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

Abstract

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.