The thermodynamic analysis of two-step conversions of CO2/H2O for syngas production by ceria

•A new solar-driven system for two-step conversions of CO2/H2O by ceria was proposed.•Exergy analysis of the system was done based on the Second Law of Thermodynamics.•The solar to chemical efficiency for CO2 conversion ranges from 4.86% to 43%.•Recuperating heat losses can increase the efficiency.•Raising gas temperature and concentration ratio can also enhance the efficiency.

Due to the challenges of demands on alternative fuels and CO2 emission, the conversion of CO2 has become a hot spot. Among various methods, two-step conversion of CO2 with catalyst ceria (cerium oxide, CeO2) appears to be a promising way. Solar energy is commonly employed to drive the conversion systems. This article proposes a solar-driven system with fluidized bed reactors (FBR) for CO2/H2O conversions. N2 is used as the gas of the heat carrier. The products of CO/H2 could be further used for syngas. To evaluate the capability of the system for exporting work, the system was analysed on the basis of the Second Law of Thermodynamics and the reaction mechanism of ceria. Heat transfer barriers in practical situations were considered. The lowest solar to chemical efficiency is 4.86% for CO2 conversion, and can be enhanced to 43.2% by recuperating waste heat, raising the N2 temperature, and increasing the concentration ratio. The analysis shows that the method is a promising approach for CO2/H2O conversion to produce syngas as an alternative fuel.

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