The bimetallic effect between Pd and Rh on the hydrodefluorination activity of RhPd/TiN: mechanism study and implication for simultaneous removal of multiple halogenated organics

Abstract

Defluorination is essential for mitigating the toxicity and persistence of fluorinated organic compounds (FOCs). However, cleaving C–F bonds remains challenging due to their high dissociation energy, typically requiring harsh conditions, such as elevated temperature/pressure or strong reductants. While Rh-catalyzed hydrodefluorination (HDF) offers promise, especially when alloyed with Pd in bimetallic systems, a comprehensive understanding of the mechanism is lacking. Here, we developed RhPd/TiN as a highly active and cost-effective HDF catalyst under environmentally relevant conditions. Using 4-fluorophenol (4-FP), a representative persistent organic pollutant, as a demo reactant, the RhPd/TiN catalyst exhibits 21.6- to 563.8-fold higher mass activity than the corresponding monometallic counterpart catalysts, with cyclohexanone as the sole product. Mechanistic studies reveal that Rh serves as the primary active site, while Pd enhances reactivity by (i) supplying reactive H species via H-spillover and (ii) modulating Rh's electronic state to promote the adsorption of 4-FP and accelerate phenol desorption. Leveraging this high activity and mechanistic insight, we designed a RhPd/TiN microparticle-based fixed-bed reactor for simultaneous conversion of diverse halogenated organics in real-world samples, e.g., polluted river water and pharmaceutical wastewater.