Copper catalysts for CO2 hydrogenation to CO through reverse water-gas shift reaction for e-fuel production: Fundamentals, recent advances, and prospects

E-fuel production, which is achieved using atmospheric or biogenic CO2 and green H-2, shows promise for reducing atmospheric CO2 levels and curtailing our reliance on fossil fuels. Notably, the hydrogenation of CO2 to CO via the reverse water-gas shift (RWGS) reaction (CO2 + H-2 <-> CO + H2O) plays a pivotal role in commercial e-fuel production. This approach is preferred over direct conversion of CO2, which remains in the nascent stage. However, the endothermic RWGS reaction is energy-intensive and it requires high operating temperatures (similar to 600-800 degrees C). Therefore, lowering the operating temperature can aid in achieving energy efficiency; however, this restricts the catalytic CO2 conversion activity. Furthermore, low temperatures of less than 400 degrees C favor the exothermic hydrogenation of CO2 to CH4, resulting in CH4 being the predominant product instead of CO during CO2 hydrogenation. Consequently, studies on RWGS catalysts have focused on CO2 conversion as well as CO selectivity for low-temperature operation. Among the various candidates for RWGS catalysts, Cu-based RWGS catalysts are targeted herein as particularly potent systems. Cu catalysts exhibit high CO2 conversion and CO selectivity, but face issues such as vulnerability to sintering. This review comprehensively explores Cu-based RWGS catalysts, from their fundamental properties (effects of Cu particle facets, particle size, and dispersion) to the latest research trends, such as novel preparation methods (deposition-precipitation, atomic layer deposition, and ion sputtering) and the use of various supports (CeO2, ZnO, and Mo2C) and promoters (FeOx and alkali metals), and their future research directions using spinel oxides and layered double hydroxides.