FeO-enabled low-temperature CO2-splitting for chemical looping carbon utilization

Abstract

Chemical looping integrated with CO₂ utilization is an attractive chemical process that can contribute greatly to on-site carbon capture and utilization. To reduce the excess energy consumption, the kinetics of the CO₂-splitting half reaction has been revisited on pure iron oxygen carriers. High CO₂-splitting rate at a very low temperature of 350 °C is discovered with an unambiguous relationship to the presence of FeO. Through controlled reduction, a nanoporous oxygen carrier enriched with active FeO, capable of 2-dimensional oxide growth with fast kinetics is formed and can be regenerated under cycling conditions of a chemical looping reverse water–gas shift model reaction at 500 °C. Over-reduction leads to the formation of low activity metallic Fe that requires additional 100 °C or more to conduct CO₂-splitting, which deactivates rapidly due to severe sintering. Density functional theory calculations reveal the minimum energy pathway involving the dissociation of adsorbed CO₂ on the Fe surface, followed by the spillover of CO to the FeO surface for desorption. These findings provide guidance for the design of a reactive iron-based oxygen carrier for low temperature CO₂-splitting in all chemical looping carbon capture utilization processes.