Highly dispersed Pd nanoparticles for electrocatalytic dechlorination: Positive and negative effects of carbon supports

It is generally known that carbon supports with a large surface area are essential for dispersion of Pd catalysts and adsorption of pollutants (e.g., chlorinated compounds), thus enabling enhanced mass transfer and increased reaction kinetics. However, we demonstrate that, in spite of contributing to achieving highly dispersed Pd nanoparticles, a high-surface-area carbon support favoring fast adsorption of 2,4-dichlorophenol negatively impacts the catalytic activity of Pd. Comparisons of catalytic performance between Pd/activated carbon (AC) catalysts with different mass loadings in a 3D electrochemical dechlorination reactor suggested that Pd(60%)/AC outperformed Pd(10%)/AC, although the latter had smaller Pd catalysts and the amount of Pd was same in these experiments. We found that the dechlorination rate constant was inversely correlated to the adsorption rate constant at Pd loadings from 10% to 60%. We further verified that the use of C3N4, an optimal carbon support with low surface area that allows good dispersion of Pd nanoparticles (10%), is critical in accelerating the dechlorination reaction kinetics due to the improved accessibility of active sites to the pollutants. This study provides information on how to select optimal supporting materials with desirable features that avoid catalyst aggregation and pre-adsorption of pollutants when the supported Pd catalysts are used as the moveable particle electrodes.