Why is silver catalytically active for NO reduction? A unique pathway via an inverted (NO)2 dimer

Area of Science:

• Heterogeneous catalysis
• Surface chemistry
• Computational materials science

Background:

• Silver (Ag) is a key catalyst for nitric oxide (NO) reduction.
• Previous mechanisms involving monomeric NO dissociation on Ag surfaces are insufficient to explain experimental observations.

Purpose of the Study:

• To elucidate the mechanism of NO reduction on Ag catalysts.
• To identify the origin of silver's catalytic activity and selectivity.

Main Methods:

• Density functional theory (DFT) calculations were employed.
• Investigated NO dissociation pathways on Ag surfaces and clusters.

Main Results:

• Monomeric NO dissociation on Ag exhibits prohibitive energy barriers, ruling it out as the primary pathway.
• A novel mechanism involving the inverted (NO)2 dimer was identified as the dominant pathway.
• The inverted (NO)2 dimer mechanism explains the high activity and selectivity observed experimentally, with N2O as the major product.
• Silver's catalytic properties stem from its weak covalent bonding and strong ionic interactions with adsorbates.

Conclusions:

• The inverted (NO)2 dimer mechanism accurately describes NO reduction over Ag catalysts.
• Silver's catalytic selectivity is determined by the varying ionic bonding strength with different reactants.
• Understanding these interactions is crucial for designing improved Ag-based catalytic systems.