Isolated Pd₁ Sites and Surface Hydrogen Cooperativity Enable Selective Direct H₂O₂ Synthesis in PdSn-Based Catalysts

Area of Science:

• Catalysis
• Materials Science
• Chemical Engineering

Background:

• Direct synthesis of hydrogen peroxide (H2O2) from H2 and O2 is an attractive alternative to the conventional anthraquinone process.
• Palladium (Pd)-based catalysts are active but often suffer from low H2O2 selectivity due to unselective O─O bond cleavage.

Purpose of the Study:

• To elucidate the mechanism behind the high selectivity of PdSn catalysts in direct H2O2 synthesis.
• To identify the key active sites and reaction pathways governing H2O2 formation.

Main Methods:

• Density functional theory (DFT) calculations were employed to study surface energetics and reaction pathways.
• Molecular dynamics (MD) simulations under working conditions simulated catalyst evolution and reaction dynamics.

Main Results:

• Pristine and O/H-covered Pd3Sn surfaces were found to favor O─O bond cleavage, contradicting experimental selectivity.
• MD simulations revealed that the PdSn alloy/SnO2 interface transforms into atomically dispersed Pd species (Pd1).
• Isolated Pd1 sites on SnO2, stabilized by surface hydrogen, promote O2 hydrogenation and suppress O─O bond cleavage.

Conclusions:

• Atomically dispersed Pd sites, particularly Pd1/SnO2, are crucial for achieving high H2O2 selectivity.
• Surface hydrogen plays a cooperative role with isolated Pd sites in tuning the electronic structure and reaction landscape.
• These findings offer mechanistic insights for designing advanced Pd-based catalysts for efficient H2O2 synthesis.