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.