Conversion of carbon dioxide to carbon monoxide: Two-step chemical looping dry reforming using Ca2Fe2O5–Zr0.5Ce0.5O2 composite oxygen carriers

Abstract

In this study, Zr0.5Ce0.5O2 (ZC) was used to improve the reactivity of Ca2Fe2O5 (CF) oxygen carriers (OCs) and alleviate sintering. The reactivity of modified OCs in Chemical looping dry reforming (CLDR) was explored using a thermogravimetric analyzer and a fixed-bed reactor, and the fresh and reacted OCs were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results revealed that CF6 (60 wt% CF + 40 wt% ZC) had the best reactivity. Owing to the addition of ZC, the carbon monoxide (CO) yield of CF6 was twice that of CF during carbon dioxide (CO2) oxidation, increasing from 72.3 mL/g to 138 mL/g. In the cyclic experiments, the CO yield from CO2 oxidation decreased from 138 mL/g in the first cycle to 34.3 mL/g in the fifth cycle and subsequently stabilized over the next 15 cycles. The decrease in cyclic performance is related to the sintering of the sample and the formation of a new phase, CaZrO3, which hindered the redox reaction in the sample. Although CF6 had a decreased cyclic performance, it still had a better reactivity than CF, which had a CO yield that was about 20% lower than that of CF6. The reason for the improvement is that ZC improved the dispersibility of CF. After 20 cycles, the generation of CO was facilitated by extending the reduction time of the OC, and the CO yield increased from 35 mL/g to 60 mL/g when the reduction time was doubled.