Highly active ultrafine Pd NPs confined in imine-linked COFs for nitrobenzene hydrogenation

The preparation and stabilization of ultrafine metal nanoparticles (NPs) are of great importance owing to the enhanced atom efficiency but still remain a challenging issue. Herein, we report that ultrafine Pd NPs with an average size of 1.8 nm could be successfully stabilized on an imine-linked covalent organic framework (COF) even with Pd loadings as high as 5 wt%. The strong interactions of Pd NPs and imine linkage were evidenced by the electron donation from imine linkage to Pd NPs. The Pd/COF catalyst with electron rich surface properties, a high surface area and regular pore channels showed much higher catalytic activity than commercial Pd/C in the hydrogenation of nitrobenzene (TOF: 906 h(-1)vs. 507 h(-1)). Furthermore, no aggregation of ultrafine Pd NPs was observed during the recycling process, demonstrating the superiority of imine-linked COFs in stabilizing ultrafine metal NPs.