Research progress on photothermal catalytic CO₂ reduction to formic acid

CO₂ utilization as resource is an indispensable part to achieve the goal of “carbon peaking and carbon neutrality”. Catalytic conversion of CO₂ to formic acid is an effective and most atomic economically viable route. However, due to the stable thermodynamic properties of CO₂, it is difficult to be activated and the conversion rate of above reaction is generally low. In order to obtain a higher formic acid yield under mild conditions, photocatalysis is combined with thermal catalysis. Photothermal catalysis is mainly reflected in photoactivation, which effectively activates CO₂ by stimulating carrier, regulating electron injection location and adsorption site. Thermal energy could further enhance the adsorption rates of CO₂, charge transfer and reaction, and activate the thermally active sites, which could improve the yield and selectivity of formic acid by combining the advantages of low energy consumption of photocatalysis and high efficiency of thermal catalysis. At present, the main challenge of photothermal CO₂ reduction to formic acid is the inherent chemical stability of CO₂ which results in a low CO₂ conversion rate, uncontrollable product and poor selectivity etc. Considering the current demand for the photothermal catalytic CO₂ conversion technology, this study introduced the principles, advantages and disadvantages of photocatalysis, thermal catalysis and photothermal catalysis. The strategies for improving CO₂ conversion and formic acid selectivity were reviewed from the aspects of catalyst modification, reaction conditions and reactor selection. The modification methods of catalyst were mainly elaborated, including the improvement of electron-hole separation degree, the regulation on the proportion of exposed surface and the improvement on the adsorption of CO₂. The key problems of photothermal CO₂ reduction to formic acid were described in detail. In future studies, the production of high-yield formic acid and large-scale industrial application of photothermal catalysis can be realized by optimizing the reaction conditions and comprehensively considering the reactor selection and catalyst design.