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.