A yolk-shell structured Pd@void@ZrO₂ catalyst for direct synthesis of hydrogen peroxide from hydrogen and oxygen

In this study, we prepared a yolk-shell structured Pd@void@ZrO₂ catalyst and tested its activity in direct hydrogen synthesis from hydrogen and oxygen. The catalyst was prepared by first encapsulating the nano Pd crystal with SiO₂ and then, the Pd core-silica shell composite (Pd@SiO₂) was encapsulated again with ZrO₂ (Pd@SiO₂@ZrO₂). The yolk-shell structure was obtained by etching the silica layer of Pd@SiO₂@ZrO₂ using 0.2 M KOH solution. Compared to the core-shell structured Pd@SiO₂, the void space in the yolk-shell structure allowed more gases to access the core Pd surface. In reaction tests, the production rate of gram Pd-specific H₂O₂ with Pd@void@ZrO₂ was approximately 1.2 times higher than with Pd@SiO₂. It was found that the optimum level of halide ion concentration in the reaction medium was between 0.1 and 0.3 mM for Pd@void@ZrO₂ catalyst.