Study on the synergistic effect and oxygen vacancy of CeO2/Fe2O3 oxygen carrier for improving reactivity in carbon monoxide chemical looping combustion
Yu Guan, Guohong Zhang, Ruru Wang, Yuanyuan Wang, Yinhe Liu
Abstract
The CeO 2 /Fe 2 O 3 oxygen carrier with oxygen vacancies exhibited higher CO oxidation efficiency in CLC. • The CeO 2 /Fe 2 O 3 oxygen carrier with oxygen vacancies was successfully synthesized. • The CeO 2 /Fe 2 O 3 -O v OC exhibited higher CO oxidation efficiency. • The oxygen vacancy formation energy was calculated by DFT and that of the CeO 2 /Fe 2 O 3 OC is lower than Fe 2 O 3 . • The CO CLC reaction on CeO 2 /Fe 2 O 3 -O v OC abided the MvK mechanism. Chemical looping combustion (CLC) is a promising way for CO 2 separation and capture. The oxygen carrier (OC) plays a key role in CLC by delivering lattice oxygen for oxidation reaction. Herein, CeO 2 /Fe 2 O 3 oxygen carrier with oxygen vacancies is successfully synthesized, and the synergistic effect of Ce and Fe in CeO 2 /Fe 2 O 3 OC is investigated by thermogravimetric analysis (TGA) tests and theoretical calculations. The reactivity of OCs is also tested in a fixed bed. Experimental results show that the CeO 2 /Fe 2 O 3 oxygen carrier exhibits higher CO oxidation efficiency than CeO 2 and Fe 2 O 3 , which may be caused by the synergistic effect of Ce and Fe. Moreover, the CeO 2 /Fe 2 O 3 composite OC shows a downward trend and achieved a weight loss rate of 4.1% which is higher than that of Fe 2 O 3 and CeO 2 in the TGA test. In addition, the electron paramagnetic resonance (EPR) spectra of oxygen carrier demonstrates that the typical signal peaks of oxygen vacancies around at g = 2.003 of CeO 2 , Fe 2 O 3 and CeO 2 /Fe 2 O 3 OC were observed, which can rapidly facilitate migration of lattice oxygen from interior to the surface of OC due to the existence of oxygen vacancies. Further, the oxygen vacancy formation energy was calculated by DFT, showing that the figure of the CeO 2 /Fe 2 O 3 OC (3.95 eV) is lower than Fe 2 O 3 (9.56 eV), which indicates that the addition of CeO 2 can efficiently reduce the oxygen vacancy formation energy. Finally, based on the results of reactivity and characterization test of OCs, it is demonstrated that the CO CLC reaction with CeO 2 /Fe 2 O 3 oxygen carrier follows Mars-van Krevelen (MvK) mechanism. This work reveals new insights into the synergistic improvement of the performance of Ce-Fe oxygen carriers with oxygen vacancies.