Precisely Designed Nitrogen-Doped Mesoporous Carbon Sphere-Confined Electron-Deficient Pd Nanoclusters with Enhanced Catalytic Hydrogenation Performance

The controlled fabrication of metal nanocluster-based catalysts with high catalytic performance and stability is currently a research hotspot, while it is still a research challenge. Herein, nitrogen-doped mesoporous carbon spheres (CS-N) with a regular and open structure were precisely designed and prepared. Pd nanoclusters with an average size of 1.44 nm were highly dispersed and stably confined in the radial mesoporous structure of CS-N, forming Pd/CS-N catalysts. The obtained Pd/CS-N catalysts showed high catalytic performance in the hydrogenation of phenol to cyclohexanone and hydrogenation of benzoic acid to cyclohexanecarboxylic acid (yield of almost 99%) under mild reaction conditions, outperforming most reported Pd nanoparticle-based catalysts. Theoretical calculation illustrates that the Pd nanocluster exists as an electron-deficient state on Pd/CS-N, thus can efficiently facilitate reactant preadsorption and activation, and also reduce the Gibbs free energy of the rate-determining step of the hydrogenation reactions. Moreover, the Pd/CS-N catalyst exhibited good reusability and stability. Thus, this work will promote the precise construction of stable metal nanocluster-based catalysts, enabling highly efficient catalytic hydrogenation reactions.