Catalytic Hydrogen Transfer of Ketones over Ni@SiO2 Yolk-Shell Nanocatalysts with Tiny Metal Cores

Abstract

In the present work, we report the synthesis of Ni@SiO2 yolk-shell nanocatalysts that bear tiny nickel cores with an average diameter of 3 nm. The nickel nanoparticles were coated with silica through the microemulsion method, and the resulting Ni@SiO2 core-shell nanoparticles were partially etched by acid treatment. The calcination of the particles yielded yolk-shell nanocatalysts with a uniform structure. The catalysts were employed for heterogeneous hydrogen-transfer reactions of acetophenone. The optimized reaction condition used 0.03 mol % of the catalysts in the presence of 20 mol % of base at 423 K for 30 min. Under this condition, the conversion reached 90%, and the TOF was calculated to be 6000 h-1, which is at least 60 times higher than the previous results using nickel catalysts. The catalysts were highly stable and more than six times recyclable without any loss of catalytic activity. This rational yolk-shell design of the nanocatalysts can be employed for various organic reactions with the advantages of high reactivity and eusability.