Cooperation of active site isolation and charge transfer in intermetallic Al-Co catalysts boosting the semi-hydrogenation of phenylacetylene

Abstract

The long-term scientific challenge and pursuit for semi-hydrogenation of alkynes to alkenes can be satisfied by regulating metal active centers or developing new catalytic materials. Herein, Al-Co_x intermetallic catalysts are successfully prepared by reducing metal oxides using LiCl-CaH₂ composite molten salts, which are utilized for the semi-hydrogenation of phenylacetylene to styrene. The AlCo intermetallic catalyst with amorphous alumina encapsulation, resulting from the non-stoichiometric ratio feeding, exhibits significantly high styrene selectivity (83 %) at 99 % conversion of phenylacetylene under 100 °C and 0.3 MPa H₂, which is much better than those of surface Co-rich samples and Co/Al₂O₃ catalyst. The selectivity enhancement in phenylacetylene semi-hydrogenation is attributed to the alteration in the adsorption mode of styrene over AlCo intermetallic catalyst surface, which facilitates by the electron-rich and isolated Co active sites. Moreover, in hydrogenation of alkyne with different functional groups and steric hindrances, the corresponding alkene selectivity is similarly satisfactory, and the catalyst is easy to separate and has a stable structure. This work offers a valuable approach for tailoring the catalytic performance of intermetallic compounds formed by transition metal aluminides, and expanding their potential applications in efficient hydrogenation catalysts.