Photothermal Catalytic CO₂ Conversion: Beyond Catalysis and Photocatalysis

In recent years, the combination of both thermal and photochemical contributions has provided interesting opportunities for solar upgrading of catalytic processes. Photothermal catalysis works at the interface between purely photochemical processes, which involve the direct conversion of photon energy into chemical energy, and classical thermal catalysis, in which the catalyst is activated by temperature. Thus, photothermal catalysis acts in two different ways on the energy path of the reaction. This combined catalysis, of which the fundamental principles will be reviewed here, is particularly promising for the activation of small reactive molecules at moderate temperatures compared to thermal catalysis and with higher reaction rates than those attained in photocatalysis, and it has gained a great deal of attention in the last years. Among the different applications of photothermal catalysis, CO₂ conversion is probably the most studied, although reaction mechanisms and photonic-thermal synergy pathways are still quite unclear and, from the reaction route point of view, it can be said that photothermal-catalytic CO₂ reduction processes are still in their infancy. This article intends to provide an overview of the principles underpinning photothermal catalysis and its application to the conversion of CO₂ into useful molecules, with application essentially as fuels but also as chemical building blocks. The most relevant specific cases published to date will be also reviewed from the viewpoint of selectivity towards the most frequent target products.