(55h) Solar Hydrocarbon Fuel Production from H2o and CO2 Via Ceria Based Catalytic Thermochemical Cycles

Metal oxide based solar thermochemical H₂O and CO₂ splitting cycles are an attractive and sustainable route for the production of clean and carbon-neutral chemical fuels such as H₂ or syngas. Several metal oxides have been tested towards solar fuel production via thermochemical H₂O and CO₂ splitting cycles and among all these ceria is a promising candidate. There are several reasons for ceria to be a better candidate such as ease of reduction and oxidation cycling with respect to the variations in the temperature or oxygen partial pressures, high mobility of the O₂ ions in its lattice, higher melting point, relative abundance, and faster reaction kinetics towards thermochemical H₂O and CO₂ splitting reactions. In past, the researchers put their efforts towards improving the H₂ or syngas production via doping ceria with heterocations or by manufacturing porous ceramics containing ceria materials to improve the heat/mass transfer and reaction kinetics. In this investigation, we propose direct production of hydrocarbon fuels (C_xH_yO_z) from H₂O and CO₂ using ceria based catalytic thermochemical cycle. Due to the production of hydrocarbon fuel (instead of syngas) from H₂O and CO₂, the second stage conversion such as methanation or Fischer–Tropsch processes can be eliminated. In addition, the production of syngas from fossil fuel and its storage and transportation would not be needed, making the overall process vary much economical. Therefore, in this study, catalytically doped ceria materials were synthesized via co-precipitation of hydroxide method and these materials were further tested towards production of hydrocarbon fuel directly from H₂O and CO₂ via thermochemical cycles. Selected dopants from alkaline earth metals, lanthanides, and transition metals were used as the catalytic material to dope in the ceria crystal structure. The synthesized doped ceria materials were characterized using XRD, BET, SEM, TEM, XPS, and ICP. Furthermore, the hydrocarbon fuel production ability of the derived doped ceria materials were examined by performing thermochemical H₂O and CO₂ splitting cycles using a thermogravimetric analyzer and a packed bed reactor set-up. The activation of the material was achieved via thermal reduction at higher temperatures (1400 to 1500^oC). On the other hand, the re-oxidation/splitting reactions were carried out at lower temperatures (500 to 700^oC). The products exiting the reactor were analyzed using GC and MS. Multiple thermochemical cycles were performed for continuous production of hydrocarbon fuel from H₂O and CO₂ and the reacted catalytic doped ceria materials were further analyzed to identify the physico-chemical properties after performing multiple thermochemical cycles.