Zeolitic Imidazolate Framework Cores Decorated with Pd Nanoparticles and Coated Further with Metal-Organic Framework Shells (ZIF-8@Pd@MOF-74) as Nanocatalysts for Chemoselective Hydrogenation Reactions

The selective hydrogenation of Ar-Câ• C in the presence of Ar-NO2 is a long-standing challenge because of the uncontrolled nonselective nature of hydrogenation. In this study, the core-shell nanocatalyst ZIF-8@Pd@MOF-74 is developed for the preferential reduction of the Ar-CC group. The ZIF-8 core can act as an effective support for Pd nanoparticles (NPs), and the MOF-74 shell can prevent Pd NPs from leaching and oxidation. Compared with Pd/C and ZIF-8@Pd catalysts, our ZIF-8@Pd@MOF-74 nanocatalyst shows enhanced activity and selectivity for conversion of nitrostyrene to 1-ethyl-4-nitrobenzene (>98% yield) without the use of pressured hydrogen, and the turnover frequencies (TOF) can reach 330 h-1. Theoretical and experimental results reveal that the high chemoselectivity is attributed to the preferential adsorption and activation of the Ar-CC on the MOF-74 shell. Given its outstanding catalytic performance under mild conditions and facile preparation protocol, it would be of considerable interest to develop other MOFs@MNPs@MOFs core-shell nanocatalysts.