Recyclable heterogeneous Pd nanoparticles supported on plant polyphenol-modified γ-Al2O3 for hydrodechlorination of 2,4-dichlorophenols

Heterogeneous Pd catalysts were developed by immobilizing Pd nanoparticles (Pd NPs) onto plant polyphenol (bayberry tannin, BT) decorated γ-Al2O3. The abundant hydroxyls of plant polyphenols were capable of stabilizing the Pd NPs. Transmission electron microscopy observation confirmed that the Pd NPs with the diameter of 3.75 ± 0.5 nm were highly dispersed in the catalyst. The as-prepared Al2O3–BT–Pd catalysts were found to be highly active in mild hydrodechlorination (HDC) of 2,4-dichlorophenols (DCPs) using formic acid as a hydrogen source. The 2,4-DCPs were completely dechlorinated in 4 h at 30°C and under atmospheric pressure. During the catalytic HDC, the stabilizing capability of BT successfully prevented the leakage and aggregation of Pd NPs, thus ensuring a high cycling stability with stable and high catalytic activity. The Al2O3–BT–Pd catalysts were recycled six times, without obvious loss of activity. In the sixth cycle, the catalytic HDC yield still reached 98.29% under the same reaction conditions, superior to the control catalysts, including γ-Al2O3 supported Pd NPs (Al2O3–Pd) and powdered activated carbon supported Pd NPs (AC–Pd). Furthermore, the Al2O3–BT–Pd also showed high activity in the mild catalytic HDC of 2,4,6-trichlorophenols and chlorobenzene derivatives. Our results demonstrated efficient catalysts to address the environmental issue of chlorophenol pollution.