Sabatier Phenomenon in Hydrogenation Reactions Induced by Single-Atom Density

The Sabatier principle is a fundamental concept in heterogeneouscatalysis that provides guidance for designing optimal catalysts withthe highest activities. For the first time, we here report a new Sabatierphenomenon in hydrogenation reactions induced by single-atom densityat the atomic scale. We produce a series of Ir single-atom catalysts(SACs) with a predominantly Ir-1-P-4 coordinationstructure with densities ranging from 0.1 to 1.7 atoms/nm(2) through a P-coordination strategy. When used as the catalysts forhydrogenation, a volcano-type relationship between Ir single-atomdensity and hydrogenation activity emerges, with a summit at a moderatedensity of 0.7 atoms/nm(2). Mechanistic studies show thatthe balance between adsorption and desorption strength of the activatedH* on Ir single atoms is found to be a key factor for the Sabatierphenomenon. The transferred Bader charge on these Ir SACs is proposedas a descriptor to interpret the structure-activity relationship.In addition, the maximum activity and selectivity can be simultaneouslyachieved in chemoselective hydrogenation reactions with the optimizedcatalyst due to the uniform geometric and electronic structures ofsingle sites in SACs. The present study reveals the Sabatier principleas an insightful guidance for the rational design of more efficientand practicable SACs for hydrogenation reactions.