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

• Published in: Applied surface science 2022-12, Vol.604, p.154464, Article 154464
• Main Authors: Yoon, Jihwan, Han, Geun-Ho, Lee, Min Woo, Lee, Seok-Ho, Lee, Seong Ho, Lee, Kwan-Young
• Format: Article
• Language: English
• Subjects: Amine-fuctionalization; Direct synthesis of hydrogen peroxide; Electron-deficient; Lattice expansion; Pd catalyst
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2022.154464

[Display omitted] •Amine groups lead to charge deficiency and lattice expansion of Pd catalyst.•Thermal pretreatment is a key step to inducing lattice expansion of Pd.•Proper amount of amine group can gain the largest amount of Pdδ+ species.•The electron-deficient Pd is preferable for selective H2O2 synthesis.•DFT reveals thermodynamic advantages of electron-deficient Pd(1 0 0) model. 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 Pdδ+ 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 Pdδ+ 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.