Aqueous-phase catalytic hydrodechlorination of 1,2-dichloroethane over palladium nanoparticles (nPd) with residual borohydride from nPd synthesis

1,2-Dichloroethane (1,2-DCA) is among the most frequently detected chlorinated organic compounds (COCs) at contaminated sites. Possible carcinogenicity and recalcitrance towards abiotic dechlorination has created considerable interest in developing remediation technologies to successfully treat 1,2-DCA. Recently, aqueous-phase catalyzed hydrodechlorination has emerged as a field-applicable technology showing promising results in reducing various COCs. However, there has been limited success in applying this technology to treat 1,2-DCA, even at the bench scale. In the current study, the feasibility of aqueous-phase catalyzed hydrodechlorination of 1,2-DCA was investigated over Pd nanoparticles (nPd) with the residual borohydride from nPd synthesis as a hydrogen (H-2) source. nPd particles were synthesized via aqueous chemical reduction by sodium borohydride. Complete removal of 1,2-DCA (32 mg L-1) in < 7 days was achieved with both bare and stabilized nPd (1 g L-1) particles and the reaction followed pseudo-first-order kinetics. No additional injections of borohydride or any other H-2 source were needed. Ethane was the main reaction product indicating hydrogenolysis as the major dechlorination pathway. Different synthesis parameters were found to affect the oxidation state, elemental composition and the catalytic activity of nPd and consequently 1,2-DCA dechlorination. Detailed surface characterization including TEM, SEM/EDX, XPS and XRD of nPd particles was conducted. This study is an initial step to show that even recalcitrant COCs like 1,2-DCA can be successfully treated in the aqueous-phase via nPd-borohydride suspensions, and likely other nanocatalysts, without any external/additional H-2 source. However, further research is needed to provide more insight on how to transfer this technology from ideal laboratory conditions to real-field situations. The results also help provide clues on the development of a process level understanding of 1,2-DCA dechlorination via nanocatalysts.