Effects of reduced sulfur compounds on Pd-catalytic hydrodechlorination of trichloroethylene in groundwater by cathodic H₂ under electrochemically induced oxidizing conditions

Reduced sulfur compounds (RSCs) poison Pd catalysts for catalytic hydrodechlorination of contaminants in anoxic groundwater. This study investigates the effects of RSCs on Pd-catalytic hydrodechlorination of trichloroethylene (TCE) in oxic groundwater. Water electrolysis in an undivided electrolytic cell is used to produce H₂ for TCE hydrodechlorination under oxidizing conditions. TCE is efficiently hydrodechlorinated to ethane, with significant accumulation of H₂O₂ under acidic conditions. The presence of sulfide at concentrations less than 93.8 μM moderately inhibits TCE hydrodechlorination and H₂O₂ production. The presence of sulfite at low concentrations (≤1 mM) significantly enhances TCE decay, while at high concentration (3 mM) inhibits initially and enhances afterward when sulfite concentration declines to less than 1 mM. Using radical scavenging experiments and an electron spin resonance assay, SO₃^•-, which is generated from sulfite under oxidizing conditions, is validated as the new reactive species contributing to the enhancement. This study reveals a distinct mechanism of effect of sulfite on TCE hydrodechlorination by Pd and H₂ in oxic groundwater and presents an alternative approach to increasing resistance of Pd to RSCs poisoning.