Dennis U Nielsen, Xin-Ming Hu, Kim Daasbjerg, Troels Skrydstrup
Carbon dioxide is ubiquitous and a vital molecule for maintaining life on our planet. However, the ever-increasing emission of anthropogenic CO2 into our atmosphere has provoked dramatic climate changes. In principle, CO2 could represent an important one-carbon building block for the chemical industry, yet its high thermodynamic and kinetic stability has limited its applicability to only a handful of industrial applications. On the other hand, carbon monoxide represents a more versatile reagent applied in many industrial transformations. Here we review the different methods for converting CO2 to CO with specific focus on the reverse water gas shift reaction, main element reductants, and electrochemical protocols applying homogeneous and heterogeneous catalysts. Particular emphasis is given to synthetic methods that couple the deoxygenation step with a follow-up carbonylation step for the synthesis of carbonyl-containing molecules, thus avoiding the need to handle or store this toxic but highly synthetically useful diatomic gas.