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.