Pd6Ir32@UiO-66 has excellent thermodynamic stability. Importantly, the catalytic efficiency of Pd-Ir@UiO-66 is improved owing to the transferred electrons from Pd-Ir alloy clusters to UiO-66 framework. Furthermore, with the support effect of UiO-66 on Pd-Ir clusters, the Pd-Ir clusters dispersed in the UiO-66 pores to prevent metal clusters from agglomeration, but their thermodynamic stability are not changed after supporting on UiO-66 materials. In addition, the coordination number of Pd/Ir atoms in Pd-Ir clusters becomes fewer due to the support effect of UiO-66 on Pd-Ir nanoclusters. Moreover, the Pd-Ir clusters are firmly adsorbed on UiO-66, which contributes to improve the catalytic activities of Pd-Ir@UiO-66.