Enhancing hydride formation and transfer for catalytic hydrogenation via electron-deficient single-atom silver.

Abstract

Metal hydrides are sensitive to H₂O and O₂, which reduces the atom efficiency of the hydride donors. Silver (Ag) is an inexpensive coinage metal; however, its lower activity compared to gold, platinum, and palladium limits its application in catalytic hydrogenation. Here, electron-deficient metallic single-atom Ag (AgSA) was loaded onto γ-Al₂O₃ using a benzoquinone- and KNO₃- assisted photolysis approach. The obtained AgSA/Al₂O₃ catalyst exhibited high rates, high tolerance to side reactions with O₂ and H₂O, and high NaBH₄ atomic efficiency for the catalytic hydrogenation of nitroaromatics in aqueous media. It showed a low kinetic barrier for B-H activation, leading to silver hydride formation and nitrobenzene hydrogenation, while presenting a high kinetic barrier for OH activation, which inhibited H₂ production. This behavior contrasts with that of Ag-nanoparticle-loaded γ-Al₂O₃. The high activity of AgSA is attributed to its electron-deficient nature and atomic dispersion, whereas its high selectivity is possibly ascribed to the involvement of a dihydrogen bond-containing intermediate. Our findings highlight the potential of AgSA to modulate the formation and reactivity of silver hydrides.