Electronic modulation of Ni sites via intermetallic structure in Al-Ni/Al2O3 catalysts for efficient semi‑hydrogenation of alkynes

The semi‑hydrogenation of alkynes to alkenes remains a challenging topic in the purification of polymer monomers. Achieving selective hydrogenation of alkynes requires careful control of alkene adsorption strength on the catalyst surface while avoiding the production of over‑hydrogenated compounds. The reaction is fundamentally influenced by the electronic structure of the metal active sites on the catalyst surface. In this study, Al 2 O 3 -supported Al Ni intermetallic nanoparticles catalysts are synthesized through in situ reduction-doping methods using LiAlH 4 as Al sources. The coordination environment and electronic structure of the active metal Ni are finely tuned while the Al Ni stoichiometric ratio is adjusted. The turnover frequency of AlNi 3 /Al 2 O 3 (16.7 h -1` ) and AlNi/Al 2 O 3 (9.1 h −1 ) are higher than that of the Ni/Al 2 O 3 catalyst (8.6 h −1 ). The optimal AlNi/Al 2 O 3 catalyst with AlNi intermetallic structure exhibits the high styrene selectivity (>90 %) when the phenylacetylene conversion exceeds 99 %. The metal bond between Al and Ni atoms strengthens electronic coupling, resulting in the hybridization of Al p orbital and s orbital with Ni d orbital. The resulting isolated and electron-rich Ni sites (Ni δ- ) are key to achieving high selectivity for styrene. These sites govern the π-adsorption of styrene molecules. Furthermore, the kinetic selectivity advantage of this unique Ni ensemble (AlNi, an intermetallic compound) has been verified. A lower reaction rate and higher activation energy (Ea = 132 kJ·mol −1 ) for hydrogenation of styrene over AlNi/Al 2 O 3 catalyst are observed. Moreover, the high stability of this catalyst and its broad applicability in the hydrogenation of various alkyne compounds provide valuable insights for selective hydrogenation applications of Al-based intermetallic catalysts, enabling the exploration of their properties and applications.