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

Abstract

The solar-driven chemical looping methane reforming using the non-stoichiometric ceria redox cycle (CeO2/CeO2-δ) 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 °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 (δ), 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 δ, in turn leading to a substantial enhancement in the syngas yields that reached up to 8.08 mmol/gCeO₂. 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 δ and syngas production yield validated material stability. The maximum δ 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.