Understanding the Roles of Thiophenol-Ligated Ag-Based Nanoclusters on TiO2during the Catalytic Hydrogenation of Nitroarenes

Elucidating the correlations between the core structure of atomically precise nanoclusters and their catalytic activities is fundamentalfor exploring highly efficient nanocatalysts. Herein, a series of Ag-based nanoclusters protected by 2,4-dimethylphenylthiophenol (specifically Ag4Pd2(SPhMe2)8and Ag24M(SPhMe2)18where M = Ag, Pd, and Pt) were synthesized and deposited on TiO2supports as heterogeneous catalysts for the selective hydrogenation of nitroarenes with NaBH4as the reductant. It was found that Ag4Pd2(SPhMe2)8could spontaneously lose its ligands during catalysis, leading to the formation of polydispersed AgPd nanoparticles. This transformation endows the system with extraordinary activity for driving the hydrogenation of nitroarenes. However, the Ag24M (M = Ag, Pd, and Pt) systems, maintain their core structures during catalysis. They follow the generally reported ligand-mediated hydride-involved process, with catalytic activities depending on the central atom (Pt > Pd > Ag), which affects the hydride transferred from the nanoclusters to the reactant to regulate the catalysis.