The Binding Strength of Reactive H*: A Neglected Key Factor in Rh-Catalyzed Environmental Hydrodefluorination Reaction

Abstract

The catalyzed reduction process plays an important role in the safe handling of environmental contaminants. It is generally believed that the adsorption of pollutants and cleavage of chemical bonds with high stability is the key and rate-determining step. Herein, using the H2–D2 exchange experiment, we observed a rapid decrease in the yield of HD on the Rh nanocatalyst, a state-of-the-art choice for the reduction of fluorinated organics, which indicates that the overadsorption of H/D atoms poisoned the Rh surface. The high binding energy of H/D on Rh decreases its reactivity as a reductant and is unfavorable for the adsorption/activation of the C–F bond. This dilemma is easily overcome by depositing Rh atoms onto Pd nanowires or commercial Pd/Al2O3. In addition to reducing the size of the Rh ensemble and therefore decreasing the H binding energy, Pd also directly spills over reactive H to the nearby Rh center; Pd@Rh shows 50 times higher mass activity and can remove persistent pollutants such as hexafluorobenzene and perfluorooctane acid under environmentally relevant conditions. Interestingly, the Pd@Rh catalyst hydrogenates halogenated phenols into value-added cyclohexanone with high selectivity. This work provides new insight into the design of advantageous nanocatalysts for environmental improvement and the recovery of resources from wastewater.