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
(Pd1.72, Co1.23 wt %) exhibits good catalytic behaviors
(conversion90.5%, selectivity to 4-aminophenol (4-AP) >
99.0%,
and conversion11.0%, selectivity to 4-aminophenol (4-AP) >
99.0%, TOFturnover frequency44.2 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.