Appraising Multinuclear Cu²⁺ Structure Formation in Cu-CHA SCR Catalysts via Low-T Dry CO Oxidation with Modulated...

Area of Science:

• Catalysis
• Environmental Science
• Materials Science

Background:

• Copper-exchanged chabazite (CHA) is a key catalyst for selective catalytic reduction (SCR) of NOx in diesel engines.
• The redox mechanisms of copper sites (Cu2+ to Cu+) during SCR operation are not fully understood.
• Multinuclear Cu2+ species are proposed as initial active sites in the low-temperature reduction half-cycle (RHC).

Purpose of the Study:

• To investigate the role of ammonia (NH3) in the formation of active copper species during CO oxidation.
• To correlate NH3 pre-adsorption and solvation effects with catalytic activity.
• To elucidate the NH3 role in the low-temperature SCR redox mechanism and identify active catalyst sites.

Main Methods:

• Utilized dry CO oxidation experiments to probe copper site behavior.
• Employed modulated NH3 feed phases prior to CO oxidation.
• Analyzed CO2 production enhancements and correlated them with NH3 solvation extent.

Main Results:

• NH3 pre-adsorption significantly enhanced CO2 production, indicating a positive effect on catalytic activity.
• CO2 production enhancements were directly correlated with the degree of Cu2+ ion solvation by NH3.
• Observed second-order kinetic dependence on the oxidized Cu2+ fraction, similar to SCR-RHC phase dynamics.

Conclusions:

• Ammonia solvation enhances Cu2+ ion mobility, promoting the formation of binuclear complexes that catalyze CO oxidation.
• The study provides evidence for NH3's crucial role in the low-temperature SCR redox mechanism.
• Novel insights into the nature of active copper catalyst sites in Cu-CHA for NOx abatement were gained.