Catalytic hydrodechlorination of chlorophenols by Pd/Fe nanoparticles: Comparisons with other bimetallic systems, kinetics and mechanism

This study investigated dechlorination of 4-chlorophenol (4CP), 2,4-dichlorophenol (24DCP), and 2,4,6-trichlorophenol (246TCP) with Pd/Fe nanoparticles. The reaction rates were significantly faster than those achieved with Pt/Fe, Ni/Fe, Cu/Fe and Co/Fe nanoparticles. The chlorophenols (CPs) could be completely reduced to phenol by Pd/Fe following the pseudo-first-order kinetics, and the rates followed the order of 246TCP < 24DCP < 4CP. The 246TCP reduction rate with Pd/Fe increased with temperature and the estimated activation energy was 29.8 kJ/mol. The CPs dechlorination rate increased linearly with Pd loading, suggesting that Pd catalyst could be the only reactive site. Based on rigorous analysis of the transient formations and concentrations of various intermediates, a scheme of transformation pathways and the reaction mechanism was proposed to delineate 246TCP dechlorination to phenol. The influence of pH on the CPs dechlorination was investigated, and weak acidic condition is more favorable to the dechlorination reaction. H2 evolution or iron corrosion rate initially followed the pseudo-first-order kinetics, and was reverted to the zero-order kinetics for prolonged reaction (>24 h).