Direct Synthesis of Hydrogen Peroxide from Hydrogen and Oxygen over Mesoporous Silica-Shell-Coated, Palladium-Nanocrystal-Grafted SiO₂ Nanobeads

Many studies have been conducted on core-shell structured nanocatalysts thanks to their high thermal and physical stability. However, for a typical core-shell structure, shell thickness and pore size that affect mass transfer through the shell are difficult to control. Herein, we synthesized a different type of core-shell catalyst, in which a mesoporous silica shell encapsulates the Pd-nanocrystals-grafted-SiO₂ nanobeads. With the preparation method introduced, we successfully controlled the thickness of the shell layer and generated a mesoporous texture over the shell layer. In activity tests, the production rate of hydrogen peroxide significantly increased when using the mesoporous shell catalyst over the microporous shell catalyst of similar shell thickness. The thickening of the mesoporous shell layer reduced the production rate of hydrogen peroxide. Thus, the thinner the thickness of a mesoporous shell, the more favorable in terms of pore-diffusion rate. However, the shell thickness should be adequately adjusted, because an extremely thin shell layer cannot protect the core Pd crystals from thermal agglomeration in a calcination and reduction process.