Heterogeneous Pd catalysts were developed by immobilizing Pd nanoparticles (Pd NPs) onto plant polyphenol (bayberry tannin, BT) decorated $\gamma$-Al$_2$O$_3$. 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 $3.75\pm 0.5$ nm were highly dispersed in the catalyst. The as-prepared Al$_2$O$_3$–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$^{\circ}$C and under atmospheric pressure. During the catalytic HDC, the stabilizingcapability of BT successfully prevented the leakage and aggregation of Pd NPs, thus ensuring a high cycling stability withstable and high catalytic activity. The Al$_2$O$_3$–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 controlcatalysts, including $\gamma$-Al$_2$O$_3$ supported Pd NPs (Al$_2$O$_3$–Pd) and powdered activated carbon supported Pd NPs (AC–Pd).Furthermore, the Al$_2$O$_3$–BT–Pd also showed high activity in the mild catalytic HDC of 2,4,6-trichlorophenols andchlorobenzene derivatives. Our results demonstrated efficient catalysts to address the environmental issue of chlorophenolpollution.