Pd core–silica shell catalysts were prepared with different functional molecules. The catalyst Pd_KBr@SiO₂ had the highest H₂O₂ selectivity and productivity in the direct synthesis of hydrogen peroxide.

Hydrogen peroxide (H₂O₂), as a clean and green oxidant, is widely used in many fields. The direct synthesis of H₂O₂ (DSHP) from H₂ and O₂ has attracted most research interest because it relates to a facile, environmentally friendly, and economic process. Yolk–shell Pd-M@HCS (hollow carbon sphere) (M = Co, Ni, Cu) nanocatalysts, in which the bimetal nanoparticle is the core and porous carbon works as the shell layer, are reported in this work. It was found that catalytic activities were enhanced because of the introduced M metals. Additionally, the different mass ratios of Pd to Co (mPd/mCo) were further investigated to improve the catalytic performance for the DSHP. When mPd/mCo was 4.4, the prepared Pd-Co@HCS-(4.4) catalyst, with an average Pd nanoparticle size of 7.30 nm, provided the highest H₂O₂ selectivity of 87% and H₂O₂ productivity of 1996 mmolg_Pd⁻¹·h⁻¹, which were increased by 24% and 253%, respectively, compared to Pd@HCS.

Pd_Multi@HCS catalysts ensure the maximum exposure of Pd active sites and optimal transfer and diffusion ability for H₂O₂ synthesis.