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

Abstract

A B S T R A C TElectrochemical 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 Al 2 O 3 substrate, and the bimetallic Pd-In structure was confirmed via X-ray photoelectron spectroscopy (XPS). Electrochemical removal of trichloroacetic acid (TCAA) by the PdIn/Al 2 O 3 catalyst was performed in a three-dimensional reactor. 94% of TCAA with the initial concentration of 500 mg L À1 could be degraded within 30 min under a relatively low current density (0.9 mA cm À2 ). In contrast to the presence of refractory intermediates (dichloroacetic acid (DCAA)) found in the Pd/Al 2 O 3 system, TCAA could be thoroughly reduced to monochloroacetic acid (MCAA) using Pd-In/ Al 2 O 3 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.

Electrochemical dehalogenation of disinfection by-products and iodine-containing contrast media: A review

“…As was observed in other studies, the reductive dechlorination of TCAA and DCAA was relatively rapid but the reduction of MCAA to acetic acid was quite slow and deemed to proceed via the indirect reduction of MCAA by atomic H* generated at Pd nuclei formed on the electrode surface. The acceleration of the EC reduction of HAAs by atomic H* was also observed in another study [29] which utilized an EC-controlled bimetallic Pd/In catalyst that promoted the formation of atomic H*. The catalyst was incorporated into an EC reactor whose operations resulted in a rapid removal of TCAA yet MCAA again was observed to form as a final product.…”

Recent advances in electrocatalysts for halogenated organic pollutant degradation

“…The synergistic effect of metals can upgrade the activity and selectivity of catalysts and relieve catalyst aging and loss. 197 Experimental parameters (e.g., pH value, applied current, electrolyte) also impact the performance of cathodes heavily. 185,198,199 Take the cathode potential as an example, Jiang et al 199 found that the applied potential had a great influence on the evolution of three different hydrogen species, namely adsorbed atomic hydrogen (H* ads ), absorbed atomic hydrogen (H* abs ), and molecular hydrogen (H 2 ).…”

“…However, it should be noted that there is still lacking of fundamental principles for interpreting the dehalogenation mechanism of a typical HOP without experimental examination due to that fact that there are many unexpected observations related to the mechanisms mentioned above. 187,195,197,212,215 For instance, Liu et al 197 found that atomic H* ads formation function and the electron transfer process both existed in the trichloroacetic acid (TCAA) removal process, while the enhanced indirect atomic H* ads reduction process played a principal role in the degradation process ( Fig. 11).…”

Insights into Electroreductive Dehalogenation Mechanisms of Chlorinated Environmental Pollutants

“…Indirect atomic hydrogen reduction, i. e., the electrocatalytic hydro‐dechlorination, is another effective strategy for the electroreductive dehalogenation of organic chlorides, where atomic hydrogen species is produced on the catalyst surface and acts as a strong reductant for triggering the C−Cl bonds breaking reaction (shown in Figure a) …”

“…Due to the costly materials used and the intriguing catalytic properties of nanomaterials, electrocatalysis on shape‐controlled noble metal nanoparticles has received an increasing attention for the reductive dehalogenation over the past several years, e. g., For instance, the Pd NPs loaded on different supporting materials exhibit remarkable electrocatalytic hydro‐dechlorination performances for the various aryl chlorides including chlorophenols and chlorophenoxyacetic acids, where the exposed (111) facets was considered to be highly active for triggering the reductive dechlorination reactions …”