Reductive dechlorination of trichloroacetic acid (TCAA) by electrochemical process over Pd-In/Al2O3 catalyst

•TCAA was efficiently removed by Pd-In/Al2O3 based electro-reductive process.•The active species for TCAA electroreduction involved electron (e−) and atomic H*.•The atomic H* played a major contribution to TCAA removal.

Electrochemical reduction treatment was found to be a promising method for dechlorination of Trichloroacetic acid (TCAA), and acceleration of electron transfer or enhancement of the concentration of atomic H* significantly improve the electrochemical dechlorination process. Bimetallic Pd-based catalysts have the unique property of simultaneously catalyzing the production of atomic H* and reducing target pollutants. Herein, a bimetallic Pd-In electrocatalyst with atomic ratio of 1:1 was evenly deposited on an Al2O3 substrate, and the bimetallic Pd-In structure was confirmed via X-ray photoelectron spectroscopy (XPS). Electrochemical removal of trichloroacetic acid (TCAA) by the Pd-In/Al2O3 catalyst was performed in a three-dimensional reactor. 94% of TCAA with the initial concentration of 500 μg L−1 could be degraded within 30 min under a relatively low current density (0.9 mA cm−2). In contrast to the presence of refractory intermediates (dichloroacetic acid (DCAA)) found in the Pd/Al2O3 system, TCAA could be thoroughly reduced to monochloroacetic acid (MCAA) using Pd-In/Al2O3 catalysts. According to scavenger experiments, an electron transfer process and atomic H* formation function both existed in the TCAA reduction process, and the enhanced indirect atomic H* reduction process (confirmed by ESR signals) played a chief role in the TCAA removal. Moreover, the synergistic effects of Pd and In were proven to be able to enhance both direct electron transfer and indirect atomic H* formation, indicating a promising prospect for bimetallic electrochemical reduction treatment.

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