Iridium nanoparticles stabilized by metal organic frameworks (IrNPs@ZIF-8): synthesis, structural properties and catalytic performance

Today, the synthesis of well-defined metal nanoparticles stabilized by the metal-organic frameworks (MOFs), which provide high specific surface areas, tunable pore sizes, and guest interactable organic linkers, and the discovery of their unique properties are still challenging goals. The chemically robust zeolitic imidazole framework (ZIF) is a subclass of MOF. In this study, the microporous sodalite-like ZIF-8 (Zn(MeIM); MeIM = 2-methylimidazole) was selected as host matrix to stabilize guest iridium nanoparticles (IrNPs). The iridium loading was achieved via gas phase infiltration of Ir(COD)(MeCp) (methylcyclopentadienyl)(1,5-cyclooctadiene)iridium(I)) precursor followed by hydrogenolysis of the inclusion compound Ir(COD)(MeCp)@ZIF-8 to form the IrNPs@ZIF-8. The characterization of IrNPs@ZIF-8 by ICP-MS, P-XRD, XPS, C-13 MAS NMR, TEM, HRTEM, STEM, STEM-EDX, HAADF-STEM, DR-UV-vis, EA analyses and N-2-adsorption-desorption techniques reveal the formation of well-dispersed iridium nanoparticles (3.3 +/- 1.7 nm) within the framework of ZIF-8 (IrNPs@ZIF-8) by keeping the host framework intact. The catalytic application of IrNPs@ZIF-8 in terms of activity, selectivity, reusability and durability was demonstrated in the hydrogenation of cyclohexene and phenylacetylene under mild conditions, in which they were found to be highly active catalysts. Moreover, they show great durability against sintering and leaching throughout the catalytic runs that make them highly reusable catalysts. They retain their inherent catalytic activity even at the fifth catalytic run in the hydrogenation of cyclohexene and phenylacetylene.