Homonuclear Dual-Atom Cobalt Sites for Enhanced Selective Hydrogenation

Single-atom catalysts based on non-noble metals have demonstrated remarkable selectivity in selective hydrogenation. However, their electron-deficient metal sites and the absence of adjacent metal sites often limit their hydrogenation activity. In this study, a homonuclear dual-atom cobalt site catalyst (Co-DAC) containing Co─Co bonds was synthesized by adsorbing a Co₂-complex onto ZIF-8 through a simple impregnation-pyrolysis process. The intrinsic activity of Co-DAC in selective hydrogenation, including nitroarene hydrogenation to arylamines and alkyne semi-hydrogenation to alkenes, was then investigated. The turnover frequency of Co-DAC was 431 h^{- 1} in nitrobenzene hydrogenation and 1665 h^{- 1} in phenylacetylene semi-hydrogenation. These values were 6.8-fold and 17.5-fold higher than those of the single-atom catalyst, respectively. Moreover, it demonstrated broad substrate scope in these two reactions. Mechanistic studies revealed that the Co─Co dual-atomic sites enhanced the adsorption capacity for nitro groups. Simultaneously, due to the electron coupling between Co─Co atom pairs, the electron density on the Co atoms increased. This facilitated the activation of H₂ and the desorption of aniline from the Co sites. Furthermore, the Co─Co sites enabled the homolytic cleavage of H₂ with a lower activation energy barrier. Therefore, Co-DAC exhibited significantly improved catalytic performance in selective hydrogenation.