Improving the Chemical Utilization Efficiency of Pd Hydrodechlorination Catalysts through Hydrogen-Spillover Empowered Synergy between Pd and TiNiN Support

The sustainable and affordable environmental application of Pd catalysis needs further improvement of Pd mass activity. Besides the well-recognized importance of physical utilization efficiency─the ratio of surface atoms forming reactant-accessible reactive sites─a lesser-known fact is that the congestion of these reactive sites, which we term as the chemical utilization efficiency, also influences the mass activity. Herein, by leveraging the 100% physical utilization efficiency of a fully exposed Pd cluster (Pd_n) and the hydrogenation activity of TiNiN, we developed Pd_n/TiNiN as a high physical and chemical utilization efficiency catalyst. During the catalytic hydrodechlorination of 4-chlorophenol and the subsequent hydrogenation of phenol, Pd_n focuses on H₂ dissociation and C–Cl cleavage, while TiNiN facilitates the subsequent hydrogenation of phenol into less toxic cyclohexanone via H-spillover. This synergy results in a 20–40-fold increase in the hydrodechlorination rate. The enhanced chemical utilization efficiency of Pd informs the design of Pd_n/TiNiN microspheres for the conversion of halogenated organics from pharmaceutical wastewater and the design of a fixed-bed reactor to transfer trace amounts of 4-CP from river water. Ultimately, this approach decentralizes the use of Pd in environmental catalysis and reduction processes.