Neighboring Catalytic\nSites Are Essential for Electrochemical\nDechlorination of 2‑Chlorophenol

The electrocatalytic reduction process is a promising\ntechnology\nfor decomposing chlorinated organic pollutants in water but is limited\nby the lack of low-cost catalysts that can achieve high activity and\nselectivity. In studying electrochemical dechlorination of 2-chlorophenol\n(2-CP) in aqueous media, we find that cobalt phthalocyanine molecules\nsupported on carbon nanotubes (CoPc/CNT), which is a highly effective\nelectrocatalyst for breaking the aliphatic C–Cl bonds in 1,2-dichloroethane\n(DCA) and trichloroethylene (TCE), are completely inactive for reducing\nthe aromatic C–Cl bond in 2-CP. Detailed mechanistic investigation,\nincluding volcano plot correlation between dechlorination rate and\natomic hydrogen adsorption energy on various transition metal surfaces,\nkinetic measurements, in situ Raman spectroscopy, and density functional\ntheory calculations, reveals that the reduction of the aromatic C–Cl\nbond in 2-CP goes through a hydrodechlorination mechanism featuring\na bimolecular reaction between adsorbed atomic hydrogen and 2-CP on\nthe catalyst surface, which requires neighboring catalytic sites,\nwhereas the aliphatic C–Cl bonds in DCA and TCE are cleaved\nby direct electron transfer from the catalyst, which can occur on\nisolated single sites. This investigation leads to the discovery of\nmetallic Co as a highly selective and active electrocatalyst for 2-CP\ndechlorination. This work provides new insights into the fundamental\nchemistry and catalyst design of electrochemical dechlorination reactions\nfor wastewater treatment.