(706a) Exploiting Metal Nodes of Ni-Mfu-4l MOF for Hydrogenation Reaction: Effect of Side Ligand

Metal-organic frameworks (MOFs) as an emerging class of materials offer the tunability required to design new catalysts for decarbonization that aims to use hydrogen as a new source of energy. Though active MOF-supported hydrogenating catalysts are reported, the use of non-noble based MOF nodes as catalysts is not studied. Given the reducing nature of hydrogenation , formation of sub-nanometric clusters and nanoparticles are possible, especially at elevated temperatures, where several MOFs may not withstand.

Herein, we used nodes of the highly robust Ni-MFU-4l MOF, where to every Ni²⁺ in the node, a Cl^- ligand is coordinated. We hypothesized that subjective to a thermal treatment under a H₂ environment, a Ni-H species could form that is active for catalyzing ethylene hydrogenation as a probe reaction. Further insights on the catalysis and hydrogen activation were obtained through H/D exchange experiments. Post-catalysis ex-situ x-ray photoelectron spectroscopy (XPS) along with in-situ pair distribution function (PDF) concluded that the MOF is prone to partial deformation at high temperature treatment, upon which nanoparticles are formed. Thus, we leveraged the tunability of the MOF to exchange the -Cl side ligand to more labile ligands such as -OH and -HCOO so that a milder treatment can facilitate the formation of Ni-H species, upon removal of the ligand. This approach successfully reduced the required treatment temperature (150 ◦C) yet did not result in deformation of the MOF or nanoparticle formation, while offering activity for ethylene hydrogenation and hydrogen activation. Using in-situ PDF, we further investigated that the onset temperature for nanoparticle formation, as a result of partial deformation of the MOF, varies with the side ligand. Thus, we propose a straightforward post-synthetic modification approach for MOFs as a tunable class of materials to generate active sites for catalysis in the gas-phase, without compromising the integrity of the MOF structure.