CO2 Valorization Via Solar Thermochemical CexZryHfzO2-Cycle

The concentration of CO₂ in environment has reached upto 392 ppm by volume as of 2011, which was 280 ppm in pre-industrial times and if this trend continues, by 2050 CO₂ concentration is expected to raise upto 550 ppm. Because of the adverse effects of CO₂ discharge on the global environment, the development of strategies for the utilization of captured CO₂ has become increasingly important. As a promising option, the liberated CO₂ can be re-energized into CO via metal oxide based solar thermochemical cycles. The CO produced via solar thermochemical CO₂-splitting can be combined with H₂ derived from 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.

In this investigation, solar thermochemical Ce_xZr_yHf_zO_2-δ cycle was examined towards conversion of CO₂ into CO. At first, various combinations of Ce_xZr_yHf_zO_2-δ  redox materials were synthesized via co-precipitation method and subsequent calcination at different temperatures in air. The calcined powders were characterized by powder X-ray diffraction, BET surface area analysis, scanning (SEM) and transmission electron microscopy (TEM), etc. Synthesized Ce_xZr_yHf_zO_2-δ redox materials were further examined towards thermochemical CO₂-splitting reaction with the help of a high-temperature thermogravimetric analyzer (TGA). Multiple thermal reduction and oxidation cycles were performed at various operating conditions by using TGA. The O₂ and CO produced during multiple cycles was quantified by gas chromatography. The findings indicate that Ce_xZr_yHf_zO_2-δ is capable of producing constant and high yield of CO in comparison with the other ceria based redox materials in multiple thermochemical cycles. The results related to synthesis, physiochemical characterization, and thermogravimetric experiments will be presented in detail.