Unveiling Alkali-Induced Redox Modulation: In-Situ Spectroscopic Insights from RWGS on Alkali-Modified ZrO₂-Supported...

Area of Science:

• Heterogeneous catalysis
• Surface chemistry
• Reaction mechanisms

Background:

• Alkali-modified solid catalysts are promising for various applications.
• The precise role of alkali metals in catalysis, particularly sodium (Na+), remains under investigation.
• Understanding these roles is key to designing efficient catalytic systems.

Purpose of the Study:

• To synthesize and characterize Na-modified ZrO2-supported Cu catalysts for the reverse water-gas shift (RWGS) reaction.
• To elucidate the specific role of Na+ in the catalytic performance and reaction mechanism.
• To compare different synthesis methods for optimizing catalyst preparation.

Main Methods:

• Synthesis of Na-modified ZrO2-supported Cu catalysts using one-pot and wet impregnation methods.
• Catalytic activity testing for the RWGS reaction.
• In-situ Electron Paramagnetic Resonance (EPR) and in-situ CO-Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) studies.

Main Results:

• Catalyst activity was highly dependent on the preparation method; the one-pot method yielded three times higher activity than wet impregnation.
• The one-pot method enhanced Cu0 dispersion and prevented site loss.
• In-situ studies revealed that the redox mechanism, not the associative mechanism, is dominant for CO formation.
• Na+ facilitates the reoxidation of Cu0 sites by CO2 dissociation, a key step in CO formation.

Conclusions:

• A high density of accessible Cu0 sites with enhanced redox activity is essential for superior catalytic performance in the RWGS reaction.
• Na+ plays a critical role in promoting the reoxidation step of the redox mechanism.
• These findings enable rational design of alkali-modified catalysts with improved active sites and redox properties.