Research article Enhanced performance of the CeO2-MgO oxygen carrier by NiO for chemical looping CO2 splitting

Chemical looping CO2 splitting is a novel technology to coproduce syngas and pure CO. Herein, a series of xNiO/(CeO2-MgO) (x = 0, 1, 5, 7, 10 and 15 wt%) oxygen carriers were prepared by a co-precipitation method. The physicochemical characterizations suggest that the addition of NiO into the CeO2-MgO oxygen carrier significantly enhances the activity for the CH4 and CO2 conversion. In particular, the addition of 10 wt% NiO increases the CH4 conversion from 15.62% to 59.64% with a CO selectivity of nearly 100% in multiple redox tests at 800 degrees C. The produced syngas also maintains a stable H-2/CO molar ratio of 2.0 during the CH4 reduction step. The oxygen exchange between oxygen carriers and CO2 becomes easier, which enhances the yields of CO up to 1.75 mmol/g in the CO2 splitting step. The formation of CeO2-NiO and NiO-MgO double solid solutions is found in the oxygen carriers, which avoids the agglomeration of NiO and improves the redox stability of the oxygen carrier. In addition, some Ni species in solid solutions migrate from the bulk to the surface after redox cycles, which contributes to the greater contact opportunity with the reacting gas to promote the CH4 conversion and CO2 activation.

Automated summary

Adding NiO into CeO2-MgO oxygen carrier significantly enhances the activity for CH4 and CO2 conversion, especially at 800 degrees C. The addition of NiO also improves the selectivity and yield of CO. The formation of CeO2-NiO and NiO-MgO double solid solutions contributes to the stability of the oxygen carrier.