Facile synthesis and electronic structure optimization of sub-nanometer palladium clusters for efficient direct synthesis of H2O2†

Direct synthesis of hydrogen peroxide (H₂O₂) from hydrogen and oxygen is an atom-efficient and environmentally benign method. However, achieving high H₂O₂ selectivity and productivity with sub-nanometer Pd clusters remains challenging due to the tendency of undercoordinated surface sites to cleave O–O bonds and form water. Herein, sub-nanometer Pd clusters are confined to ammonia-treated ZIF-8-derived mesoporous carbon (ZDC) with controlled nitrogen configurations, which facilitates the effective direct synthesis of H₂O₂ by optimizing the electronic structure of Pd atoms via a strong metal–support interaction (SMSI). The sub-nanometer catalyst Pd/ZDC_1.0 achieves a remarkable H₂O₂ selectivity of 81.6% and productivity of 3323 mmol g_Pd⁻¹ h⁻¹, which are 12.5% and 122.8% higher than those of the sub-nanometer catalyst Pd/XC-72 without nitrogen doping, respectively. Structural characterization shows that the pore structure and pyridine nitrogen content of Pd/ZDC_X are proportional to the ammonia treatment time. Theoretical calculations demonstrate that there is a strong electron transfer between sub-nanometer Pd clusters and pyridine nitrogen sites, leading to a downward shift in the d-band center of Pd atoms. The electronic effect weakens the adsorption of reactive intermediates on undercoordinated surface sites and suppresses O–O bond dissociation, contributing to enhanced selectivity and preventing water formation.