Porosity Control of Pd@SiO2 Yolk-Shell Nanocatalysts by the Formation of Nickel Phyllosilicate and Its Influence on Suzuki Coupling Reactions

The surface of Pd@SiO2 core-shell nanoparticles (1) was simply modified by the formation of nickel phyllosilicate. The addition of nickel salts formed branched nickel phyllosilicates and generated pores in the silica shells, yielding Pd@SiO2-Niphy nanoparticles (Niphy = nickel phyllosilicate; 2, 3). By removal of the silica residue, Pd@Niphy yolk shell nanoparticles (4) was uniformly obtained. The four distinct nanostructures (1-4) were employed as catalysts for Suzuki coupling reactions with aryl bromide and phenylboronic acid, and the conversion yields were in the order of 1 < 2 < 3 < 4 as the pore volume and surface area of the catalysts increased. The reaction rates were strongly correlated with shell porosity and surface exposure of the metal cores. The chemical inertness of nickel phyllosilicate under the basic conditions rendered the catalysts reusable for more than five times without loss of activity.