Solar Thermochemical Conversion of CO2 into Synthetic Fuels Via Ferrite Based Redox Reactions

The recent energy trends indicate that the global energy requirement will increase from 14 TW to 30 TW by the year 2050. Currently, fossil fuels such as petroleum oil, coal and natural gas are used as the major energy source for the fulfillment of the energy requirement. However, emission of greenhouse gases such as CO₂ resulting from the combustion of fossil fuels is believed to be one of the major causes of global warming. To overcome the problems related to the continuously rising of oil prices and global warming due to the CO₂ induced greenhouse effect, there is a pressing need to develop technologies to produce carbon free renewable fuels. As a promising option, the liberated CO₂ can be re-energized into CO via ferrite based thermochemical looping process using concentrated solar energy. The CO produced via solar thermochemical CO₂-splitting can be combined with H₂ derived from ferrite based solar thermochemical water-splitting process to produce solar syngas which can be further processed to liquid fuels such as Methanol, Diesel, and Kerosene via the Fischer-Tropsch process. The current research trends in solar thermochemical community are focused towards high and constant levels of solar fuel production in multiple cycles and it is believed that non-volatile mixed metal oxides such as ferrites will significantly improve the production of solar fuels.

 In this study, various ferrite based redox materials such as Ni-ferrite, Co-ferrite, Zn-ferrite, etc. were synthesized using sol-gel method. The metal salts were dissolved in ethanol with the help of a sonic bath and a predetermined amount of propylene oxide was added to this solution for the formation of ferrite gel. As-synthesized gels were dried and heated upto different temperature in air. Obtained calcined powder was characterized using various analytical techniques such as powder X-ray diffraction, BET surface area analysis, scanning (SEM) & transmission electron microscopy (TEM), and Inductively coupled plasma spectrometer (ICP). Synthesized ferrite powders were further examined for their solar fuel production ability by performing multiple thermal reduction/oxidation (in presence of CO₂) cycles in a high-temperature thermogravimetric analyzer (TGA). The ferrite powder was thermally reduced at 1400 – 1450^oC while the oxidation was performed at different temperatures. O₂ and CO release was further monitored by gas chromatography. The results obtained indicate that the sol-gel derived ferrite materials produced high and constant levels of CO in multiple thermochemical cycles. The results related to synthesis, characterization and thermochemical conversion of CO₂ into solar fuels will be presented in detail.