Atomic-Dispersed Rh Enables Efficient Catalytic Nitrile Hydrogenation: Size Effect and Metal-Dependent Effect

Abstract

The hydrogenation of nitriles to amines, as an atom-economical synthetic route, has attracted wide attention in industrial production. Despite that some catalysts for nitrile hydrogenation have been investigated in recent years, achieving high activity and selectivity in this process remains a major challenge. Here, we fabricated an atomically dispersed Rh catalyst anchored on defect-rich nanodiamond-graphene (ND@G) via a deposition–precipitation strategy (Rh1/ND@G), which showed the highest activity (TOF = 2592 h–1) in the hydrogenation of benzonitrile reaction among all the known catalysts under mild reaction conditions (333 K, 0.6 MPa H2), and delivered high selectivity (>99%) toward secondary amines. Significantly, we prepared the Rh-cluster catalyst (Rhn/ND@G) and a series of atomically dispersed M1 catalysts (M = Rh, Ru, Pd, Ir, and Pt) to understand the size effect and metal-dependent effect in the hydrogenation of benzonitrile. Experimental and theoretical investigations revealed that the Rh1/ND@G catalyst has higher selectivity toward dibenzylamine than Rhn/ND@G, as it is less likely to form benzylamine on the Rh1 active sites. Meanwhile, the difference of adsorption energies (as a catalyst descriptor) between benzylideneimine and benzonitrile was used to understand the activity of benzonitrile hydrogenation influenced by the metal-dependent effect of M1 catalysts. Modulating the size and metal-dependent effects could lead to high catalytic performance, paving the way to design efficient nitrile hydrogenation catalysts.