(583ap) Perchloroethene Hydrodechlorination Using Pd-On-Au Nanoparticle Catalysts At Ambient Conditions

Perchloroethene (PCE), a commonly used dry-cleaning solvent, is frequently detected a groundwater contaminant. Pump-and-treat and air stripping have currently been deployed but are limited in their ability to cost-effectively remove PCE from contaminated groundwater. In our previous studies, palladium-on-gold nanoparticles (Pd-on-Au NPs) have been shown to be highly catalytically active in the hydrodechlorination (HDC) of trichloroethene (TCE) and other chlorinated compounds. However, the catalytic chemistry of such nanoparticles for PCE HDC in water has not been systematically addressed in the literature. 4-nm Pd-on-Au NPs have thus been synthesized and tested for water-phase PCE HDC under ambient conditions (room temperature, pH = 7, atmospheric H₂), and 4-nm Pd NPs, and Pd/Al₂O₃ were tested equally as controls. The catalysts activity showed a volcano shape dependence upon the Pd surface coverage, with the most active one at ~80±0.8 sc% coverage (pseudo-first order rate constant of ~5000 L/g_Pd/min), which was ~20× and ~80× higher than that for Pd NPs and Pd/Al₂O₃. All three types of Pd based catalysts converted PCE into ethane via a sequential reduction pathway, where the formation and subsequent reaction of daughter products (TCE, dichloroethene isomers, vinyl chloride, and ethene) followed the stepwise dechlorination of the PCE chlorine groups. A complete mechanistic model of PCE HDC that coupled gas-liquid mass transfer with the surface reactions was developed and was shown to match nicely with the observed concentration-time profiles. This study establishes the enhanced degradation chemistry of PCE using model Pd-on-Au catalysts and suggests the volcano-shape structure-activity dependence can be generalized from PCE and TCE to other organohalides. Implementing reactors containing supported Pd-on-Au NPs to catalytically reduce PCE on site at contaminated locations would be an attractive option for remediation efforts.