Water-Driven Surface Lattice Oxygen Activation in MnO₂ for Promoted Low-Temperature NH₃-SCR

Area of Science:

• Heterogeneous Catalysis
• Environmental Chemistry
• Materials Science

Background:

• Water is a common component in heterogeneous catalysis, influencing reaction pathways.
• The precise role of water in catalytic processes, particularly in selective catalytic reduction (SCR), is not fully understood.
• Low-temperature SCR is crucial for efficient nitrogen oxide (NO) emission control.

Purpose of the Study:

• To elucidate the mechanism by which water enhances low-temperature ammonia selective catalytic reduction (NH₃-SCR) over γ-MnO₂.
• To investigate the role of water in activating surface lattice oxygen in γ-MnO₂.
• To provide a deeper understanding of water promotion in NO elimination.

Main Methods:

• Utilized comprehensive in situ characterizations.
• Performed theoretical calculations.
• Investigated the γ-MnO₂ catalyst for low-temperature NH₃-SCR.

Main Results:

• Demonstrated that water dissociation activates surface lattice oxygen in γ-MnO₂.
• Achieved a doubling of catalytic activity, reaching 90% NO conversion at 100 °C, with remarkable stability.
• Revealed that proton diffusion weakens the Mn-O bond, creating oxygen vacancies for O₂^- formation and improving redox properties.

Conclusions:

• Water plays a critical role in activating surface lattice oxygen via proton dissociation on γ-MnO₂.
• This water-driven activation significantly enhances NH₃-SCR performance at low temperatures.
• The findings offer new insights into water promotion mechanisms in environmental catalysis.