Synergistic Effects in Low-Temperature CO Oxidation on Cerium Oxide Surfaces

Area of Science:

• Surface science
• Catalysis
• Computational chemistry

Background:

• The reaction between carbon monoxide (CO) and activated dioxygen (O2) on metal oxides to produce CO2 is crucial but poorly understood.
• The roles of oxygen vacancies and activated O2 species in this process require further elucidation.

Purpose of the Study:

• To investigate the low-temperature CO oxidation mechanism on a cerium dioxide (CeO2) model system.
• To determine the role of oxygen vacancies and activated O2 species in CO oxidation.

Main Methods:

• Infrared reflection-absorption spectroscopy (IRRAS) was used to study the reaction on monocrystalline CeO2(111).
• Spin-polarized density functional theory (DFT) calculations were employed to explore reaction mechanisms and energetics.

Main Results:

• Exposing reduced CeO2 to O2 at 80 K did not form superoxo or peroxo species.
• In the presence of adsorbed CO, low-temperature oxidation occurred, consuming CO and oxidizing the CeO2 substrate.
• Oxygen vacancies were found to migrate from the subsurface to the surface, activating O2 and forming intermediates.

Conclusions:

• A novel mechanism involving subsurface oxygen vacancy migration is proposed for low-temperature CO oxidation.
• The peroxo-mediated pathway is identified as more favorable than the carbonate pathway for CO oxidation at low temperatures.
• Subsurface oxygen vacancies play a dynamic role in O2 activation and CO oxidation on CeO2.