Fabrication of Magnetic Pd/MOF Hollow Nanospheres with Double-Shell Structure: Toward Highly Efficient and Recyclable Nanocatalysts for Hydrogenation Reaction.

MNPs@MOF catalysts obtained by encapsulating metal nanoparticles (NPs) into metal-organic frameworks (MOFs) show fascinating performance in heterogeneous catalysis. The improvement of catalytic activity and reusability of MNPs@MOF catalysts has been a great challenge for a long time. Herein, we demonstrate well-designed Pd/MOFs, featuring hollow double-shell structure and magnetic property, exhibiting high reusability, efficient catalytic activity, and size selectivity for hydrogenation reaction. The as-synthesized Pd/MOF, denoted as Void nFe3O4@Pd/ZIF-8@ZIF-8, possesses diverse functional structural features. The hollow cavity can improve mass transfer; superparamagnetic Fe3O4 NPs embedded in the inner MOF shell can enhance the separation and recyclability; Pd NPs are highly dispersed in the matrix of the inner MOF shell, and the outer MOF shell acts as a protector to prevent the leaching of Pd NPs and a sieve to achieve size selectivity. As a proof of concept, the Void nFe3O4@Pd/ZIF-8@ZIF-8 catalyst exhibited excellent performance for the hydrogenation of styrene at room temperature. The activity only reduced 10% after 20 cycles for the higher conversions (>90%), and the lower conversion only decreased 3.6% (from 32.5 to 28.9% conversion) after twenty consecutive cycles, indicating the good and intrinsic reusability of the catalyst. The proposed structure in this work provides a strategy to effectively improve the reusability of MNPs@MOF catalysts, which would increase their practical applications.