Bimetallic PdCo and PdNi Nanoparticles Supported on Covalent Organic Frameworks as Catalysts for the Hydrogenation of 4-Nitrophenol

To obtain a recyclable and environmentally friendly solid catalyst with excellent catalytic properties and selectivity for 4-nitrophenol (4-NP) hydrogenation, herein, covalent organic frameworks (COFs) are used as the support. Tiny PdCo alloy particles are confined in the pores of the COFs to acquire PdCo/COFs, with an extremely narrow PtCo size distribution (6.28 ± 2.85 nm). The effect of Pd+Co loading and the Pd/Co atomic ratio on the catalytic behaviors of PdCo/COFs for 4-NP hydrogenation is explored. The as-gained PdCo/COFs catalyst (Pd─1.72, Co─1.23 wt %) exhibits good catalytic behaviors (conversion─90.5%, selectivity to 4-aminophenol (4-AP) > 99.0%, and conversion─11.0%, selectivity to 4-aminophenol (4-AP) > 99.0%, TOF─turnover frequency─44.2 min–1) for 4-NP hydrogenation under quite moderate reaction conditions (40 °C, 3.0 MPa hydrogen pressure), and PdCo/COFs have superior stability. Additionally, the catalytic property of PdCo/COFs is better than that of monometallic supported catalysts (Pd/COFs or Co/COFs) and PdNi/COFs. It can be considered that the formation of the PdCo alloy particles is beneficial to the activation of 4-NP. The PdCo/COFs catalysts are analyzed by XRD, XPS, ICP-OES, SEM-EDX, BET, TEM, HRTEM, STEM-EDX elemental analysis, and aberration-corrected STEM (AC-STEM), confirming that tiny PdCo alloy particles are uniformly loaded on the COFs. The PdCo/COFs samples have the advantages of outstanding stability and thus their own desired industrial application potential.