Understanding Your Support System: The Design of a Stable Metal-Organic Framework/Polyazoamine Support for Biomass Conversion

Introducing oligomeric or polymeric units into metal- organic frameworks (MOFs) can result in composites that have significantly improved properties when compared with the individual MOF or polymer building blocks. With such synergy in mind, this work presents the design of a novel MOF/polyazoamine support that is used to stabilize Pd nanoparticles (NPs). The resulting composite catalyst, tested in the reductive amination of levulinic acid, is found to have a markedly improved lifetime when compared to just the MOF or polymer support containing Pd. It is demonstrated, for the first time, that the lifetime enhancement stems directly from the polymer, which plays a dual role: (i) the oligomer stabilizes the MOF support through the elimination of certain vibrational modes associated with the framework ligand and likely pore-filling effects in the largest MOF pore and (ii) the Lewis base functionality on the oligomer backbone binds to the surface of the Pd NPs, thus, increasing their activity and inhibiting their aggregation. Several complementary spectroscopic (IR, X-ray photoelectron spectroscopy, Raman spectroscopy) and computational tools (pore space and topology analysis, molecular mechanics, and density functional theory simulations) are used to describe the nature of the MOF-oligomer interaction and identify the most likely location of the polymer within the MOF pore.