Tailoring Nitrogen-Doped Carbons as Hosts for Single-Atom Catalysts

The application of nitrogen-doped carbons (NDCs) as host materials for single-atom catalysts (SACs) is increasing because of the strong binding affinity of the heteroatom with transition metals. Establishment of the relation between the properties of NDCs, their interaction with metals, and the performance of the resulting catalysts is crucial to guide the design of more effective SACs but has not been critically addressed. Here, a series of NDCs is prepared and studied as hosts for palladium atoms. The amount of nitrogen incorporated primarily depends on the choice of carbon followed by the doping temperature and nitrogen source. Pyridinic and pyrrolic species predominate in all cases, especially at lower doping temperatures. The stabilization of palladium atoms is successful above a critical nitrogen content that depends on the carbon type. Evaluation in the catalytic semi-hydrogenation of 2-methyl-3-butyn-2-ol readily distinguishes the reactivity of single atoms and nanoparticles, which correlates with the electronic properties of palladium described by the average oxidation state. Comparison with SACs based on compositionally-related carbon nitride hosts shows that similarly high stability and tunability of the metal is achievable over NDCs, despite their lower nitrogen contents and greater heterogeneity of coordination sites.