Trace of Atomically Dispersed Pd Enables Unprecedented Butadiene Semihydrogenation Performance Over Copper Catalyst

Semihydrogenation plays a key role in industrial hydrorefining of light alkenes, with a market above 400 billion by 2027. The high cost of commercial palladium-based catalysts strongly calls for innovation but with great challenges. Herein, copper nanoparticles decorated with a minimized ppm of Pd are developed through a chemical plating process to integrate the catalytic advantages of copper and palladium for achieving maximized catalysis in the semihydrogenation of a fatal impurity of butadiene in alkene feedstocks. The developed Pd-Cu catalyst (i.e., 114 ppm of Pd in Pd_0.0033Cu₁/TiO₂) exhibits an unprecedented catalytic performance superior to commercial Pd/Al₂O₃, with 100% butene selectivity above 90% of butadiene conversion over 130 h on stream at 90 °C. Further exploration reveals that the atomically dispersed Pd on Cu nanoparticles, obtained at ultralow ppm levels of Pd loading, induces a hidden but critical H₂ trap, which concentrates H₂ on the Pd site for further H₂ dissociation that offers intermediate hydrogen atoms to the tandem butadiene semihydrogenation over the third layer of Cu atoms neighboring Pd through hydrogen spillover. Moreover, a threshold on Pd density was identified at Pd/Cu surficial atomic ratio of 1/138 (i.e., Pd_0.0033Cu₁/TiO₂) for maximizing butadiene semihydrogenation performance, based on an extreme collaboration between Pd for H₂ dissociation and Cu for butadiene hydrogenation. This work provides important guidance for developing noble metal-saving catalysts in industrial applications.