Insight into Direct and Indirect Electrocatalytic Dechlorination of Organic Chlorides By Ultrafine Pd Nanoparticles

Abstract

Electrocatalytic dehalogenation occurs via both direct and in-direct pathways at the cathode surface playing significant roles in the fields of organic synthesis and environmental remediation. To distinguish these two reduction routes and establish their quantitative relationships in the dehalogenation process are of fundamental interest for unraveling the electrocatalytic dehalogenation mechanisms. However, few studies have been conducted so far. In this work, we prepared ultrafine Pd nanoparticles (NPs) with high dispersibility by simply using N,N-dimethylformamide as solvent and metal-biding agent. The electrochemically active surface area of Pd NPs was 40 m2•g-1, 1.50 times higher than that of commercial Pd/C catalysts. By using the as-prepared Pd NPs as model catalyst, we first showed the direct and indirect reduction of 4-chlorophenol (4-CP) under aqueous conditions in the cyclic voltammogram. The dissociative electron transfer to 4-CP over the Pd NPs electrode was indicated to follow the concerted mechanism. The atomic hydrogen species exclusively existed in the forms of adsorbed hydrogen (H*ads) and absorbed hydrogen (H*abs), which all contributed to the excellent dehalogenation performance. A detailed voltammetric analyses allowed to establish the quantitative relationship between direct and indirect dehalogenation mechanisms, which showed comparable contributions to the electrocatalytic dehalogenation process. This discovery is very important and corrects the previous assertion that the indirect reduction pathway plays a predominant role in the dehalogenation process. This work provides insights into distinguishing the direct and indirect electrocatalytic dehalogenation pathways and successfully bringing the knowledge gap to quantitatively build connection between both dehalogenation routes.