Amine functionalization derived lattice engineered and electron deficient palladium catalyst for selective production of hydrogen peroxide

To improve the availability of commercialization for hydrogen peroxide (H₂O₂) direct synthesis, previous studies have demonstrated that electron-deficient palladium can increase the selectivity of H₂O₂. We adopted amine functionalization to modify the electronic state of Pd to be electron deficient. Meanwhile, from both bulk-scale XRD and atomic-scale HRTEM analysis, an unexpected expansion of the Pd is obviously identified, which is found to be in line with the electron-deficiency of Pd from XPS analysis. As a result, characterizations collectively demonstrate that a unique interaction between Pd and N atoms produces Pd^δ+ species as well as lattice expansion. A key to triggering the interaction is revealed to be thermal pretreatment, especially under air conditions. The amount of Pd^δ+ species is strongly correlated to the selectivity, thereby achieving 96% H₂O₂ selectivity over amine-functionalized Pd/SiO₂ compared to 52% over a nonfunctionalized Pd/SiO₂. Density functional theory demonstrates that the deficiency of electrons not only suppresses O₂ dissociation but also facilitates the synthesis of H₂O₂. In addition, H₂O₂ decomposition shows that electron-deficient Pd strongly inhibits H₂O₂ decomposition. Conclusively, we discover a meaningful modification to obtain an ideal catalytic activity over a Pd catalyst, with profound investigations on lattice engineering and electron-states as well as their origins.