Modulation of Fe-based oxygen carriers by low concentration doping of Cu in chemical looping process: Reactivity and mechanism based on experiments combined with DFT calculations

Fe-based oxygen carriers (OCs) are currently the crucial material basis for chemical looping technology to realize industrial applications. However, the relatively low reactivity of pure Fe-based OCs limits their extensive applications. One strategy to enhance reactivity in the chemical looping process is the introduction of another metallic element by doping. This study prepared a series of Fe-based OCs (Cu2xFe2(1-x)O3) with low concentration doping of Cu. The reaction mechanism and reactivity modulation of Cu2xFe2(1-x)O3 OCs in the chemical looping process were systematically investigated by means of experiments and density function theory (DFT) calculations. Activation energies for Cu2xFe2(1-x)O3 ranging between 72 and 37 kJ/mol were detected using H-2 and the thermogravimetric analyzer (TGA) test, indicating enhanced reactivity in the chemical looping process as compared with that of pure Fe-based OCs of 84 kJ/mol. Thus, the low concentration doping of Cu can effectively improve the reactivity of Fe-based OCs. Furthermore, comprehensive DFT calculations upon the transition state indicated the reaction energy barrier for Cu2xFe2(1-x)O3 with different doping concentration and configurations to be in the range of 1.68-1.02 eV, lower than that of pure Fe2O3 of 2.30 eV. The Cu doping and the modulation of the reaction pathways are important reasons for the enhanced reactivity of Cu2xFe2(1-x)O3 OCs. Additionally, this study proposed a lattice oxygen release mechanism of Cu2xFe2(1-x)O3 OCs during chemical looping combustion. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

This study investigated the reactivity modulation of Fe-based oxygen carriers doped with low concentration of Cu in the chemical looping process. Experimental results showed a decrease in activation energies for Cu2xFe2(1-x)O3 compared to pure Fe-based OCs, indicating enhanced reactivity. DFT calculations revealed lower reaction energy barriers for Cu2xFe2(1-x)O3 with different doping concentrations and configurations, highlighting the importance of Cu doping and reaction pathway modulation in improving reactivity.