Electron-Localized Active Sites Enable Sustainable 1,2-DCA Dechlorination to Ethylene by Zero-Valent Iron

The reductive transformation of persistent halogenated alkanes, such as 1,2-dichloroethane (1,2-DCA), presents a long-standing challenge. Achieving rapid cleavage of the inert C-Cl bond of 1,2-DCA requires forceful electron transfer, but this often accelerates competing hydrogen evolution and ethylene overhydrogenation, undermining the electron efficiency, product selectivity, and long-term stability. Here, we report a mechanochemically engineered zero-valent iron (ZVI) functionalized with electron-localized O-CoN₄ sites that reconciles this conflict of interest, using cobalt tetramethoxyphenylporphyrin as the Co precursor. This architecture maximizes the utilization of Co atoms, resulting in a Co-normalized dechlorination rate 2 to 40 times superior to those of reported benchmarked ZVIs. Spectroscopic and computational analyses reveal that electron accumulation at the Co center reduces the C-Cl bond cleavage barrier while creating proton-limited microenvironments that suppress hydrogen evolution and stabilize ethylene against further reduction. Consequently, the material achieves a 144-fold improvement in electron efficiency and a 65-fold enhancement in ethylene selectivity compared to pristine ZVI. Crucially, the system maintained activity and selectivity under continuous-flow operation and 100 day aging in real groundwater, consistently reducing 1,2-DCA below regulatory thresholds. This work provides a mechanochemically engineered strategy for the selective dehalogenation of halogenated alkanes, advancing sustainable remediation of halogenated pollutants.