Synthesis and characterization of Pd functionalized UiO-66 and UiO-67 MOFs for C-C Coupling reactions

Abstract

Metal-organic frameworks (MOFs) have emerged as versatile porous materials thanks to their tuneable structures and compositional diversity. These features have positioned MOFs as promising candidates for a range of applications, particularly as platforms for heterogeneous catalysts. Among these, their potential to stabilize isolated metal atoms has attracted growing attention, opening new avenues in the development of single-atom catalysts[1]. Previous work carried out within the group of Szilágyi has demonstrated the immobilization of nanoclusters and single atoms of Pd incorporated into UiO-66 type metal-organic frameworks and has tested the catalytic activity of these Pd-laden MOFs in reactions such as the thermal hydrogenation of CO2. It was of interest to look for a reaction that demonstrates the catalytic activity of Pd single atoms embedded in functionalized UiO-66, and to investigate how Pd is incorporated in UiO-67 with new linkers. In this work, new functionalized linkers have been synthesized and incorporated into UiO-66 and UiO-67 MOFs, followed by metalation of the frameworks with Pd. Characterization has been done to confirm the structure of the material, and to understand the speciation of the incorporated Pd. The catalytic performance of the Pd immobilized frameworks for Stille coupling reaction has been assessed and the preliminary results are outlined. Functionalized terephthalic acid-based linkers and BPDC have first been synthesized and integrated into the UiO-66 and UiO-67 topology following an established synthesis protocol[2]. Metalation of these modified MOFs was achieved through the incorporation and subsequent in-situ reduction of a Pd precursor, allowing the integration of neutral Pd atoms within the MOF pores. Comprehensive structural analysis was performed using techniques such as X-ray diffraction (XRD), thermogravimetric analysis (TGA), Brunauer-Emett-Teller (BET) surface area measurements, scanning electron microscopy (SEM), and microwave plasma atomic emission spectroscopy (MP-AES), enabling insights into the distribution and chemical state of Pd. Advanced characterization confirmed that palladium was successfully incorporated into the MOFs in both UiO-66 and UiO-67 type MOFs. BET measurements show that UiO-67 type MOFs have much larger surface area due to the larger size of the linkers used. The catalytic performance of the synthesized UiO-66 type MOFs in the Stille coupling reaction has been examined and confirmed in this work, with the obtention of biphenyl using the synthesized MOFs as catalysts.