Dual Role of KBr in Hollow Core–Shell Pd Catalysts: Pd Electronic Structure Modulation and Stability Enhancement for Direct Synthesis of Hydrogen Peroxide

The direct synthesis of H₂O₂ from H₂ and O₂ is a sustainable alternative to the anthraquinone process, but its selectivity is severely limited by competing side reactions together with H₂O₂ hydrogenation and decomposition, while catalyst degradation and Pd leaching during operation further aggravate the loss of selectivity. In this study, we address these challenges by developing KBr-modified hollow core-shell Pd catalysts. The catalysts were synthesized with controlled KBr incorporation and subjected to thermal treatment to stabilize their electronic structure. Comparative catalytic tests, combined with electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction, and elemental analysis, revealed that KBr modification combined with thermal treatment helps maintain the stability of Pd²⁺ species, preventing their reduction during catalyst preparation and reaction, while also suppressing Pd leaching. Meanwhile, the hollow core-shell architecture physically confines Pd nanoparticles and minimizes detachment. As a result, the modified catalysts exhibited significantly improved selectivity and long-term cycling stability. These findings demonstrate that halide modification enhances catalyst performance not through simple site poisoning but via electronic modulation and structural stabilization, providing a new strategy for designing selective and durable catalysts for direct H₂O₂ synthesis.