In situ transformation of Pd to metal–metalloid alloy Pd2B for alkyne semi-hydrogenation

Abstract

In this work, we report alumina-supported metal-metalloid alloy nanoparticles (Pd₂B/Al₂O₃) as highly efficient alkyne semi-hydrogenation catalysts. The mentioned catalysts contain orthorhombically distorted hcp Pd₂B nanoparticles and were prepared by in situ transformation of Pd/Al₂O₃ with borane dimethylamine complex by a solvothermal method. The synthesized Pd₂B/Al₂O₃ demonstrated greatly enhanced semi-hydrogenation performance. Under reaction conditions of 30 °C, 0.1 MPa of H₂ and a substrate/Pd molar ratio of 1000/1, the conversions of 3-hexyne-1-ol could reach 99.8% in 15 min with a yield of cis-3-hexen-1-ol of 93.3%. Importantly, the alkene and cis- to trans-alkene selectivity only slightly decreases with an extended reaction time, showing the inhibition of deep hydrogenation. Experimental studies and density functional theory calculations indicate that the catalytic enhancement is originated from the formation of Pd₂B alloy, which alters the electronic and geometric properties of surface species, thus suppressing the deep hydrogenation with the enhanced alkene selectivity.