A collaborative research team has developed a heteronuclear rhodium-cobalt (Rh-Co) dual-atom catalyst that enables highly efficient nitrile hydrogenation under mild conditions, breaking the long-standing activity-selectivity trade-off in this important industrial reaction.

The study was published in Nature Communications.

Secondary amines are prevalent in pharmaceuticals, agrochemicals, and functional materials, and the global annual production of amines exceeds six million tons. Catalytic hydrogenation of nitriles is a key method for producing these valuable compounds. However, traditional noble metal catalysts suffer from poor selectivity (typically 60–75% toward the desired secondary amine) due to overhydrogenation or coupling side reactions. Alternatively, they require harsh conditions, such as temperatures greater than 373 K and H₂ pressures of 3–10 MPa.

Although single-atom catalysts offer enhanced selectivity through isolated active sites, a single metal center struggles to co-activate both H₂ and bulky nitrile substrates, leading to insufficient catalytic activity.

To address this challenge, researchers from the Institute of Metal Research of the Chinese Academy of Sciences, Peking University, and Chongqing University constructed an atomically dispersed heteronuclear Rh-Co dual-atom catalyst supported on defective graphene, designated Rh₁Co₁/ND@G.

Using a stepwise anchoring strategy, the researchers first immobilized Rh atoms on the support and subsequently introduced Co(NH₃)₄²⁺ complexes followed by hydrogen reduction. This process successfully generated Rh-Co atomic pairs with an average interatomic distance of approximately 2.55 Å. Electronic structure analysis further revealed strong electronic coupling between the two metal atoms.

The resulting catalyst demonstrated exceptional performance in the hydrogenation of benzonitrile to dibenzylamine under mild conditions of 333 K and a hydrogen pressure of 0.6 MPa. A turnover frequency of 4068 h^-1 was recorded, which is 1.6 times higher than that of the Rh single-atom counterpart, while the selectivity toward dibenzylamine exceeded 98%. These results surpass the performance of previously reported heterogeneous catalysts for this reaction.

The catalyst also demonstrated excellent durability, maintaining over 85% product yield after 12 recycling runs. Moreover, it showed broad substrate tolerance, efficiently converting various electron-rich or electron-deficient aromatic nitriles, heterocyclic nitriles and even acetonitrile into the corresponding secondary amines with high yields.

Mechanistic studies combining kinetic experiments, temperature-programmed desorption, in situ infrared spectroscopy, and density functional theory calculations elucidated the synergistic catalytic mechanism. The Rh site primarily activates and dissociates molecular hydrogen, and the Co site enhances benzonitrile adsorption, particularly through π-interactions with the aromatic ring. 

This cooperative interaction polarizes the carbon-nitrogen triple bond and lowers the activation energy barrier of the rate-determining step from 0.81 eV on the Rh single-atom catalyst to 0.61 eV on the Rh-Co dual-atom catalyst, thereby kinetically promoting the reaction at lower temperature.

This work provides a new strategy for designing high-performance atomically dispersed hydrogenation catalysts for green chemistry and fine chemical synthesis.

Catalyst structural characterization. (a‑c) HAADF-STEM images, (d) interatomic distance distribution. (Image by IMR)

Catalytic performance of benzonitrile hydrogenation. (a) Time-conversion profiles, (b) TOF comparison, (c) apparent activation energy, (d) recycling stability. (Image by IMR)

Mechanistic studies. (a‑b) Kinetic studies, (c) BN-TPD, (c) BN in situ FTIR spectra, (e) DFT calculations. (Image by IMR)

Schematic illustration of benzonitrile hydrogenation catalyzed by Rh₁Co₁/ND@G. (Image by IMR)