Recent developments in photothermal reactors with understanding on the role of light/heat for CO₂ hydrogenation to fuels: A review

Carbon dioxide and sunlight are two main resources that are available in abundance within the earth's atmosphere. Carbon dioxide is a very useful feedstock for hydrogenation reactions to produce green fuels. Photothermal CO₂ hydrogenation reactions are gaining interest as it utilizes solar energy to generate thermal energy to drive the endothermic reaction. Moreover, both photochemical and thermochemical routes occur during the photothermal reaction, which is reported to further enhance production of hydrocarbons. This review is focusing on the reactor technologies utilized for photothermal CO₂ hydrogenation. In order to establish the mechanisms of photothermal catalysis, the definition and overview of thermal catalysis, photocatalysis and photothermal catalysis are thoroughly reviewed. The specific role of heat and light for activating CO₂ molecules has been specifically deliberated. The photothermal catalysis is described as the generation of heat via photo-to-thermal effects and coupling of solar energy with additional heating. Different operating parameters such as type of feed, temperature and light source are considered to investigate their effects on the photoreactor efficiency for the photothermal reactions. Finally, various reactor design considerations, challenges and limitations for photothermal hydrogenation reaction are critically discussed.