RESUMO
Pd nanoparticles were immobilized on a highly porous, hydrothermally stable Eu-MOF via solution impregnation and H2 reduction to yield a novel Pd@Eu-MOF nanocatalyst. This composite was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), inductively coupled plasma optical emission spectroscopy (ICP-OES), powder X-ray diffraction (PXRD) and X-ray photoelectron spectroscopy (XPS). Unprecedentedly, the Pd@Eu-MOF nanocatalyst could be applied with excellent results in two strikingly different, mechanistically distinct, reactions i.e., Suzuki-Miyaura cross-coupling and cycloaddition of CO2 to a range of epoxides. Under the best reaction conditions, 98-99% yields have been attained in both catalytic processes. Moreover, in either case the heterogeneous catalyst was easily recovered and efficiently reused for more than four cycles, indicating its high stability and reproducibility. PXRD, TEM and XPS measurements on the recycled catalyst confirmed that it maintained its original structure and morphology; no Pd NP agglomeration was observed.
RESUMO
An array of heterobimetallic Pd/Ln MOFs (1-4) with Sm, Eu, Tb, Dy as preferred metal nodes and 1,1'-di(p-carboxybenzyl)-2,2'-diimidazole (H2L) as a fairly suitable bifunctional organic linker have been synthesized, fully characterized and tested as catalysts in cross-coupling reactions. These robust MOFs, ensuring a uniform distribution of Pd, showed excellent stability in air and high catalytic activity in Suzuki-Miyaura reactions conducted in neat water, neat ethanol as well as water-ethanol mixture. Depending on the solvent, complex 1 could be effectively recycled 4-8 times without significant loss of catalytic activity. Importantly, this complex was found to be pH responsive in a reversible way, enabling convenient recovery from acidic aqueous solutions, indicating good recyclability as well as environment-friendly separation of the metal residues after the reaction.
