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

Thehydrogenation of nitriles to amines, as an atom-economicalsynthetic route, has attracted wide attention in industrial production.Despite that some catalysts for nitrile hydrogenation have been investigatedin recent years, achieving high activity and selectivity in this processremains a major challenge. Here, we fabricated an atomically dispersedRh catalyst anchored on defect-rich nanodiamond-graphene (ND@G) viaa deposition-precipitation strategy (Rh-1/ND@G),which showed the highest activity (TOF = 2592 h(-1)) in the hydrogenation of benzonitrile reaction among all the knowncatalysts under mild reaction conditions (333 K, 0.6 MPa H-2), and delivered high selectivity (>99%) toward secondary amines.Significantly, we prepared the Rh-cluster catalyst (Rh- n /ND@G) and a series of atomically dispersed M-1 catalysts (M = Rh, Ru, Pd, Ir, and Pt) to understand thesize effect and metal-dependent effect in the hydrogenation of benzonitrile.Experimental and theoretical investigations revealed that the Rh-1/ND@G catalyst has higher selectivity toward dibenzylaminethan Rh- n /ND@G, as it is less likely toform benzylamine on the Rh-1 active sites. Meanwhile, thedifference of adsorption energies (as a catalyst descriptor) betweenbenzylideneimine and benzonitrile was used to understand the activityof benzonitrile hydrogenation influenced by the metal-dependent effectof M-1 catalysts. Modulating the size and metal-dependenteffects could lead to high catalytic performance, paving the way todesign efficient nitrile hydrogenation catalysts.