Fabrication of yolk-shell Pd@ZIF-8 nanoparticles with excellent catalytic size-selectivity for the hydrogenation of olefins

In this work, we fabricate new yolk-shell Pd@ZIF-8 (ZIF = zeolitic imidazolate framework) nanoparticles (NPs) through reactions of the preformed core-shell Pd@ZnO NPs with 2-methylimidazole under mild conditions. In this method, ZnO is used as the self-template and the Zn2+ source for the formation of the ZIF-8 shell. The morphology, composition and structure of the as-prepared yolk-shell nanomaterial are characterized by scanning electron microscopy, transmission electron microscopy, high resolution transmission electron microscopy, powder X-ray diffraction, energy dispersive X-ray spectroscopy, and inductively coupled plasma atomic emission spectroscopy. The formation of this well-defined yolk-shell nano-structure is highly dependent on the solvent system and reaction time. This nanomaterial can be employed as an excellent heterogeneous catalyst for the liquid-phase hydrogenation of olefins with high size-selectivity at room temperature, which is mainly due to the inherent porous structure of the outer ZIF-8 shell along with the enclosed Pd NPs. The nanocatalyst system can be recycled at least three times without any evident loss of the catalytic efficiency.