CO₂ Reduction by Hydrogen Pre-Reduced Acceptor-Doped Ceria

Area of Science:

• Materials Science
• Catalysis
• Surface Chemistry

Background:

• Acceptor-doped ceria materials, such as Gd0.10Ce0.90O2-δ (GDC10) and Sm0.15Ce0.85O2-δ (SDC15), are investigated for their catalytic properties.
• The reverse water-gas shift (RWGS) reaction involves the reduction of carbon dioxide (CO2) to carbon monoxide (CO).
• Oxygen vacancies are known reactive sites in ceria-based catalysis for CO2 reduction.

Purpose of the Study:

• To investigate the reactivity of pre-reduced GDC10 and SDC15 materials in the context of CO2 reduction via the RWGS reaction.
• To elucidate the role of dissolved hydrogen as a reactive species in CO2 reduction on ceria-derived materials.
• To understand the formation, stability, and reactivity of surface carbonate species during the reaction.

Main Methods:

• In situ infrared (IR) spectroscopy was employed to monitor surface species and the oxidation state of cerium.
• Materials were subjected to oxidative (O2) and reductive (H2) treatments prior to reactivity testing.
• The formation and stability of carbonate species were analyzed under reaction conditions.

Main Results:

• Both oxygen vacancies and dissolved hydrogen were identified as reactive species for CO2 reduction.
• The formation of surface carbonates precedes CO2 reduction, with varying thermal stability.
• Pre-reduced (defective) samples showed increased formation of mono-dentate carbonates and carboxylates.
• Ce4+ reduction to Ce3+ by H2 and re-oxidation by CO2 were directly observed using IR spectroscopy.

Conclusions:

• Dissolved hydrogen must be considered alongside oxygen vacancies and formates in mechanistic discussions of the RWGS reaction on ceria.
• Surface carbonate species play a crucial role, exhibiting largely reversible adsorption/desorption behavior.
• The reactivity of acceptor-doped ceria in CO2 reduction is a complex interplay between oxygen vacancies, dissolved hydrogen, and surface chemistry.