Mid-temperature CO2 deoxygenation to CO over Fe-CeO2

Abstract

CO₂ capture and utilization is a must for easing the global warming caused by the uses of fossil fuels. We examine M-CeO₂ (M = Cu, Co, and Fe @M/Ce = 2/8) prepared by coprecipitation and hard template synthesis. Fe-CeO₂ is the only one showing thermal CO₂ deoxygenation to CO at below 700 °C after reduction. XRD analyses of as prepared Fe-CeO₂ demonstrate the presence of segregated Fe₂O₃ and CeO₂ phases with partial mixing. Both Fe₂O₃ phase and CeO₂ phase show redox during sequential TPR (temperature-programmed reduction)-CO₂-TPRx (temperature-programmed reaction) up to 700 °C. The evolved Fe⁰ after TPR appears to be the main active phase for CO₂ deoxygenation which becomes oxidized back to Fe₂O₃ after CO₂-TPRx. The results indicate that the interface (interphase) between Fe-domain and CeO₂-domain is involved leading to the observed deoxygenation reactivity. That the stripped oxygen from CO₂ over Fe-domain can spillover to CeO₂ domain is considered as a possible explanation. We perform isothermal CO₂ deoxygenation test at 600 °C over TPR-treated Fe-CeO₂ using oxygen-conducting membrane reactor, and the CO₂ deoxygenation capacity is found significantly higher than that observed when in the absence of oxygen conducting membrane. This demonstrates not only the possible oxygen spillover but also the possibility of achieving a sustainable CO₂ deoxygenation process.