Microenvironment and electronic state modulation of Pd nanoparticles within MOFs for enhancing low-temperature activity towards DCPD hydrogenation

Abstract

Precise control of the local environment and electronic state of the guest is an important method of controlling catalytic activity and reaction pathways. In this paper, guest Pd NPs were introduced into a series of host UiO-67 MOFs with different functional ligands and metal nodes, the microenvironment and local electronic structure of Pd is modulated by introducing bipyridine groups and changing metal nodes (Ce₆O₆ or Zr₆O₆). The bipyridine groups not only promoted the dispersion Pd NPs, but also facilitated electron transfer between Pd and UiO-67 MOFs through the formation of Pd-N bridges. Compared with Zr₆ clusters, the tunability and orbital hybridisation of the 4f electronic structure in the Ce₆ clusters modulate the electronic structure of Pd through the construction of the Ce-O-Pd interfaces. The optimal catalyst Pd/UiO-67(Ce)-bpy presented excellent low-temperature activity towards dicyclopentadiene hydrogenation with a conversion of > 99% and a selectivity of > 99% (50 °C, 10 bar). The results show that the synergy of Ce-O-Pd and Pd-N promotes the formation of active Pd^δ+, which not only enhances the adsorption of H₂ and electron-rich C=C bonds, but also contributes to the reduction of proton migration distance and improves proton utilization efficiency. These results provide valuable insights for investigating the regulatory role of the host MOFs, the nature of host-guest interactions, and their correlation with catalytic performance.