Syngas production via solar-driven chemical looping methane reforming from redox cycling of ceria porous foam in a volumetric solar reactor

The solar-driven chemical looping methane reforming using the non-stoichiometric ceria redox cycle (CeO2/CeO2-delta) was experimentally investigated for both syngas production and isothermal H2O/CO2 splitting using a directly irradiated volumetric solar reactor in the temperature range of 950-1050 degrees C. Experiments were performed via two-step redox cycling encompassing endothermic ceria reduction with methane (partial oxidation of methane) and exothermic oxidation of reduced ceria with H2O/CO2 under the same operating temperature. Ceria was used as oxygen carrier material in the form of reticulated porous foam structure and different operating parameters (methane flow-rate and reduction temperature) were varied in order to emphasize their impact on the bed-averaged oxygen non-stoichiometry (delta), syngas yield, methane conversion as well as solar reactor performances. The ceria cycling stability was also examined. The increase of both the methane flow-rate and reduction temperature promoted the delta, in turn leading to a substantial enhancement in the syngas yields that reached up to 8.08 mmol/g(CeO2). However, they showed an adverse impact on the carbon formation associated with methane cracking reaction. Fifteen successive ceria redox cycles with stable patterns in the delta and syngas production yield validated material stability. The maximum d achieved during ceria reduction was up to 0.38, complete oxidation yield with either water or CO2 was achieved, while the highest solar-to-fuel energy conversion efficiency reached 5.22% and the energy upgrade factor was in the range of 0.97-1.10.