Pd–IL@H-UiO-66-NH2: a hollow multi-functional hierarchical composite for tandem catalysis

Abstract

In the current investigation, the base-metal hollow multifunctional catalyst, Pd–IL@H-UiO-66-NH₂, was fabricated utilizing a hydrothermal method followed by etching and supporting processes. The results of the effort demonstrate that Pd–IL@H-UiO-66-NH₂ displays significantly enhanced activity and product selectivity in catalysis of the one-pot Knoevenagel condensation–hydrogenation reaction, as well as a high level of generality in promoting hydrogenation reactions of unsaturated hydrocarbons. The excellent properties of Pd–IL@H-UiO-66-NH₂ are ascribed to its rationally designed spatial distribution of catalytically active sites within its hierarchical structure, which is comprised of surface wrinkles that increase hydrophobicity and exposure of the active sites, and hollow structures that serve as nanoreactors to enrich substrate interactions and improve mass transfer. Furthermore, the catalytic stability of Pd–IL@H-UiO-66-NH₂ was shown to be largely maintained after its use in five successive catalytic cycles. The stability of the new tandem catalyst benefits from strong confinement effects associated with its hollow structure and electronic interactions between the Pd and ILs that effectively restrict leaching and aggregation of Pd nanoparticles (NPs).