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

Abstract

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 delta+ 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 delta+ 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 O-2 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.